中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 1

The Bipolar JunctionTransistor (BJT)

張大中中央大學 通訊工程系

dcchang@ce.ncu.edu.tw

CO2005: Electronics I

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 2

Bipolar Transistor Structures

1910DN1510DN

1710PN

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

Forward-Active Mode in the NPN Transistor

e

Because of the large concentrationgradient in the base region, electronsinjected from the emitter diffuseacross the base into the BC space-charge region, where the E-fieldsweeps them into the collector region.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 4

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 isindependent of the reverse-biased BC voltage. Hence, the collector current is controlled bythe BE voltage.

Base Current: BE forward-biased current Base recombination current

Currents in Emitter, Collector, and Base

1Bi2Bi

CBCBE

BC

BPED

iiiiiii

NN

1

1

,,

,

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 5

Common-Emitter Configuration

B

C

ii

BCBE iiii )1(

EC ii)1(

Common-emitter current gain

The power supply voltage Vccmust be sufficiently large tokeep BC junction reversebiased.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 6

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 7

Forward-Active Mode in the PNP Transistor

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 8

Circuit Symbols and Conventions

The arrowhead isalways placed onthe emitter terminal,and it indicates thedirection of theemitter current.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 9

Common-Emitter Circuits

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 10

The collector current is nearlyindependent of the CB voltageas long as the BC junction isreverse biased.

Current-Voltage Characteristics for CB Voltage

11

E

CF i

i

Emitter is like aconstant-currentsource.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 11

For forward-active mode, the BC junction must be reverse biased, which means that Vcemust be greater than approximately Vbe(on). There is a finite to the curves.

Current-Voltage Characteristics for CE Voltage

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 12

When the current-voltage characteristic curves are extrapolated to zero current, they meetat 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 isfinite. The resistance is not critical in the dc analysis.

Early Voltage

.

1

constvCE

C

oBE

vi

r

currentcollectorquiescentthe:

,

C

C

Ao

IIV

r

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 13

Leakage Currents

CBOI

CEOI

: the normal leakage current in the reverse-biased BC pn junction

: the BE current which is is induced by the forward-biased BE pn junction

CBOCEOCEO III

CBOCBO

CEO II

I )1(1

Open-emitterconfiguration

Open-baseconfiguration

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 14

Common-Base CharacteristicsFor the curves in which , breakdown begins earlier. The carriers flowing across thejunction initiates the breakdown avalanche process at somewhat lower voltages.

Breakdown Voltage

0Ei

Emitter isopen.

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 15

Common-Emitter Characteristics

Breakdown Voltage

6~3,

,

nBV

BV

BVBV

n

CBOCEO

CBOCEO

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 16

DC Analysis of Common-Emitter Circuit for NPN

BCB

BEBBB II

RVV

I and

)on(

CCCCCECECCCC RIVVVRIV

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 17

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 18

DC Analysis of Common-Emitter Circuit for PNP

BCB

EBBBB II

RVV

I

and)on(

CCCCEC RIVV

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 19

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

Load Line

25 CE

C

CE

C

CCC

CCCCCE

VRV

RV

I

RIVV

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 21

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 22

Bipolar DC Analysis Technique

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 23

Voltage Transfer Characteristics

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

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 35

Cutoff and SaturationCutoff:

Saturation:

Transistor Circuit Application: Switch

CCO

CBBEI

VviionVv

0),(

)(/,

satVvRRVv

CEO

CBCCI

B

BEIB R

onVvi

)(

C

CECCCc R

satVVsatIi

)()(

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 36

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 37

Bipolar Inverter

Multiple-input NOR gate

Transistor Circuit Application: Digital Logic

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 38

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 39

Transistor Circuit Application: Digital Logic

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 40

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 41

Single Base Resistor Biasing

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 42

Using the same values of the resistances, the shift of Q-point is significant due to thevariation of the value of .

Q-Point

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 43

Voltage Divider Biasing

21 // RRRTH

CCTH VRR

RV

21

2

EBQBETHBQTH RIonVRIV )1()(

ETH

BETHBQ RR

onVVI

)1()(

BQCQ II

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

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 46

Bias Stability

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 47

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 48

Positive and Negative Voltage Biasing

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

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 51

For integrated circuits, we wouldlike to eliminate as many resistorsas possible since, in general, theyrequire a larger surface thantransistors.

Integrated Circuit Biasing

VonVRI BE )(0 11

11

))((R

VonVI BE

22

2

212111

)2

1(2

2

CC

C

BCBBC

II

I

IIIIII

112 )2

1( IIIC

Reference current

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 52

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 53

Multistage Circuits

1.12I5V5

B2C1

21010.7V5

I C1B2

2.39mAI0.0237mA,I E2B2

0.22V2.3925V0.48V,V E2C1

1.445V2.371.55VC2

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