A SPATIOTEMPORAL DIFFERENTIATION LIGHT SENSOR

We present an optical differentiator consisting of 19 transistors asso ciated with a photodiode. This circuit is to be used as a processing e lement in an analog retina for spatial or temporal differentiation. A test circuit has been processed with 1.5 mu m single-poly CMOS technol ogy, Photocarrier leakage due to minority-carrier diffusion of a pixel -size distance is reduced to less than 0.05%. The differentiator opera tes with a sample rate up to 50 kHz and a differential sensitivity of 13 mV (W m(-2))(-1) or 0.02 mV lux(-1). It can work with a sample rate as low as a few dozen hertz and the lowest limit of a detectable ligh t signal can be several lux. The input dynamic range can reach four de cades. (C) 1997 Elsevier Science S.A.