Design Considerations of Biomedical Telemetry Devices

The specifications for an implantable medical device (IMD) are provided by the application but share a common set of constraints in size, power, and functionality. This chapter provides a brief overview of the design of biomedical telemetry devices and in particular IMDs using inductive links. The basic system architecture and inductive link fundamentals are discussed, as well as methods and circuits for power transfer and data communication. Safety issues relating to overheating of body tissue as a result of increase of temperature are also examined. There are several methods of harvesting energy for IMDs such as kinetic, thermoelectric, fuel cells, infrared radiation, low-frequency magnetic fields, and inductive links. Data communication is called the downlink from the transmitter to the implant, and the uplink from the implant to the transmitter. Due to dual data and power transfer, the carrier amplitude is greater than or equal to the supply voltages.