Abstract: An analog to digital converter for use in a digital voltmeter includes a periodic source of reference signal in ramp form starting at a negative potential and increasing to a given positive potential. The ramp signal and an analog signal to be measured form the inputs for a first comparator which provides a given output level as long as the ramp signal is less than the analog signal. A source of clock signals and the output of the first comparator are connected to a first logic circuit which provides an output of clock signals during the period that the first comparator is at the given level. A second comparator is connected to the ramp signal and ground potential and provides a given output level until the ramp signal reaches ground potential. A second logic circuit is connected to the output of the second comparator and the first logic circuit and provides clock signals during the period that the ramp signal is above ground potential and less than the analog signal.