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The Bipolar Junction Transistor (BJT)

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The Bipolar Junction Transistor (BJT) CO2005: Electronics I The Bipolar Junction Transistor (BJT) 張大中 中央大學 通訊工程系 [email protected] 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 1 Bipolar Transistor Structures 19 17 N D 10 N P 10 15 N D 10 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 2 Forward-Active Mode in the NPN Transistor Because of the large concentration gradient in the base region, electrons injected from the emitter diffuse across the base into the BC space- charge region, where the E-field e sweeps them into the collector region. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 3 Currents in Emitter, Collector, and Base Emitter Current: Exponential function of the BE voltage Collector Current: Ignoring the recombination in the base region (the base width is very tiny, micrometer), the collect current is proportional to the emitter injection current and is independent of the reverse-biased BC voltage. Hence, the collector current is controlled by the BE voltage. Base Current: BE forward-biased current iB1 N D,E N P,B Base recombination current iB2 iC iB1, iE iB iC iB1 iC 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 4 Common-Emitter Configuration i C Common-emitter current gain iB The power supply voltage Vcc iE iB iC (1)iB must be sufficiently large to keep BC junction reverse i i biased. C (1) E 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 5 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 6 Forward-Active Mode in the PNP Transistor 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 7 Circuit Symbols and Conventions The arrowhead is always placed on the emitter terminal, and it indicates the direction of the emitter current. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 8 Common-Emitter Circuits 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 9 Current-Voltage Characteristics for CB Voltage The collector current is nearly independent of the CB voltage as long as the BC junction is reverse biased. iC F 1 iE 1 Emitter is like a constant-current source. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 10 Current-Voltage Characteristics for CE Voltage For forward-active mode, the BC junction must be reverse biased, which means that Vce must be greater than approximately Vbe(on). There is a finite to the curves. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 11 Early Voltage When the current-voltage characteristic curves are extrapolated to zero current, they meet at a point on the negative voltage axis at Vce=-Va, the early voltage. The slope of the curves indicates that the output resistance looking into the collector is finite. The resistance is not critical in the dc analysis. 1 i C ro vCE vBE const. VA ro , IC IC : the quiescent collector current 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 12 Leakage Currents ICBO : the normal leakage current in the reverse-biased BC pn junction ICEO : the BE current which is is induced by the forward-biased BE pn junction ICEO ICEO ICBO I I CBO (1)I CEO 1 CBO Open-emitter Open-base configuration configuration 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 13 Breakdown Voltage Common-Base Characteristics ForthecurvesinwhichiE 0 , breakdown beginsearlier. The carriers flowing across the junction initiates the breakdown avalanche process at somewhat lower voltages. Emitter is open. 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 14 Breakdown Voltage Common-Emitter Characteristics BVCEO BVCBO , BVCBO BVCEO ,n 3 ~ 6 n 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 15 DC Analysis of Common-Emitter Circuit for NPN VBB VBE (on) I B and IC I B RB VCC IC RC VCE VCE VCC IC RC 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 16 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 17 DC Analysis of Common-Emitter Circuit for PNP VBB VEB (on) I B and IC I B RB VEC VCC IC RC 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 18 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 19 Load Line VCE VCC IC RC VCC VCE VCE IC 5 RC RC 2 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 20 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 21 Bipolar DC Analysis Technique 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 22 Voltage Transfer Characteristics 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 23 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 24 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 25 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 26 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 27 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 28 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 29 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 30 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 31 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 32 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 33 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 34 Transistor Circuit Application: Switch Cutoff and Saturation Cutoff: vI VBE (on), iB iC 0 vO VCC Saturation: vI VCC , RB / RC vO VCE (sat) vI VBE (on) iB RB VCC VCE (sat) ic IC (sat) RC 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 35 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 36 Transistor Circuit Application: Digital Logic Bipolar Inverter Multiple-input NOR gate 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 37 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 38 Transistor Circuit Application: Digital Logic 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 39 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 40 Single Base Resistor Biasing 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 41 Q-Point Using the same values of the resistances, the shift of Q-point is significant due to the variation of the value of . 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 42 Voltage Divider Biasing RTH R1 // R2 VTH I BQ RTH VBE (on) (1)I BQ RE V V (on) R2 TH BE V V I BQ TH CC R (1)R R1 R2 TH E ICQ I BQ 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 43 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 44 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 45 Bias Stability 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 46 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 47 Positive and Negative Voltage Biasing 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 48 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 49 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 50 Integrated Circuit Biasing For integrated circuits, we would like to eliminate as many resistors as possible since, in general, they require a larger surface than transistors. 0 I1R1 VBE (on) V (VBE (on) V ) I1 Reference current R1 I1 IC1 I B1 I B2 IC1 2I B2 2I 2 I C 2 (1 )I C 2 C 2 2 I I (1 ) I C 2 1 1 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 51 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 52 Multistage Circuits 5 V C1 I 1.12 5 B2 5 V 0.7 I C1 B2 1012 IB2 0.0237mA, IE2 2.39mA VC1 0.48V, VE2 5 2 2.39 0.22V VC2 5 1.5 2.37 1.445V 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 53 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 54 中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 55.
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