學(xué)科競賽chppt課件(已修改)
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【正文】 Ch6 Basic BJT Amplifiers Graphical Analysis SmallSignal Model Analysis CommonEmitter Amplifiers AC Analysis of Transistor Circuits AC Analysis of Transistor Circuits(CH4) Analog Signals ? A signal contains some type of information. There are two kinds of signals: analog and digital. ? Analog signal, such as temperature, pressure, velocity, can take on any value and may vary continuously with time. The magnitude of digital signal has a finite number of digits at an instant of time, and no longer is a continuous function of time. ? Electronic circuits that process analog signals are called analog circuit. Graphical Analysis 1. AC and DC Values + ? i B R C v O V BB i C V BE R B + ? V CC + ? V CE + ? v S Commonemitter circuit ? We add a sinusoidal signal source in series with the dc source. ? vs produces ac vbe superimposed on VBE, so vBE=VBE+vbe iB =IB+ib iC =IC+ic vCE =VCE+vce (1) CommonEmitter Circuit Graphical Analysis 1. AC and DC Values QIBQVB E QvBE/ViB/ uAttvBE/ViB/ uAQ`Q` `204060 Q I CQ V C E Q v CE /V i C / m A v CE /V i C / m A t t L oa d l i n e Q` Q ` ` 20 uA 40 uA 60 uA Graphical Analysis 1. AC and DC Values Conclusions: 1. vi?? vBE?? iB?? iC?? vCE?? |vo| ? 2. Phases of vo and vi are opposite__inverter. 3. Getting voltage gain. 4. Determining the max of vo . When the circuit is operating， are the real directions of iB and iC changing, and real voltage polarity of vCE is changing？ v o i c + ? R C + ? v i RB R L + ? T v ce + ? T he AC e qu iv ale nt c ircu it Graphical Analysis 2. AC Load Line vce= ic? (Rc //RL) ? From ac equivalent circuit, we get ? Due to vce= vCE VCEQ ic= iC ICQ and assume R?L = Rc//RL so, vCE VCEQ= (iC ICQ )?R?L ? That is iC = (1/R?L)? vCE + (1/R?L) VCEQ+ ICQ R B R C v o + ? ?R L T V CC + ? ?+ + C 2 C 1 v i Com m on E m it te r Circu it ? The ac and dc load lines are different. ?The ac load line must pass through the Qpoint, and its slope is 1/R?L , so we plot the ac line shown in fig. Graphical Analysis S l o p e 1 R C Q V C E Q I CQ I BQ R C V CC V CC v CE i C S l o p e 1 R C // R L 2. AC Load Line Graphical Analysis 3. Nonlinear Distortion 非線性失真 ?There are three regions for iv characteristic. If Qpoint is not suitable, there are saturation or cutoff distortions occurred
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