CMOS active pixel image sensor with in-pixel CDS for high-speed cameras

Abstract

This paper presents a high-speed CMOS image sensor whose frame rate exceeds 2000 frames/sec (fps). The pixel includes a photodiode, a charge-transfer amplifier, and circuitry for correlated double sampling (CDS) and global electronic shuttering. Reset noise, which is the major random noise factor, is reduced by the CDS combined with the charge-transfer amplifier. The total number of devices in the pixel is 11 transistors and 2 MOS capacitors. Test circuits were fabricated using the 0.25 um CMOS process. The sensitivity of the 20 x 20 um² pixel using the floating diffusion capacitor of 6.2 fF and the photodiode area of 15 x 12.7 um^2 is 34 V/lux-sec. At 1000 fps, noise level is 2.43 mVrms (dark). The noise level and the sensitivity are greatly improved compared to the non-charge-transfer pixel without global shutter (3Tr-type) implemented with the same technology, and to a previous version of the APS with in-pixel CDS.