| 摘要 |
A gain-controlled amplifier is provided which utilizes both controlled load impedance variation and controlled emitter degeneration variation to vary the gain of the amplifier. The amplifier includes an amplifying transistor which is direct-current coupled in a common emitter configuration. The collector load impedance of the amplifying transistor includes a first controlled resistance device having a base electrode coupled to the collector electrode of the amplifying transistor, an emitter electrode coupled to receive a first gain controlling current, and a collector electrode coupled to a point of reference potential. The emitter impedance of the amplifying transistor includes a second controlled resistance device having a base electrode coupled to the emitter electrode of the amplifying transistor, an emitter electrode coupled to receive a second gain controlling current and a collector electrode coupled to a point of reference potential. At signal frequencies, the base-to-emitter junctions of the controlled resistance devices act as resistances which can be varied inversely with the flow of gain controlling current through the emitter-to-collector paths of the devices. The total gain reduction range of the amplifier is the product of the ranges due to both the collector load impedance and the emitter degeneration controlled gain reduction. The gain controlling currents which are applied to the two devices may be independently controlled, serially controlled, or may be varied simultaneously.
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