Intheearlyyearsofradiocircuits,fading(definedasslowvariationsintheamplitudeofthereceivedsignals)requiredcontinuingadjustmentsinthereceiver’sgaininordertomaintainarelativeconstantoutputsignal.Suchsituationledtothedesignofcircuits,whichprimaryidealfunctionwastomaintainaconstantsignallevelattheoutput,regardlessofthesignal’svariationsattheinputofthesystem.Originally,thosecircuitsweredescribedasautomaticvolumecontrolcircuits,afewyearslatertheyweregeneralizedunderthenameofAutomaticGainControl(AGC)circuits[1,2].
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