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A large voltage swing active pixel structure for complementary metal-oxide-semiconductor (CMOS) image sensors is presented. The sensor has a 1.5 × 1.5 mm die area, and it is fabricated by using 0.13 μm 1P8M digital CMOS technology. The pixel size is 5 × 5 μm . It has a two-step readout and 0.72 V output voltage swing with a power supply of 1.25 V. Three different photodetectors, including n-well/p-sub, n+/p-sub, and photogate, are implemented in a 32 × 92 array and tested. A maximum 61 dB dynamic range is measured from the photogate pixel, and the signal-to-noise ratio is 53 dB. The measured root-mean-square temporal noise is below 0.6% for three different pixel arrays. A ring oscillator readout circuit is also implemented to generate a frequency output according to pixel signal. A digital counter is used to further record the frequency signal, therefore an extra analog-to-digital converter is not required.