Gain-controlled amplifier circuits
AssigneeFerranti Limited
InventorHugh McPherson
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Abstract
Apparatus for controlling the gains of a pair of gain-matched amplifiers includes means for applying a pilot tone of constant amplitude to each amplifier through separate attenuators during a repeated correction time interval. Three control loops are provided, one of which compares the output of one amplifier with a reference signal at times other than a correction time interval to control the gain of that amplifier. A second loop compares the output of the other amplifier with the same reference signal only during each correction time interval to control the gain of the second amplifier. Finally, the third loop compares the output of the first amplifier and the reference signal during each correction time interval to produce a signal controlling the two attenuators.
Claims8
A gain-controlled amplifier circuit which includes a pair of gain-controlled amplifiers, signal generating means operable to generate a pilot signal of constant amplitude during a repeated correction time interval, attenuator means operable to control the level at which said pilot signal is applied equally to the inputs of said two amplifiers, a first automatic gain control loop comprising means for subtracting the output of one amplifier from a reference gain control signal at a time other than during the correction time interval to derive a first error signal for application to the gain control input of said one amplifier, a second automatic gain control loop comprising means for subtracting the output of the other amplifier from the reference gain control signal to derive a second error signal for application to the gain control input of the said other amplifier only during the correction time interval, and a correction loop comprising means for subtracting the output of said one amplifier from the reference gain control signal to derive a correction signal for application to the attenuator means during the correction time interval to control the level of the pilot signal applied to the two amplifiers.
Dependencies are inferred from the claim text.