A sigma-delta modulator (200) for an ADC, passes an input signal to a loop filter (20), then to a multi-bit quantizer (30) of the modulator (200). An output of the quantizer (30) is passed to a digital filter (50), and a feedback signal is passed back to the loop filter (20), the feedback signal having fewer bits than are produced by the multi-bit quantizer (30). No separate feedback loop for the digital filter (50) is used, so as to reduce the need to adjust the loop filter for stable operation. The digital filter (50) can have an order greater than one in the passband of the sigma-delta modulator (200).