3. Generic Implant Architecture and Organization

An archetypal implantable microsystem comprises two separate structural units: an external controlling module and a component placed inside the human body (the implant). The internal unit can be partitioned into several sections. These sections include the analog front end, memory, microprocessor (CPU), communication, and power management sections. The analog front end takes care of sensing and stimulation functions. The sensing function decides the magnitude, time, and extent of therapy to be given. It also monitors the therapy of the patient. The stimulation function looks after the output voltage or current pulse delivered by the device to the relevant part of the body. The memory unit stores the computer program and data. The microprocessor is the brain of the implanted device. Communication is established between the implanted device and the external controller for initially setting the device and for its subsequent control. The subsequent control is done to fine-tune the therapeutic parameters. Apart from data telemetry, communication is used for power delivery in rechargeable battery implants. Power management is essential to make best use of the battery life or to minimize the time duration between two consecutive charging steps, if a rechargeable battery is used.