| 摘要 |
PURPOSE:To reduce the cost of an electronic device by using only one expensive changeover switch at the time of simultaneously switching a transfer function of an smplifier corresponding to each signal transmission path in response to the operating mode of the electronic device. CONSTITUTION:In incresing a potential at a control terminal 24 to turn on transistors (TRS) 6, 8, the level of an inverting input terminal 18 is made nearly equal to the reference potential. On the other hand, since a TR 7 is cut off, differential amplifier circuit comprising TRs 3, 5 is operated. Further, a negative feedback circuit 17 is refered to a load, but there is no problem when the circuit 17 has a sufficiently higher impedance than a load 23. In decreasing the level of the control terminal 24 to bring the TRs 6,8 into the cut-off state, the TR 7 is turned on and the level of the inverting input 19 is made nearly equal to the reference potential, the differential amplifier circuit comprising the TRs 3, 4 is activated. The negative feedback circuit 16 is refered to a load, but there is no problem when the impedance of the circuit 16 is sufficiently higher than the load 23.
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