To solve the problems, wherein the amount of phase shift is changed delicately between phase measurement ranges and hence measurement precision cannot be improved when the frequency of an input signal to be measured is changed, since propagation delay times are not strictly the same in inverted and non-inverted operation when phase is inverted by an exclusive OR circuit, or the like.
A phase difference measuring apparatus has a phase shifting circuit 14 for shifting the phase of one of two input signals 1, 2, for example the input signal 1, and controls the amount of phase shift according to the detection result of a phase difference detection circuit 13 when shifting a phase by the phase shifting circuit 14. Additionally, by detecting the amount of phase shift in the input signal 1 by the phase shifting circuit 14 by using a phase difference detection circuit 15, phase deviation caused by inserting the phase shifting circuit 14 into the signal path of the input signal 1 is detected. The detected phase deviation is added to the detection result of a phase difference detection circuit 16 by an addition circuit 17 for correction as the phase difference information between the two input signals 1, 2.
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