| 摘要 |
An encoder is adapted to be opposed to a scale provided with a plurality of marks or slits arranged in a first direction such that a distance between centers of adjacent marks or slits in the first direction assumes a first length. Each of photo detectors has a light receiving region adapted to receive light emitted from a photo emitter and transmitted by way of the marks or slits, and is operable to output a detection signal in accordance with a quantity of the light received by the light receiving region. The photo detectors are arranged in a second direction perpendicular to the first direction while being shifted in the first direction by a second length which is one-sixteenth of the first length. Each of signal generators is operable to generate an output signal based on at least the detection signal outputted from one of the photo detectors. Each of exclusive-OR logic circuits is operable to perform a logical exclusive-OR calculation with respect to the output signals from two of the signal generators to generate an exclusive-OR signal. Some of the output signals and the exclusive-OR signals are output from the encoder. The level of the detection signal is changed in accordance with a relative movement between the marks or slits and the photo detectors, so as to have a first frequency. Each of the output signals has a second frequency which is double of the first frequency.
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