a method for generating a ramp comprises providing a voltage reference source , providing a summing amplifier , providing n switched capacitor elements coupled in parallel between the voltage reference source and the summing amplifier , and selectively activating a predetermined number of the switched capacitor elements to first store charge on each activated switched capacitor element and then to measure the sum of the charges on the activated capacitor switch elements in each of a fixed - integer number of time slots in a cyclical manner , the predetermined number being between 0 and n .