Time-domain correlation image sensor: CMOS design and integration of demodulator pixels

We describe CMOS pixel design and fabrication results of the time-domain correlation image sensor, which has been proposed and studied in our laboratory. This sensor can essentially be regarded as an array of demodulators--it computes temporal correlation between incident light intensity and a global reference signal every frame. The correlation detection allows sensitivity to high frequency illumination, and makes various applications possible by using this sensor together with active sensing methods such as modulated illumination and camera motion. The prototype pixel, based on a transconductance multiplier with a photodiode current source and a pair of capacitive loads, is designed as a MOS pair with its common source and drains extended to form a photodiode and capacitors, respectively. Based on this design, 64 times 64-pixel sensors were fabricated with a 1.2-micron CMOS process. Experiments under sinusoidally modulated illumination confirmed temporal correlation performance of the fabricated sensors. Application examples such as lock-in photometry and vibrometry are also presented.