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23 February 2005 Distributed and fractal pixel sensors
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A CMOS active pixel sensor array with anti-aliasing using distributed photodiodes that exhibit a 2-D sinc-like function has been fabricated and tested. Unlike the traditional rectilinear photodiode shapes, the sinc-function diode configurations are interleaved with neighboring pixels. This passive form of focal plane signal processing requires no additional circuitry or power, and depends only on the shape of each pixels sensor. Two such distributed sensor arrays were implemented on a single chip, one with pixels including first-order orthogonal side lobes, and one with first and second-order orthogonal side lobes as well as 1st-order diagonal side lobes. For comparisons, a conventional array with rectangular photodiodes was implemented on the same chip, with the same total sensor area as the second distributed version. Simulations of the filtering effectiveness of various pixel shapes will be presented, as well as measurements of pixel performance including leakage and noise. Of interest, distributed pixel sensors have a relatively larger periphery and hence higher capacitance, increased well-capacity and decreased charge-to-voltage gain relative to equal-area square sensors. The larger periphery raises a concern about increased leakage and noise. However, measurements showed less than 2% increase in leakage current and similarly small differences in noise.
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Stuart Kleinfelder, Yandong Chen, and Arezou Koohi "Distributed and fractal pixel sensors", Proc. SPIE 5678, Digital Photography, (23 February 2005);


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