| 摘要 |
PURPOSE:To form an inexpensive signal selection circuit by giving outputs of two system of amplifiers to a 3db directional coupler and making the amplifier just before the directional coupler always operative. CONSTITUTION:Preamplifiers 2, 12 are switched complementarily by switching a power switch 40. Post-stage amplifiers 3, 13 are brought into operating state regardless of the switching of the switch 40. Thus, only the signal amplified by the system including either of the amplifiers 2, 12 brought into the operating state by the operation of the switch 40 is obtained at an output terminal 8 of the 3db directional coupler 20. Then the selection circuit is formed by using the inexpensive directional coupler in place of an expensive PIN diode.
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