| 摘要 |
An encoder sampling a first phase (A) signal and second phase (B) signal with phases differing from each other by about 90 degrees at the same timing, converting them from an analog to digital format, and detecting an angle signal based on the obtained digital signals, provided with offset detection circuits using a second phase A/D converted value (B<SUB>D</SUB>) of when a first phase A/D converted value (A<SUB>D</SUB>) is near a first value (X<SUB>A</SUB>) to find a second phase (B) offset value (Bofs), using a first phase A/D converted value (A<SUB>D</SUB>)of when a second phase A/D converted value (B<SUB>D</SUB>) is near a second value (X<SUB>B</SUB>) to find a first phase (A) offset value (Aofs), and using the currently found first offset value (Aofs) for the first value (X<SUB>A</SUB>) and the currently found second offset value (Bofs) for the second value (X<SUB>B</SUB>)when calculating the next first offset value (Aofs) and second offset value (Bofs) and a subtraction circuits using a first offset value (Aofs) and second offset value (Bofs) to correct offsets of the first phase signal and second phase signal, whereby correct offset amounts can be obtained with regard as to the length of the sampling periods or the magnitudes of the offsets.
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