Efficient estimation of noise and signal transfer functions of a continuous-time ΣΔ modulator

Determining the Noise and Signal Transfer Functions (NTF and STF) of a Continuous-Time Delta-Sigma Modulator (CTDSM) is an important aspect of the design verification process. In several practical CTDSM designs, like those with Switched Capacitor (SC) and Return-to-Open (RTO) feedback DACs, the loop filters are time varying, rendering traditional methods incorrect and/or time consuming. In this work, we exploit the linearity of the loop filter to determine the Signal and Noise Transfer Functions (NTF) of a modulator using time domain techniques that need far less simulation time than conventional methods.