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 mm(2). 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 mu s 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.