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Safety Ensuring Retinal Prosthesis With Precise Charge Balance and Low Power Consumption

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3 Author(s)
Hosung Chun ; Dept. of Electr. & Electron. Eng., Univ. of Melbourne, Melbourne, VIC, Australia ; Yuanyuan Yang ; Lehmann, T.

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.

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Biomedical Circuits and Systems, IEEE Transactions on  (Volume:8 ,  Issue: 1 )