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

The Bipolar Junction Transistor (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

1910DN

1510DN

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 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 sweeps 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 is independent of the reverse-biased BC voltage. Hence, the collector current is controlled by the BE voltage.

Base Current: BE forward-biased current Base recombination current

Currents in Emitter, Collector, and Base

1Bi

2Bi

CBCBE

BC

BPED

iiiii

ii

NN

1

1

,,

,

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

Common-Emitter Configuration

B

C

i

i

BCBE iiii )1(

EC ii)1(

Common-emitter current gain

The power supply voltage Vcc must be sufficiently large to keep BC junction reverse biased.

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

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.

Current-Voltage Characteristics for CE Voltage

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

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.

Early Voltage

.

1

constvCE

C

oBE

v

i

r

currentcollector quiescent the:

,

C

C

Ao

I

I

Vr

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

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

Breakdown Voltage

0Ei

Emitter is open.

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

DC Analysis of Common-Emitter Circuit for NPN

BCB

BEBBB II

R

VVI

and

)on(

CCCCCECECCCC RIVVVRIV

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

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

DC Analysis of Common-Emitter Circuit for PNP

BCB

EBBBB II

R

VVI

and

)on(

CCCCEC RIVV

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

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

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

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

Cutoff and Saturation

Cutoff:

Saturation:

Transistor Circuit Application: Switch

CCO

CBBEI

Vv

iionVv

0 ),(

)(

/ ,

satVv

RRVv

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. 21

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

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. 23

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 24

Single Base Resistor Biasing

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 25

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. 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

Bias Stability

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

Positive and Negative Voltage Biasing

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 31

For integrated circuits, we would like to eliminate as many resistors as possible since, in general, they require a larger surface than transistors.

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. 32

中央大學通訊系 張大中 Electronics I, Neamen 3th Ed. 33

Multistage Circuits

1.12I5

V5B2

C1

2101

0.7V5I C1

B2

2.39mAI0.0237mA,I E2B2

0.22V2.3925 V0.48V,V E2C1

1.445V2.371.55VC2

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