Photographic exposure meter circuit having temperature compensat

Details Photographic exposure meter circuit having temperature compensat Photographic exposure meter circuit having temperature compensat

1976-11-10

1977-09-27

Gonzales, John

Optics: measuring and testing

Range or remote distance finding

With photodetection

354 60E, 356223, G03B 1718, G01J 144

Patent

active

040514900

ABSTRACT:
An exposure meter circuit includes a photo diode 2 and associated components 1, 3-6 for producing a first logarithmically compressed voltage V.sub.1 proportional to the apex value B.sub.v of the sensed brightness level. The temperature characteristic of the transistor 1 coupled to the diode 2 is compensated for by developing a second logarithmically compressed voltage V.sub.2 and subtracting V.sub.1 from it in an operational amplifier 9. The voltage V.sub.2 is produced by a transistor 11 whose base is coupled to the cathode of a light emitting diode 13 and whose collector output is returned to the power supply through a diode wired transistor 12. The temperature characteristic of the LED is the same as that of a transistor, whereby compensation is realized.

REFERENCES:
patent: 3863263 (1975-01-01), Itagaki

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