推 kela12340: 03/26 21:16
推 kela12340:請問一下您可以解釋一下Rout的式子嗎(最後一行~ 03/26 23:27
推 kela12340:是從Drain看進去的Rout公式延伸的嗎?(用Vt/It從output) 03/26 23:30
→ big1p:是，不過這是BJT，所以是從collect端看入(not drain) 03/27 08:37
→ kela12340:嗯，我打錯啦~..XD 謝謝!! 03/27 22:54
※ 引述《kela12340 (Avanlandis)》之銘言：
: 題目: 考慮如圖電路，已知電晶體的偏壓電流為IE1=1mA，IE2=0.4mA，
: β=100，VA=75伏，求Rin、Rout、Iout/Iin 各是多少？
: 附上圖
: http://i.imgur.com/B2BOA.jpg
: http://i.imgur.com/hSmvp.jpg?1
: 第二章圖的鉛筆筆跡是我算的結果..
: 與答案不同，但我也不知道錯在哪= ="
: 像是Rof
: 算出來約144 kΩ
: 那Rout不就是將RL從Rof中扣除而已嗎(sampling為series的形式)
: 很不解為何答案是1.83x10^4 kΩ..
: 所以來請教一下!!
: 感謝!
A network analysis
Vπ1=Ii[Rs//(RE2+Rf)//RB//rπ1]
Vb2 = -gm1Vπ1{ro1//Rc1//[rπ2+(1+β)(RE2//Rf)]}
Vb2 Io
Io≒ ------------- (neglect ro2)，A≡----≒-201.45
re2+(RE2//Rf) Ii
Ri = Rs//(RE2+Rf)//RB//rπ1 = 1.535 kΩ
Rc1//ro1
Ro = (RE2//Rf) + re2 + ---------- = 2.69 kΩ (neglect ro2)
1+β
β network analysis
If RE2
β≡---- = - -------- = -0.254，thus 1+βA = 52.1
Io RE2+Rf
Ri 1
Rif = -------- = 29.5 Ω，Rin = -----------≒29.5Ω
1+βA 1 1
--- - ---
Rif Rs
Io A
Rin≒Rif，it follows A network that Iin≒Is. Af≡---- = ------- = -3.87
Is 1+βA
The required current gain is given by
Iout Iout Rc2 Ic Rc2 Io
----≒----- = --------．----≒ --------．----
Iin Is RL+Rc2 Is RL+Rc2 Is
Iout
Thus，----- = -3.44
Is
Rof = Ro(1+βA)≒140.1 kΩ，Rout = ro2[1+gm2(rπ2//Rof)] = 18.1 MΩ
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