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

`R_i` = 400k//`r_π`

= 400k//1.25k ≒ 1.25kΩ

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

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

將電路圖化成交流等效電路(如下圖)，由交流等效電路可以看出

`V_o` = `-β*i_b*(R_(B2)*R_C)/(R_(B2)+R_C)`

= `-β * i_b * R_o`

`V_i` = `i_b*r_π`

`A_v` = `V_o/V_i`

= `(-β*i_b* R_o ) / (i_b*r_π)`

= `(-β* R_o ) / r_π`

= `(-β* R_o ) / ((β+1)*r_e)`

≒ `(- R_o ) / r_e`

將電路圖化成交流等效電路(如下圖)，由交流等效電路可以看出

R_o = R_B2 // R_C

將電路圖化成交流等效電路(如下圖)，由交流等效電路可以看出

R_i = R_B1 // r_π

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_i` = `i_o/i_i` = `(8k)/(8k+2k)*100*(4k)/(4k+4k)` = 40