Inverter based readout circuit for implanted glucose sensor

An integrated circuit which performs both sensor signal amplification and analog to digital conversion for a continuous blood glucose monitoring micro implant is presented. It is designed for a piezoresistive pressure sensor employed in a novel type of glucose sensor that measures osmotic pressure across a semipermeable membrane that selectively blocks glucose. A differential input signal is obtained from a single resistive divider between a piezo- and reference resistor (i.e. without Wheatstone bridge) by alternately switching the sensor´s supply polarity. A subthreshold inverter in a switched capacitor (SC) amplifier configuration is employed for initial amplification and time-to-digital conversion to finally obtain a digital representation of the glucose level. The resulting circuit features low complexity and low power consumption and reduced thermal noise at the output voltage of the SC. Simulation shows that a single sample requires activating of the power supply for 60μs during which the average power consumption is 121μW, resulting in an energy consumption per sample of 7.2nJ, a 30% reduction compared with the predecessor.