▁much ▁larger ▁common - mode ▁signals ▁without ▁cli pping ▁than ▁would ▁be ▁the ▁case ▁if ▁they ▁were ▁separate ▁and ▁had ▁the ▁same ▁gain . ▁Another ▁benefit ▁of ▁the ▁method ▁is ▁that ▁it ▁boost s ▁the ▁gain ▁using ▁a ▁single ▁res istor ▁rather ▁than ▁a ▁pair , ▁thus ▁avoid ing ▁a ▁res istor - match ing ▁problem , ▁and ▁very ▁convenient ly ▁allowing ▁the ▁gain ▁of ▁the ▁circuit ▁to ▁be ▁changed ▁by ▁changing ▁the ▁value ▁of ▁a ▁single ▁res istor . ▁A ▁set ▁of ▁switch - select able ▁resist ors ▁or ▁even ▁a ▁pot enti ometer ▁can ▁be ▁used ▁for ▁, ▁providing ▁easy ▁changes ▁to ▁the ▁gain ▁of ▁the ▁circuit , ▁without ▁the ▁complexity ▁of ▁having ▁to ▁switch ▁matched ▁pairs ▁of ▁resist ors . ▁ ▁The ▁ideal ▁common - mode ▁gain ▁of ▁an ▁instrument ation ▁ampl ifier ▁is ▁zero . ▁ ▁In ▁the ▁circuit ▁shown , ▁common - mode ▁gain ▁is ▁caused ▁by ▁mismatch ▁in ▁the ▁res istor ▁r ati os ▁ ▁and ▁by ▁the ▁mis - match ▁in ▁common ▁mode ▁g ains ▁of ▁the ▁two ▁input ▁op - amps . ▁ ▁Ob tain ing ▁very ▁closely ▁matched ▁resist ors ▁is ▁a ▁significant ▁difficulty ▁in ▁fabric ating ▁these ▁circ uits , ▁as ▁is ▁optim izing ▁the ▁common ▁mode ▁performance . ▁ ▁An ▁instrument ation ▁amp ▁can ▁also ▁be ▁built ▁with ▁two ▁op - amps ▁to ▁save ▁on ▁cost , ▁but ▁the ▁gain ▁must ▁be ▁higher ▁than ▁two ▁(+ 6   d B ). ▁ ▁Inst rument ation ▁ampl ifiers ▁can ▁be ▁built ▁with ▁individual