| 摘要 |
A common-emitter-amplifier transistor with tuned collector circuit has its gain controlled by the variation of an emitter degeneration resistance responsive to an automatic gain control voltage. This emitter degeneration resistance is provided by the collector-to-emitter path of a gain-controlling transistor having relatively large emitter-base junction area and receiving the automatic gain control voltage at its base electrode. The amplifier transistor is provided temperature compensated base biasing so its emitter-follower action maintains its emitter electrode at a voltage, which applied as the emitter-to-collector voltage of the gain controlling transistor conditions the gain controlling transistor to operate in saturation. Under strong signal conditions the increase in emitter degeneration resistance reduces the severity of cross-modulation and inter-modulation effects. The disclosure describes an AM radio receiver using this type of automatic gain control for its r-f and i-f amplifier stages. Circuitry for avoiding overload distortion in the r-f amplifier is also described.
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