Nikaido, Marmelstein, Murray & Oram
Displacement sensing apparatus for a movable member
 A light receiving portion which receives light from a light emitting portion through slits formed in a rotating disc is provided with, first, second and third photodiodes. With an output of the second photodiode as a reference value, an output of the first photodiode is compared with the reference value and pulsed by a first comparator, and an output of the third photodiode is compared with the reference value and pulsed by a second comparator. With such a light receiving apparatus, since the output (reference value) of the second photodiode similarly decreases when the outputs of the first and third photodiodes decrease due to a decrease of the light quantity of the light emitting portion, the deviation of the phase difference never occurs between outputs of the first and second comparators. 
Rohm Co., Ltd.
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Tadayoshi Masashi
Ogawa Sano