A charge pump for driving CMOS active pixel reset |
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Authors: | Jiang-tao Xu Bin-qiao Li Su-ying Yao and Zhong-yan Sun |
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Affiliation: | (1) School of Electronics Information Engineering, Tianjin University, Tianjin, 300072, China |
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Abstract: | To overcome the limitation of low image signal swing range and long reset time in four transistor CMOS active pixel image
sensor, a charge pump circuit is presented to improve the pixel reset performance. The charge pump circuit consists of two
stage switch capacitor serial voltage doubler. Cross-coupled MOSFET switch structure with well close and open performance
is used in the second stage of the charge pump. The pixel reset transistor with gate voltage driven by output of the pump
works in linear region, which can accelerate reset process and complete reset is achieved. The simulation results show that
output of the charge pump is enhanced from 1.2 to 4.2 V with voltage ripple lower than 6 mV. The pixel reset time is reduced
to 1.14 ns in dark. Image smear due to non-completely reset is eliminated and the image signal swing range is enlarged. The
charge pump is successfully embedded in a CMOS image sensor chip with 0.3 × 106 pixels.
This work has been supported by the National Natural Science Foundation of China (No.60806010); the Science and Technology
Innovation Special Funds of Tianjin (No.05FZZDGX00200) |
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Keywords: | |
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