| 摘要 |
PURPOSE:To make an exposing time accurate without receiving the effect in deviation of integration starting point and offset voltage, etc., of an operational amplifier and a comparator by detecting the increasing portion of the integral value of a photocurrent. CONSTITUTION:When an integration starting signal is received from a shutter button, etc., a switch 4 is turned off. At this time, a switch 5 is turned on and a switch 10 is turned off, and then a capacitor 3 begins to be charged with the photocurrent from a photodiode 1 and a current from a current source 6. When the charged voltage is integrated in the operational amplifier 2 and an output Vout reaches a decision voltage Vc through the comparator 7, a control circuit 12 precedes a front curtain and at the same time the switch 5 is tuned off and then switch 10 is turned on. From this time the capacitor 3 is charged only with the photocurrent from the diode 1. And when the Vout reaches the new decision voltage Vc raised by a current source 11, a rear curtain precedes. Therefore, the accurate control of exposure can be possible without receiving the effect of the offset voltage.
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