Random chopping in ΣΔ modulators

Abstract

ΣΔ modulators make a clever use of oversampling and exhibit inherent monotonicity, high linearity and large dynamic range but a restricted frequency range. As a result ΣΔ modulators are often the preferred option for sensor and instrumentation. Offset and Flicker noise are usual concerns for this type of applications and one way to minimize their effects is to use a chopper in the front-end integrator of the modulator. Frequency-shaped random chopping has been proposed to minimize the impact of reference voltage interference. It is shown in this paper that the chopper signal is not the only term that modulates the offset and Flicker noise and that unwanted crosstalk can significantly degrade the performance of the modulator.