Chapter #6: Bipolar Junction...
Transcript of Chapter #6: Bipolar Junction...
![Page 1: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/1.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
1
Chapter #6: Bipolar Junction Transistors
![Page 2: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/2.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
2
Introduction
• IN THIS CHAPTER YOU WILL LEARN• The physical structure of the bipolar transistor and how it works.
• How the voltage between two terminals of the transistor controls the current that flows through the third terminal, and the equations that describe these current-voltage relationships.
• How to analyze and design circuits that contain bipolar transistors, resistors, and dc sources.
• How the transistor can be used to make an amplifier.
• How to obtain linear amplification from the fundamentally nonlinear BJT.
• The three basic ways for connecting a BJT to be able to construct amplifiers with different properties.
• Practical circuits for bipolar-transistor amplifiers that can be constructed by using discrete components.
![Page 3: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/3.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
3
Introduction
• This chapter examines another three-terminal device.
• bipolar junction transistor
• Presentation of this material mirrors chapter 5.
• Three-terminal device• Multitude of applications
• Signal amplification/Digital logic/Memory circuit/Switch
• Voltage between two terminals to control the current flowing in third terminal
• BJT was invented in 1948 at Bell Telephone Laboratories
• Ushered in a new era of solid-state circuits
• It was replaced by MOSFET as predominant transistor used in modern electronics.
![Page 4: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/4.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
4
4.1. Device Structure and Physical Operation
• Figure 4.1. shows simplified structure of BJT
• Consists of three semiconductor regions:
• emitter region (n-type)
• base region (p-type)
• collector region (n-type)
• Type described above is referred to as npn
• However, pnp types do exist
![Page 5: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/5.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
5
4.1.1. Simplified Structure and Modes of Operation
• Transistor consists of two pn-junctions:
• emitter-base junction (EBJ)
• collector-base junction (CBJ)
• Operating mode depends on biasing
• active mode – used for amplification
• cutoff and saturation modes – used for switching
• Bipolar(electron and hole) participate in conduction
![Page 6: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/6.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
6
4.1.2. Operation of the npn-Transistor in the Active Mode
• Active mode is “most important”
• Two external voltage sources are required for biasing to achieve it
• Refer to Figure 4.3
Figure 4.3: Current flow in an npn transistor biased to operate in the active mode. (Reverse current components due to drift of thermally generated minority carriers
are not shown.)
![Page 7: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/7.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
7
Current Flow
• Forward bias on emitter-base junction will cause current to flow
• This current has two components:
• electrons injected from emitter into base
• holes injected from base into emitter
• It will be shown that first (of the two above) is desirable
• This is achieved with heavy doping of emitter, light doping of base
![Page 8: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/8.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
8
Current Flow
• emitter current (iE) – is current which flows across EBJ
• Flows “out” of emitter lead
• minority carriers – in p-type region
• These electrons will be injected from emitter into base.
• Opposite direction
• Because base is thin, concentration of excess minority carriers within it will exhibit constant gradient
![Page 9: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/9.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
9
0
0
( ) concentration of minority carriers a position x (where 0 represents EBJ boundary) thermal-equilibrium value of minority carrier (elect
/
ron) concentration in base
0
reg
(eq6.1) 0 BE
p
p
Tv
nn
Vp
x
n e
pn
pn
0
0
0
ionvoltage applied across base-emitter junction
thermal voltage (constant)
p
pBE
pT
nn
nv
V
Oxford University PublishingMicroelectronic Circuits by Adel S. Sedra and Kenneth C. Smith (0195323033)
Straight line represents constant gradient
Figure 4.4
(eq4.1)
![Page 10: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/10.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
10
Current Flow
• Concentration of minority carrier np at boundary EBJ is defined by (4.1)
• Concentration of minority carriers np at boundary of CBJ is zero• Positive vCB causes these electrons to be swept across junction
0
0
( ) concentration of minority carriers a position x (where 0 represents EBJ boundary) thermal-equilibrium value of minority carrier
/
(electron) concentration in ase
0
b
(eq6 0.1)
p
p
BE T
x
n
v V
n
pn e
pn
pn
0
0
0
regionvoltage applied across base-emitter junction
thermal voltage (constant)
p
pE
p
B
T
nn
nv
V
(eq4.1)
![Page 11: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/11.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
11
Current Flow
• Tapered minority-carrierconcentration profile exists
• It causes electrons injected into base to diffusethrough base toward collector
• As such, electron diffusion current (In) exists.
cross-sectiona area of the base-emitter junction magnitude of the electr
this simplificationmay be made if
gradient assumedto be straight line
(e
(eq6.2)
q6.2)
0
E
p
n E n
p
E n
Aq
n
dn xI A qD
dx
dnAI qD
W
on charge electron diffusivity in base
width of basenD
W
(eq4.2)
(eq4.2)
![Page 12: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/12.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
12
Current Flow
• Some “diffusing” electrons will combine with holes(majority carriers in base)
• Since base is very thin and lightly doped, recombination is minimal
• Recombination does, however, cause gradient to take slightly curved shape
• The straight line is assumed
![Page 13: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/13.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
13
0
0
( ) concentration of minority carriers a position x (where 0 represents EBJ boundary) thermal-equilibrium value of minority carrier (elect
/
ron) concentration in base
0
reg
(eq6.1) 0 BE
p
p
Tv
nn
Vp
x
n e
pn
pn
0
0
0
ionvoltage applied across base-emitter junction
thermal voltage (constant)
p
pBE
pT
nn
nv
V
Oxford University PublishingMicroelectronic Circuits by Adel S. Sedra and Kenneth C. Smith (0195323033)
Recombination causes actual gradient to be curved, not straight.
Figure 4.4
(eq4.1)
![Page 14: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/14.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
14
The Collector Current
• It is observed that most diffusing electrons will reach boundary of collector-basedepletion region
• Because collector is more positive than base, these electrons are swept into collector• collector current (iC) is
approximately equal to In
• iC = In intrinsic carrier density doping concentration of base
/
0
2
(eq6.3)
saturation current:
(eq6.4)
BE Tv VC S
E
n
n p
S
E n iS
A
iNA
i I
A qD nI
W
A qD nI
W N
e(eq4.3)
(eq4.4)
![Page 15: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/15.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
15
The Collector Current
• Magnitude of iC is independent of vCB
• As long as collector is positive, with respect to base
• saturation current (IS) – is inversely proportional to W and directly proportional to area of EBJ
• Typically between 10-12 and 10-18A
• Also referred to as scale current
![Page 16: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/16.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
16
The Base Current
• base current (iB) – composed of two components:
• ib1 – due to holes injected from base region into emitter
• ib2 – due to holes that have to be supplied by external circuit to replace those recombined
![Page 17: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/17.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
17
The Base Current
• common-emitter current gain(b.) – is influenced by two factors:
• width of base region (W)
• relative doping of base emitter regions (NA/ND)
• High Value of b 50~200, >1000
• thin base (small W in nano-meters)
• lightly doped base / heavily doped emitter (small NA/ND)
transistor parameter
/
(eq6.5)
(eq6.6) BE T
CB
v VSB
ii
Ii
b
b
b
e
(eq4.5)
(eq4.6)
![Page 18: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/18.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
18
The Emitter Current
• All current which enters transistor must leave
• iE = iC + iB• Equations (4.7)
through (4.13) expand upon this idea
• α : common-base current gain (less than but very close to unity)
this expression is generated through combination of (6.5) and (6.7)
/(eq6.8/6.9)
(eq6.10)
(eq6.11
1
)
1
BE T
C
v VE C S
C E
i
i i I
i i
b b
b b
b
b
e
this parameter is reffered
/
toas
(eq6.13)
(eq6.1
1 1
2)
,
BE Tv VSE
Ii
b
common-base current gain
e
(eq4.8/4.9)
(eq4.10)
(eq4.11)
(eq4.12)
(4.5) and (4.7)
(eq4.13)
![Page 19: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/19.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
19
Recapitulation and Equivalent-Circuit Models
• Previous slides present first-order BJT model.
• Assumes npn transistor in active mode
• Basic relationship is collector current (iC) is related exponentially to forward-bias voltage (vBE)
• It remains independent of vCB as long as this junction remains reverse biased
• vCB > 0
• iB is much smaller than iC• Nonlinear voltage-controlled current source
![Page 20: Chapter #6: Bipolar Junction Transistorstioh.weebly.com/uploads/2/5/4/3/25433593/12week__chapter_4__-_ti.pdf · Chapter #6: Bipolar Junction ... •The three basic ways for connecting](https://reader031.fdocuments.us/reader031/viewer/2022021801/5b2bdae77f8b9a5c478bb665/html5/thumbnails/20.jpg)
Microelectronic Circuits, Kyung Hee Univ. Fall, 2015
20
Figure 4.5: Large-signal equivalent-circuit models of the npn BJT operating in the forward active mode.
Common base model
Common emitter model