A compact, low-power, digitally-assisted sensor interface for biomedical applications is presented. It exploits oversampling and mixed-signal feedback to reduce system area and power, while making the system more robust to interferers. Antialiasing is achieved using a charge-sampling filter with a sinc frequency response and programmable gain. A mixed-signal feedback loop creates a sharp, programmable notch for interference cancellation. A prototype was implemented in a 0.18-μm CMOS process. The on-chip blocks operate from a 1.5-V supply and consume between 255 nW and 2.5 μW depending on noise and bandwidth requirements.