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19-0266; Rev 2a; 9/96

           EVALUATION KIT
             AVAILABLE           High-Frequency Waveform Generator

                                                                                                                                MAX038
 _______________General Description                              ____________________________Features
The MAX038 is a high-frequency, precision function               o 0.1Hz to 20MHz Operating Frequency Range
generator producing accurate, high-frequency triangle, 
sawtooth, sine, square, and pulse waveforms with a               o Triangle, Sawtooth, Sine, Square, and Pulse
minimum of external components. The output frequency                Waveforms
can be controlled over a frequency range of 0.1Hz to             o Independent Frequency and Duty-Cycle
20MHz by an internal 2.5V bandgap voltage 
reference and an external resistor and capacitor. The               Adjustments
duty cycle can be varied over a wide range by applying           o 350 to 1 Frequency Sweep Range
a ±2.3V control signal, facilitating pulse-width modula-
tion and the generation of sawtooth waveforms.                   o 15% to 85% Variable Duty Cycle
Frequency modulation and frequency sweeping are                  o Low-Impedance Output Buffer:  0.1 
achieved in the same way. The duty cycle and 
frequency controls are independent.                              o Low-Distortion Sine Wave:  0.75%
Sine, square, or triangle waveforms can be selected at           o Low 200ppm/°C Temperature Drift
the output by setting the appropriate code at two 
TTL-compatible select pins. The output signal for all             ______________Ordering Information
waveforms is a 2VP-P signal that is symmetrical around                 PART             TEMP. RANGE           PIN-PACKAGE
ground. The low-impedance output can drive up 
to ±20mA.                                                         MAX038CPP               0°C to +70°C        20 Plastic DIP
                                                                  MAX038CWP               0°C to +70°C        20 SO
The TTL-compatible SYNC output from the internal
oscillator maintains a 50% duty cycle-regardless of               MAX038C/D               0°C to +70°C        Dice*
the duty cycle of the other waveforms-to synchronize              MAX038EPP             -40°C to +85°C        20 Plastic DIP
other devices in the system. The internal oscillator can          MAX038EWP             -40°C to +85°C        20 SO
be synchronized to an external TTL clock connected 
to PDI.                                                          *Contact factory for dice specifications.



________________________Applications                              __________________Pin Configuration
        Precision Function Generators
        Voltage-Controlled Oscillators
        Frequency Modulators                                           TOP VIEW
        Pulse-Width Modulators                                                       REF 1                    20 V-
        Phase-Locked Loops                                                          GND 2                     19 OUT
        Frequency Synthesizer                                                         A0 3                    18 GND
        FSK Generator-Sine and Square Waves                                           A1 4      MAX038        17 V+
                                                                                    COSC 5                    16 DV+
                                                                                     GND 6                    15 DGND
                                                                                    DADJ 7                    14 SYNC
                                                                                    FADJ 8                    13 PDI
                                                                                     GND 9                    12 PDO
                                                                                      IIN 10                  11 GND

                                                                                                 DIP/SO



                         ________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.



     High-Frequency Waveform Generator

    ABSOLUTE MAXIMUM RATINGS
    V+ to GND ................................................................-0.3V to +6V      Continuous Power Dissipation (TA = +70°C)
    DV+ to DGND...........................................................-0.3V to +6V            Plastic DIP (derate 11.11mW/°C above +70°C) ..........889mW
    V- to GND .................................................................+0.3V to -6V       SO (derate 10.00mW/°C above +70°C).......................800mW
    Pin Voltages                                                                                  CERDIP (derate 11.11mW/°C above +70°C)...............889mW
       IIN, FADJ, DADJ, PDO .....................(V- - 0.3V) to (V+ + 0.3V)                     Operating Temperature Ranges
       COSC .....................................................................+0.3V to V-      MAX038C_ _ .......................................................0°C to +70°C
MAX038 A0, A1, PDI, SYNC, REF.........................................-0.3V to V+                 MAX038E_ _ ....................................................-40°C to +85°C
       GND to DGND ................................................................±0.3V        Maximum Junction Temperature .....................................+150°C
    Maximum Current into Any Pin .........................................±50mA                 Storage Temperature Range .............................-65°C to +150°C
    OUT, REF Short-Circuit Duration to GND, V+, V- ...............30sec                         Lead Temperature (soldering, 10sec) .............................+300°C

     Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional
     operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
     absolute maximum rating conditions for extended periods may affect device reliability.

    ELECTRICAL CHARACTERISTICS
    (Circuit of Figure 1, GND = DGND = 0V, V+ = DV+ = 5V, V- = -5V, VDADJ = VFADJ = VPDI = VPDO = 0V, CF = 100pF,
    RIN = 25k , RL = 1k , CL = 20pF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
                 PARAMETER                           SYMBOL                                CONDITIONS                              MIN         TYP        MAX        UNITS
      FREQUENCY CHARACTERISTICS
      Maximum Operating Frequency                         Fo          15pCF   15pF, IIN = 500µA                                   20.0         40.0                    MHz
      Frequency Programming                                           VFADJ = 0V                                                  2.50                     750
      Current                                            IIN                                                                                                            µA
                                                                      VFADJ = -3V                                                 1.25                     375
      IIN Offset Voltage                                 VIN                                                                                  ±1.0         ±2.0         mV
      Frequency Temperature                            Fo/°C          VFADJ = 0V                                                               600
      Coefficient                                                                                                                                                    ppm/°C
                                                       Fo/°C          VFADJ = -3V                                                              200
                                                      ( Fo/Fo)
                                                         V+           V- = -5V, V+ = 4.75V to 5.25V                                           ±0.4        ±2.00
      Frequency Power-Supply
      Rejection                                       ( F                                                                                                              %/V
                                                             o/Fo)
                                                          V-          V+ = 5V, V- = -4.75V to -5.25V                                          ±0.2        ±1.00
      OUTPUT AMPLIFIER (applies to all waveforms)
      Output Peak-to-Peak Symmetry                     VOUT                                                                                     ±4                      mV
      Output Resistance                                ROUT                                                                                    0.1          0.2           
      Output Short-Circuit Current                      IOUT          Short circuit to GND                                                      40                      mA
      SQUARE-WAVE OUTPUT (RL = 100 )
      Amplitude                                        VOUT                                                                        1.9         2.0          2.1        VP-P
      Rise Time                                           tR          10% to 90%                                                                12                      ns
      Fall Time                                           tF          90% to 10%                                                                12                      ns
      Duty Cycle                                         dc           VDADJ = 0V, dc = tON/t x 100%                                 47          50          53           %
      TRIANGLE-WAVE OUTPUT (RL = 100 )
      Amplitude                                        VOUT                                                                        1.9         2.0          2.1        VP-P
      Nonlinearity                                                    Fo = 100kHz, 5% to 95%                                                   0.5                       %
      Duty Cycle                                         dc           VDADJ = 0V (Note 1)                                           47          50          53           %
      SINE-WAVE OUTPUT (RL = 100 )
      Amplitude                                        VOUT                                                                        1.9         2.0          2.1        VP-P
                                                                      Duty cycle adjusted to 50%                                               0.75
      Total Harmonic Distortion                         THD                                                                                                              %
                                                                      Duty cycle unadjusted                                                    1.50


     2 _______________________________________________________________________________________



                               High-Frequency Waveform Generator

                                                                                                                                     MAX038
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, GND = DGND = 0V, V+ = DV+ = 5V, V- = -5V, VDADJ = VFADJ = VPDI = VPDO = 0V, CF = 100pF,
RIN = 25k , RL = 1k , CL = 20pF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
         PARAMETER                    SYMBOL                          CONDITIONS               MIN      TYP       MAX      UNITS
 SYNC OUTPUT
 Output Low Voltage                     VOL        ISINK = 3.2mA                                        0.3       0.4        V
 Output High Voltage                    VOH        ISOURCE = 400µA                             2.8      3.5                  V
 Rise Time                               tR        10% to 90%, RL = 3k , CL = 15pF                      10                   ns
 Fall Time                               tF        90% to 10%, RL = 3k , CL = 15pF                      10                   ns
 Duty Cycle                           dcSYNC                                                            50                   %
 DUTY-CYCLE ADJUSTMENT (DADJ)
 DADJ Input Current                    IDADJ                                                  190       250       320       µA
 DADJ Voltage Range                    VDADJ                                                           ±2.3                  V
 Duty-Cycle Adjustment Range             dc        -2.3V   VDADJ   2.3V                        15                  85        %
 DADJ Nonlinearity                    dc/VFADJ -2V   VDADJ   2V                                          2         4         %
 Change in Output Frequency
 with DADJ                            Fo/VDADJ -2V   VDADJ   2V                                        ±2.5        ±8        %
 Maximum DADJ Modulating
 Frequency                              FDC                                                              2                  MHz
 FREQUENCY ADJUSTMENT (FADJ)
 FADJ Input Current                     IFADJ                                                 190       250       320       µA
 FADJ Voltage Range                    VFADJ                                                           ±2.4                  V
 Frequency Sweep Range                   Fo        -2.4V   VFADJ   2.4V                                 ±70                  %
 FM Nonlinearity with FADJ            Fo/VFADJ -2V   VFADJ   2V                                        ±0.2                  %
 Change in Duty Cycle with FADJ dc/VFADJ -2V   VFADJ   2V                                               ±2                   %
 Maximum FADJ Modulating
 Frequency                               FF                                                              2                  MHz
 VOLTAGE REFERENCE
 Output Voltage                         VREF       IREF = 0                                   2.48      2.50      2.52       V
 Temperature Coefficient              VREF/°C                                                           20                 ppm/°C
                                                   0mA   IREF   4mA (source)                             1         2
 Load Regulation                      VREF/IREF -100µA   IREF   0µA (sink)                               1         4       mV/mA
 Line Regulation                      VREF/V+ 4.75V   V+   5.25V (Note 2)                                1         2       mV/V
 LOGIC INPUTS (A0, A1, PDI)
 Input Low Voltage                       VIL                                                                      0.8        V
 Input High Voltage                     VIH                                                    2.4                           V
 Input Current (A0, A1)                IIL, IIH    VA0, VA1 = VIL, VIH                                             ±5       µA
 Input Current (PDI)                   IIL, IIH    VPDI = VIL, VIH                                                ±25       µA
 POWER SUPPLY
 Positive Supply Voltage                 V+                                                   4.75                5.25       V
 SYNC Supply Voltage                    DV+                                                   4.75                5.25       V
 Negative Supply Voltage                 V-                                                   -4.75               -5.25      V
 Positive Supply Current                 I+                                                             35         45       mA
 SYNC Supply Current                    IDV+                                                             1         2        mA
 Negative Supply Current                  I-                                                            45         55       mA
Note 1: Guaranteed by duty-cycle test on square wave.
Note 2: VREF is independent of V-.

                        _______________________________________________________________________________________ 3



          High-Frequency Waveform Generator

          __________________________________________Typical Operating Characteristics
          (Circuit of Figure 1, V+ = DV+ = 5V, V- = -5V, VDADJ = VFADJ = VPDI = VPDO = 0V, RL = 1k , CL = 20pF, TA = +25°C, unless 
          otherwise noted.)

                                                                                                             OUTPUT FREQUENCY                                                                                   NORMALIZED OUTPUT FREQUENCY
                                                                                                               vs. IIN CURRENT                                                                                              vs. FADJ VOLTAGE
MAX038                         100M                                                                                                                                         2.0
                                                                                                                                                                            1.8                                                   IIN = 100µA, COSC = 1000pF
                                                                                                                                               MAX038-08 33pF                                                                                                                           MAX038-09
                                                                                       10M                                                                                  1.6
                                                                                                                                               100pF                        1.4
                                                                                                                                               330pF                        1.2
                                                                                        1M                                                                                  1.0
                                                                                                                                               3.3nF              NORMALIZED 0.8
                                                                                       100k                                                                      F OUT 0.6
                                                                                                                                               33nF                         0.4
                                                                                        10k                                                    100nF                        0.2
                                                                                                                                                                                        0
                                                                                                                                                                                                          -3       -2             -1          0            1                2      3
                               OUTPUT FREQUENCY (Hz)                                     1k                                                    1µF                                                                                      VFADJ (V)
                                                                                                                                               3.3µF
                                                                                       100                                                                                                                        DUTY CYCLE vs. DADJ VOLTAGE
                                                                                                                                               10µF                     100
                                                                                                                                               47µF                             90
                                                                                        10                                                                                                                                                                                                           MAX038-16B
                                                                                                                                               100µF                            80
                                                                                                                                                                                70
                                                                                         1                                                                                      60
                                                                                                                                                                                50
                                                                                        0.1                                                                                     40
                                                                                               1                 10                  100    1000                 DUTY CYCLE (%) 30
                                                                                                                IIN CURRENT (µA)                                                20
                                                                                                                                                                                10                                                                 IIN = 200µA
                                                                                                                                                                                        0
                                                                                                                                                                                                          -3       -2             -1          0            1                2      3
                                                                                                                                                                                                                                        DADJ (V)

                                                                                                    NORMALIZED OUTPUT FREQUENCY                                                                                           DUTY-CYCLE LINEARITY
                                                                                                               vs. DADJ VOLTAGE                                                                                                  vs. DADJ VOLTAGE
                                                                                       1.10                                                                                       2.0
                                                                                                     I                                                                                                                                              I
                                                                                                          IN = 10µA                                                                                                                                  IN = 500µA
                                                                                                                                                MAX038-17                         1.5                                                                                                                              MAX038-18
                                                                                       1.05                IIN = 25µA                                                             1.0
                                                                                                                 IIN = 50µA                                                       0.5                                                                                I
                                                                                       1.00                                                                                                                                                                               IN = 250µA
                                                                                                                                                                                              0
                                                                                                                                                                                                                                                                I
                                                                                                                                                                             -0.5                                                                                    IN = 100µA
                                                                                       0.95                     IIN = 100µA                                                  -1.0
                                                                                                             IIN = 250µA
                                                                                       0.90                                                                                  -1.5                                                  IIN = 50µA
                                                        NORMALIZED OUTPUT FREQUENCY                       IIN = 500µA                                              DUTY-CYCLE LINEARITY ERROR (%) -2.0                            IIN = 25µA
                                                                                                                                                                                                                            I
                                                                                       0.85                                                                                  -2.5                                                IN = 10µA
                                                                                                                                                                                                          -2.0           -1.0           0                1.0               1.5     2.5
                                                                                                                         DADJ (V)                                                                                                        DADJ (V)


          4 _______________________________________________________________________________________



                                      High-Frequency Waveform Generator

                                                                                                                                  MAX038
 ____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, V+ = DV+ = 5V, V- = -5V, VDADJ = VFADJ = VPDI = VPDO = 0V, RL = 1k , CL = 20pF, TA = +25°C, unless 
otherwise noted.)

                                   SINE-WAVE OUTPUT (50Hz)                                            SINE-WAVE OUTPUT (20MHz)












                     TOP:  OUTPUT 50Hz = Fo                                            IIN = 400µA
                     BOTTOM:  SYNC                                                     CF = 20pF
                     IIN = 50µA
                     CF = 1µF TRIANGLE-WAVE OUTPUT (50Hz)                                       TRIANGLE-WAVE OUTPUT (20MHz)












                     TOP:  OUTPUT 50Hz = Fo                                             IIN = 400µA
                     BOTTOM:  SYNC                                                      CF = 20pF
                     IIN = 50µA
                     CF = 1µF                                        SQUARE-WAVE OUTPUT (50Hz)












                                                       TOP:  OUTPUT 50Hz = Fo
                                                       BOTTOM:  SYNC
                                                       IIN = 50µA
                                                       CF = 1µF
                         _______________________________________________________________________________________ 5



          High-Frequency Waveform Generator

           ____________________________Typical Operating Characteristics (continued)
          (Circuit of Figure 1, V+ = DV+ = 5V, V- = -5V, VDADJ = VFADJ = VPDI = VPDO = 0V, RL = 1k , CL = 20pF, TA = +25°C, unless 
          otherwise noted.)

                                 SQUARE-WAVE OUTPUT (20MHz)                                  FREQUENCY MODULATION USING FADJ

MAX038


                                                                                                                                 0.5V
                                                                                                                                 0
                                                                                                                                 -0.5V
                      IIN = 400µA                                                        TOP:  OUTPUT
                      CF = 20pF                                                          BOTTOM:  FADJ


                               FREQUENCY MODULATION USING IIN                                  FREQUENCY MODULATION USING IIN












                     TOP:  OUTPUT                                                        TOP:  OUTPUT
                     BOTTOM:  IIN                                                        BOTTOM:  IIN


                                                             PULSE-WIDTH MODULATION USING DADJ

                                                                                                          +1V

                                                                                                          0V

                                                                                                          -1V


                                                                                                          +2V

                                                                                                          0V

                                                                                                          -2V


                                                         TOP:  SQUARE-WAVE OUT, 2VP-P
                                                         BOTTOM:  VDADJ, -2V to +2.3V

          6 _______________________________________________________________________________________



                                                  High-Frequency Waveform Generator

                                                                                                                                                                                            MAX038
 ____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, V+ = DV+ = 5V, V- = -5V, VDADJ = VFADJ = VPDI = VPDO = 0V, RL = 1k , CL = 20pF, TA = +25°C, unless 
otherwise noted.)

                                          OUTPUT SPECTRUM, SINE WAVE                                                           OUTPUT SPECTRUM, SINE WAVE
                                                    (Fo = 11.5MHz)                                                                      (Fo = 5.9kHz)
                              0                                                                                  0
                                         RIN = 15k  (VIN = 2.5V), CF = 20pF,                                                                                               12B
                                                                                                                                 RIN = 51k  (VIN = 2.5V), CF = 0.01µF, 
                       -10               VDADJ = 40mV, VFADJ = -3V                                        -10                    V
                                                                                 MAX038-12A                                       DADJ = 50mV, VFADJ = 0V                         MAX038
                       -20                                                                                -20
                       -30                                                                                -30
                       -40                                                                                -40
                       -50                                                                                -50
                       -60                                                                                -60
               ATTENUATION (dB) -70                                                               ATTENUATION (dB) -70
                       -80                                                                                -80
                       -90                                                                                -90
                   -100                                                                               -100
                                       0 10 20 30 40 50 60 70 80 90 100                                                   0    5 10 15 20 25 30 35 40 45 50
                                                    FREQUENCY (MHz)                                                                    FREQUENCY (kHz)


______________________________________________________________Pin Description

  PIN        NAME                                                                              FUNCTION
    1        REF                        2.50V bandgap voltage reference output
 2, 6, 9,    GND                        Ground*
 11, 18
    3         A0                        Waveform selection input; TTL/CMOS compatible
    4         A1                        Waveform selection input; TTL/CMOS compatible
    5        COSC                       External capacitor connection
    7        DADJ                       Duty-cycle adjust input
    8        FADJ                       Frequency adjust input
   10         IIN                       Current input for frequency control
   12        PDO                        Phase detector output. Connect to GND if phase detector is not used.
   13        PDI                        Phase detector reference clock input. Connect to GND if phase detector is not used.
                                        TTL/CMOS-compatible output, referenced between DGND and DV+. Permits the internal oscillator to be
   14        SYNC                       synchronized with an external signal. Leave open if unused.
   15        DGND                       Digital ground
   16        DV+                        Digital +5V supply input. Can be left open if SYNC is not used.
   17         V+                        +5V supply input
   19        OUT                        Sine, square, or triangle output
   20         V-                        -5V supply input

*The five GND pins are not internally connected. Connect all five GND pins to a quiet ground close to the device. A ground plane is
recommended (see Layout Considerations).




                                       _______________________________________________________________________________________ 7



          High-Frequency Waveform Generator


                                                                                                                                   3                  4
                                                                                                                                  A0                  A1
                                                 5     COSC                           TRIANGLE
                                                                                                                          SINE
                                                                 OSCILLATOR           OSC A                SINE
                              CF                 6     GND                            OSC B               SHAPER
MAX038                                                                                                        TRIANGLE                                       OUT    19
                                                                                                                                          MUX
                                                                                                                   SQUARE
                                                 8     FADJ                                                                                                         R
                                                                   OSCILLATOR                                                                                            L    CL
                                                 7                       CURRENT                        COMPARATOR
                                                       DADJ         GENERATOR

                                                10     IIN

                                                                                                                                                MAX038
                  RF          RD       RIN                                  -250µA

                                                                                                                                                            SYNC    14
                                                                                                        COMPARATOR
                                                 1     REF                2.5V
                                                                         VOLTAGE
                                                                    REFERENCE

                        *                       17     V+                                                                                                   PDO     12
           +5V                                                                                            PHASE
                                                20     V-
           -5V                                                                                           DETECTOR                                            PDI    13
                                       2, 9, 11, 18    GND



                                                                                                                     DGND                      DV+
                                                                                                                       15                      16

                                                                                                                                  * 
                                    = SIGNAL DIRECTION, NOT POLARITY                                                                    +5V
                                    =  BYPASS CAPACITORS ARE 1µF CERAMIC OR 1µF ELECTROLYTIC IN PARALLEL WITH 1nF CERAMIC.
                         *
          Figure 1.  Block Diagram and Basic Operating Circuit

          _______________Detailed Description                                                            with constant currents, simultaneously producing a tri-
          The MAX038 is a high-frequency function generator                                              angle wave and a square wave (Figure 1). The charg-
          that produces low-distortion sine, triangle, sawtooth, or                                      ing and discharging currents are controlled by the cur-
          square (pulse) waveforms at frequencies from less than                                         rent flowing into IIN, and are modulated by the voltages
          1Hz to 20MHz or more, using a minimum of external                                              applied to FADJ and DADJ. The current into IIN can be
          components. Frequency and duty cycle can be inde-                                              varied from 2µA to 750µA, producing more than two
          pendently controlled by programming the current, volt-                                         decades of frequency for any value of CF. Applying
          age, or resistance. The desired output waveform is                                             ±2.4V to FADJ changes the nominal frequency (with
          selected under logic control by setting the appropriate                                        VFADJ = 0V) by ±70%; this procedure can be used for
          code at the A0 and A1 inputs. A SYNC output and                                                fine control.
          phase detector are included to simplify designs requir-                                        Duty cycle (the percentage of time that the output wave-
          ing tracking to an external signal source.                                                     form is positive) can be controlled from 10% to 90% by
          The MAX038 operates with ±5V ±5% power supplies.                                               applying ±2.3V to DADJ. This voltage changes the CF
          The basic oscillator is a relaxation type that operates by                                     charging and discharging current ratio while maintaining
          alternately charging and discharging a capacitor, C                                            nearly constant frequency.
                                                                                                  F,

          8 _______________________________________________________________________________________



                           High-Frequency Waveform Generator

                                                                                                                               MAX038
A stable 2.5V reference voltage, REF, allows simple          VFADJ = 0V, the fundamental output frequency (Fo) is
determination of IIN, FADJ, or DADJ with fixed resistors,    given by the formula:
and permits adjustable operation when potentiometers                 F
are connected from each of these inputs to REF. FADJ                      o (MHz) = IIN (µA) ÷ CF (pF)       [1]
and/or DADJ can be grounded, producing the nominal           The period (to) is:
frequency with a 50% duty cycle.                                     to (µs) = CF (pF) ÷ IIN (µA)            [2]
The output frequency is inversely proportional to            where:
capacitor CF. CF values can be selected to produce                   I
frequencies above 20MHz.                                             IN = current injected into IIN (between 2µA and 
                                                                     750µA)
A sine-shaping circuit converts the oscillator triangle              C
wave into a low-distortion sine wave with constant                        F = capacitance connected to COSC and GND 
                                                                     (20pF to >100µF).
amplitude. The triangle, square, and sine waves are
input to a multiplexer. Two address lines, A0 and A1,        For example:
control which of the three waveforms is selected. The                0.5MHz = 100µA ÷ 200pF
output amplifier produces a constant 2VP-P amplitude         and
(±1V), regardless of wave shape or frequency.                        2µs = 200pF ÷ 100µA
The triangle wave is also sent to a comparator that pro-
duces a high-speed square-wave SYNC waveform that            Optimum performance is achieved with IIN between
can be used to synchronize other oscillators. The SYNC       10µA and 400µA, although linearity is good with IIN
circuit has separate power-supply leads and can be           between 2µA and 750µA. Current levels outside of this
disabled.                                                    range are not recommended. For fixed-frequency oper-
                                                             ation, set I
Two other phase-quadrature square waves are gener-                            IN to approximately 100µA and select a suit-
                                                             able capacitor value. This current produces the lowest
ated in the basic oscillator and sent to one side of an      temperature coefficient, and produces the lowest fre-
"exclusive-OR" phase detector. The other side of the         quency shift when varying the duty cycle.
phase-detector input (PDI) can be connected to an
external oscillator. The phase-detector output (PDO) is      The capacitance can range from 20pF to more than
a current source that can be connected directly to           100µF, but stray circuit capacitance must be minimized
FADJ to synchronize the MAX038 with the external             by using short traces. Surround the COSC pin and the
oscillator.                                                  trace leading to it with a ground plane to minimize cou-
                                                             pling of extraneous signals to this node. Oscillation
                              Waveform Selection             above 20MHz is possible, but waveform distortion
The MAX038 can produce either sine, square, or trian-        increases under these conditions. The low frequency
gle waveforms. The TTL/CMOS-logic address pins (A0           limit is set by the leakage of the COSC capacitor and
and A1) set the waveform, as shown below:                    by the required accuracy of the output frequency.
                                                             Lowest frequency operation with good accuracy is usu-
      A0          A1          WAVEFORM                       ally achieved with 10µF or greater non-polarized
       X           1          Sine wave                      capacitors.
       0           0          Square wave                    An internal closed-loop amplifier forces IIN to virtual
       1           0          Triangle wave                  ground, with an input offset voltage less than ±2mV. IIN
                                                             may be driven with either a current source (IIN), or a
     X = Don't care                                          voltage (VIN) in series with a resistor (RIN). (A resistor
Waveform switching can be done at any time, without          between REF and IIN provides a convenient method of
regard to the phase of the output. Switching occurs          generating IIN:  IIN = VREF/RIN.) When using a voltage
within 0.3µs, but there may be a small transient in the      in series with a resistor, the formula for the oscillator fre-
output waveform that lasts 0.5µs.                            quency is:
                                                                     F
                                     Waveform Timing                      o (MHz) = VIN ÷ [RIN x CF (pF)]    [3]
                                                             and:
                                       Output Frequency
The output frequency is determined by the current                    to (µs) = CF (pF) x RIN ÷ VIN           [4]
injected into the IIN pin, the COSC capacitance (to
ground), and the voltage on the FADJ pin. When


                  _______________________________________________________________________________________ 9



          High-Frequency Waveform Generator

          When the MAX038's frequency is controlled by a volt-                  to = period when VFADJ = 0V.
          age source (VIN) in series with a fixed resistor (RIN), the    Conversely, if V
          output frequency is a direct function of V                                            FADJ is known, the frequency is given
                                                     IN as shown in      by:
          the above equations. Varying VIN modulates the oscilla-
          tor frequency. For example, using a 10k  resistor for                 Fx = Fo x (1 - [0.2915 x VFADJ])       [8]
          RIN and sweeping VIN from 20mV to 7.5V produces                and the period (tx) is:
          large frequency deviations (up to 375:1). Select R
MAX038                                                          IN so           t
          that I                                                                x = to ÷ (1 - [0.2915 x VFADJ])        [9]
               IN stays within the 2µA to 750µA range. The band-
          width of the IIN control amplifier, which limits the modu-                                               Programming FADJ 
          lating signal's highest frequency, is typically 2MHz.          FADJ has a 250µA constant current sink to V- that must
          IIN can be used as a summing point to add or subtract          be furnished by the voltage source. The source is usu-
          currents from several sources. This allows the output          ally an op-amp output, and the temperature coefficient
          frequency to be a function of the sum of several vari-         of the current sink becomes unimportant. For manual
          ables. As VIN approaches 0V, the IIN error increases           adjustment of the deviation, a variable resistor can be
          due to the offset voltage of IIN.                              used to set VFADJ, but then the 250µA current sink's
                                                                         temperature coefficient becomes significant. Since
          Output frequency will be offset 1% from its final value        external resistors cannot match the internal tempera-
          for 10 seconds after power-up.                                 ture-coefficient curve, using external resistors to pro-
                                                           FADJ Input    gram VFADJ is intended only for manual operation,
          The output frequency can be modulated by FADJ,                 when the operator can correct for any errors. This
          which is intended principally for fine frequency control,      restriction does not apply when VFADJ is a true voltage
          usually inside phase-locked loops. Once the funda-             source.
          mental, or center frequency (Fo) is set by IIN, it may be      A variable resistor, RF, connected between REF (+2.5V)
          changed further by setting FADJ to a voltage other than        and FADJ provides a convenient means of manually
          0V. This voltage can vary from -2.4V to +2.4V, causing         setting the frequency deviation. The resistance value
          the output frequency to vary from 1.7 to 0.30 times the        (RF) is:
          value when FADJ is 0V (Fo ±70%). Voltages beyond                      R
          ±2.4V can cause instability or cause the frequency                         F = (VREF - VFADJ) ÷ 250µA        [10]
          change to reverse slope.                                       VREF and VFADJ are signed numbers, so use correct
                                                                         algebraic convention. For example, if V
          The voltage on FADJ required to cause the output to                                                           FADJ is -2.0V
                                                                         (+58.3% deviation), the formula becomes:
          deviate from Fo by Dx (expressed in %) is given by the
          formula:                                                              RF = (+2.5V - (-2.0V)) ÷ 250µA
               VFADJ = -0.0343 x Dx                 [5]                               = (4.5V) ÷ 250µA 
          where VFADJ, the voltage on FADJ, is between                                = 18k 
          -2.4V and +2.4V.                                                                                            Disabling FADJ 
          Note: While IIN is directly proportional to the fundamen-      The FADJ circuit adds a small temperature coefficient
          tal, or center frequency (Fo), VFADJ is linearly related to    to the output frequency. For critical open-loop applica-
          % deviation from Fo. VFADJ goes to either side of 0V,          tions, it can be turned off by connecting FADJ to GND
          corresponding to plus and minus deviation.                     (not REF) through a 12k  resistor (R1 in Figure 2). The 
          The voltage on FADJ for any frequency is given by the          -250µA current sink at FADJ causes -3V to be devel-
          formula:                                                       oped across this resistor, producing two results. First,
                                                                         the FADJ circuit remains in its linear region, but discon-
               VFADJ = (Fo - Fx) ÷ (0.2915 x Fo) [6]                     nects itself from the main oscillator, improving tempera-
          where:                                                         ture stability. Second, the oscillator frequency doubles.
               Fx = output frequency                                     If FADJ is turned off in this manner, be sure to correct
                                                                         equations 1-4 and 6-9 above, and 12 and 14 below by
               Fo = frequency when VFADJ = 0V.                           doubling Fo or halving to. Although this method doubles
          Likewise, for period calculations:                             the normal output frequency, it does not double the
               VFADJ = 3.43 x (tx - to) ÷ tx        [7]                  upper frequency limit. Do not operate FADJ open cir-
                                                                         cuit or with voltages more negative than -3.5V. Doing
          where:                                                         so may cause transistor saturation inside the IC, lead-
               tx = output period                                        ing to unwanted changes in frequency and duty cycle.

          10 ______________________________________________________________________________________



                                            High-Frequency Waveform Generator

                                                                                                                                                                               MAX038
                                                  ­5V +5V                                                                    PRECISION DUTY-CYCLE ADJUSTMENT CIRCUIT

                                                                                                                              R4              R3
                                                 20 17       4                                                      ­2.5V                            +2.5V
  FREQUENCY                                                                                                                  100k            100k
                               1                  V-                              C2
                                    REF                   V+ A1          3        1µF                                                                         REF
                C1    C3                                           AO
               1µF    1nF

    RIN                        7 DADJ MAX038
    20k                                                                          R2                                                                                  MAX038
                                                                                50 
                              10                                         19
                                    IIN                           OUT                               SINE-WAVE
                               8                                                                    OUTPUT                    R7              R5
                                    FADJ                                                                                     100k            100k
                                                                         16
               R1                                                 DV+             N.C.
                                                                         15
           12k                                               DGND                                                                    R6
                                                                         14                                                          5k 
                                                             SYNC                 N.C.
                                                                         13
                                                                  PDI
                               5                                         12                   2 x 2.5V
                                    COSC                          PDO                     Fo = R                                                              DADJ
                                                                                               IN x CF
                                     GND GND GND GND GND
                      CF             6      2    9 11 18

                                                                                                                         ADJUST R6 FOR MINIMUM SINE-WAVE DISTORTION


Figure 2.  Operating Circuit with Sine-Wave Output and 50% Duty Cycle; SYNC and FADJ Disabled


With FADJ disabled, the output frequency can still be                                                DADJ can be used to reduce the sine-wave distortion.
changed by modulating IIN.                                                                           The unadjusted duty cycle (VDADJ = 0V) is 50% ±2%;
                                                                                                     any deviation from exactly 50% causes even order har-
                                           Swept Frequency Operation                                 monics to be generated. By applying a small
The output frequency can be swept by applying a vary-                                                adjustable voltage (typically less than ±100mV) to
ing signal to IIN or FADJ. IIN has a wider range, slightly                                           VDADJ, exact symmetry can be attained and the distor-
slower response, lower temperature coefficient, and                                                  tion can be minimized (see Figure 2).
requires a single polarity current source. FADJ may be
used when the swept range is less than ±70% of the                                                   The voltage on DADJ needed to produce a specific
center frequency, and it is suitable for phase-locked                                                duty cycle is given by the formula:
loops and other low-deviation, high-accuracy closed-                                                          VDADJ = (50% - dc) x 0.0575                             [11]
loop controls. It uses a sweeping voltage symmetrical                                                or:
about ground.                                                                                                 V
Connecting a resistive network between REF, the volt-                                                              DADJ = (0.5 - [tON ÷ to]) x 5.75                   [12]
age source, and FADJ or IIN is a convenient means of                                                 where:
offsetting the sweep voltage.                                                                                 VDADJ = DADJ voltage (observe the polarity)
                                                                               Duty Cycle                     dc = duty cycle (in %)
The voltage on DADJ controls the waveform duty cycle                                                          tON = ON (positive) time
(defined as the percentage of time that the output                                                            to = waveform period.
waveform is positive). Normally, VDADJ = 0V, and the
duty cycle is 50% (Figure 2). Varying this voltage from                                              Conversely, if VDADJ is known, the duty cycle and ON
+2.3V to -2.3V causes the output duty cycle to vary                                                  time are given by:
from 15% to 85%, about -15% per volt. Voltages                                                                dc = 50% - (VDADJ x 17.4)                               [13]
beyond ±2.3V can shift the output frequency and/or                                                            tON = to x (0.5 - [VDADJ x 0.174]) [14]
cause instability.

                             ______________________________________________________________________________________ 11



          High-Frequency Waveform Generator

                                                 Programming DADJ        for low temperature coefficient over the whole tempera-
          DADJ is similar to FADJ; it has a 250µA constant cur-          ture range. NPO ceramics are usually satisfactory.
          rent sink to V- that must be furnished by the voltage          The voltage on COSC is a triangle wave that varies
          source. The source is usually an op-amp output, and            between 0V and -1V. Polarized capacitors are generally
          the temperature coefficient of the current sink becomes        not recommended (because of their outrageous tem-
          unimportant. For manual adjustment of the duty cycle, a        perature dependence and leakage currents), but if they
          variable resistor can be used to set V
MAX038                                             DADJ, but then the    are used, the negative terminal should be connected to
          250µA current sink's temperature coefficient becomes           COSC and the positive terminal to GND. Large-value
          significant. Since external resistors cannot match the         capacitors, necessary for very low frequencies, should
          internal temperature-coefficient curve, using external         be chosen with care, since potentially large leakage
          resistors to program VDADJ is intended only for manual         currents and high dielectric absorption can interfere
          operation, when the operator can correct for any errors.       with the orderly charge and discharge of C
          This restriction does not apply when V                                                                       F. If possi-
                                                      DADJ is a true     ble, for a given frequency, use lower IIN currents to
          voltage source.                                                reduce the size of the capacitor.
          A variable resistor, RD, connected between REF
          (+2.5V) and DADJ provides a convenient means of                                                        SYNC Output
          manually setting the duty cycle. The resistance value          SYNC is a TTL/CMOS-compatible output that can be
          (RD) is:                                                       used to synchronize external circuits. The SYNC output
                                                                         is a square wave whose rising edge coincides with the
               RD = (VREF - VDADJ) ÷ 250µA           [15]                output rising sine or triangle wave as it crosses through
          Note that both VREF and VDADJ are signed values, so            0V. When the square wave is selected, the rising edge
          observe correct algebraic convention. For example, if          of SYNC occurs in the middle of the positive half of the
          VDADJ is -1.5V (23% duty cycle), the formula becomes:          output square wave, effectively 90° ahead of the output.
               RD = (+2.5V - (-1.5V)) ÷ 250µA                            The SYNC duty cycle is fixed at 50% and is indepen-
                                                                         dent of the DADJ control.
                      = (4.0V) ÷ 250µA = 16k                             Because SYNC is a very-high-speed TTL output, the
          Varying the duty cycle in the range 15% to 85% has             high-speed transient currents in DGND and DV+ can
          minimal effect on the output frequency-typically less          radiate energy into the output circuit, causing a narrow
          than 2% when 25µA < IIN < 250µA. The DADJ circuit is           spike in the output waveform. (This spike is difficult to
          wideband, and can be modulated at up to 2MHz (see              see with oscilloscopes having less than 100MHz band-
          photos, Typical Operating Characteristics).                    width). The inductance and capacitance of IC sockets
                                                             Output      tend to amplify this effect, so sockets are not recom-
          The output amplitude is fixed at 2VP-P, symmetrical            mended when SYNC is on. SYNC is powered from sep-
          around ground, for all output waveforms. OUT has an            arate ground and supply pins (DGND and DV+), and it
          output resistance of under 0.1 , and can drive ±20mA           can be turned off by making DV+ open circuit. If syn-
          with up to a 50pF load. Isolate higher output capaci-          chronization of external circuits is not used, turning off
          tance from OUT with a resistor (typically 50 ) or buffer       SYNC by DV+ opening eliminates the spike.
          amplifier.                                                                                          Phase Detectors
                                          Reference Voltage                                              Internal Phase Detector
          REF is a stable 2.50V bandgap voltage reference capa-          The MAX038 contains a TTL/CMOS phase detector that
          ble of sourcing 4mA or sinking 100µA. It is principally        can be used in a phase-locked loop (PLL) to synchro-
          used to furnish a stable current to IIN or to bias DADJ        nize its output to an external signal (Figure 3). The
          and FADJ. It can also be used for other applications           external source is connected to the phase-detector
          external to the MAX038. Bypass REF with 100nF to min-          input (PDI) and the phase-detector output is taken from
          imize noise.                                                   PDO. PDO is the output of an exclusive-OR gate, and
                                                                         produces a rectangular current waveform at the
                        Selecting Resistors and Capacitors               MAX038 output frequency, even with PDI grounded.
          The MAX038 produces a stable output frequency over             PDO is normally connected to FADJ and a resistor,
          time and temperature, but the capacitor and resistors          R
          that determine frequency can degrade performance if                 PD, and a capacitor CPD, to GND. RPD sets the gain
                                                                         of the phase detector, while the capacitor attenuates
          they are not carefully chosen. Resistors should be             high-frequency components and forms a pole in the
          metal film, 1% or better. Capacitors should be chosen          phase-locked loop filter.

          12 ______________________________________________________________________________________



                                          High-Frequency Waveform Generator

                                                                                                                                                          MAX038
                                                                                         charge CPD, so the rate at which VFADJ changes (the
                                        +5V -5V                C1
                                                               1µF                       loop bandwidth) is inversely proportional to CPD.
                                                               C2                        The phase error (deviation from phase quadrature)
                                                               1µF                       depends on the open-loop gain of the PLL and the ini-
                               14 16 17 20         4
  CENTER                                                                                 tial frequency deviation of the oscillator from the exter-
  FREQUENCY                     SYNC DV+ V+ V- A1
                         1                                     3                         nal signal source. The oscillator conversion gain (Ko) is:
                              REF                        A0                                    KO =   o ÷  VFADJ                      [17]
            RD           7 DADJ                                       ROUT               which, from equation [6] is:
                                                                      50 
                        10                                     19                              KO = 3.43 x  o (radians/sec)           [18]
                              IIN                       OUT
                         8            MAX038                                       RF
                              FADJ                                                       The loop gain of the PLL system (KV) is: 
                                                                               OUTPUT
                   R                                                                           KV = KD x KO                           [19]
                   PD
                                                               13                        where:
                                                        PDI
                        5                                      12                              K
                              COSC                                                                  D = detector gain
                                                        PDO
   CPD       CF
                              GND GND GND GND GND DGND                                         KO = oscillator gain.
                              2 6     9 11 18 15                                         With a loop filter having a response F(s), the open-loop
                                                                                         transfer function, T(s), is:
                                                                                               T(s) = KD x KO x F(s) ÷ s              [20]
     EXTERNAL OSC INPUT                                                                  Using linear feedback analysis techniques, the closed-
                                                                                         loop transfer characteristic, H(s), can be related to the
                                                                                         open-loop transfer function as follows:
Figure 3.  Phase-Locked Loop Using Internal Phase Detector                                     H(s) = T(s) ÷ [1+ T(s)]                [21]
                                                                                         The transient performance and the frequency response
PDO is a rectangular current-pulse train, alternating                                    of the PLL depends on the choice of the filter charac-
between 0µA and 500µA. It has a 50% duty cycle when                                      teristic, F(s).
the MAX038 output and PDI are in phase-quadrature                                        When the MAX038 internal phase detector is not used,
(90° out of phase). The duty cycle approaches 100%                                       PDI and PDO should be connected to GND.
as the phase difference approaches 180° and con-
versely, approaches 0% as the phase difference                                                                            External Phase Detectors
approaches 0°. The gain of the phase detector (KD)                                       External phase detectors may be used instead of the
can be expressed as:                                                                     internal phase detector.  The external phase detector
     K                                                                                   shown in Figure 4 duplicates the action of the MAX038's
          D = 0.318 x RPD (volts/radian)                               [16]              internal phase detector, but the optional ÷N circuit can
where RPD = phase-detector gain-setting resistor.                                        be placed between the SYNC output and the phase
When the loop is in lock, the input signals to the phase                                 detector in applications requiring synchronizing to an
detector are in approximate phase quadrature, the duty                                   exact multiple of the external oscillator.  The resistor net-
cycle is 50%, and the average current at PDO is 250µA                                    work consisting of R4, R5, and R6 sets the sync range,
(the current sink of FADJ). This current is divided                                      while capacitor C4 sets the capture range.  Note that
between FADJ and RPD; 250µA always goes into FADJ                                        this type of phase detector (with or without the ÷N cir-
and any difference current is developed across RPD,                                      cuit) locks onto harmonics of the external oscillator as
creating VFADJ (both polarities). For example, as the                                    well as the fundamental.  With no external oscillator
phase difference increases, PDO duty cycle increases,                                    input, this circuit can be unpredictable, depending on
the average current increases, and the voltage on RPD                                    the state of the external input DC level.
(and VFADJ) becomes more positive. This in turn                                          Figure 4 shows a frequency phase detector that locks
decreases the oscillator frequency, reducing the phase                                   onto only the fundamental of the external oscillator.
difference, thus maintaining phase lock. The higher                                      With no external oscillator input, the output of the fre-
RPD is, the greater VFADJ is for a given phase differ-                                   quency phase detector is a positive DC voltage, and
ence; in other words, the greater the loop gain, the less                                the oscillations are at the lowest frequency as set by
the capture range. The current from PDO must also                                        R4, R5, and R6.

                                ______________________________________________________________________________________ 13



          High-Frequency Waveform Generator


                                                                                                                                         +5V -5V                                   C1
                                                                                                                                                                                   1µF
                                                                                                                                                                                   C2
                                                                                                                                                                                   1µF
                                                      ÷N
                                                                                                                          14         16 17      20           4
                                                                              CENTER
MAX038                                                                                                                        SYNC DV+ V+             V- A1
                                                                              FREQUENCY                             1                                                         3
                                                                                                                         REF                                           A0

                                                                                           R2
                                                                                    CW

                                                                                           R3                       7 DADJ             MAX038                                             R1
                                                                                                                                                                                          50 
                                        PHASE DETECTOR                                                         10                                                             19
                                                                R4                                                       IIN                                      OUT                                                       RF
                                                                                                                    8                                                                                                       OUTPUT
                                                                                                                         FADJ
                                                                       R5                              R6                                                                     13
                                                                OFFSET                                 GAIN
                       EXTERNAL                                                                                                                                        PDI
                                                                                                               5                                                              12
                       OSC INPUT                                                                                         COSC                                     PDO
                                                                             -5V
                                                                                                                         GND GND GND GND GND DGND
                                                                                     C4                C3                2      6      9 11 18               15
                                                                        CAPTURE FREQUENCY




          Figure 4.  Phase-Locked Loop Using External Phase Detector





                                                                                                                                                                                    +5V -5V                         C1
                                                                                                                                                                                                                    1µF
                                                                                                                                                                                                                    C2
                                                                                                                                                                                                                    1µF
                                                                 ÷N
                                                                                                                                                       14              16 17              20      4
                                                                                                              CENTER                                       SYNC DV+ V+                          V- A1
                                                                                                              FREQUENCY                         1                                                              3
                                                                                                                                                      REF                                                A0

                                                                                                                                R2
                                                                                                                    CW

                                                                                                                                R3              7
                                    FREQUENCY PHASE DETECTOR                                                                                          DADJ                    MAX038                                       R1
                                                                                                                                                                                                                           50 
                                                                                                                                                10                                                             19
                                                                                                 R4                                                   IIN                                              OUT
                                                                                                                                                8 FADJ                                                                                    RF
                                                                                                                                                                                                                                      OUTPUT
                                                                                                       R5                               R6
           EXTERNAL                                                                                                                                                                                            13
                                                                                                 OFFSET                                 GAIN
          OSC INPUT                                                                                                                                                                                     PDI
                                                                                                                                                5                                                              12
                                                                                                                                                      COSC                                             PDO
                                                                                                             -5V
                                                                                                                                                      GND GND GND GND GND DGND
                                                                                                                         C4             C3            2           6           9 11 18             15
                                                                                                        CAPTURE FREQUENCY




          Figure 5.  Phase-Locked Loop Using External Frequency Phase Detector


          14 ______________________________________________________________________________________



                                                    High-Frequency Waveform Generator

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             MAX038
                                                                                                                                                                                                                                                                                                                                                       SIGNAL OUTPUT                                                                                                                                                                                                              SYNC OUTPUT
                                                                                                                                                                                                                                                                                                                                                                                                      56pF
                                                                                                                                                                                            +5V                                                                                   50                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           -5V


                                                                                                                                                                                                                                                                                                 220nH                                                                                       110pF
                                                                                                                                                                                                                              , 50MHz 50 LOWPASS FILTER
                                                                                                                                                                                                                                                                                        220nH                                                                                        56pF




                                                                                                                                                                                                                                                                                                                       50.0                                                                                                                            100
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            µF0.1                                                                                                                                                                                                                                                                                                                                                                                                                                                                FREQUENCY SYNTHESIZER 1kHz RESOLUTION; 8kHz TO 16.383MHz
                                                                                                                                                                                                                                                                                                                               µF0.1
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             0.1 µF

                                                                                                                                                                                                                                               20                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    11
                                                                                                                                                                                                                                                               V-                                                                               OUT                                                                              V+
                                                                                                                                                                                                                                                                                                                                                                        GND                                                                                                       DV+                                                                                                                                                                     PDI
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     DGND                                 SYNC                                                                                                                              PDO                                                  GND1
                                                                                                                                                                 µA
                               1N914                                                                                                               2µA to 750
                                                                                                                                                                                                                                                                                                                                                                                                                                             MAX038
                                                                              2N3906
                                        1k                                                                                                                                                                                                                           VREF                                                               GND1                                   A0                                                      A1                                 COSC                                                               GND1                 DADJ                                                                    FADJ                                                      GND1                                                  IIN
                                                                    7                                                                                                                                                                     1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    10
                                                                                                                                                                                                           WAVEFORM SELECT
                                                          8                                                    4                                                                                                                                                                                                                                                                                                                                              35 pF
                                                                                        MAX412
                                                     6                                                                   5                                                                         2.7M

                                              1k
                                                                                                                               1                                       3.33k                                                                          +2.5V                                                                                                                                                                                                                                                                                                                                              ±2.5V
                                                                                                     2N3904                                                                                                                                                                                                                                            µF0.1
                                                                                                                                    MAX412
                                                                                                                    3                          2 0V TO 2.5V                                                                                                                                                                                                                                                   10k
                                                                                                                                                                                                                                                                                                          µF                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               µF
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        7.5k
                                                                                                                                                                                                                                                                                                                0.1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              0.1
                                                                         1                                                                                                            18
                                                                                                  OUT1                                         RFB                                                                                                                                                                                                                                                                                                                                              µF                                                                                                                                                               6
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      0.1
                                                                                                  OUT2                                        VREF                                                                                                                                                                                                                                                                                                                                                                                                                                                  7                                                                                                                                                4
                                                                                                  GND                                          VDD
                                                                                                                              MX7541                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         MAX427
                                                                                                  BIT1                                        BIT12                                                                                                                                                                                                                                                                                                                                                                                                                                            2                                                                                                                   3                                                                                                                          µF
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         33k
                                                                                                  BIT2                                        BIT11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        33k                                      0.1
                                                                                                  BIT3                                        BIT10
                                                                                                  BIT4                                         BIT9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               3.3M                                                                                                                                 3.3M                                                                                                                                           µF
                                                                                                  BIT5                                         BIT8                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         0.1
                                                                                                  BIT6                                         BIT7
                                                               9                                                                                                                10                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    PDV                                                       PDR

                                                                                                                                                                                                                                                                                                                                                                                                                     14                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       1
                 1kHz                                                                                                                                                                                                                                                                                                                                                                                                                                               N3                                          N2                                          N1                           N0                             FV
                 2kHz                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        PDV                                              PDR                               RA2                               RA1                  RA0                                                    OUT           V DD V SS                                                 F IN
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               PD1
                 4kHz
                 8kHz
                16kHz                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         MC145151                                                                                                                                                                                                                                                                      OUT                                           IN
                32kHz
                                                                                                                                                                                                                                                                                                                                                                                                                                                              N4                                                      N5                             NN6                           N7                             N8                                                                   N9                                              T/R                               N12                                             N13    N10                                     N11                          OSC                                           OSC          LD
                64kHz                                                                                                                                                                                                                                                                                                                                                                                                      15
               128kHz                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              28
               256kHz
               512kHz                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              8.192MHz
             1.024MHz
             2.048MHz                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    35pF
             4.096MHz                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 20pF
             8.192MHz

Figure 6.  Crystal-Controlled, Digitally Programmed Frequency Synthesizer-8kHz to 16MHz with 1kHz Resolution

                         ______________________________________________________________________________________ 15



   High-Frequency Waveform Generator

                              Layout Considerations              tor compares the ÷N output with the MAX038 SYNC
   Realizing the full performance of the MAX038 requires         output and sends differential phase information to U5.
   careful attention to power-supply bypassing and board         U5's single-ended output is summed with an offset into
   layout. Use a low-impedance ground plane, and con-            the FADJ input. (Using the DAC and the IIN pin for
   nect all five GND pins directly to it. Bypass V+ and V-       coarse frequency control allows the FADJ pin to have
   directly to the ground plane with 1µF ceramic capaci-         very fine control with reasonably fast response to switch
                                                                 changes.)
MAX038 tors or 1µF tantalum capacitors in parallel with 1nF
   ceramics. Keep capacitor leads short (especially with         A 50MHz, 50  lowpass filter in the output allows pas-
   the 1nF ceramics) to minimize series inductance.              sage of 16MHz square waves and triangle waves with
   If SYNC is used, DV+ must be connected to V+, DGND            reasonable fidelity, while stopping high-frequency noise
   must be connected to the ground plane, and a second           generated by the ÷N circuit.
   1nF ceramic should be connected as close as possible
   between DV+ and DGND (pins 16 and 15). It is not
   necessary to use a separate supply or run separate
   traces to DV+. If SYNC is disabled, leave DV+ open.                ___________________Chip Topography
   Do not open DGND.
   Minimize the trace area around COSC (and the ground                        GND      REF        V-     OUT
   plane area under COSC) to reduce parasitic capaci-
   tance, and surround this trace with ground to prevent                AO                                      GND
   coupling with other signals. Take similar precautions
   with DADJ, FADJ, and IIN. Place CF so its connection
   to the ground plane is close to pin 6 (GND).                                                                 V+
    __________Applications Information                                  A1                                      DV+
                              Frequency Synthesizer                                                             DGND
                                                                      COSC
   Figure 6 shows a frequency synthesizer that produces
   accurate and stable sine, square, or triangle waves with                                                            0.118"
   a frequency range of 8kHz to 16.383MHz in 1kHz incre-                                                         (2.997mm)
   ments. A Motorola MC145151 provides the crystal-con-
   trolled oscillator, the ÷N circuit, and a high-speed phase
   detector. The manual switches set the output frequency;                                                      SYNC
                                                                       GND
   opening any switch increases the output frequency.             
   Each switch controls both the ÷N output and an                     DADJ                                      PDI
   MX7541 12-bit DAC, whose output is converted to a cur-
   rent by using both halves of the MAX412 op amp.  This                      FADJ GND IIN        GND    PDO
   current goes to the MAX038 IIN pin, setting its coarse                               0.106"
   frequency over a very wide range.                                                  (2.692mm)
   Fine frequency control (and phase lock) is achieved
   from the MC145151 phase detector through the differ-          TRANSISTOR COUNT:  855
   ential amplifier and lowpass filter, U5. The phase detec-     SUBSTRATE CONNECTED TO GND











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