A 0.5 V/1.8 V High Dynamic Range CMOS Imager for Artificial Retina Applications

This paper presents a 0.5 V/1.8 V high dynamic range (HDR) sense-and-stimulus (SAS) CMOS imager with adaptive gain control for artificial retina applications. The proposed dual-supply SAS pixel consists of a 0.5 V HDR pulse-width-modulation (PWM) image sensor (for sense) and a 1.8 V pulse-to-current stimulator (for stimulus) to achieve a highly integrated and low-power solution. The 0.5 V operated HDR image sensor [1] is adopted to reduce power consumption with dynamic range extension for in-vivo requirement and mimicking the eyesight capability. The 1.8 V operated in-pixel pulse-to- current stimulator provides a biphasic current pulse with sufficient intensity to activate neuron cells for artificial vision recovery applications.

The time-to-voltage (T-V) conversion technique with a programmable gain is employed to achieve a reduced fixed-pattern-noise (FPN) and an adaptive sensitivity. A prototype chip has been implemented and verified with a sensing array of 40×40, a pixel size of 30×30 μm2, and a fill factor of 33.3%. The maximum driving capability of biphasic stimulation current is ±50 μA with a 7.5 kΩ electrode model. The measurement results show an array FPN of 0.63 % and a tunable dynamic range of 36 dB. The chip consumes a total power of 2.1 mW with current stimulator at 16.9 frame/s, which achieves an iFOM of 77.7 nW/frame-pixel.

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