A 30 mu W Remotely Powered Local Temperature Monitoring Implantable System

An implantable local temperature monitoring system for a laboratory mouse is presented. Magnetic coupling is used to remotely power the passive implant. The temperatures of two local points are monitored by thermistors. A low-power readout circuit is implemented by directly amplifying and resolving the sensor response in the time domain. A free-running oscillator operating at 868 MHz transmits the sensor data to the base station. The average power dissipation of the implant is decreased by time interleaving between the sensor readout and the data communication. The power transfer to the implant is also time interleaved with other operations to avoid interference with data communication. A voltage regulation loop for the implant based on controlling the duration of powering the base station power amplifier is also described. A prototype chip is implemented in 0.18 mu m CMOS. The implant requires average RF power of 29.5 mu W for operation and is capable of measuring two thermistors with accuracy of +/- 0.05 degrees C.