A Fully-Integrated 0.068-mm³ Implantable Pressure Sensing Device With Wireless Energy Harvesting and Data Telemetry

This paper reports a fully-integrated sub-0.1 mm³ wireless pressure sensing device for implantable applications. The miniature device integrates a customized system-on-a-chip (SoC) and an off-the-shelf half-bridge piezoresistive pressure transducer, eliminating off-chip passive components. The SoC mainly comprises a resistance-to-time converter, a 915 MHz inductively coupled energy harvester with an on-chip coil, and a backscatter telemetry. Key innovations enabling low power, small size and high precision include: (1) A source-input common-gate amplifier based R-V converter, that reuses the transducer's bias current, (2) Advanced noise management via chopper stabilization and supply noise cancellation, and (3) A compact high-Q on-chip multi-layer stacked coil design for wireless link. The active circuits consume 9.75 $\boldsymbol{\mu}$W, fully supplied by the energy harvested wirelessly through the on-chip coil. The sensing data is transmitted wirelessly to an external recorder through the RF backscatter link. Fabricated in a 65-nm CMOS technology, the SoC occupies a die area of 400 µm × 490 µm, and the entire fully-integrated sensor has a volume of only 0.068 mm³, enabling syringe injection through a ≤0.5 mm needle. Experiments with the sensing device covered by pork have demonstrated that the device can operate at an implant depth of up to 10 mm with excellent misalignment tolerance. It offers a pressure sensing resolution of 3.1 mmHg over a relative pressure range of 0-200 mmHg and a temperature sensing resolution of 0.18°C.