2.电压并联负反馈电路 R R IU A U。R2 R f usf U F. R lu RR2. 电压并联负反馈电路 s s o sf o f 1 1 U F R U A U I F ui u ui =   =        1 2 s s f o 2 f 1 1 1 R R F R A U R I F i u u i u   = − = = −     