Time domain ADC for blood glucose implant

An analogue-to-time and time-to-digital converter (related to an integrating ADC) optimised for the sensor interface of a pill-sized wireless micro-implant for continuous blood sugar monitoring is presented. The application requires ultra-low power consumption and aggressive miniaturisation (i.e. single ASIC integration, with only three discrete capacitors) and is characterised by an extremely low sampling rate of one sample per 5 minutes. The system power consumption is significantly reduced compared to a predecessor by choosing this faster ADC and by only powering the implant for a single conversion. Transient noise simulation data is presented that predicts 10ENOB and an energy consumption per sample of 10.2 nJ. This includes power for the major system components: the sensor, on-chip clock and bias generation, and power-up and power-down overheads when taking but a single sample.