PURPOSE: To continuously measure a phase with respect to all of angles, by providing a tracking converter part outputting the output of an incremental and decremental counter corresponding to the positive and negative of the output signal of an adder-subtractor as the response wave phase shift of the response signal of a system to be measured.
CONSTITUTION: The signals (d), (e) outputted from a reference oscillator 3 and the signal (a) supplied from a system 2 to be measured through an input attenuator 4 are multiplied by a multiplier 1 to output signals (b), (c). Next, the signals (b), (c) are applied to a tracking converter part 22. A trigonometric function generator 8 receives the output of an incremental and decremental counter 12 to outputs signals (h), (i). The signals (h), (i) are multiplied by the signals (b), (c) by multipliers 6, 7 to output signals (f), (g) which are, in turn, added and subtracted by an adder-subtractor 9 to output a signal (j). The signal (j) is inputted to a zero point comparator 10 to perform the judgement of positive and negative and an incremental and decremental counter control signal (k) is formed. At the same time, the signal (j) is also applied to a voltage control pulse oscillator 11 to generate a signal l and the signals (k), l are counted by the counter 12 to be outputted as incremental and decremental count outputs.
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