Wireless front-end with power management for an implantable cardiac microstimulator

Inductive coupling is presented with the help of a high-efficiency Class-E power amplifier for an implantable cardiac microstimulator. The external coil inductively transmits power and data with a carrier frequency of 256 kHz into the internal coil of electronic devices inside the body. The detected cardiac signal is fed back to the external device with the same pair of coils to save on space in the telemetry device. To maintain the power reliability of the microstimulator for long-term use, two small rechargeable batteries are employed to supply voltage to the internal circuits. The power management unit, which includes radio frequency front-end circuits with battery charging and detection functions, is used for the supply control. For cardiac stimulation, a high-efficiency charge pump is also proposed in the present paper to generate a stimulated voltage of 3.2 V under a 1 V supply voltage. A phase-locked-loop (PLL)-based phase shift keying demodulator is implemented to efficiently extract the data and clock from an inductive AC signal. The circuits, with an area of 0.45 mm², are implemented in a TSMC 0.35 μm 2P4M standard CMOS process. Measurement results reveal that power can be extracted from the inductive coupling and stored in rechargeable batteries, which are controlled by the power management unit, when one of the batteries is drained. Moreover, the data and clock can be precisely recovered from the coil coupling, and a stimulated voltage of 3.2 V can be readily generated by the proposed charge-pump circuits to stimulate cardiac tissues.