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Proceedings Paper

Method for estimating quantum efficiency for CMOS image sensors
Author(s): Boyd A. Fowler; Abbas El Gamal; David X. D. Yang; Hui Tian
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Paper Abstract

The standard method for measuring QE for a CCD sensor is not adequate for CMOS APS since it does not take into consideration the random offset, gain variations, and nonlinearity introduced by the APS readout circuits. The paper presents a new method to accurately estimate QE of an APS. Instead of varying illumination as in the CCD method, illumination is kept constant and the pixel output is continuously observed - sampling at regular intervals. This makes it possible to eliminate random offset. The experiment is repeated multiple times to obtain good estimates of the pixel output mean and variance at each sample time. The sensor response is approximated by a piecewise linear function and using the Poisson statistics of shot noise gain, charge and read noise are estimated for each line segment. This procedure is repeated at no illumination so that dark charge may be estimated and subtracted from the total charge estimates. The method can also be used to estimate readout noise and gain FPN. Results from 64 X 64 pixel APS test structures implemented in a 0.35 micrometers CMOS process are reported. Using 6 different chips and 16 pixels per chip QE equals 0.37, gain FPN equals 2 percent, dark charge equals 832e-, and readout noise equals 40e-, are estimated.

Paper Details

Date Published: 1 April 1998
PDF: 8 pages
Proc. SPIE 3301, Solid State Sensor Arrays: Development and Applications II, (1 April 1998); doi: 10.1117/12.304561
Show Author Affiliations
Boyd A. Fowler, Stanford Univ. (United States)
Abbas El Gamal, Stanford Univ. (United States)
David X. D. Yang, Stanford Univ. (United States)
Hui Tian, Stanford Univ. (United States)

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

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