Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1997-11-05
1999-10-12
Allen, Stephone
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
257294, 327 94, G11C 1928, H01L 2714, H01L 2702
Patent
active
059658711
ABSTRACT:
An active pixel sensing structure includes an array of pixel unit cells each of which an adapted to alternate between a light sensing mode wherein the cell outputs an image signal and a reset mode wherein the cell outputs a reset signal. The image signal is proportional to light incident on the cell, and the reset signal is proportional to a predefined reference potential. An improved readout circuit according to the present invention includes a first sample and hold component for receiving and storing the image signal, and second sample and hold component for receiving and storing the reset signal. A signal amplifier is provided for each sample and hold component. A switching circuit is operable between a first mode and a second mode. In the second mode, the first and second sample and hold components are operatively decoupled from the corresponding signal amplifiers while input terminals of the signal amplifiers are connected to a source of predetermined reference potential. With the switching circuit in the second mode, fixed pattern noise (FPN) attributable to the amplifiers is determined. With the switching means in the first mode, a voltage, D2, is determined across outputs of the signal amplifiers. The voltage, D2, is proportional to a voltage equal to the difference between the image signal and the reset signal plus the FPN voltage. A processing means subtracts the voltage, D1, from the voltage, D2, to develop a signal proportional to the light detected by the cell.
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Zhou et al., "A CMOS Active Pixel Image Sensor With Amplification And Reduced Fixed Pattern Noise", IEEE Workshop on Charge-Coupled Devices and Advanced Image Sensors, (Apr. 1995) 5 pgs.
Mendis et al., "CMOS Active Pixel Image Sensors For Highly Integrated Imaging Systems", IEEE Journal of Solid-State Circuits, vol. 32, No. 2 (Feb. 1997) pp. 187-197.
Li Wei
Shih Li-yen
Zhang Zhongxuan
Zhou Zhimin
Allen Stephone
Boyce Justin
Donnelly Oppenheimer W.
Hamrick Claude A. S.
PixArt Technology, inc.
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