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Abstract

Apparatus of judging delay time, capable of judging whether or not delay time for delaying an input signal is equal to a desired delay, includes: a shift clock supply unit which supplies a shift clock whose phase is delayed by the desired delayed time against a phase of a reference clock; a phase comparing unit which compares a phase of the shift clock to a phase of a delay clock for which the reference clock is delayed by a delay circuit, and then outputs a comparison signal; and a judging unit which judges whether or not the delay time of the delay circuit is equal to the desired delay time. A method therefor includes: generating a shift clock which delays a phase of a reference clock by a predetermined amount based on a desired delay time; comparing a phase of the delay clock to that of the shift clock; judging whether or not the phase of the shift clock matches that of the delay clock; and repeating a step of generating the shift clock, a step of comparing the phase and a step of judging until the phase of the delay clock matches that of the shift clock.

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First Claim