Comparator-less digital implementation of AC-coupled ΣΔ A/D converters

A simple and successful design for a sigma-delta (SigmaDelta) modulator with only digital active components is presented. Low frequency compensation of the input threshold variations of the digital gate used as a comparator achieves good spurious-free dynamic range. The only drawback is the addition of a low cutoff frequency, which results in an AC-coupled analogue-to-digital converter.