PPM generation:

The PWM pulses obtained at the comparator output are applied to a monostablemultivibrator. The monostable is negative edge is triggered.

Hence corresponding to each trailing edge of PWM signal, the monostable output goes high. It remains high for a fixed time decided by its own RC components.

Thus as the trailing edges of the PWM signal keep shifting in proportion with the modulating signal x (t) , the PPM pulses also keep shifting.

Demodulation/Degeneration of PPM:

Operation:

The noise corrupted PPM waveform is received by the PPM demodulator circuit.

The pulse generator develops a pulsed waveform at its output of fixed duration and applies these pulses to the rest pin (R) of a SR flip-flop.

A fixed period reference pulse is generated from the incoming PPM waveform and the SR flip-flop is set by the reference pulses.

Due to the set and reset signals applied to the flip-flop, we get a PWM signal at its output. The PWM signal can be demodulated using the PWM modulator.