The purpose of this study is to design a low voltage differential amplifier circuit driven by the audio interface to realize the sensing device without external power supply. The pseudo-differential amplifier was designed using a inverter-based subtracting circuit with 0.18μm standard CMOS process. The maximum differential gain was measured as 51.4dB at 1V supply voltage, and the CMRR was 45.1dB. The input offset temperature drift is 1.5μV/ 'C. In addition, the simulation was carried out for the sensing circuit in the smartphone configuration.