我看到cascode是這樣想的
如你所說gm1 = gm2 = 0.5mA/25mV = 20mA/V
hfe = 100
=> rpi = hfe/gm = 100V/20mA = 5k ohm
re = 1/gm = 50 ohm
fT = 400MHz
Cu = 2pF
fT = gm/2pi(Cu+Cpi)
=> Cpi = gm/2pi fT - Cu = 5.96pF
open circuit STC
fp1 = 1/Cpi1(rpi1//10k) = 8MHz (Cpi1)
fp2 = 1/Cu1(rpi1//10k + re2*(1+gm(rpi//10k))) = 11MHz (Cu1)
fp3 = 1/Cpi2re2 = 534MHz (Cpi2)
fp4 = 1/Cu210k = 8MHz (Cu2)
看到有三個極點接近
所真正的f 3dB ~ (1/Στ)/2π ~ 3MHz
或是 f 3dB ~ (1/√(Σ τ^2))/2π ~5MHz
我不知道你法一怎麼求出那個幾個pole
我的作法是這樣@@
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※ 編輯: deathcustom 來自: 220.135.83.97 (03/10 18:10)