[閒聊] DC的電子學入門 - 1 基本元件
電子電路中的基本元件及其對應常用公式
I. 被動元件
比如電容、電感、電阻
Zc = 1/jwC
Zl = jwL
Zr = R
II. 主動元件
主要提三個
1. diode
Id ~ Is*exp(Vd/Vt)
Vt = kT/e = 1.38e-23*300/1.6e-19 = 25.875mV
典型上會用25mV或是26mV
Is通常是10fA(1e-14 A)
計算Rd則
Rd = 1/(dId/dVd) = Vt/Id
典型值大約是4-5 ohm
2. BJT
IC = betta*IB
IB => 看成diode IB = Is*exp(VBE/Vt)
Is = qDn/W (Smith中典型值也是用10fA)
IE = IC+IB
在Smith中因為通常IB只會有10uA =>VBE = Vt*9*ln(10) = 540mV
(Smith中的典型值選用600mV,對照的IB = 97uA =>Ic = 9.7mA)
rpi = vbe/ib = 1/(dIB/dVBE) = Vt/IB, Smith 典型值大約25mV/10uA = 2.5k
re = vbe/ie = rpi/(1+betta), Smith 典型值大約25
gm = ic/vbe = betta*IB/Vt = IC/Vt, Smith典型值大約1mA/25mV = 40mA/V
ro = vce/ic => Early Effect, ro = Va/Ic
3. MOS
ID = (1/2)*(k')*(W/L)*(VGS -VTH)^2*(1+Vds/Va) [saturation region]
ID = (k')(W/L)*[(VGS-VTH)*VDS - 0.5*VDS^2] [triode region]
gm = id/vgs = (k')*(W/L)*(VGS-VTH) = 2ID/Vov = sqrt[2(k')(W/L)ID]
ro = vds/id = Va/ID
當VDS ~ 0 的時候
rds = vds/id = 1/gds, gds = (k')*(W/L)*(VGS -VTH) [跟sat. gm的公式一樣XD]
--
會趁有空的時間把我過去念書、以及家教學生實際遇到的概念
還有板上常有的問題統整寫上來
未來涵蓋的範圍還會包括基本的數位電路,ADC, DSM, PLL (loop filter, oscillator)
但是不知道有沒有完成的一天Orz
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