▁driven ▁by ▁varying ▁the ▁di ode ' s ▁capac it ance ▁by ▁applying ▁a ▁varying ▁bias ▁voltage . ▁The ▁circuit ▁that ▁var ies ▁the ▁di ode ' s ▁capac it ance ▁is ▁called ▁the ▁" p ump " ▁or ▁" driver ". ▁In ▁mic row ave ▁electron ics , ▁wave guide / Y AG - based ▁paramet ric ▁oscill ators ▁operate ▁in ▁the ▁same ▁fashion . ▁Another ▁important ▁example ▁is ▁the ▁optical ▁paramet ric ▁oscill ator , ▁which ▁converts ▁an ▁input ▁las er ▁light ▁wave ▁into ▁two ▁output ▁waves ▁of ▁lower ▁frequency ▁( ). ▁ ▁When ▁operated ▁at ▁p ump ▁levels ▁below ▁oscill ation , ▁the ▁paramet ric ▁oscill ator ▁can ▁ampl ify ▁a ▁signal , ▁forming ▁a ▁paramet ric ▁ampl ifier ▁( par amp ). ▁Var actor ▁paramet ric ▁ampl ifiers ▁were ▁developed ▁as ▁low - no ise ▁ampl ifiers ▁in ▁the ▁radio ▁and ▁mic row ave ▁frequency ▁range . ▁The ▁advantage ▁of ▁a ▁paramet ric ▁ampl ifier ▁is ▁that ▁it ▁has ▁much ▁lower ▁noise ▁than ▁an ▁ampl ifier ▁based ▁on ▁a ▁gain ▁device ▁like ▁a ▁trans istor ▁or ▁vac u um ▁t ube . ▁This ▁is ▁because ▁in ▁the ▁paramet ric ▁ampl ifier ▁a ▁react ance ▁is ▁varied ▁instead ▁of ▁a ▁( no ise - produ cing ) ▁resistance . ▁They ▁are ▁used ▁in ▁very ▁low ▁noise ▁radio ▁rece ivers ▁in ▁radio ▁teles cop es ▁and ▁space craft ▁communication ▁anten nas . ▁ ▁Param et ric ▁reson ance ▁occurs ▁in ▁a ▁mechanical ▁system ▁when ▁a ▁system ▁is ▁param etr ically ▁excited