A 2-2 Discrete Time Cascaded ΣΔ Modulator With NTF Zero Using Interstage Feedback

Abstract

A novel discrete time cascaded sigma-delta modulator topology is presented. The overall noise transfer function (NTF) may be modified by means of an additional error feedback in the analog circuitry. Mismatch properties do not depend on the additional feedback path, and therefore the signal to noise ratio (SNR) may be improved by proper location of NTF zeros. Moreover, one of the NTF zeros may be programmable by means of analog trimming while digital cancellation filters remains unaffected. A low oversampling ratio (OSR) 2-2 cascade sigma-delta modulator is presented as a design example.