A fourth-order cascaded full feed-forward sigma-delta modulator

Abstract

This paper presents a structure of a fourth-order cascaded full feed-forward Sigma-delta modulator. Because there is no feedback but only feed-forward path between two stages, cascaded sigma-delta modulator is unnecessary to consider the stability problems, and has the identical performance with ideal high-order single-loop sigma-delta modulator. The system level simulation results show that the signal to noise rate (SNR) of the designed sigma-delta modulator is 148 and the effective number of bits (ENOB) is 24.4 when the oversampling ratio (OSR) is 128.