Patent ID: 7352304

Claim:
An interpolation apparatus in an encoder, comprising: an analog-to-digital converter which digitizes a sine wave signal and a cosine wave signal, respectively, the sine wave signal and the cosine wave signal being produced in response to position displacement of an object to be measured; an amplitude level detecting circuit which detects each amplitude level of the sine wave signal and the cosine wave signal, which have been digitized; a computing circuit which multiplies the amplitude level of one of the sine wave signal and the cosine wave signal by an interpolation position parameter according to a tangent value at an interpolation position to be set in accordance with the number of interpolations of a phase angle of the sine wave signal and the cosine wave signal; a comparing circuit which compares a first output from the computing circuit for the one of the sine wave signal and the cosine wave signal to a second output from the amplitude level detecting circuit for the other of the sine wave signal and the cosine wave signal, the comparison being made at every said interpolation position; and a region detecting circuit which identifies a region sectionalized by the interpolation positions adjacent to each other based on an output from the comparing circuit corresponding to each said interpolation position, the phase angle of the sine wave signal and the cosine wave signal existing in the region.