A 1/2.5 inch VGA 400 fps CMOS Image Sensor With High Sensitivity for

Abstract

Machine vision requires C MOS image sensors (CISs) with high frame rate, short exposure time, and fine spatial res- olution. Recently, capacitive transimpedance ampli fier (CTIA) is used in the high-speed pixel circui t to achieve high sensitivity by expediting the charge transfer from the photodiode to a tiny inte- gration capacitor ( ). Existing CTIA pixel designs have large pixel sizes due to the multiple sampling capacitors and switches for global shutter and CDS, which unfavorably limits the spatial reso- lution. In this paper, we present a 400 fps CIS design with 640 × 480 pixel array for machine vision. With simpli fied pixel circuits, the new sensor has a CTIA pixel size of 8.7 × 8.22 µm 2,w h i c hi st h e smallest in the category. The pix el implements a new multi-layer MOM capacitor with good uniformity as the tiny ,w h i c h achieves high sensitivity (36.5 V/lux·s) without calibration. Pixel- wise CDS is implemented in this global-shutter CIS to minimize the pixel noise. The pixel signals are quantized by 640 column pro- cessing slices with 12 bit resolution at 411 kS/s. The size of the column SAR ADC is minimized with a simple calibration tech- nique. The CIS is fabricated in a 0.18 µm mixed-signal CMOS process. The temporal noise is 15.6 e .W i t ht h en e wM O Mc a - pacitor, FPN of the CIS is 0.55% without calibration. The new pixel design achieves the highest sensitivity per unit area.