| 摘要 |
Electric charge generated according to the quantity of incident light to a photodiode(PD)is accumulated in the integral capacity element of an integration circuit(10),and a voltage value V<sb>10</sb> according to an accumulated charge quantity is output.The voltage value V<sb>10</sb> is input to a comparison circuit(20)and compared with a specified threshold value for magnitude,and,when the input voltage value reaches the threshold value,a saturation signal(F1)indicating the reaching is output.An electric charge injection circuit(30)injects into an integral capacity element a constant quantity of charge reverse in polarity to charge accumulated in the integral capacity element in the integration circuit(10).A counting circuit(40)counts the number of times at which the voltage value V<sb>10 </sb>output from the integration circuit(10)reaches the threshold value based on a saturation signal output from the comparison circuit(20).A quantity of incident light is detected based on the count value by the counting circuit(40)and an output voltage value from the integration circuit(10).
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