| 摘要 |
PROBLEM TO BE SOLVED: To correct an offset even when a system integrated with the amplifier circuit is operated and to enhance the correction accuracy by decreasing the offset correction time. SOLUTION: The amplifier circuit with an operational amplifier 1 is provided with an offset correction circuit consisting of a comparator circuit 3, a level shift circuit 5, and an adder circuit including a resistor R3. When the amplifier circuit amplifies no input signal S, a center level E0 of the signal S is applied to an input of the operational amplifier 1 through a changeover circuit 2. Then the comparator circuit 3 compares an output of the operational amplifier 1 with the level E0, a counter 6 counts up by one for each prescribed time according to the comparison result, and a D/A converter 7 gives an analog value corresponding to the count to a resistor R3 of the adder circuit. Then the offset of the operational amplifier is corrected by adding a correction voltage with a prescribed changing amount at a summing rate depending on the resistance of the resistor R3.
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