PURPOSE: To achieve a higher accuracy by an A/D converter, a branching filter, a multiplier, a cumulative adder, a divider, an inverse tangential circuit and the like.
CONSTITUTION: An analog input signal A is converted into a digital signal B with an A/D converter 1 and separated into a sine wave signal C and a cosine wave signal D with a phase difference branching filters 2 and 3 of a 90° phase difference branching filter 12. An output E of a variable digital sine wave oscillator 4 turns to an output F through a phase difference branching filter 5 to be multiplied by the signal C with a multiplier 6 and an output G is inputted into an cumulative adder 8 to obtain an output J. The output F and the signal D are multiplied with a multiplier 7 and an output H is inputted into a cumulative adder 9 to obtain an output J. The output I is divided by the output J with a divider 10 and the resulting output K is applied to an inverse tangential circuit 11 to obtain a phase L of a selection frequency thereby achieving a higher accuracy with ease.
WADA SHIGENORI
MIYAGI NIPPON DENKI KK