CO2005: Electronics I. Transistor (BJT) Electronics I, Neamen 3th Ed. 1

Transcription

1 O2005: Electronics The Bipolar Junction Transistor (BJT) Electronics, Neamen 3th Ed. 1

2 Bipolar Transistor Structures N P N D N D Electronics, Neamen 3th Ed. 2

3 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 space- charge region, where the E-field sweeps them into the collector region. Electronics, Neamen 3th Ed. 3

4 urrents in Emitter, ollector, and Base 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 i B1 i B Base recombination current 2 i N D, E N P, B i E i i B B1, i i B1 i Electronics, Neamen 3th Ed. 4

5 ommon-emitter onfiguration i i B E B ommon-emitter current gain i i i ( 1 ) i i i E ( 1 ) B The power supply voltage Vcc must be sufficiently large to keep B junction reverse biased. Electronics, Neamen 3th Ed. 5

6 Forward-Active Mode in the PNP Transistor Electronics, Neamen 3th Ed. 6

7 ircuit Symbols and onventions The arrowhead is always placed on the emitter terminal, anditindicatesthe indicates the direction of the emitter current. Electronics, Neamen 3th Ed. 7

8 ommon-emitter ircuits Electronics, Neamen 3th Ed. 8

9 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. Electronics, Neamen 3th Ed. 9

10 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 V ro i v A, E v BE const. : the quiescent collector current Electronics, Neamen 3th Ed. 10

11 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 Electronics, Neamen 3th Ed. 11

12 Electronics, Neamen 3th Ed. 12

13 D Analysis of ommon-emitter ircuit for PNP B V BB V R EB B (on) and B V E V R Electronics, Neamen 3th Ed. 13

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18 Electronics, Neamen 3th Ed. 18

19 Transistor ircuit Application: Switch utoff and Saturation utoff: v v V ( on), i i 0 V BE O V B Saturation: v v O V V E, R B ( sat) / R i i B c v V R BE R B ( sat) ( on) V V R E ( sat) Electronics, Neamen 3th Ed. 19

20 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 20

21 Bipolar nverter Transistor ircuit Application: Digital Logic Multiple-input NOR gate Electronics, Neamen 3th Ed. 21

22 Electronics, Neamen 3th Ed. 22

23 Single Base Resistor Biasing Electronics, Neamen 3th Ed. 23

24 Voltage Divider Biasing R R // R TH 1 2 R 2 VTH V R1 R2 V R V ( on) (1 ) TH BQ BQ TH BE VTH VBE ( on) R (1 )R TH Q BQ E BQ R E Electronics, Neamen 3th Ed. 24

25 Electronics, Neamen 3th Ed. 25

26 Electronics, Neamen 3th Ed. 26

27 Positive and Negative Voltage Biasing Electronics, Neamen 3th Ed. 27

28 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 0 R VBE ( on ) V ( V 1 BE ( on) V R B1 R 1 B2 2 2 (1 ) 2 ) ( ) Reference current 2 B2 Electronics, Neamen 3th Ed. 28

29 Electronics, Neamen 3th Ed. 29

30 Multistage ircuits 5 V 5 1 B B2 5 V V B2 1 V mA, 0.48V, V E2 E2 2.39mA V V Electronics, Neamen 3th Ed. 30

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32 Electronics, Neamen 3th Ed. 32