A four-million pixel CCD image sensor

The authors have developed an ultra-high-resolution, full-frame CCD imager of 2048*2048 pixels. The pixel size is 9 mu m*9 mu m. The sensor has dual readout registers to increase the data rate. It is designed for a horizontal clock rate of 20 MHz. With the dual line readout mode, it takes 114 ms to read a frame. The experimental device has less than 0.5 nA/cm/sup 2/ dark current at room temperature, corresponding to about 25 electrons of dark shot noise at 200 ms frame time, including both integration and read time. The output amplifier, made of a two-stage source follower, has a sensitivity of 10 mV per electron. With correlated double sampling, the output amplifier contributes about 10 noise electrons at the 20 MHz data rate. Thus, the dark shot noise is the dominant noise component unless the imager is cooled. The charge capacity of the CCD is 85000 electrons, giving a dynamic range of 3000. A charge transfer efficiency of 0.99999 has been observed.<
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