SQUARE WAVE GENERATOR

A typical application for a comparator is as a square wave

oscillator. The circuit below generates a square wave whose

period is set by the RC time constant of the capacitor C

resistor R

signal propagation delay of the comparator, and by the ca-

pacitive loading at the output, which limits the output slew

rate.

To analyze the circuit, consider it when the output is high.

That implies that the inverted input (V

non-inverting input (V

through R

non-inverting input. The value of V

If R

At this point the comparator switches pulling down the output

to the negative rail. The value of V

If R

The capacitor C

age V

comparator switches again, bringing it back to the initial

stage. The time period is equal to twice the time it takes to

discharge C

1

from 2V

to V

which is given by

R

F = 1/(2.R

20080055

FIGURE 6. Negative Peak Detector

20080056

20080057

FIGURE 7. Squarewave Oscillator

www.national.com

13