| 摘要 |
PURPOSE:To attain the low power voltage by supplying a current to a connecting point of emitters of a differential pair and a connecting point of emitters of a transistor pair and varying the current ratio flowing thereto respectively according to a control signal. CONSTITUTION:Currents Ie3, Ie4 flowing to the differential pair 151 of a differential amplifier 15 and a transistor pair 161 of a current shunt circuit 16 are controlled by making currents Ie1, Ie2 of current sources 5, 6 constant and giving control currents Ic1, Ic2 from a control circuit 17 to constant current sources 5, 6 so as to increase/decrease the currents Ie3, Ie4 flowing to the differential pair 151 of the differential amplifier 15 and to the TR pair 161 of the circuit 16. It is required to change the current ratio of a current of the differential amplifier 15 to that of the circuit 16 in this case while keeping the current sum flowing to load resistors 9, 10 in order to prevent a DC level of an output signal from being changed. Thus, the control circuit 17 controls the current of the circuit 16 to keep the sum of the currents flowing to the load resistors 9, 10 constant.
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