O2005: Electronics The Bipolar Junction Transistor (BJT) 張大中 中央大學通訊工程系 dcchang@ce.ncu.edu.tw 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 1
Bipolar Transistor Structures N P 17 10 N D 19 10 N D 15 10 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 2
Forward-Active Mode in the NPN Transistor e Because of the large concentration gradient in the base region, electrons injected from the emitter diffuse across the base into the B spacecharge region, where the E-field sweeps them into the collector region. 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 3
Emitter urrent: Exponential function of the BE voltage ollector urrent: gnoring 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 B voltage. Hence, the collector current is controlled by the BE voltage. Base urrent: BE forward-biased current Base recombination current urrents in Emitter, ollector, and Base i B1 i B2 N i i E D, E i i N B B1, i P, B i B1 i 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 4
ommon-emitter onfiguration i i B E i i i ( 1 ) i B i i E ( 1 ) ommon-emitter current gain B The power supply voltage Vcc must be sufficiently large to keep B junction reverse biased. 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 5
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Forward-Active Mode in the PNP Transistor 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 7
ircuit Symbols and onventions 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, Neamen 3th Ed. 8
ommon-emitter ircuits 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 9
The collector current is nearly independent of the B voltage as long as the B junction is reverse biased. urrent-voltage haracteristics for B Voltage i F i E 1 1 Emitter is like a constant-current source. 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 10
urrent-voltage haracteristics for E Voltage For forward-active mode, the B 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, 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 r o i v V ro A, E v BE const. : the quiescent collector current 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 12
Leakage urrents BO EO : the normal leakage current in the reverse-biased B pn junction : the BE current which is is induced by the forward-biased BE pn junction EO EO BO 1 BO EO (1 ) BO Open-emitter configuration Open-base configuration 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 13
Breakdown Voltage ommon-base haracteristics For the curves in which i E 0, breakdown begins earlier. 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, Neamen 3th Ed. 14
ommon-emitter haracteristics Breakdown Voltage BV BV EO EO BV BO, BVBO, n n 3 ~ 6 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 15
D Analysis of ommon-emitter ircuit for NPN V B V BB V R R BE B V (on) E and V E V B R 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 16
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D Analysis of ommon-emitter ircuit for PNP B V BB V R EB B (on) and B V E V R 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 18
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Load Line V E V V R V R E R V 2 5 E 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 20
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Bipolar D Analysis Technique 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 22
Voltage Transfer haracteristics 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 23
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utoff and Saturation utoff: v v O V BE Transistor ircuit Application: Switch V ( on), i i 0 B Saturation: v v O V V E, R B ( sat) / R i i B c v V R BE B ( sat) ( on) V V R E ( sat) 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 35
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Bipolar nverter Transistor ircuit Application: Digital Logic Multiple-input NOR gate 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 37
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Transistor ircuit Application: Digital Logic 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 39
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Single Base Resistor Biasing 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 41
Using the same values of the resistances, the shift of Q-point is significant due to the variation of the value of. Q-Point 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 42
Voltage Divider Biasing R TH R 1 // R 2 V R 2 TH V R1 R 2 V R V ( on) (1 ) TH BQ BQ V R TH TH Q BQ TH BE V BE ( on) (1 ) R E BQ R E 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 43
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Bias Stability 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 46
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Positive and Negative Voltage Biasing 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 48
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中央大學通訊系張大中 Electronics, Neamen 3th Ed. 51 For integrated circuits, we would like to eliminate as many resistors as possible since, in general, they require a larger surface than transistors. ntegrated ircuit Biasing V on V R BE ) ( 0 1 1 1 1 ) ) ( ( R V on V BE 2 2 2 2 1 2 1 1 1 ) 2 (1 2 2 B B B 1 1 2 ) 2 1 ( Reference current
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Multistage ircuits 5 V 5 1 B2 1.12 B2 5 V 1 0.7 1012 V B2 1 V 2 0.0237mA, 0.48V, V E2 E2 2.39mA 5 2 2.39 0.22V 5 1.5 2.37 1.445V 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 53
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