例3:求电路的电压放大倍数Af R R V+1A 3R3+R1 R 03=11+26 R 3 v A R R。+R203 R R +R R,+R R4人R5+R6八R3例3：求电路的电压放大倍数Avf A1 R1 R8 R2 vo R3 R4 vi R7 R6 R5 A2 A3 v+3 vo3 v+1 o v R R R v 3 4 4 3 + + = 3 5 6 3 1  +        = + v R R vo 3 8 7 8 1 o v R R R v + + =         +         +         + = = 8 7 8 5 6 5 4 3 4 R R R R R R R R R v v A i o vf