| 摘要 |
In a differential amplifier and an operational amplifier each for amplifying a signal, a differential signal composed of first and second signals is inputted to a couple of input terminals ( 1, 2 ). When the voltage of the first signal is, e.g., less than the voltage value of a reference voltage source ( 15 ), a comparator ( 13 ) senses it and a switch circuit ( 12 ) switches to a first current source ( 6 ) and a current from a third current source ( 11 ) flows into the first current source ( 6 ) so that a current is inhibited from flowing in the first differential couple ( 4 ). As a result, the inputted differential signal is amplified and outputted only through a second differential couple ( 5 ). In a situation in which the voltage of the first signal exceeds the voltage of the reference voltage source ( 15 ), on the other hand, the switch circuit ( 12 ) switches to a current source ( 7 ) so that the inputted differential signal is amplified and outputted only through the first differential couple ( 4 ). As a result, a gain is equal over the entire range of input operating voltage and a high-speed operation is performed.
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