System digital signal modulation.

In a system for processing a stream of digital input data, a method for producing an output signal encoded as a function of a change in a parameter unique variable of said input signal, comprising the steps of generating a first bit coded pulse width lasting a multiple of a basic clock period when said input signal represents no change of that parameter; generating a second coded bit pulse width when the input signal represents a first type of change in the parameter; and generating a third coded bit pulse width when said input signal represents a second type of change in said parameter being said first to third bits different from each other.