| 摘要 |
A variable attenuator comprises a plurality of attenuator stages connected in series along a transmission line signal path. Each attenuator stage comprises a resstive pi-section attenuating pad which may be selectively inserted into the signal path to increase attenuation along the path. Each series element of the pad is selectively inserted or removed from the signal path by opening or closing a parallel connected switching device, while each shunt element of the pad is selectively connected to or disconnected from ground by closing or opening a corresponding series connected switching device. The switching devices each comprise an NPN bipolar transistor and a PNP bipolar transistor, the emitter of each transistor being coupled to the emitter of the other and the collector or each transistor being connected to the collector of the other, to provide a low impedance AC signal path from collector to emitter when the transistors are active.
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