An Energy-Efficient Implantable Transponder for Biomedical Piezo-Resistance Pressure Sensors

An implantable transponder with wireless link for biomedical applications is presented. The application specific integrated circuit (ASIC) is energy optimized for a Wheatstone configured piezoresistive pressure sensor. The system takes advantage of an extremely low duty cycle reducing significantly the energy consumption. A net differential input swing voltage is obtained from only a single resistive sensor branch by interchanging the sensor supply polarity alternately. The ASIC was fabricated in TSMC 90 nm CMOS process with an area of 0.37 mm². The transponder is powered by a 13.56 MHz radio frequency signal and performs sensor signal amplification, analog to digital conversion and uplink data transmission through load shift keying within 96 μs every 5 min. This results in a total energy consumption for the complete system on the implant side of 12.5 nJ per sample for a resolution of 7.03 effective bits.