On low power design of feedforward continuous-time sigma delta modulators with excess loop delay

Abstract

In high order single loop continuous-time (CT) sigma delta modulators, excess loop delay may cause instability. In this paper, previous techniques in compensation of internal quantizer and feedback DAC delays are studied especially for the feedforward structure. Two alternative low power feedforward continuous-time sigma delta modulators with excess loop delay compensation are proposed. Simulation based CT synthesis from discrete time topologies is adopted to obtain the loop filter coefficients. Design examples are given to illustrate the proposed structure and the synthesis methodology.