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A 32/spl times/32 array of photosensors with pulse frequency outputs uses standard 2 /spl mu/m CMOS technology. The photosensors use pulse-frequency encoding to achieve a linear dynamic range of 10/sup 6/ in optical energy. Power dissipation of the photosensor is proportional to the frequency of the pulse outputs, and under typical illumination and bias conditions, the entire 32/spl times/32 array dissipates <100 nW. A/D conversion of incident optical energy is directly by counting the number of pulses in a fixed time period or by measuring the time interval between successive pulses. Each photosensor element is implemented with a photodiode and low-power CMOS circuitry for pulse frequency encoding and readout. The resulting fill-factor of each 107/spl times/107 /spl mu/m/sup 2/ photosensor is approximately 12%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
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Wenxing Yang (2002) studied this question.