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1、Analogue Electronic Principles,DG2X 34,Bipolar Junction Transistor,晶体管 (BJT) 的结构和符号 (symbol ),从E区到达B区的电子 (I B + I CBO)， 则必有(I B + I CBO) 电子到达C区： I C =(I B + I CBO) + I CBO =I B + (1 +) I CBO =I B + I CEO (穿透电流) I B (电流放大) I E = I B + I CBO +(I B + I CBO) = I B + I C,E 区电子扩散注入 B 区，C 结强电场将其拉入 C 区， 由于到
2、达 C 区电子来自 E 区，因此反映了 E 结电压规律。,晶体管工作在放大区的电流分配关系,I CEO =I CBO + I CBO = (1 +) I CBO I CEO ： 从 C 区穿透 B 区到达 E 区,穿透电流 I CEO (leakage current) 与 反向漂移电流 I CBO,晶体管的输入特性曲线 input characteristic,晶体管的输出特性曲线 output characteristic,晶体管的输出特性曲线,AC current gain,Active region,Saturation region,Cut-off region,三极管工作状态： 1
3、、放大：E 结正偏 C 结反偏 此时 IC = IB 2、截止：E 结正偏不足/反偏 此时 IB 0 3、饱和：E 结 C结均正偏 此时 IB IC,The Quality of BJT,1、截止区小（ICEO 小，温度稳定性好）； 2、曲线间距宽（ 高）； 3、曲线平（IC 只受 IB 控制）；,静态工作点 (Q点)： Quiescent point、 Operating point、 Working point。,Description for an NPN bipolar junction transistor device: An NPN bipolar junction transi
4、stor consists of two PN junctions. It has a P-type base and N-type collector and emitter. When transistor operates in saturation region the two junctions of the transistor are forward-biased. For a constant base current, the collector current increases as VCE increases from 0V to about 0.7V. When tr
5、ansistor operates in active region, as a linear amplifier, the VCE exceeds about 0.7V, the collector-base junction becomes reverse-biased. The collector current depends on the base current only and is independent from VCE. Ic = IB, the bipolar transistor is a current controlled device. When transist
6、or operates in cut-off region the base-emitter junction is not forward-biased enough or so much as reverse-biased, there is no the forward base current and thus the collector current is nearly zero (when IB = 0, Ic = ICEO, the leakage current).,Transistor application,Common-Emitter Amplifier,静态工作点设置
7、： 调 RB 定 IBQ，调 RC 定 VCEQ ，使 BJT 工作在放大区。,CE Amp.,放大交流信号 ： Vi VBE IB IC VRC VCE,VBE = 0.7V + Vi，IB = IBQ + ib， IC = ICQ + ic， VCE = VCEQ + VRC,放大交流信号 ： Vi VBE IB IC VRC VCE Vo,capacitive resistance coupling,地：输入、输出、直流电源公共端； CE：E 接地 有源器件：加直流电源下才可正常工作的器件 有源器件作用：按输入信号规律把直流电源能量转换成交流输出能量,RC Coupling CE Amp
8、lifier (阻容耦合式),Q点：I BQ = （VCC 0.7V）/ RB (Fixed IB biased 固定偏置电路 ) I CQ = I BQ VCC = I CQ RC + V CEQ (DC Load line：Q点的规律),DC.负载线斜率：- 1 / RC （RC ：CE 间直流负载）,AC.负载线斜率：- 1 / RC | RL （RC | RL ：CE 间交流负载）,EC,UBEQ,UBE,IBQ,IB,Ui,Q,UBE = UBEQ + Ui,Uo,IB2,IB1,IB1,IB2,IC1,IC2,AC Load line 交流负载线方程 (过Q点) ： IC - IC
9、Q 1 - = - - VCE VCEQ RC| RL 在 Vi 作用下 IC VCE 的规律 (交直流共存),图解法,Distortion 失真,Ic,VCE,Ec,Q,AC Load line AC. 负载线,最大输出 Maxmum output,饱和失真 (切底) Saturation distortion,Ic,VCE,Ec,Q,AC. 负载线,最大输出,截止失真 (切顶) Cut-off distortion,Ic,VCE,Ec,Q,AC. 负载线,输出最大,前级信号较弱 Q点较低不会失真 且节约供电,末级信号强 Q位于AC负载线中点 使输出最大,Vo,Vo,Vo,t,t,t,例 工
10、作点稳定电路,The operation of circuit for a sinusoidal input signal: 结构特点：This is a working-point stabilization common-emitter amplifier. 各元件作用： RB1 and RB2 are voltage divider which fix the base level. RC is the collector resistor. RE is the emitter resistor which provides stabilization of the Q-point. C
11、1 and C2 are coupling capacitors. CE is an emitter bypass capacitor. 工作过程： In the positive half-cycle of the input: The input is coupled to the base by C1 , which causes IB increase, and IC increases, then voltage across RC increases, collector level decreases and is coupled to the load by C2 and re
12、sults the output voltage decrease. Vi IB IC VRC VC VO negative During negative half-cycle of the input: The base current and collector current will be reduced, resulting in an increase in the output voltage. Thus the common-emitter amplifier is an inverting voltage amplifier with phase reversal of 1
13、80 degrees between input and output.,电路计算： Voltage at the base, assuming IB is ignored because RE 10 RB2 Voltage at the emitter, assuming VBEQ = 0.7 V VE = VB VBEQ = 1.75V 0.7V = 1.0 V Voltage at the collector, assuming IC IE ICQ IEQ = VE / RE = 1V / 1K = 1m A VC = VCC ICQ RC = 10V ( 1mA 4.7K ) = 5.
14、3 V Voltage between collector and emitter VCEQ = VCC ICQ RC ICQ RE = 10V ( 1mA 4.7K ) ( 1mA 1K ) = 4.3 V The expressions of input resistance, output resistance, and voltage gain.,结构特点： 1) The overall current gain equals to the product of the two current gains of the individuals: 1 2 2) The base-emit
15、ter voltage is twice the individual one, about 1.4V. 3) The emitter current of the first transistor is the base current of the second one. 4) The input impedance is higher than the individual: rbe = rbe1 + ( 1 + 1 ) rbe2,The operation of a Darlington pair: A Darlington pair consists of two bipolar j
16、unction transistors configured as shown. The device is a single package, or in IC form.,A CE amp. using Darlington pair :,优质三极管标准： 1、截止区小（ICEO 小，温度稳定性好）； 2、曲线间距宽（ 高）； 3、曲线平（rCE 小）； 4、UCE 1V后，输入特性尽量重合（内反馈小）：,CE hModel (共射 h 参数模型),h21,h11,Simplified h-Model (简化 h 参数模型),Class A Power Amplifiers 小功率甲类功率
17、放大电路,QDE：最大交流输出功率,OABC：电源功率,Transformer Coupling 变压器耦合甲类功率放大电路,Ic时：,- +,最大交流输出功率,电源功率,变压器耦合乙类推挽功率放大电路 Pull-Push,OTL 电路,单电源,静态时 B、E 均,Vcc 2,OCL 电路,双电源,静态时 B、E 均 0V,BTL电路（双入双出）,单电源,静态时 B、E 均,Vcc 2,由于发射结存在导通电压， 当输入过 0 时，输出电压产生失真！ （出现交越失真时两管均截止）,Crossover Distortion 乙类功率放大电路的交越失真现象,Class AB Amp. to reduce crossover distortion 甲乙类功率放大电路消除交越失真,偏流,中点,