Analysis of Chopped Integrators, and Its Application to Continuous-Time Delta-Sigma Modulator Design

Chopping is a commonly used technique to eliminate flicker noise in amplifiers. We investigate the use of chopping in the input integrator of a continuous-time oversampling (Δ Σ) converter. Unlike an amplifier, the integrator in a continuous-time delta-sigma modulator is subject to out-of-band signals that are several orders of magnitude higher than the (desired) in-band component. This necessitates a careful analysis of frequency translation effects in a chopped integrator. This paper treats the chopped integrator as a linear periodically time-varying system, and exploits the adjoint (inter-reciprocal) network concept to simplify the analysis of aliasing effects in such an integrator. Simulation results that confirm the theory are given.