A CMOS image sensor using floating capacitor load readout operation

Abstract

In this paper, a CMOS image sensor using floating capacitor load readout operation has been discussed. The floating capacitor load readout operation is used during pixel signals readout. And this operation has two features: 1. in-pixel driver transistor drives load capacitor without current sources, 2. parasitic capacitor of pixel output vertical signal line is used as a sample/hold capacitor. This operation produces three advantages: a smaller chip size, a lower power consumption, and a lower output noise than conventional CMOS image sensors. The prototype CMOS image sensor has been produced using 0.18 μm 1-Poly 3-Metal CMOS process technology with pinned photodiodes. The chip size is 2.5 mmH x 2.5 mmV, the pixel size is 4.5 μmH x 4.5 μmV, and the number of pixels is 400H x 300V. This image sensor consists of only a pixel array, vertical and horizontal shift registers, column source followers of which height is as low as that of some pixels and output buffers. The size of peripheral circuit is reduced by 90.2 % of a conventional CMOS image sensor. The power consumption in pixel array is reduced by 96.9 %. Even if the power consumption of column source follower is included, it reduced by 39.0 %. With an introduction of buried channel transistors as in-pixel driver transistors, the dark random noise of pixels of the floating capacitor load readout operation CMOS image sensor is 168 μVrms. The noise of conventional image sensor is 466 μVrms; therefore, reduction of 63.8 % of noise was achieved. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.