Optical encoder with inactive photodetectors

Details Optical encoder with inactive photodetectors Optical encoder with inactive photodetectors

1989-12-11

1991-03-05

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

25023114, 250237G, H01J 4014

Patent

active

049980130

ABSTRACT:
An optical shaft angle encoder has a plurality of active photodiodes in an array on a semiconductor chip. A rotary code wheel has alternating areas for alternately illuminating or not illuminating the active photodiodes in response to the rotation of the wheel. Errors in the duty cycle involving the end active photodiodes in the array are largely avoided by having a plurality of inactive photodiodes at each end of the array with width and electrical properties effectively the same as the active photodiodes so that leakage current to each end active photodiode of the array is substantially equal to the leakage current to active photodiodes remote from the end of the array. Similarly, leakage current may affect the duty cycle of individual photodiodes may be minimized by surrounding the individual photodiodes with a reverse biased photodiode junction.

REFERENCES:
patent: 4293877 (1981-10-01), Tsunekawa et al.
patent: 4630121 (1986-12-01), Suzuki et al.
patent: 4675549 (1987-06-01), Steffe et al.
patent: 4691101 (1987-09-01), Leonard
patent: 4763197 (1988-08-01), Masuda

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