An Implantable Phase Locked Loop MEMS-Based Readout System for Heart Transplantation

An implantable readout circuit using a MEMS pressure sensor has been designed and implemented to monitor the heart activity after heart transplant surgery. It features a time domain architecture using two identical voltage-controlled oscillators and phase locked loop circuits. The circuit was implemented in a 65 nm CMOS technology with 1 V power supply. It consumes 100~\mu \text{W} power and provides a digital output that is proportional to the analog sensor input with a bandwidth of up to 4 kHz. The SNR of the system is 53 dB. Measurements show the operation of the readout chip with the MEMS sensor.