Abstract: A series resistor-capacitor combination is coupled across a source of supply potential so that the capacitor will charge toward the supply potential through the resistor. The capacitor is discharged through a shunt connected switch that is operated by means of a latch. A pair of inverters coupled to the capacitor respond to the capacitor charge and operate through logic means to set and reset the latch. The inverters are made to have similar but different thresholds. When the capacitor charge is below both thresholds, the latch is set to turn the switch off so that the capacitor charges. When both thresholds are exceeded, the logic resets the latch to turn the switch on and discharge the capacitor. The capacitor therefore normally charges and discharges between the two thresholds and this threshold difference parameter is substantially independent of circuit fabrication variables.