This paper deals with the design of MEMS-based sensors with piezoresistive transduction. It is demonstrated that when the sensor topology does not allow a perfect matching of resistances in the conditioning circuit (typically a Wheatstone bridge), the resolution of the system is limited by the ability to reject power supply noise. As this ability increases when the output offset of the bridge decreases, the proposed architecture implements a feedback loop to control MOS transistors inserted in the Wheatstone bridge to compensate resistor mismatches. This zero-offset bridge exhibits a very good offset cancellation and therefore a better resolution.