1 如圖所示，若RB = 400kΩ、RC = 1kΩ、RE = 1kΩ、VCC=10.7V、β=100 求 AV?
A -80
B -100
C -125
D -150
先算 `r_π`
`400k*I_B+0.7+1k*I_E` = 10.7
`400k*I_B+100k*I_B` = 10
`500k*I_B` = 10
`I_B` = `10/(500k)`
`I_B` = 0.02 mA
`r_π` = `(25m)/(0.02m)`
=1250Ω
化成交流等效電路，如下圖
`A_V` = `V_o/V_i` = `(-100*i_b*1k)/(i_b*1.25k)`
= `-100/1.25` = - 80
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