| 摘要 |
PURPOSE:To switch a signal having a large input potential by constituting the titled circuit by a 1st amplifier, a 2nd amplifier installed at the output side of the 1st amplifier and an operation selection circuit selecting the operating current to the 1st and 2nd amplifiers so as to switch the operation. CONSTITUTION:With an input signal VINA selected, a base-emitter Zener voltage VZ1 of a transistor (TR)20 and a base-emitter diode voltage VF1 of a TR 22 in the 1st amplifier 18B are ensured. Moreover, the Zener voltage VZ2 and the diode voltage VF2 of the 2nd amplifier 30B are ensured. Thus, a dielectric strength VW with respect to an input potential difference >=V is expressed as VW=VZ1+VF1+VZ2+VF2. The constitution of the dielectric voltage VW in this way is similar to a 1st and 2nd amplifiers 18A, 30A. Since the dielectric voltage VW is nearly 15V, it is enough to switch an audio signal thereby expanding the dynamic range.
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