?S MODULATOR AND ?S ANALOG/DIGITAL CONVERTING CIRCUIT

摘要

A ?S modulator of frequency modulation system wherein the requirement of linearity for an oscillator is lessened. The ?S modulator comprises an oscillating apparatus the frequency of which varies in accordance with an input signal; a quantizing means (16) for quantizing the frequency modulation signal from the oscillating apparatus into a binary signal; and an arithmetic circuit (18,20) for operating the digital signal from the quantizing means (16). The oscillating apparatus has an oscillator (10) the frequency of which varies in accordance with an input signal; a reference signal source (11) for providing a reference signal having a predetermined frequency; a mixer (12) for receiving the signals from the oscillator (10) and from the reference signal source (11); and a lowpass filter (14) for passing the low frequency components of signals from the mixer (12). The center oscillation frequency of the oscillator (10) is established such that it is higher than the center oscillation frequency of a target signal.