Detector/CCD coupling for hybrid focal planes

Direct coupling of photovoltaic infra-red detectors to a signal processing CCD offers uniform, high performance for scanned imaging systems with Time Delay and Integration (TDI) to improve sensitivity. Under some conditions the background charge from the detector is too large to directly sum in the CCD shift register, whose size is limited by focal plane packing density requirements. A new buffer circuit is described which reduces the charge input into the CCD while maintaining the detector S/N. Experimental evaluation of the circuit performance has demonstrated that an overall noise figure of less than 1.25 is obtained with a CCD input charge reduced to less than 10% of that obtained from the detector.