Improved Class A Based Transmitter System for Wireless Retinal Implant Data Telemetry

Abstract

Purpose: : This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. The specific purpose of this poster is to present a class A transmitter for data telemetry. This circuit delivers data wirelessly via an inductive link to a retinal prosthesis. It represents an improvement in wireless range and in signal integrity over our previous data transmitter circuits.

Methods: : A number of possible circuits were examined, and the Class A circuit was chosen. Impedance matching was done for our 13.56MHz carrier, between the amplifier output, cable, and load with hand calculations, and the performance of the circuit was verified and optimized with spice simulation software. Choke and impedance match inductors were hand-wound on torroidal cores, and were measured on a 30MHz LCR meter. A 25 ohm cable was used, and the resonant capacitor and Q degradation resistor were added to the primary coil. The telemetry system was tested with secondary coils monitored by op amp buffer circuits to verify amplitude and harmonic distortion of the waveforms. The system was then tested with our implant stimulator chip, to verify that the data can be received without error.

Results: : The class A based transmitter delivers sufficient signal power to the secondary coil, and has improved harmonic properties. The maximum transmission distance for data received by our implant chip has been increased from just over 1 cm with our previous transmitter to over 3 cm with this version. We are currently using this transmitter to test our implant prototypes.

Conclusions: : A class A power amplifier circuit is used for wireless data telemetry to our retinal prosthesis. The circuit was simulated and optimized, and has been built and tested. The class A circuit is impedance matched to a cable, with our primary data transmission coil at the distal end. The class A transmitter is currently in use, driving our prototype implants during assembly testing.

Keywords: retina • retinitis • retinal connections, networks, circuitry