Digitally programmable gain control circuit for charge-domain signal processing

A simple, nearly passive circuit for programmable gain control of charge-domain signals is described. The circuit is functionally equivalent to a multiplying digital-to-analog converter (MDAC) and is implemented in a 3- mu m double-poly, double-metal charge-coupled device (CCD) process. Two implementations of the circuit are reported: a single-stage recursive converter, and a ten-stage pipeline converter. The latter occupies 0.4 mm/sup 2/ of chip area and consumes approximately 2 mu W for a 1-kHz conversion rate. The circuit is shown experimentally to have all 8-b equivalent accuracy in both differential and integral linearity and is expected to find application in focal-plane image processing for both detector nonuniformity correction and convolution weighting.<
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