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US 3,944,370 AGranted
Exposure time indication apparatus
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorMasahiro Kawasaki
Life of this patent
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Abstract
A voltage proportional to the APEX indication quantity for exposure time is coupled to one terminal of a meter through a buffer stage transistor. Circuit means produce a reference potential which is applied to the other terminal of the meter. The buffer stage transistor is biased by circuitry including a feedback stage transistor with the biasing being such that substantially constant collector current operation is ensured.
Claims3
Exposure time indication apparatus comprising:
- circuit means for producing a reference potential;
- a two-terminal meter having one terminal connected to receive the reference potential;
- an exposure time measurement section including an output stage transistor having base and emitter electrodes between which there is developed a voltage porportional to the APEX indication quantity for exposure time;
- a buffer stage junction transistor having its base-emitter junction connected in series between the base electrode of the output stage transistor and the other terminal of the meter;
- biasing means for causing the buffer stage transistor to operate with a substantially constant collector current, the biasing means including a feedback stage junction transistor having its collector and base electrode respectively connected to the emitter and collector electrodes of the buffer stage transistor;
- and
- wherein one of the buffer stage and feedback stage transistors is of the p-n-p type and the other is of the n-p-n type.
4 more elements
Dependencies are inferred from the claim text.