输入电阻计算 R Ui Ib Ibe +(1+B)IbR =be+(1+)R R=R∥[0+(+B)R1] 张 孝3．输入电阻计算 Ri=RB∥ b e L b b b e b L b i i r R I I r I R I U R = + +  + +   = = (1 ) (1 )          be RL r + (1+ ) 