Transcutaneous transmission of digital data and energy in a cochlear prosthesis system

This paper describes the inductive power and data link employed in the CAP Cochlear Prosthesis System (CAP stands for Combined Analog and Pulsative Stimulation Strategy). The inductive link consisting of a parallel-tuned receiver resonant circuit weakly coupled to a series-tuned transmitter resonant circuit, is driven by a self-oscillating class-E-tuned power amplifier. The class-E concept allows coupling-insensitive high-efficiency transcutaneous transmission of power. In the CAP implant, variations of the coil distance within a range of 0 to 9 mm result in changes of the implant supply voltage which are lower than 10%. Within this coil distance range, the mean overall efficiency is 49%. In view of the excellent switching properties of the class-E tuned power oscillator, a practical scheme for data transmission is ASK (Amplitude Shift Keying). To ensure constant energy flow and easy synchronization of the bitstream in the implant, a self-clocking bit format is employed.