Automatic control for amplitude-modulated signal source

Claim 2

An automatic level control comprising gain-controlled signal translating means through which a carrier signal is passed to an output terminal, envelope detection means connected to said output terminal and developing an output signal corresponding to the instantaneous amplitude level of the input signal thereto, signal comparison means, a reference signal source corresponding to a desired peak carrier level applied as a first input to said signal comparison means, the output from said envelope detection means applied as a second input to said signal comparison means, said signal comparison means being adapted to provide an output signal the average value of which is proportional to the relative time periods during which the output from said envelope detector exceeds said carrier level reference source, and means responsive to the output from said signal comparison means to control the gain of said gain-controlled signal translating means, whereby the carrier level of the output from said gain-controlled signal translating means is maintained at a level as set by said reference signal source.

Claim 3

A level control as defined in claim 1 wherein said signal comparison means comprises an operational amplifier receiving the output from said envelope detector, said operational amplifier being adapted to produce a saturated output in a positive direction during said time periods when the output from said envelope detector exceeds that of said reference signal source and a zero output during the periods of time when the output from said envelope detector is less than said reference signal source, averaging means receiving the output from said operational amplifier, and the output of said averaging means applied to said gain-controlled signal translating means.

Claim 4

A level control as defined iN claim 1 further comprising a source of modulating signal, differential amplifier means, said source of modulating signal and the output of said envelope detector being applied as respective first and second inputs to said different amplifier means, a variable gain amplifier, said modulating signal source being applied to the input of said variable gain amplifier, said variable gain amplifier including means to receive the output from said differential amplifier means as a gain controlling input thereto, means for summing the output from said signal comparison means and said variable gain amplifier, the output from said means for summing being applied as a gain controlling input to said gain-controlled signal translating means.

Claim 5

A level control as defined in claim 3 wherein said gain-controlled signal translating means comprises a variable attenuator the attenuation of which is directly proportional to the output from said means for summing.

Claim 6

A level control as defined in claim 3 further comprising a unilateral conduction device through which said source of modulating signal is applied as said first input to said differential amplifier, said unilateral conduction device exhibiting an offset voltage characteristic corresponding to the threshold level intrinsic to said envelope detector.

Claim 7

An automatic level control by means of which an amplitude-modulated carrier signal may be independently controlled as to average peak carrier level and modulation index, comprising a first gain-controlled signal translating means through which said carrier signal is supplied to an output terminal, envelope detection means connected to said output terminal and developing an output signal corresponding to the modulation envelope of the signal applied thereto, first signal comparison means receiving the output from said envelope detector and a reference voltage the magnitude of which is set to equal a desired average peak carrier level, said first signal comparison means developing an output signal the average value of which is proportional to the percentage of time that the output from said envelope detector means exceeds said reference signal, second signal comparison means receiving the output from said envelope detector and a modulating signal source, said second signal comparison means developing an output signal corresponding to the instantaneous differential between said envelope detector output signal and said modulating signal source, a further variable gain signal translating means receiving said source of modulating signal, means applying the output from said second signal comparison means as a gain controlling second input to said further variable gain signal translating means, and means combining the outputs from said first comparator and said further variable gain signal translating means as a composite controlling input to said first gain-controlled signal translating means.

Claim 8

An automatic level control by means of which an amplitude-modulated carrier signal may be independently controlled as to average peak carrier level and modulation index, comprising a first gain-controlled signal translating means through which said carrier signal is supplied to an output terminal, envelope detection means connected to said output terminal and developing an output signal corresponding to the modulation envelope of the signal applied thereto, first signal comparison means receiving the output from said envelope detector and a reference voltage the magnitude of which is set to equal a desired average peak carrier level, said first signal comparison means developing an output signal the average value of which is proportional to the percentage of time that the output from said envelope detector means exceeds said reference signal, second signal comparison means receiving the output from said envelope detector and a modulating signal source, said second signal comparison means developing an output signal corresponding to the instantaneous differential between said envelope detector output signal and said modulating signal source, a further variable gain signal translating means receiving said source of modulating signal, means applying the output from said second signal comparison means as a gain controlling second input to said further variable gain signal translating means, and means combining the outputs from said first comparator and said further variable gain signal translating means as a composite controlling input to said first gain-controlled signal translating means.