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 transistors 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 adaptation 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-noise ratio is low). A chip with 20x20 pixels has been fabricated in 1.2µm ORBIT CMOS nwell technology.