Abstract: This system generates output pulses in successive periods of time, each including sub-intervals during which the output pulses may be varied in accordance with a pre-determined scheme. The time periods and sub-intervals within the periods are defined by means of signals derived from a fundamental clock frequency generation circuit and first and second parallel sets of frequency division circuits connected to the fundamental frequency generation circuit. The first set of frequency division circuits is used together with a sub-interval timing circuit to define the sub-intervals of time included in each period.