▁hard ▁logic , ▁depending ▁on ▁the ▁F P GA . ▁ ▁C lock ing ▁ ▁Most ▁of ▁the ▁circuit ry ▁built ▁inside ▁of ▁an ▁F P GA ▁is ▁synchron ous ▁circuit ry ▁that ▁requires ▁a ▁clock ▁signal . ▁F PG As ▁contain ▁dedicated ▁global ▁and ▁regional ▁routing ▁networks ▁for ▁clock ▁and ▁reset ▁so ▁they ▁can ▁be ▁delivered ▁with ▁minimal ▁ske w . ▁Also , ▁F PG As ▁generally ▁contain ▁analog ▁phase - locked ▁loop ▁and / or ▁delay - locked ▁loop ▁components ▁to ▁synth es ize ▁new ▁clock ▁frequencies ▁as ▁well ▁as ▁at ten uate ▁j itter . ▁Complex ▁designs ▁can ▁use ▁multiple ▁clock s ▁with ▁different ▁frequency ▁and ▁phase ▁relationships , ▁each ▁forming ▁separate ▁clock ▁domains . ▁These ▁clock ▁signals ▁can ▁be ▁generated ▁locally ▁by ▁an ▁oscill ator ▁or ▁they ▁can ▁be ▁recovered ▁from ▁a ▁high ▁speed ▁serial ▁data ▁stream . ▁Care ▁must ▁be ▁taken ▁when ▁building ▁clock ▁domain ▁crossing ▁circuit ry ▁to ▁avoid ▁met ast ability . ▁F PG As ▁generally ▁contain ▁block ▁RAM s ▁that ▁are ▁capable ▁of ▁working ▁as ▁dual ▁port ▁RAM s ▁with ▁different ▁clock s , ▁a iding ▁in ▁the ▁construction ▁of ▁building ▁FI FO s ▁and ▁dual ▁port ▁buff ers ▁that ▁connect ▁differ ing ▁clock ▁domains . ▁▁ 3 D ▁architect ures ▁ ▁To ▁shr ink ▁the ▁size ▁and ▁power ▁consumption ▁of ▁F PG As , ▁vend ors ▁such ▁as ▁Tab ula ▁and ▁X il inx ▁have ▁introduced ▁ 3 D ▁or ▁stack ed ▁architect ures . ▁Following ▁the ▁introduction ▁of ▁its ▁ 2 8  