Silicon Retina with Adaptive Filtering Properties

Abstract

This paper describes a small, compact circuit that captures the temporal and adaptation properties both of the photoreceptor and of the laminar layers of the fly. This circuit uses only six transis(cid:173) tors and two capacitors. It is operated in the subthreshold domain. The circuit maintains a high transient gain by using adaptation to the background intensity as a form of gain control. The adapta(cid:173) tion time constant of the circuit can be controlled via an external bias. Its temporal filtering properties change with the background intensity or signal-to-noise conditions. The frequency response of the circuit shows that in the frequency range of 1 to 100 Hz, the circuit response goes from highpass filtering under high light levels to lowpass filtering under low light levels (Le., when the signal-to(cid:173) noise ratio is low). A chip with 20x20 pixels has been fabricated in 1.2J.Lm ORBIT CMOS nwell technology.