Optical encoder using sufficient inactive photodetectors to make leakage current equal throughout
US4904861A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 27, 1988 |
| Grant date | Feb 27, 1990 |
| Priority date | — |
| Expiry date | Dec 27, 2008 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03M1/301
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An optical shaft angle encoder has a plurality of active photodiodes in an array on a semiconductor chip. A rotating 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 which may affect the duty cycle of individual photodiodes may be minimized by surrounding the individual photodiodes with a reverse biased photodiode junction.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.