CCD controller requirements for ground-based optical astronomy

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Abstract
Astronomical CCD controllers are being called upon to operate a wide variety of CCDs in a range of ground-based astronomical applications. These include operation of several CCDs in the same focal plane (mosaics), simultaneous readout from two or four corners of the same CCD (multiple readout), readout of only a small region or number of regions of a single CCD (sub-image or region of interest readout), continuous readout of devices for drift scan observations, differential imaging for low contrast polarimetric or spectroscopic observations and very fast readout of small devices for wavefront sensing in adaptive optics systems. These applications all require that the controller electronics not contribute significantly to the readout noise of the CCD, that the dynamic range of the CCD by fully sampled (except for wavefront sensors), that the CCD be read out as quickly as possible from one or more readout ports, and that considerably flexibility in readout modes (binning, skipping and signal sampling) and device format exist. A further requirement imposed by some institutions is that a single controller design be used for all their CCD instruments to minimize maintenance and development efforts. A controller design recently upgraded to meet these requirements is reviewed. It uses a sequencer built with a programmable DSP to provide user flexibility combined with fast 16-bit A/D converters on a programmable video processor chain to provide either fast or slow readouts.

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