Pi = `100^2 /(1k)`

= `10000 /(1k)`

= 10

Po = `30^2 /9`

= `900 /9`

= 100

Ap(dB) = `10 log (100/10)`

= `10 log 10`

= 10 dB

20 = 20 log Av

1 = log Av

Av = 10

喇叭發出的音量與送至喇叭的功率成正比

P(dB)=`10log(4/1)`

= 10 log 4

=10 log(2^2)

=20 log 2

=6 dB

dBm 是以 1mW為參考基準

輸出為10 dBm，所以輸出功率

10 = `10 log (P_o/(1m))`

1 = ` log (P_o/(1m))`

10 = `(P_o/(1m))`

`P_o` = 10mW

`P = V^2/R`

10m = `V^2/25`

`V^2`=0.25

`V`=0.5 V

dBm 是以 1mW為參考基準

20 = `10 log (P/(1m))`

2 = `log (P/(1m))`

100 = `(P/(1m))`

P = 100mW

第一級 電壓增益 20dB，所以電壓放大 10倍。第二級 電壓增益 40dB，所以電壓放大 100倍。 第二級電壓輸出 1μ *10 *100 = 1mV

`P = V^2/R`

100m = `V^2/(1k)`

`V^2` = 100

V = 10 V

第總電壓增益 = `20log (V_o/V_i)`

= `20 log(100/(1μ))`

= `20 log(10^7)`

= `140 dB

Av = `V_o / V_i`

= `(-i_(c2)*1k) / (i_(b1)*1k)`

= `(-i_(b2)*100) / (i_(b1))` (`i_(b2)` = `-1/2i_(c1)`；100k省略，1kΩ 與1kΩ分流)

= `(1/2*i_(c1)*100) / (i_(b1))`

= `(1/2*i_(b1)*100*100) / (i_(b1))`

= 5000

直接交連（耦合）放大器交直流皆可放大

Q1電晶體:

`I_(B1)`*100k+0.7+`I_(E1)`*1k = 10.7

`I_(B1)`*100k+`I_(B1)`*(99+1)*1k = 10

200k`I_(B1)` = 10

`I_(B1)` = 10/200k = 0.05mA

Q2電晶體:

流過 `R_(C1)` 電阻的電流 = `I_(C1)+I_(B2)`

`(I_(C1)+I_(B2))*1k+0.7+I_(E2)*1k` = 10.7

`(99*I_(B1)+I_(B2))*1k+0.7+(48+1)*I_(B2)*1k` = 10.7

`4.95+I_(B2)*1k+49k*I_(B2)` = 10

`50k*I_(B2)` = 5.05

`I_(B2)` = 5.05/50k = 0.101mA

第一級輸入化成戴維寧等效電路：

等效電壓 = `9 * (100k) /(100k+50k)` = 3V

等效電阻 = 100k// 50k = 33kΩ

`33k * I_(B1) + 100 *I_(B1) * 3k` = `3 - 0.7`

`333k * I_(B1)` = 2.3

` I_(B1)` = `2.3/(333k)`

` I_(E1)` = `230/(333k)`

`V_(E1)` = `9-230/(333k)*5k` = 5.54V

` I_(E2)` = `(9-0.7-5.54)/(2k)` =1.38mA

` V_(C2)` 電壓 = ` R_(C2)` 兩端電壓

` V_(C2)` = 1.38m * 3k = 4.14V

直流部份：

V_B = 15 × 5k15k = 5V

V_E = 5 - 0.7 = 4.3V

I_E = 4.31k = 4.3mA

r_e = 264.3 = 6Ω

交流部份：

A_V = VoVi

A_V = －i_c2 × 1ki_b1 × r_π

i_c2 = i_c1 = β × i_b1

A_V = - β × i_b1 × 1ki_b1 × r_π

= - β×1kr_π

= - 1kr_e

= - 1k6 = -165