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Proceedings Paper

Memory read-out approach for a 0.5-um CMOS image sensor
Author(s): Willem Hoekstra; Andre van der Avoird; Marq Kole; Guido G. Schrooten; Chris J. Schaeffer
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Paper Abstract

In image sensors with passive pixels the column capacitance is large compared to the capacitance of the pixel. The charge-to-voltage conversion occurs in the column amplifier relatively far from the pixel. This may result in a high sensitivity to interference, especially in cases other electronic circuitry is located on the same chip. Two types of CIF CMOS imagers are presented that use different read- out options to counter this effect. Both designs use differential read-out as DRAM's do. This means that the pixel is compared to a reference cell. The first type uses a reference cell on the same row; the second type utilizes a fully symmetrical way of read-out, similar to digital memories by having this reference on the same column. Furthermore, two other means of image quality improvement are applied. A boost circuit is sued to generate a negative voltage for driving the selecting transistor to insure that it is completely switched on during pixel reset. By this, threshold differences between pixels do not affect the reset voltage. The second is a well thought-out column amplifier that calibrates its offset before reading the pixel information.

Paper Details

Date Published: 1 April 1998
PDF: 7 pages
Proc. SPIE 3301, Solid State Sensor Arrays: Development and Applications II, (1 April 1998); doi: 10.1117/12.304557
Show Author Affiliations
Willem Hoekstra, Philips Imaging Technology (Netherlands)
Andre van der Avoird, Philips Research (Netherlands)
Marq Kole, Philips Research (Netherlands)
Guido G. Schrooten, Philips Semiconductors (Netherlands)
Chris J. Schaeffer, Philips Semiconductors (Netherlands)

Published in SPIE Proceedings Vol. 3301:
Solid State Sensor Arrays: Development and Applications II
Morley M. Blouke, Editor(s)

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