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Photosensing Using GaAs Light Emitting Diode

IP.com Disclosure Number: IPCOM000094228D
Original Publication Date: 1966-Jul-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Krajewski, WF: AUTHOR

Abstract

This position transducing system consists of a light emitting GaAs diode and a light sensor with an intervening mask assembly.

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Photosensing Using GaAs Light Emitting Diode

This position transducing system consists of a light emitting GaAs diode and a light sensor with an intervening mask assembly.

In position transducing, photoenergy must be supplied in a continuous manner, i. e., by DC powering. GaAs diodes are an excellent source of photoenergy, but when used with DC powering there is a degradation of output with time. In the system, a mechanical motion, e. g., a mask, is employed to chop or interrupt the photon stream from the photoenergy source.

In addition, the light sensors are low-frequency response devices due to the large internal capacitances, i. e., they act as an integrator. Thus the equivalent of constant illumination of a phototransistor sensor can be achieved by pulsing the sensor at a rapid rate with a photon source. This permits increased performance from the position transducing system, since GaAs diodes are less subject to time degradation when pulsed at a low duty cycle. By this technique extended life of the light emitting diode is achieved without adverse effect on the light sensing ability of the system or the ability to follow the mechanical motion of the mask. This is because the pulsing rate is much greater than the motion of the mask.

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