Automatic resolution changing method and circuit for use in digital conversion of two-phase sinusoidal wave signals

A automatic resolution changing circuit for use in a high-precision digital conversion of two-phase sinusoidal wave signals, said automatic resolution changing circuit having:

• a first converter for receiving a two-phase-sinusoidal-wave-like A-phase output, which is outputted based on rotation of a rotor with respect to a stator, and for outputting a first converter output (sin θ·cos φ·f(t));
• a second converter for receiving a two-phase-sinusoidal-wave-like B-phase output, which is outputted based on rotation of said rotor with respect to said stator, and for outputting a second converter output (cos θ·sin φ·f(t));
• a compensator for outputting an angular velocity (dφ/dt) of said rotor from the difference (sin(θ−·φ)·f(t)) between the first converter output (sin θ·cos φ·f(t)) and the second converter output (cos θ·sin φ·f(t)) through a phase sensitive detection circuit;
• and
• a counter for integrating the angular velocity (dφ/dt) of said rotor, which is outputted from said compensator, said digital conversion circuit adapted to perform digital conversion of the rotation angle (θ) of said rotor with respect to said stator and to output a result of the digital conversion,
• said automatic resolution changing circuit for use in a high-precision digital conversion of two-phase sinusoidal wave signals, further comprising:
• a changing circuit for reducing the resolution of said counter in a case where the angular velocity (dφ/dt) is equal to or higher than a first percentage of a follow-up speed at a current resolution of said counter when the result of the digital conversion is outputted, and for increasing the resolution of said counter in a case where the angular velocity (dφ/dt) is equal to or lower than a second percentage of the follow-up speed at the current resolution of said counter when the result of the digital conversion is outputted.