▁of ▁the ▁de ple tion ▁zone ▁and ▁therefore ▁the ▁var actor ' s ▁j unction ▁capac it ance . ▁Gener ally , ▁the ▁de ple tion ▁region ▁thick ness ▁is ▁proportional ▁to ▁the ▁square ▁root ▁of ▁the ▁applied ▁voltage , ▁and ▁capac it ance ▁is ▁in vers ely ▁proportional ▁to ▁the ▁de ple tion ▁region ▁thick ness . ▁Thus , ▁the ▁capac it ance ▁is ▁in vers ely ▁proportional ▁to ▁the ▁square ▁root ▁of ▁applied ▁voltage . ▁ ▁All ▁di odes ▁exhib it ▁this ▁variable ▁j unction ▁capac it ance , ▁but ▁var act ors ▁are ▁manufact ured ▁to ▁explo it ▁the ▁effect ▁and ▁increase ▁the ▁capac it ance ▁variation . ▁ ▁The ▁figure ▁shows ▁an ▁example ▁of ▁a ▁cross ▁section ▁of ▁a ▁var actor ▁with ▁the ▁de ple tion ▁layer ▁formed ▁of ▁a ▁p – n ▁j unction . ▁This ▁de ple tion ▁layer ▁can ▁also ▁be ▁made ▁of ▁a ▁M OS ▁or ▁a ▁Sch ott ky ▁di ode . ▁This ▁is ▁important ▁in ▁C M OS ▁and ▁MM IC ▁technology . ▁ ▁Use ▁in ▁a ▁circuit ▁ ▁Tun ing ▁circ uits ▁Gener ally ▁the ▁use ▁of ▁a ▁var ic ap ▁di ode ▁in ▁a ▁circuit ▁requires ▁connecting ▁it ▁to ▁a ▁tun ed ▁circuit , ▁usually ▁in ▁parallel ▁with ▁any ▁existing ▁capac it ance ▁or ▁induct ance . ▁A ▁DC ▁voltage ▁is ▁applied ▁as ▁reverse ▁bias ▁across ▁the ▁var ic ap ▁to ▁alter ▁its ▁capac it ance . ▁ ▁The ▁DC ▁bias ▁voltage ▁must ▁be ▁blocked ▁from ▁entering ▁the ▁tun ed ▁circuit