CMOS retinal prosthesis with on-chip electrode impedance measurement

A retinal prosthesis device with built-in self-test capability is proposed and demonstrated. The measurement of electrode impedance as a self-test is achieved without increasing the chip area by employing analogue multiplexers to allow the electrodes to be used for both stimulation of retinal cells and measurement of impedance. Measurement is performed using a four-terminal method to ensure good accuracy. A prototype stimulus chip with 16×16 channels is fabricated using standard 0.6 μm CMOS technology, and is demonstrated to provide self-test functionality with error of as little as 0.05% in the frequency range of 100 Hz to 100 kHz.