Pulse Position modulation is digital or not?

Answer 1

Pulse position modulation can be analog or digital, it depends on the signal and/or the modulator used to obtain the modulation.

If an analog signal is applied at the input of the modulator, the position of the pulse can assume an infinity of different timing states (the signal vary continuously) and hence an analog modulation is realised in PPM.

On the contrary if the signal is digitized previously in a series of discrete states, the pulse at the output will have discrete timing interval (not continuosly). Then a digital modulation is obtained.

If the signal is analog, but the modulator is digital, we will have again a number of finite state in output timing, and the PPM will be digital.

To be noted that, if the number of steps in the digital modulator, is higher then the dinamic range required, the performance of the digital and analog PPM will be exactly the same.

Cecking the front of the pulse of PPM with a digital oscilloscope capable of jitter measurament, we will see immediately if the position of the pulses will be continuosly variable or a number of discrete steps will be presented.

We can then consider analog and digital PPM physically different.