1 如圖所示電路，RS=1.5kΩ，RB1=40kΩ，RB2=10kΩ，RC=4kΩ，RE=1kΩ，RL=4kΩ，BJT之切入電壓 VBE(t) = 0.7V，β = 100，熱當電壓 VT = 26mV，交流等效輸出電阻ro = ∞，則 Vo/Vi約為何?
A -95.3
B -57.6
C -48.9
D -30.5
近似解法：
`V_B` = `10*(10k)/(10k+40k)` = 2V
`V_E` = `2-0.7` = 1.3V
`I_E` = `(1.3)/(1k)` = 1.3mA
`r_π` = `(26m*100)/(1.3m)` = 2kΩ
電路化成電晶體的交流等效電路(如下圖)
`A_v` = `v_o/(v_i)` = `-(100i_b*4k////4k)/(i_b*2k)` = `-(200k*i_b)/(2k*i_b)` = -100
`Z_i` = 8k//2k = 1.6kΩ
`V_i*(1.6k)/(1.6k+1.5k) = Vi`
`A_v` = `(1.6k)/(1.6k+1.5k)*A_v` = `(1.6k)/(3.1k)*-100` = -51.6
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