_______________Detailed Description

The MAX038 is a high-frequency function generator

that produces low-distortion sine, triangle, sawtooth, or

square (pulse) waveforms at frequencies from less than

1Hz to 20MHz or more, using a minimum of external

components. Frequency and duty cycle can be inde-

pendently controlled by programming the current, volt-

age, or resistance. The desired output waveform is

selected under logic control by setting the appropriate

code at the A0 and A1 inputs. A SYNC output and

phase detector are included to simplify designs requir-

ing tracking to an external signal source.

The MAX038 operates with ±5V ±5% power supplies.

The basic oscillator is a relaxation type that operates by

with constant currents, simultaneously producing a tri-

angle wave and a square wave (Figure 1). The charg-

ing and discharging currents are controlled by the cur-

rent flowing into IIN, and are modulated by the voltages

applied to FADJ and DADJ. The current into IIN can be

varied from 2µA to 750µA, producing more than two

±2.4V to FADJ changes the nominal frequency (with

fine control.

Duty cycle (the percentage of time that the output wave-

form is positive) can be controlled from 10% to 90% by

charging and discharging current ratio while maintaining

nearly constant frequency.

High-Frequency Waveform Generator

8

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MAX038

OSCILLATOR

OSCILLATOR

CURRENT

GENERATOR

2.5V

VOLTAGE

REFERENCE

OSC B

OSC A

TRIANGLE

SINE

SHAPER

COMPARATOR

COMPARATOR

PHASE

DETECTOR

MUX

COSC

GND

5

6

8

7

10

FADJ

DADJ

IIN

REF

1

17

20

2, 9, 11, 18

V+

V-

GND

+5V

-5V

-250

µA

SINE

TRIANGLE

SQUARE

A0

A1

OUT

SYNC

PDO

PDI

19

14

12

13

3

4

DGND

DV+

15

16

+5V

*

= SIGNAL DIRECTION, NOT POLARITY

= BYPASS CAPACITORS ARE 1

µF CERAMIC OR 1µF ELECTROLYTIC IN PARALLEL WITH 1nF CERAMIC.

*

*

Figure 1. Block Diagram and Basic Operating Circuit