An energy-efficient implant transponder for continuous glucose monitoring

The paper presents an integrated transponder with an inverter based readout circuit for continuous glucose monitoring in a wireless micro-implant. For this application the system takes advantage of an extremely low duty cycle and reduces power consumption significantly by only being powered for 96 μs every 5 minutes. It is powered by a 13.56 MHz radio frequency (RF) signal and performs sensor signal amplification, analog to digital conversion (ADC) and uplink data transmission through load shift keying (LSK). It is energy-optimized for a piezoresistive pressure sensor as employed in a recently presented glucose sensor that transduces glucose concentration into osmotic pressure. The transponder has been produced in 90 nm CMOS technology. The total energy consumption on the implant side after rectification (including sensor power as the major energy drain) is 14.4 nJ per sample for 8.42 effective bits. With a sampling rate of once per every 5 minutes this translates into a continuous consumption of 48.5 pW, so even considering a very low efficiency of the wireless power transmission the implant would no longer figure as a limiting factor for the battery lifetime of a reader unit.