A CMOS Color and Brightness Sensor Chip Based On Buried Double Junction (BDJ) Photodiode
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Buried double junction (BDJ) photodiodes have been used for color sensing for some time. The state of art CMOS image sensor usually needs a color filter array placed over the photosensitive area to recognize colors. After applying signal processing techniques according to the filter types, the color of the object can be restored. Since the BDJ output current ratio is corresponds to the light wavelength, it is possible to detect color by getting rid of the color filters, which greatly increase the production costs. In this work, an 8×8 BDJ photodiode sensor array with pixel-level readout circuitry, column summing amplifiers and control logic circuit are presented. Each sensor can recognize color and intensity of the incident light at the same time. Since the output signal is logarithmically related to the current, the output dynamic range is dramatically enhanced. Both the intensity detection and color detection functionality are verified, as is the operation of the array. The sensor chip is designed using Cadence Virtuoso and tape out in ON-semi CMOS 0.5&mgr;m process (3M2P) via MOSIS. The total power consumption is 59.5mW with 5-V supply voltage. It is believed that this is the first example of an array of these devices.