Amplifiers – With semiconductor amplifying device – Including gain control means
Patent
1979-07-17
1981-11-10
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including gain control means
330281, 330284, H03G 332
Patent
active
043001041
ABSTRACT:
In an automatic gain control circuit specifically adapted to control the gain of an amplifier for operating a noise cancelling circuit, a detector is provided for detecting a detector input signal, such as detected noise pulses. The detector includes a differential amplifier comprising a transistor pair connected to a constant current source. According to the detector input signal level, the constant current is switched between the transistor pair. The normally off transistor of the pair is connected to a third transistor, through which a substantially invariant current flows to relatively slowly charge a capacitor in a time constant circuit when the input signal level exceeds a reference level given by the difference between a pair of bias voltages for the transistor pair. The voltage accumulated across the capacitor serves as an automatic gain control signal, which rapidly disappears when the input signal level decreases below the reference level. The automatic gain control circuit may additionally comprise a similar detector responsive to an amplifier input signal supplied to the gain-controlled amplifier for likewise charging the capacitor through the third transistor.
REFERENCES:
patent: 3750032 (1973-07-01), Andrews
Amazawa Kiyoshi
Tanaka Kouichi
Clarion Co. Ltd.
Mullins James B.
Nippon Electric Co.
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