A motion sensor with sigma-delta analog-to-digital converter (ADC) having improved bias instability is presented herein. Differential outputs of a differential amplifier of the sigma-delta ADC are electrically coupled, via respective capacitances, to differential inputs of the differential amplifier. To minimize bias instability corresponding to flicker noise that has been injected into the differential inputs, the differential inputs are electrically coupled, via respective pairs of electronic switches, to feedback resistances based on a pair of switch control signals. In this regard, a first feedback resistance of the feedback resistances is electrically coupled to a first defined voltage, and a second feedback resistance of the feedback resistances is electrically coupled to a second defined reference voltage. The differential outputs are electrically coupled to differential inputs of a differential comparator of the sigma-delta ADC, and complementary outputs of the differential comparator comprise the pair of switch control signals.