Patent ID: 7476844

Claim:
An encoder, 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, comprising: a photo emitter, operable to emit light; a plurality of photo detectors, each of which has a light receiving region adapted to receive the light emitted from the 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 including a first photo detector, a second photo detector, a third photo detector and a fourth photo detector which are arranged in a second direction perpendicular to the first direction while being shifted in the first direction by a second length which is [m+(½ n+3 )] of the first length; a first signal generator, operable to generate a first signal based on at least the detection signal output from the first photo detector; a second signal generator, operable to generate a second signal based on at least the detection signal output from the second photo detector; a third signal generator, operable to generate a third signal based on at least the detection signal output from the third photo detector; a fourth signal generator, operable to generate a fourth signal based on at least the detection signal output from the fourth photo detector; a first exclusive-OR logic circuit, operable to perform a logical exclusive-OR calculation with respect to the first signal and the third signal to generate a first exclusive-OR signal; a second exclusive-OR logic circuit, operable to perform a logical exclusive-OR calculation with respect to the second signal and the fourth signal to generate a second exclusive-OR signal; a first output terminal, adapted to output one of the first signal, the second signal, a third signal and the fourth signal; a second output terminal, adapted to output another one of the first signal, the second signal, a third signal and the fourth signal; a third output terminal, adapted to output the first exclusive-OR signal; and a fourth output terminal, adapted to output the second exclusive-OR signal, wherein: m is an integer no less than zero; n is an integer no less than one; 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; and each of the first signal, the second signal, the third signal and the fourth signal has a second frequency which is 2 n -times of the first frequency.