A Time-to-First-Spike CMOS Image Sensor

A time-to-first-spike (TTFS) imager was designed such that each pixel outputs a single digital pulse whose timing encodes pixel illumination. For still image applications, this time representation provides a tremendous increase in dynamic range, similar to that of other existing time-based imagers. However, a major advantage of the TTFS imager is that this wide dynamic range can be achieved even for 30 frames/s video applications. A prototype 32times32 TTFS image sensor was fabricated in AMI 0.5 mum CMOS technology. The prototype chip demonstrates a 104 dB dynamic range (limited by the optical equipment), 42 V/electron conversion gain, 1.25 nA/cm² dark current, and 3.1 mW power consumption at 30 frames/s.