Comparator applications

If necessary, an op-amp can be pressed into service as a poorly performing comparator, but its slew rate will be impaired.

are nominally the positive and negative supply voltages (which are not shown in the diagram).

[1]: 5 [2]: 7 [3] Like other detectors, this device functions as a voltage switch, but with an important difference.

From Kirchhoff's Current Law, this value depends on Vin and the output voltage of the threshold detector itself, both multiplied by a resistor ratio.

Further examination of the Va equation reveals that Vin can exceed zero (positive or negative) by a certain magnitude before the output of the detector is caused to switch.

By adjusting the value of R1, the magnitude of Vin that will cause the detector to switch can be increased or decreased.

Its positive feedback has a faster transition, so it is used in timing applications such as frequency counters.

It is also used in astable multivibrators found in instruments such as function generators.

The magnitude of the output voltage is a property of the operational amplifier and its power supply.

Applications include converting an analog signal into a form suitable for frequency measurements, in phase locked loops, or controlling power electronics circuits that must switch with a defined relationship to an alternating current waveform.

This detector exploits the property that the instantaneous frequency of an FM wave is approximately given by

is the time difference between adjacent zero crossings of FM wave [4] A bistable multivibrator implemented as a comparator with hysteresis.

By using an RC network to add slow negative feedback to the inverting Schmitt trigger, a relaxation oscillator is formed.

The feedback through the RC network causes the Schmitt trigger output to oscillate in an endless symmetric square wave (i.e., the Schmitt trigger in this configuration is an astable multivibrator).