This paper proposes an interface circuit for wirelessly powered implants for mice temperature monitoring. The circuit contains the read-out circuit and a data converter. By using a novel approach to cancel the non-linear effects of thermistor sensors, the circuit achieves 27dB higher SFDR. The system is designed in UMC CMOS 0.18 mu m technology, which has 200KHz sampling rate, 8-bit resolution, and total power-consumption of 29 mu W. The successive approximation analog-to-digital convertor (SAR ADC) is fabricated. The measurement result shows an Effective Number of Bits (ENOB) of 7.