Analysis and Modeling of the Non-Linear Sampling Process in Switched-Current Circuits - Application to Bandpass Sigma-Delta Modulators

Abstract

This paper presents a precise model for the transient behaviour of Fully Differential (FD) SwItched-current (SI) memory cells placed at the front-end of high-speed A/D interfaces. This model allows us to analyze the main errors associated to the S/H process, namely: excess transfer-function delay and harmonic distortion. For the latter, the analysis is extended to BandPass Σ∆ Modulators (BP-Σ∆Ms) and a closed-form expression is derived for the third-order intermodulation distortion. Time-domain simulations and experimental measurements taken from a 0.8µm CMOS 4th-order BP-Σ∆M silicon prototype validate our approach.