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2025-01-25 09:13本頁面
【正文】 there are saturation or cutoff distortions occurred. The iv characteristic of npn Graphical Analysis 3 .Nonlinear Distortion ? Qpoint is low, or vs is too large, cutoff distortion occurs. Graphical Analysis ? Qpoint is high, or vs is too large, saturation distortion occurs. Conclusions: 1. Qpoint must be suitable. 2. vs is small enough to yield linear relation. 3. Max symmetrical swing can be determined If we want get the max range of vO, we must: ? set Qpoint at the middle of active region, ? have suitable ac load line, 3. Nonlinear Distortion Graphical Analysis ? The range of vO 3. Nonlinear Distortion Graphical Analysis 1. Answer following questions: 斜率 1R cQV C E QI CQ I BQR cV CCV CCv CEi C（ 1） RC increases， how can load line and Qpoint change？ （ 2） RC increases , how can load line and Qpoint change ？ （ 3） VCC decreases, how can load line and Qpoint change ？ 斜率QV C E QR cV CCQV C E V C E QI CQI BQ斜率 1R cQI CQI BQR cV CCV CCv CEi C（ 4） RL decreases, how can load line and Qpoint change ？ Review Questions Graphical Analysis R B R C v o + ? ?R L T V CC + ? ?+ + C 2 C 1 v i b c e Common E mitt e r Ci rc u it 2. When VCE of BJT is nearly equal VCC , Which region is it operating in? What may the reasons? Cutoff region Answer： Reasons may: ? Rb may open circuit, IB=0, IC=0, VCE= VCC IC Rc= VCC . ? C1 may short circuit VBE=0， IB=0， IC=0， VCE= VCC IC Rc= VCC . end Review Questions Nonlinear Distortion R B R C v o + ? ?R L T V CC + ? ?+ + C 2 C 1 v i b c e Common E mitt e r Ci rc u it SmallSignal Model Analysis ? Why we consider the smallsignal model? As we know, BJT is a nonlinear device, it is difficult to analyze BJT circuits. The smallsignal model is a linear model of nonlinear device BJT, and can simplify the analysis and the design of BJT circuits. ? How can we built smallsignal model? When the input ac voltage is very small, we can use the piecewise linear approximation techniques for the iv characteristics, and take a BJT as a linear device. SmallSignal Model Analysis ? From transfer process of carries we know: i C + ? v BE T + ? v C E b e c i B Twoport work of BJT TBETBE ee ESESE VvVv III ??? )1(TBEeESB VvII??? 1vbe= ibr? ? 1/r? is slope of input curve. TBQTESQBEBπTBEeVIVIVirVv ??????)1(1?So CQTBQTbbeπ IVIVivr ????? r? is baseemitter input resistor. 1. Hybrid? Equivalent Circuit of BJT Transconductance傳遞電導(dǎo)
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