US 4,465,370 AGranted

Light measuring device

AssigneeMinolta Camera Kabushiki Kaisha

InventorsYoshio Yuasa, Nobukazu Kawagoe

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Abstract

A light measuring device includes one or more photodiodes, which generate current in relation to the received light, and at least one capacitor for integrating the generated current. The amount of charge stored in the at least one capacitor at the completion of the integration is roughly detected by the number of capacitors used and/or the voltage across the capacitor. A current source capable of producing different levels of current in accordance with the detected amount of charge is provided for changing the amount of charge stored in the at least one capacitor. The time needed to change the amount of charge stored in the at least one capacitor is measured so as to obtain the value of total amount of the change in the charge stored in the at least one capacitor and to thus obtain the value of the received amount of light intensity.

Claims35

Dependent claims

A light measuring device having a plurality of ranges for measuring light and comprising:

a light responsive means for receiving light and for producing an electrical signal as a function of the received light;
an integration means including a capacitor means for integrating said electrical signal so as to change the amount of charge stored in said capacitor means;
a first control means for controlling the integration means such that said electrical signal is integrated during a predetermined period of time;
a means for setting said capacitor means to a predetermined initial condition before the integration of said electrical signal;
a means for producing a plurality of constant currents having different levels;
a means for selecting one of said plurality of constant currents in dependence on said changed amount of charge in said capacitor means;
a second control means for controlling said constant current producing means such that said selected constant current is supplied to or withdrawn from said capacitor means subsequent to the completion of said integration of said electrical signal for said predetermined periodd of time;
so as to again place said capacitor means to its predetermined initial condition;
a means for detecting the moment of time when said capacitor means again reaches said predetermined initial condition due to said selected constant current;
and
a means for measuring the time interval from the moment of time when said constant current producing means starts to supply said selected constant current to said capacitor means to the moment of time when said detecting means detects that said capacitor means has again reached said predetermined initial condition.

8 more elements

A light measuring device having a plurality of ranges for measuring light and comprising:

a light responsive means for receiving light and for producing a voltage signal as a function of the received light;
an integration means, including both a means for generating an electric current commensurate with said voltage signal and a capacitor means, for integrating said electric current so as to change the amount of charge stored in said capacitor means;
a first control means for controlling the integration means such that said integration is effected during a predetermined period of time;
a means for setting said capacitor means to a predetermined initial condition before said integration;
a means for producing a plurality of constant currents having different levels;
a means for selecting one of said constant currents in dependence upon said voltage signal;
a second control means for controlling said constant current producing means such that said selected current is supplied to or withdrawn from said capacitor means subsequent to the end of said predetermined period of time so as to again place said capacitor in its predetermined initial condition;
a means for detecting the moment of time when said capacitor means again reaches said predetermined initial condition due to said selected constant current;
and
a means for measuring the time interval from the moment of time when said constant current producing means starts to supply said selected constant current to said capacitor means to the moment of time when said detecting means detects that said capacitor means has again reached said predetermined initial condition.

7 more elements

Dependencies are inferred from the claim text.