An amplitude comparator is a circuit that tells the time instant at which the input amplitude has reached a reference level. A comparator is shown in Fig. 4.24.
Ideally, in this comparator:
vo = 0 for t < t1
vo = V for t ≥ t1
The amplitude of the output abruptly rises from 0 to V at t = t1, t1 is the time instant at which vi reaches VR.
In this section, we discuss two types of diode comparators—pick-off and break-away diode comparators.
Pick-off Diode Comparators. A simple diode comparator circuit is shown in Fig. 4.25. A base clipper is used as a comparator. The input now is a ramp and VR is the reference voltage. The circuit is required to tell the time instant at which the input reaches VR.