Power harvesting and telemetry in CMOS for implanted devices

Implanted sensors offer many advantages to those studying the behavior of the human body. Unfortunately, the need to power and communicate with devices often requires tradeoffs that compromise their usefulness. We describe a power harvesting and telemetry chip that allows operation without wires or batteries. The chip has been fabricated in 0.5 μm CMOS. The chip is able to supply 2 mA at 33 V to associated sensors using inductive coupling. Tests reveal the characteristics of this chip under different loads and at different distances from the transmission coil. With the preliminary coils, functionality could be maintained with over 28 mm between the two coils. To evaluate the performance of the chip in conditions mimicking implantation in the body, water bearing colloids were introduced between the two coils. This resulted in a small loss of transfer efficiency, with no change in the behavior of the chip.