Radiant energy – Photocells; circuits and apparatus – Temperature control of photocell
Patent
1997-05-27
1999-06-29
Le, Que T.
Radiant energy
Photocells; circuits and apparatus
Temperature control of photocell
250214C, H01J 724
Patent
active
059171839
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of temperature compensation for opto-electronic devices and more specifically for temperature compensation of opto-electronic semiconductor devices.
Opto-electronic devices are devices wherein either electrical energy is converted into light energy or light energy is converted into electrical energy. In modern technology, opto-electronic semiconductor devices have gained particular importance, namely, on the one hand, particularly the light-emitting diodes (LEDs) as light-emitting elements and, on the other hand, photo-diodes, photo-transistors, photo-resistors, photo-thyristors and the like, which sense the intensity of light impinging onto a measuring surface and output a representative electrical signal.
In the following, the method according to the present invention is described by means of an example only with respect to light-emitting diodes to be referred to as LEDs, and with respect to photo-diodes, but it will be understood that it can also be applied to other opto-electronic devices and more specifically to opto-electronic semiconductor devices.
The problem of the application of LEDs and sensor diodes in optical measurement techniques is explained in the following, using color measurements as an example: The color impression which a colored surface provides to an observer is based on a predetermined spectral distribution of the light reflected from said surface which in the eye of the observer is recognized as color. In this respect, the color-sensing function .psi.(.lambda.) as seen by the observer is given by: and S(.lambda.) being representative of the spectral distribution of the light impinging onto the surface. In other words, the color-sensing function as seen by the observer is a product of the spectral distribution of the reflection properties of the surface and the spectral distribution of the light impinging onto the surface. A changed spectral distribution of the light impinging onto the surface will result in a changed color impression for the observer.
In technology it is of great importance to correctly detect the color of surfaces, namely, on the one hand in order to reproducibly provide colors and on the other hand in order to correctly reproduce color of surfaces in printing products, films, photographs and by means of electronic devices such as cameras, television screens, computer monitors, and the like.
In conventional color measurements the surface the color of which is to be detected is irradiated with light having an accurately known spectral distribution. The reflected light is spectrally analyzed, for example using a spectral photometer, whereby the spectral reflection properties of the surface and correspondingly the color impression provided by the surface can be computed and can be displayed and compared with normalized color characteristic values.
In order to reduce the apparative efforts for such measurement devices, for some time it has been practiced to irradiate the surface to be measured using LEDs, and to measure the light reflected from said surface using semiconductor sensors, particularly photo-diodes. For example, such a device is disclosed in DE 42 02 822 A1. Therein, a plurality of LEDs arranged on a common substrate as well as a plurality of sensor diodes are used. The problem with these devices, however, is the fact that the spectral characteristics and the intensity of both the LEDs and the sensor diodes is temperature dependent such that the temperature of the LEDs and the sensor diodes has to be detected in order to enhance the measurement accuracy.
In the device mentioned above this is achieved by arranging a temperature sensor on the common substrate. In a control device of the apparatus, a plurality of spectral characteristics for the LEDs and the sensor diodes is stored, and for every measurement first the temperature of the substrate is determined and then the corresponding curve for the analysis of the measurement is selected.
This method firstly comprises the disadvantage that use of a temperature sensor in t
REFERENCES:
patent: 5530433 (1996-06-01), Morita
Article by J. Mroczka titled Temperature Stabilisation of Light-Emitting Diode Radiation, pp. 306-309, J. Phys. E. Sci. Instrum. 21 (1988). (Month unknown).
Article by Fritz Keiner and Gerhard Krause titled Einfach Schaltung Zum Sliminieren Des Temperaturkoeffizienten Von Lumineszenzdioden, pp. 14-15, Siemens-Bauteile-Informationen 11 (1973). (Month unknown).
BYK-Gardner GmbH
Le Que T.
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