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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

BJT TransistorBJT Operation and I/V Characteristics

Dr. Alaa El-Din Hussein

April 5, 2008

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

Outline

1 Introduction

2 BJT Structure

3 Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

Outline

1 Introduction

2 BJT Structure

3 Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

What is a Transistor?

Websters Dictionary: Transistor is asolid-state electronic device that is used tocontrol the flow of electricity in electronicequipment and consists of a small block ofa semiconductor (as germanium) with at

least three electrodes

Three-terminal device whosevoltage-current relationship is controlledby a third voltage or current

We may regard a transistor as a controlledvoltage or current source

TRANSISTOR is an abbreviation toTRANSfer resISTOR

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

What is a Transistor?

Websters Dictionary: Transistor is asolid-state electronic device that is used tocontrol the flow of electricity in electronicequipment and consists of a small block ofa semiconductor (as germanium) with at

least three electrodes

Three-terminal device whosevoltage-current relationship is controlledby a third voltage or current

We may regard a transistor as a controlledvoltage or current source

TRANSISTOR is an abbreviation toTRANSfer resISTOR

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I d BJ S A NPN M d l PNP A PNP M d l

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

What is a Transistor?

Websters Dictionary: Transistor is asolid-state electronic device that is used tocontrol the flow of electricity in electronicequipment and consists of a small block ofa semiconductor (as germanium) with at

least three electrodes

Three-terminal device whosevoltage-current relationship is controlledby a third voltage or current

We may regard a transistor as a controlledvoltage or current source

TRANSISTOR is an abbreviation toTRANSfer resISTOR

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I t d ti BJT St t T i t A ti NPN M d l PNP T i t A ti PNP M d l

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

What is a Transistor?

Websters Dictionary: Transistor is asolid-state electronic device that is used tocontrol the flow of electricity in electronicequipment and consists of a small block ofa semiconductor (as germanium) with at

least three electrodes

Three-terminal device whosevoltage-current relationship is controlledby a third voltage or current

We may regard a transistor as a controlledvoltage or current source

TRANSISTOR is an abbreviation toTRANSfer resISTOR

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

What is a Transistor?

Websters Dictionary: Transistor is asolid-state electronic device that is used tocontrol the flow of electricity in electronicequipment and consists of a small block ofa semiconductor (as germanium) with at

least three electrodes

Three-terminal device whosevoltage-current relationship is controlledby a third voltage or current

We may regard a transistor as a controlledvoltage or current source

TRANSISTOR is an abbreviation toTRANSfer resISTOR

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

Types of Transistors

According to the physics of the device, we can classify transistors intotwo main classes:

Field effect transistors (FET): Conduction is controlled by electric

field which is produced by voltage applied to the control terminals.So, the control draws no current and FET is a voltage-controlleddevice.

Bipolar junction transistors (BJT): Diode-based device which isusually blocked unless the control terminals are forward-biased. So,

the control is a current, and BJT is a current amplifier by nature.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

Types of Transistors

According to the physics of the device, we can classify transistors intotwo main classes:

Field effect transistors (FET): Conduction is controlled by electric

field which is produced by voltage applied to the control terminals.So, the control draws no current and FET is a voltage-controlleddevice.

Bipolar junction transistors (BJT): Diode-based device which isusually blocked unless the control terminals are forward-biased. So,

the control is a current, and BJT is a current amplifier by nature.

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t oduct o J St uctu e a s sto ct o ode s a s sto ct o ode s

Types of Transistors

According to the physics of the device, we can classify transistors intotwo main classes:

Field effect transistors (FET): Conduction is controlled by electric

field which is produced by voltage applied to the control terminals.So, the control draws no current and FET is a voltage-controlleddevice.

Bipolar junction transistors (BJT): Diode-based device which isusually blocked unless the control terminals are forward-biased. So,

the control is a current, and BJT is a current amplifier by nature.

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Outline

1 Introduction

2 BJT Structure

3 Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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BJT Structure

The BJT is simply a two P-N Junctions which may lead to either NPN or

PNP structure as shown:

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BJT Modes of Operation

Mode EBJ CBJ ApplicationActive Forward Reverse AmplifierCutoff Reverse Reverse Switch

Digital-CircuitsSaturation Forward ForwardInverse-Active Reverse Forward ??

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Outline

1 Introduction

2 BJT Structure

3 Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the hole current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the hole current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the hole current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

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Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the hole current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Transistor ActionMinority Carrier Concentration

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Transistor ActionQuantitative Description

np(0) = npoevBE/VT

In = AEqDndnp(x)

dx= AEqDn

np(0)

W

iC = In = ISevBE/VT

IS =AEqDnnpo

W

=AEqDnn

2i

NAWiB = iB1 + iB2

iB = IS

DPNAW

DnNDLP+

W2

2Dnb

evBE/VT

iB =ic

=

IS

evBE/VT

= 1/

DPNAW

DnNDLP+

W2

2Dnb

= 1/

DPNAW

DnNDLP+

W2

2Dnb

iE = iC + iB, iC = iE

= +1 CB Current Gain

= 1 CE Current Gain

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

O li

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Outline

1 Introduction

2 BJT Structure

3 Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

NPN T i M d l i A i M d

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NPN Transistor Models in Active Mode

The NPN transistor may be replaced by any of the following models in

the active region:

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

Eb M ll (EM) M d l

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Ebers-Moll (EM) Model

IS = RISC = FISE

iC = IS

exp

vBE

VT

1

IS

R

exp

vBC

VT

1

iE =IS

F

exp

vBE

VT

1

IS

exp

vBC

VT

1

iB =IS

F

exp

vBE

VT

1

+

IS

R

exp

vBC

VT

1

This model is valid for all 4 regions of

operation of the BJT. This is themodel used in CAD simulators

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

O tli

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Outline

1 Introduction

2 BJT Structure

3Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

PNP T i t A ti

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PNP Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the electron current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

PNP Transistor Action

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PNP Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the electron current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

PNP Transistor Action

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PNP Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the electron current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

PNP Transistor Action

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PNP Transistor ActionQualitative Description

Active Mode: The B-E junction is forward biased and the C-B junction is reversebiased.

Base Current: Is composed of two parts iB1 represents the electron current in theB-E junction, and iB2 represents the recombination current.

Common-Base current gain () is the ratio between the collector and emittercurrents.

What is the maximum value of? and how you can achieve this value?.

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

PNP Transistor Action

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PNP Transistor ActionQuantitative Description

Pn(0) = pnoevEB/VT

Ip = AEqDpdpn(x)

dx= AEqDp

pn(0)

W

iC = Ip = ISevEB/VT

IS =AEqDppno

W =

AEqDpn2i

NDW

iB = iB1 + iB2

iB = IS

DnNDW

DpNALn+

W2

2Dpb

evEB/VT

iB =

ic

= IS

e

vEB/VT

= 1/

DnNDW

DpNALn+

W2

2Dpb

= 1/

DnNDW

DpNALn+

W2

2Dpb

iE = iC + iB, iC = iE

=

+1 CB Current Gain= 1 CE Current Gain

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

Outline

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Outline

1 Introduction

2 BJT Structure

3 Transistor Action

4 NPN Models

5 PNP Transistor Action

6 PNP Models

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Introduction BJT Structure Transistor Action NPN Models PNP Transistor Action PNP Models

PNP Transistor Models in Active Mode

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PNP Transistor Models in Active Mode

The PNP transistor may be replaced by any of the following models in

the active region:

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