PURPOSE:To simplify a circuit deciding the end of each integration cycle by changing the integration direction alternately in plural integration cycles and calculating digital ration through addition and subtraction corresponding to the charge or discharge for the count of the integration time, thereby allowing the end of each integration cycle to be decided through the comparison between the result of integration and a common prescribed value. CONSTITUTION:An integration circuit 1 stores a charge corresponding to an analog input signal Vin and applies integration in two integration cycles composed of the discharge and the charging of the charge. A charge/discharge circuit 2 has two current sources with a different current direction from the current to switch the discharging/ charging corresponding to the switching of the integration cycle. A comparator 3 compares the integration output of the integration circuit 1 with a prescribed value V1 to vary the output polarity. A control circuit 4 controls the switching of the integration cycle and the end of A/D conversion to each section. A counting circuit 5 adds or subtracts the clock signal CK based on an instruction issued from the control circuit 4 corresponding to the output polarity from the comparator circuit 3 synchronously with the switching command of the integration cycle to digitize the analog input signal Vin.
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