Multiple techniques are presented to implement an ultra-low-power remotely powered implantable system. The temperature is monitored locally by a thermistor-type sensor. The resistive response of the sensor is amplified and resolved in the time-domain. The data is transmitted using a duty cycled free running oscillator operating at 868 MHz. In addition, the sensor interface and data transmitter are time interleaved to improve power link sensitivity. A prototype chip is fabricated in 0.18 mu m CMOS. The implant is powered with a 13.56 MHz inductive link and operates with a minimum power of 53 mu W. The system is capable of recording temperature with accuracy of +/- 0.09 degrees C when 8 times oversampling is done at the base station.