Abstract: The disclosure is directed to an analog-digital converter which includes a source having an output of fixed frequency time-spaced pulses. An oscillator having an output of time-spaced pulses, harmonically related to pulses from the source, is comprised of a plurality of digital gates connected serially in a loop. At least one of the digital gates includes impedance means such as a resister or capacitor, responsive to an analog condition to form a modulator. Change in the value of the impedance changes the time constant of the modulator to effect a change in the time-spaced pulses related to the instantaneous amplitude of the analog condition. The outputs of the source and the oscillator are applied to a comparator. Means responsive to the comparator is employed to correct the oscillator time-spaced pulses toward an in phase state relative to the time-spaced pulses from the source.