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A four-channel custom chip designed for reading out the CCDs of the proposed SNAP satellite visible imager is presented. Each channel consists of a single-ended to differential converter followed by a correlated double sampler and a novel multislope integrator. The output signal is differentially brought out of the chip by an output buffer. This circuit is designed to operate at room temperature for test purpose and at 140 K, which will be the operating temperature. The readout speed is 100 kHz. The 16-bit dynamic range is covered using 3 gains each with a 12-bit signal to noise ratio. The prototype chip, implemented in a 0.25 μm CMOS technology, has a measured readout noise of 7 μV rms at 100 kHz readout speed, a measured nonlinearity of ±0.0025% and a power consumption of 6.5 mW, with a 3.3 V supply voltage.
Date of Publication: Oct. 2004