A Miniaturized Single-Transducer Implantable Pressure Sensor With Time-Multiplexed Ultrasonic Data and Power Links

Abstract

A high-precision implantable pressure sensor with ultrasonic power-up and data uplink is presented. The fully packaged implant measures 1.7 × 2.3 × 7.8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and includes a custom IC designed in a 180-nm HV BCD process, a pressure transducer, an energy storage capacitor, and a single piezoelectric transducer (piezo). In order to reduce overall dimensions, unique circuit and system design techniques are presented to enable a single time-multiplexed piezo for both power recovery and data uplink transmission. Implant performance is characterized at significant depths, 12 cm in a tissue phantom, offering a > 13× improvement over state of the art in the depth/volume figure of merit, while demonstrating a robust ultrasonic data uplink with better than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> bit error rate. A transient charging analysis is presented to derive the optimal piezo impedance and charging specifications to maximize overall harvesting efficiency. The IC features a front end with a 10-bit SAR ADC achieving a pressure full-scale range of 800 mmHg with a pressure resolution of 0.78 mmHg, exceeding the requirements for a wide range of in vivo pressure sensing applications. The pressure sampling rate is fully externally controlled, up to 1 ksps, in order to significantly decrease implant energy consumption and to allow for adaptable programming for specific applications.