Figure shows the block diagram of a zero-crossing detector for demodulating an FM signal, its consist of a limiter, a pulse generator for producing a short pulse at each zero-crossing of the input, and a low-pass filter for extracting the modulating wave.

(a) Show that the instantaneous frequency of the input FM signals is proportional to the number of zero crossings in the time interval t ? (T₁/2) to t + (T₁/2), divided by T₁, Assume that the modulating is essentially constant during this time interval.

(b) Illustrate the operation of this demodulator, using the saw-tooth wave of Figure as the modulating wave.

Transcribed Image Text:

Output signal Low-pass filter FM Limiter Pulse generator wave