| 摘要 |
PROBLEM TO BE SOLVED: To execute an operation in spite of an input level by constituting a circuit by means of a first differential amplifying circuit for inputting input voltage and a bias, a second differential amplifying circuit which applies output to one input terminal of the first differential amplifying circuit and a third differential amplifying circuit, which sets the output of the first differential amplifying circuit to be input and current-converts input voltage. SOLUTION: An input signal IN is applied to the positive input terminal of a differential amplifier 3, and a bias similar to this in the input signal IN is applied to the negative input terminal of the differential amplifier 3. The differential amplifier 3 is negatively fed back by the output of a differential couple formed of transistors 5 and 6. The positive input terminal of the differential amplifier 3 is virtually grounded in virtual manner. Even if the level of the input signal IN changes for more than the voltage between the base/emitter of the transistor from a bias point, the operation of the differential amplifier 3 will not stop and the differential amplifier 3 can be driven satisfactorily by the input signal IN.
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