A low-voltage, ultra-low power sensor interface for electromyogram (EMG) signal acquisition is presented. The sensor interface consists of an amplifier and a SAR ADC that work from a 0.3V supply. The low-voltage amplifier topology provides a noise level of 26μVrms, 40dB gain and a state-of the art power efficiency factor (PEF) of 2.2 from a 20–425Hz bandwidth. Low-voltage supply improves the power efficiency of the amplifier compared with previous ultra-low power work. Together with the ADC, the prototype implemented in 65nm CMOS process consumes 3.8nW and has an area of 0.22mm2, which makes the sensor interface suitable for wearable IoT nodes as well as implantable devices.