Tackling SDM Feedback Coefficient Modulation in Area Optimized Frontend Readout Circuit for High Performance MEMS Accelerometers

This work evaluates a switched capacitor frontend readout circuit for high performance MEMS accelerometers composed of a sigma-delta modulator. It presents the importance of random chopping for EMC purposes and the problems attached to it in the case of a pseudo-differential sigma-delta modulator. For example, it shows with simulation on verilog models that the noise floor is raised and that there is a loss of signal information. Moreover, the choppers in the feedback loop of the sigma-delta modulator create intermodulation between the bitstream and the dummy sensor causing distortions. Finally, it shows several possible solutions.