title: Safety ensuring retinal prosthesis with precise charge balance and low power consumption.
abstract: Ensuring safe operation of stimulators is the most important issue in neural stimulation. Safety, in terms of stimulators' electrical performances, can be related mainly to two factors; the zero-net charge transfer to tissue and the heat generated by power dissipation at tissue. This paper presents a safety ensuring neuro-stimulator for retinal vision prostheses, featuring precise charge balancing capability and low power consumption, using a 0.35 μm HV (high voltage) CMOS process. Also, the required matching accuracy of the biphasic current pulse for safe stimulation is mathematically derived. Accurate charge balance is achieved by employing a dynamic current mirror at the output of a stimulator. In experiments, using a simple electrode model (a resistor (R) and a capacitor (C) in parallel), the proposed stimulator ensures less than 30 nA DC current flowing into tissue over all stimulation current ranges (32 μA-1 mA), without shorting. With shorting enabled, further reduction is achieved down to 1.5 nA. Low power consumption was achieved by utilising small bias current, sharing of key biasing blocks, and utilising a short duty cycle for stimulation. Less than 30 μW was consumed during stand-by mode, mostly by bias circuitry.
authors.forename: Hosung
authors.initials: H
authors.lastname: Chun
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Yang
authors.forename: Torsten
authors.initials: T
authors.lastname: Lehmann
mesh_terms: D017097:Electric Impedance; D055615:Electrical Equipment and Supplies / Q000592:standards*; D004867:Equipment Design / Q000592:standards; D004869:Equipment Safety; D008839:Microelectrodes / Q000592:standards; D055616:Microtechnology / Q000295:instrumentation*; D057488:Visual Prosthesis / Q000592:standards*