Patent ID: 8000414

Claim:
An amplitude detection apparatus for periodically sampling a waveform signal indicating an angle or a position of a moving body making a rotational movement or a reciprocating movement, and for detecting an amplitude of the waveform signal based on digital signals obtained by sampling, comprising: a maximum-minimum value detector detecting a maximum value and a minimum value of the digital signals by using a digital signal at a certain time point and digital signals obtained by the sampling before the certain point; a first lowpass filter having a cutoff frequency lower than a frequency of the waveform signal, and stabilizing the maximum value of the digital signals; a second lowpass filter having a cutoff frequency lower than the frequency of the waveform signal, and stabilizing the minimum value of the digital signals; a cycle detector detecting a cycle of the waveform signal from a plurality of the digital signals; a correction coefficient generator generating a numeric value of a correction coefficient expressed by a calculation with respect to the cycle of the waveform signal and a cycle of the sampling; a first multiplier generating a corrected maximum value by multiplying the maximum value of the digital signals by the correction coefficient; a second multiplier generating a corrected minimum value by multiplying the minimum value of the digital signals by the correction coefficient; and an output portion outputting at least one of the corrected maximum value and an absolute value of the corrected minimum value as the amplitude of the waveform signal wherein the correction coefficient generator calculates a correction coefficient A as: A = π ⁢ ⁢ ts T ⁢ ⁢ Sin ⁡ [ π ⁢ ⁢ ts T ] where ts indicates the cycle of the sampling, T indicates the cycle of the waveform signal, and the correction coefficient generator transmits the correction coefficient A to the first multiplier and the second multiplier.