(4)差动放大器 Ri+:r R 0 2 R1+R2 ib+=0 i22 Ri+R 2 R U =U + R1+ 0 i R Uir 2 R +R R 1 +R2 R 0 i29 (4) 差动放大器 _ +  +  R2 R1 R1 ui2 uo R2 ui1 (u u ) R R u i2 i1 1 2 o = − ib+ =0 ib- =0 ui2R2 R1 + R2 u+ = u- = u+ u- = uo R1 + ui1 R2 R1 + R2 uo R1 + ui1 R2 R1 + R2 ui2R2 R1 + R2 =