Efficient sampling of reference noise in a switched capacitor ΣΔ ADC

The implementation of an efficient sampling technique whereby the reference capacitor is selectively sampled within a switched capacitor ΣΔ ADC is presented, resulting in improved thermal noise performance. When a transition occurs in the modulator feedback, the reference capacitors are not sampled but instead discharged to ground. The introduction of a do-not-sample state requires that the ΣΔ modulator is compensated. For mid-scale inputs, the overall ADC noise is reduced by 5.6 dB, without any increase in power consumption.