Dissipating electrical charge

In circuitry of the type including analog circuit means for producing an analog output in response to an input and digital circuit means for sampling said output, said analog circuit means including a charge storage element that can become charged in response to said input, the improvement comprising charge dissipation means for dissipating the charge built up in said charge storage element during an interval prior to sampling of said output by said digital circuit means,

• wherein said digital circuit means and analog circuit means are connected in a loop and said digital means includes means for providing said input to said analog circuit and for periodically changing said input in response to changes in said sampled output,
• wherein said digital circuit means includes means for changing said input so that said output approaches a desired value,
• wherein said digital circuit means includes comparator means for measuring whether said output is above or below said desired value and includes means for adjusting said input to said analog circuit based on the output of said comparator,
• wherein said analog circuit means includes a low-pass filter which includes one or more capacitors which form said charge storage element, the response of said filter being characterized by a time constant, and
• wherein said digital circuit means includes means for varying said input so that at two successive sampling times said analog output can change from a first value greater than said desired value to a second value less than said desired value, the amount by which said second value is less than said desired value being 100 or more times smaller than the amount by which said first value exceeds said desired value, whereby the time required, without dissipation of the charge stored in said capacitors, for said output to change from being above to being below said desired value, and thereby allow said comparator output to change, is of the order of 5 or more said time constants.