Modeling of EMI propagation in switched-capacitor ΣΔ A/D converter

In this communication a model of the propagation of electromagnetic interference (EMI) in sigma-delta A/D converters is developed. After a discussion about the EMI injection points, the model takes into consideration EMI injected into the feedback path and coming from the voltage reference circuit. The model reveals that EMI are demodulated, thanks to a multiplication with the output signal, and, under certain circumstances, may fall into the baseband thus affecting the overall signal-to-noise ratio (SNR) and the precision of the A/D converter. The model is validated by means of simulation and excellent agreement is obtained between expected data and simulation results.