Multiple stage frequency modulated circuit

摘要

A signal processing circuit, including at least two stages of frequency modulation (25,20; 28, 31, 33) and demodulation of signals applied to or generated within that circuit, characterized in that the modulating and demodulating signal for each stage is an effective square wave and in that the ratio of the frequencies (F1, F2) of the modulating signals for the first and second stages corresponds substantially to the ratio of an even integer to an odd integer, or vice versa, such that there are substantially no common frequencies or harmonics between the first and second modulating signals.