Power harvesting and telemetry in CMOS for implanted devices

Implanted sensors offer many advantages to study and monitor the human body. Wires or batteries often compromise their usefulness. We describe a telemetry chip that by inductive coupling supplies power to and transmits digital data from an implantable sensor. The same two coils are used to transmit both power and data. The chip fabricated in 0.5-mu m CMOS technology supplies 1.7 mA at 3.3 V, over a distance up to 25 mm between coils. Experiments emulating the effect of human tissue by introducing water bearing colloids between the two coils revealed a negligible loss of transfer efficiency. With modified Miller encoding, the data link attained 3 10(-5) bit error rate at 10 kbps transmission speed over 25 mm distance. Repeated tests using the same colloids between coils resulted in a slight decrease in the signal to noise ratio of the data stream with increasing thickness.