Here’s is a video from Texas Instruments describing the inner workings of delta-sigma analog to digital converters. The DS ADC is broken down into it’s basic parts. The delta-sigma modulator and digital decimating filter are then discussed.
Delta-sigma converters are ideal for converting signals over a wide range of frequencies from DC to several megahertz with very high resolution results. In a delta-sigma ADC, the input signal is oversampled and then filtered by a digital/decimator filter.