On the Robustness of CMOS-Chopped Operational Amplifiers to Conducted Electromagnetic Interferences

This paper deals with the robustness of low power chopped CMOS operational amplifiers (OpAMPs) to electromagnetic interferences (EMI) conducted at the device input stage. The main differences between chopped amplifiers and standard offset uncompensated ones are analyzed in terms of EMI susceptibility, achieving three main results. First, a new model is developed to show how chopping influences the amplifier susceptibility in a broadband sense, demonstrating that chopped OpAMPs generate a lower amount of EMI-induced offset from the nonlinear distortion with respect to standard ones because of the topological differences between the respective input stages. Second, a model to predict the effects of EMI appearing at the multiples of the chopping frequency is derived, showing that chopped OpAMPs can experience dc shift peaks because of the linear distortion of the disturbances whose frequencies hit the even multiples of the chopping frequency. Finally, the simultaneous presence of the technological offset and the offset produced by the nonlinear and the linear distortion of EMI in chopped OpAMP is illustrated by means of dedicated EMI susceptibility measurements performed on several devices designed to validate the analysis.