Artefact-suppressing analog spike detection circuit for firing-rate measurements in closed-loop retinal neurostimulators

The aim of this research is to investigate low-power circuit concepts for the hardware implementation of an adaptively controlled stimulator for future retinal implants. For this specific application purpose, the circuit complexity must be low, while at the same time the functionality is extended. This paper presents the implementation of an analog spike detection circuit to detect spikes from extracellular recordings and to perform electrode individual firing-rate measurements in a spatially high-density electrode array, which has a reduced circuit complexity compared to the widely-used nonlinear energy operator (NEO) and allows stronger suppression of local oscillations following the retinal remodeling. The module is verified by emulating extracellular activities using the Hodgkin-Huxley model. This recording-unit is integrated into an eight-channel closed-loop-neurostimulator prototype. It dissipates 11.4 μW and requires an area of 0.066 mm2 by using a 350 nm CMOS process.