An improved method of mapping the capacitive contribution to cross-talk among pixels in an imaging array of sensors (typically, an imaging photodetector array) has been devised for use in calibrating and/or characterizing such an array. The method is applicable to almost all image detectors in modern electronic cameras for diverse applications, ranging from consumer cellular-telephone cameras at one extreme to high-performance imaging scientific instruments at the other extreme. In comparison with prior methods of quantifying the capacitive coupling among pixels, this method is a more efficient means of obtaining detailed information pertaining to all the pixels. Unlike the prior methods, this method does not require flat-field illumination of the array: indeed, the method does not require any illumination.

This Difference Image from a portion of an image detector containing arectangular pixel array was generated from two images: one recordedimmediately after and one recorded immediately before the second reset.The second-reset pixels were those residing at intersections of rows andcolumns at seven-pixel intervals.
The method involves a sequence of resets of subarrays of pixels to specified voltages and measurement of the voltage responses of neighboring non-reset pixels. The spacing of the reset pixels is chosen in accordance with the number of neighboring pixels over which the coupling coefficients are sought. The sequence begins with reset of all the pixels in the array to a specified first voltage level. In the next step, a subarray of pixels is reset to a specified second voltage level. Signals consisting of portions of the second reset voltage change are coupled capacitively from the pixels of the reset subarray to adjacent non-secondreset pixels. These signals can be mapped in the form of difference images from the pixel voltages measured immediately before and immediately after the second reset (see figure). The sequence as described thus far can be repeated for different subarrays of pixels, as needed, to acquire data for characterizing all pixels of interest. The entire sequence can be repeated to acquire multiple sets of data that can be combined to reduce measurement noise.

This work was done by Suresh Seshadri, David M. Cole, and Roger M. Smith of Caltech for NASA’s Jet Propulsion Laboratory.

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Refer to NPO-45223, volume and number of this NASA Tech Briefs issue, and the page number.