Patent ID: 7574311

Claim:
A time interval measuring apparatus comprising: a reference signal generator which generates a reference signal of a sine wave having a predetermined frequency; a phase shifter which receives the reference signal generated by the reference signal generator, and outputs a first analog signal and a second analog signal whose phases are shifted each other; a first analog/digital (A/D) converter which performs sampling of the first analog signal which is output from the phase shifter at an input timing of a pulse signal for time interval measurement, converts a value obtained by the sampling into a first digital sample value, and outputs the first digital sample value; a second A/D converter which performs sampling of the second analog signal which is output from the phase shifter at the input timing of the pulse signal, converts a value obtained by the sampling into a second digital sample value, and outputs the second digital sample value; an error correction unit which receives the first digital sample value and the second digital sample value which are output from the first A/D converter and the second A/D converter, and respectively corrects direct current offset errors respectively generated in the first digital sample value and the second digital sample value, and a phase error with respect to 90 degrees and an amplitude error which are generated between the first digital sample value and the second digital sample value, the errors being generated by the phase shifter, the first A/D converter and the second A/D converter; an instantaneous phase calculation unit which calculates an instantaneous phase of the reference signal at the input timing of the pulse signal based on the first digital sample value and the second digital sample value in which the errors are already corrected by the error correction unit; and an interval time calculation unit which determines a variation of the instantaneous phases from each of the instantaneous phase which is respectively calculated by the instantaneous phase calculation unit at each of the input timing of two of the pulse signals, and determines an input interval time of the pulse signals based on the variation of the instantaneous phases.