| 摘要 |
PURPOSE:To perform measurement in a wide dynamic range, by quickening the integral time of a photocurrent when the intensity of receiving light is low and making the same long when said intensity is high. CONSTITUTION:At first, a control circuit 6 brings a rest transistor Tr4A to a continuity state by a signal R1 and sets the level of a signal V1 to the potential V0 of a constant voltage source 7. By this method, the integral operation of a condenser 2 starts from the initial value V0 and, when the value V0 is set to an input range wherein a comparator 3 sufficiently performs normal operation, Vref can be allowed to sufficiently approach V0. Therefore, even when the intensity L of receiving light is low, a time ts capable of sufficiently shortening the conversion time ts before input V1 reaches Vref is measured by a timing circuit 5 to be transmitted to the circuit 6. When the intensity L is high in a certain degree or more, a reset transistor Tr4B is brought to a continuity state by a signal R2 and the signal V1 is set to an earth level. When the signal V1 becomes 0, said signal V1 differs from Vref in a certain degree and, therefore, even when the intensity L is high, a conversion time can be measured with good accuracy.
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