An on/off transient imager with event-driven, asynchronous read-out

This paper describes the implementation of a CMOS image sensor that performs a two-way rectified temporal high-pass filtering operation on the incoming visual signal. The sensor adapts to background illuminance and responds to local positive and negative illuminance transients at separately coded terminals. The transients are converted into a stream of asynchronous binary pulses, which are multiplexed onto a common address bus, where the address encodes the location of the sending pixel and the sign of the transient. Gain, response threshold, and refractory period of the pixel output signals can be regulated. The version of the imager described here has an array of 48 × 48 pixels and was implemented with 0.35 μm CMOS technology.