Circuitry formed of a two-dimensional regular array of capacitive elements 2 is coupled to decoding circuitry in the form of column decoder 8 and a row decoder 6. The decoders 8, 6 are used to select a start point and an end point within a sequence of selected capacitive elements to be connected in parallel following a horizontal raster scan arrangement. The selected capacitive elements may be used to generate an output voltage with a magnitude corresponding to the number of selected capacitive elements.