Study of Non-Linear S/H Operation in Switched-Current Circuits Using Volterra Series - Application to BandPass Sigma-Delta Modulators

Abstract

This paper analyses the transient behaviour of SwItched-current (SI) memory cells placed at the front-end of high-speed A/D interfaces. Based on the Volterra series method, the non-linear sampling process occurring in such cells is studied and closed-form expressions are obtained for the Total Harmonic Distortion (THD) and the intermodulation distortion. The analysis is extended to the case of BandPass ΣΔ Modulators (BP-ΣΔMs) using Fully-Differential (FD) SI memory cells. As a result, the third-order intermodulation distortion at the output of the modulator is derived. Time-domain simulations and experimental measurements taken from a 0.8μm CMOS 4th-order BP-ΣΔM silicon prototype validate the study.