Patent ID: 7541951

Claim:
A tracking loop type digital angle converter for detecting an input angle θ by receiving rotation detection signals S 1 =f(t)sin θ and S 2 =f(t)cos θ from the input angle θ from a rotation detector excited by an exciting signal f(t) of a periodic function, comprising: multiplying means for calculating S 1 cos φ and S 2 sin φ from the rotation detection signals S 1 and S 2 and the output signal φ; subtracting means for calculating a difference S 1 cos φ−S 2 sin φ=f(t)sin(θ−φ) of these multiplication results; synchronous detecting means for synchronously detecting the difference f(t)sin(θ−φ) to obtain a control deviation ε=sin(θ−φ); a voltage controlled oscillator for generating pulses of a frequency corresponding to the control deviation ε; a counter for counting the pulses outputted from the voltage controlled oscillator to produce an output angle φ; trigonometric function value generating means for outputting cos φ and sin φ corresponding to the output angle φ and negatively feeding back the cos φ and sin φ to the multiplying means; a detected signal sign judging section for receiving the rotation detection signals S 1 and S 2 and judging plus and minus signs of sin θ and cos θ of the rotation detection signals S 1 and S 2 ; and an output angle correcting section for detecting a quadrant of the input angle θ from the signs of sin θ and cos θ outputted from the detected signal sign judging section, detecting an angle error between θ and φ, deciding whether or not the angle error is larger than a predetermined value, and if so, phase-shifting the output angle φ by 180°.