Pulse and Digital Circuits

4.4 COMPARATORS

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:

 

v_o = 0 for t < t₁

v_o = 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 v_i reaches V_R.

4.4.1 Diode Comparators

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 V_R is the reference voltage. The circuit is required to tell the time instant at which the input reaches V_R.

FIGURE ...