A Bidirectional Digital Data Transmission System using Capacitive Tuning of Inductive Coil Link for Neural Prosthetic Devices

A bidirectional digital data transmission system has been developed for neural prosthetic devices with a data transmission rate up to 500kbps at the 2.5MHz carrier frequency in case of both forward and backward data transmission. We use single pair of transcutaneous coil link for forward power transmission and bidirectional data transmission. The amplitude-shift keying (ASK) modulation protocol is selected for simple demodulation circuit in both bidirectional cases. Power amplification of external part is based on the single ended class E concept. The capacitive tuning circuit is introduced and analyzed for backward data transmission. Modulating tuning-capacitance of the implant enables one to modulate the current amplitude of the external coil without any additional circuit or antenna in implant. This circuit has the advantage of continuous power transmission to the implant relatively to conventional resistive load switching circuit. It permits the time for processing and transmitting of the backward data transmission to be unbounded. The experimental results show that the designed system is capable of delivering at least 30mW over a coil distance of 12mm. In neural prosthetic devices, this bidirectional digital data transmission is effective method for setting of stimulation parameters, recording of neural response after electrical stimulation, and monitoring of the implantable device.