Functional Electrical Stimulation (FES) is widely adopted in neuro-engineering to partially alleviate diseased functions in the brain, retina and cochlea. We present a 32-channel wirelessly powered constant current stimulator and low power recording amplifier for FES based applications. The biphasic stimulator utilizes innovative techniques for matched positive/ negative currents and thus improves charge balance. Electrode discharging scheme is added for stimulation artifact suppression. An improved low power amplifier is incorporated for evoked response measurements. Electrical performance is characterized using simulated electrode-electrolyte impedance. Closed-loop stimulation and recording experiments have been performed. Stimulation current magnitudes of 2μA–200μA and up to 400Hz rate have been realized. Theory and limitation of discharging scheme is explored while suppressing artifacts down to 3ms. Alternate anodic-first and cathodic-first stimulation pulses are adopted for enhanced charge balancing. The low power amplifier exhibits gain of 1200 and bandwidth 350Hz–1.02KHz. A multiplexer/ demultiplexer is used to share the front-end among 32 electrodes. The inductively coupled wireless energy harvester works at 125KHz–135KHz that can remotely deliver 1.4mW at 1cm distance to an equivalent of 10K load. The system can accommodate multielectrodes with impedance up to 100KΩ. The entire hybrid analog-digital system consumes 360μW quiescent power. Miniaturization makes it suitable for in-vivo applications.
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