Phase detecting circuit

A phase detecting circuit comprising:

• an arithmetic operation circuit having first and second input terminals for receiving two-phase AC signals in a specified phase relationship and third and fourth input terminals for receiving two-phase AC signals, and producing an output signal corresponding to a phase difference between the two-phase AC signals received at the first and second terminals and those at the third and fourth input terminals;
• frequency variable signal generating means for producing an output signal with a frequency varying in accordance with the output signal from said arithmetic operation circuit;
• counting means for counting the output signal from said frequency variable signal generating means;
• and
• function generating means supplying two-phase AC signals in the specified phase relationship to the third and fourth input terminals of said arithmetic operation circuit, in response to the count data from said counting means;
• wherein count data from said counting means represents digitally the phases of the two-phase AC signals applied to the third and fourth input terminals of said arithmetic operating circuit, and the frequency of the output signal from said signal generating means changes in accordance with the output signal from said arithmetic operation circuit to decrease the phase difference.