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Chapter 13Bipolar Junction Transistors
1. Bipolar Junction Transistor Operation in amplifier circuits.
2. Load-line Analysis & Nonlinear Distortion.
3. Large-signal equivalent circuits to analyze BJT circuits.
4. Bias circuits.
5. Small-signal equivalent circuits to analyze BJT amplifiers.
6. Several Important Amplifier Configurations.
Goal
1st Transistor
Brattain and Bardeen's pnp point-contact germanium transistor operatedas a speech amplifier with a power gain of 18 on December 23, 1947
This picture shows the workbench of John Bardeen and Walter Brattainat Bell Laboratories. They were supposed to be doing fundamentalresearch about crystal surfaces. The experimental results hadn't been very good, though, and there's a rumor that their boss, William Shockley, came near to canceling the project. But in 1947, working alone, they switched to using tremendously pure materials. It dawned on them that they could build the circuit in the picture. It was a working amplifier! John and Walter submitted a patent for the first working point contact transistor. Shockley was furious and took their work and invented the junction transistor and submitted a patent for it 9 days later. The three shared a Nobel Prize. Bardeen and Brattain continued in research (and Bardeen later won another Nobel). Shockley quit to start a semiconductor company in Palo Alto. It folded, but its staff went on to invent the integrated circuit (the "chip") and to found Intel Corporation. By 1960, all important computers used transistors for logic, and ferrite cores for memory. Memory chips replaced core in the 1970's
Explanation of 1st Transistor
1948 - POINT CONTACT TRANSISTOR 1950 - SINGLE-CRYSTAL GERMANIUM 1951 - GROWN JUNCTION TRANSISTOR1952 - ALLOY JUNCTION TRANSISTOR1952 - ZONE MELTING AND REFINING 1952 - SINGLE-CRYSTAL SILICON1955 - DIFFUSED -BASE TRANSISTORS 1957 - OXIDE MASKING 1960 - PLANAR TRANSISTOR 1960 - MOS TRANSISTOR 1960 - EPITAXIAL TRANSISTOR 1961 - INTEGRATED CIRCUITS
- from Bell Laboratories Record magazine January 1975, p.74
Major Milestones in Transistor Electronics
Close-Up of 2N23 transistor by Western Electric in 1954
Transistor
The Most Basic & Important Active Component- Power Amplification- IC uses more recently : interfacing required- if no proper IC, only transistor can do something.
1948년미국 Bell Lab 의Walter Houser Brattain, John Bardeen및William Bradford Shockley는반도체격자구조의시편(試片)에가는도체선을접촉시켜주면전기신호의증폭작용을나타내는것을발견하여이를트랜지스터라고명명하였다. 이것이그동안신호증폭의구실을해오던진공관(眞空管)과대치되는트랜지스터의시초가된것이다. 트랜지스터그자체가소형이어서이를사용하는기기(機器)는진공관을사용할때에비하여소형이되며, 가볍고소비전력이적어편리하다. 초기에는잡음·주파수특성이나쁘고, 증폭도도충분하지못하였으나, 그후많이개량되어아주대전력을다룰수있는등특수한경우를제외하고는진공관에대치되었다.
-두산백과사전 -
Function: Current AmplificationType : PNP , NPN Type Code : PNP High Frequency (2SA×××)
PNP Low Frequency (2SB×××)NPN High Frequency (2SC×××)NPN Low Frequency (2SD×××)
마이너스전압측을접지로, 플러스전압측을전원으로하는회로의경우, NPN 타입쪽이사용하기쉽다.
Transistor
Lead in TransistorNPN : 2SC1815 NPN : 2SD880
품명이 인쇄되어 있는면을 바라 보았을 때,오른쪽 리드가 베이스중앙의 리드가 컬렉터왼쪽의 리드가 이미터
트랜지스터의 종류에 따라 리드의 내용이 다르기 때문에매뉴얼 등을 참조하여 확인할 필요가있다
품명이 인쇄되어 있는면을 바라 보았을 때,오른쪽 리드가 이미터중앙의 리드가 컬렉터왼쪽의 리드가 베이스
Ohmmeter’s View of Transistor’s Terminal
같은 npn 인데 리드가 다름
Transistor ManTransistor Man
“Transistor Man” observes the base current and adjusts the output rheostat in an attempt to maintain the output current hFE times larger
Basic Transistor ModelIn npn Transistor, for example1. Collector must be more positive than Emitter2. Base-Emitter and Base-Collector behave like diode3. Maximum Parameter
VCE : Voltage between Collector and Emitter at open BaseVBE : Voltage between Base and Emitter IC : Collector CurrentIB : Base CurrentPC : Power Dissipation at Collector at 25oC fT : frequency at IC = IB
4. Collector Current is proportional to Base CurrentIC = hFEIBhFE : Current Gain ≈ 100 ~ 300
Note : hFE is not a good parameter range : 100 - 300“Circuit based on a particular hFE value is a bad circuit”
Schematic of BJT Transistor
Small fraction of Emitter Current flows into Base(C-B junction : Reverse Bias , B-E Junction : Forward Bias)
Typical Junction Connection
Equations of Operation
−
= 1exp
T
BEESE V
vIi BCE iii +=
E
C
ii
=α ESs II α=
≅
T
BEsC V
vIi expα
αβ−
==1B
C
ii
BC ii β=
Schokley Equation KCLAt B-E Junction
Let
−
= 1exp
T
BEESC V
vIi α: Scale Current
Collector Current is Amplified Version of Base Current
: Typically 100
Common-Emitter Characteristics
CEBEBC vvv −= CEBEBC vvwithv << 0
B-C junction : Reverse Bias , B-E Junction : Forward Bias
NP
N
Input Output
BBC iii 100== βCEBEBC vvwithv << 0
vBE must be larger than 0.6 ~ 0.7V
Analysis of Common-Emitter Amplifier
( ) ( ) ( )tvtiRtvV BEBBBB +=+ in CECCCC viRV +=
KVL in CircuitsInput Output
DC AC
DC
AC
iB = 0
vBE = 0
Max iB
Min iB
Min vin Max vin
Load-Line Analysis of Input( ) ( ) ( )tvtiRtvV BEBBBB +=+ in
vin = 0 : Q point AC swing around Q Point
From Analysis, iB can be obtained
( ) BBBB Rtvvti /1),(, in∝DC AC Bias
CECCCC viRV +=
Load-Line Analysis of Output
From Input AnalysisiB can be SelectedMax iB
Min iB
Min vCE Max vCE
Positive vB Negative vCE : Inverting Amplifier
BC ii β=
10V
1.6V
40kΩ
2kΩ( ) )2000sin(4.0in ttv π=
1.6VA
Rvi
B
BBB µ4010
406.1 3 =×== −
Q point : only DC component
VvBB 6.1=
40µA
AiA B µµ 3515 ≤≤
vIN : 1.2 ~ 2.0VvCE : 7 ~ 3 VAv = 7/1.2 = 5
AiA B µµ 3515 ≤≤
( ) )2000sin(2.1in ttv π=
Nonlinear Distortion
Output Signal is not Exactly Sine Curve ( ) )2000sin(4.0in ttv π=
Clipping Occur : Cutoff
PNP Bipolar Junction TransistorsExcept for reversal of current directions and voltage polarities, pnp BJT is almost identical to the npn BJT.
−
= 1exp
T
BEESE V
vIi
BCE iii +=
BC ii β=
Very Typical Transistor Connection Common-Emitter Amplifier
When iC becomes zero, we say that the transistor is cutoff. When vCE≈ 0.2 V, we say that the transistor is in saturation.
≅
Operating Region of Transistors
Large-Signal DC Circuit
DC Bias
Active RegionSaturationCut-off
C
CC
Rv
CCvB
BB
Rv
BBv
Large-Signal DC Circuit Model
Active-Region Saturation-Region Cutoff-Region
TR : Dependant Current Source with Base Voltage ≈ 0.7V
TR : Constant Voltage Sourceof -0.2V Collector Voltage
TR : Open Circuit
Input Output
Cut-off Saturation Active
B
BB
Rv
BBv
C
CC
Rv
CCv
IB
Ωk200Ωk1
V15Analysis of Fixed Base Bias Circuit
Ω= k200BR Ω= k1CR V15=CCV
100=β
AR
viB
CCB µ5.717.0
=−
= mAR
viC
CCC 8.142.0
=−
=
mAAii BC 15.75.71100 =×== µβ
VIRVV CCCCCE 85.7=−=
: iB > 0 & iC > βiB Active Region
003=β
AR
viB
CCB µ5.717.0
=−
= mAR
viC
CCC 8.142.0
=−
=
mAAii BC 45.215.71300 =×== µβIB
Ωk200Ωk1
V15
iB > 0 & iC < βiB Saturation Region
VVCE 2.0=
EEBB RIv += 7.0
( ) EB
BEBB RR
VVI1++
−=
β
15V
5V
2kΩ
2kΩ
mAR
VIE
BE 15.27.0
=−
=
BCE iii += BC ii β=
EECECCCC RIvRIv ++=
6.422.147.143006.442.1321.3100
VCE(V)IC(mA)IB(µA)β
Analysis of Four-Resistor Bias Circuit
2121 11
1 RRRR
RB =+
=
21
2
RRRVV CCB +
=
Thévenin Equivalent :
Two Resistor connected to Base Set vB,RB,iB
EECCCCCE IRIRVV −−=
BC IβI =( ) EB
BEBB RR
VVI1++
−=
β
EEBEBBB IRVIRV ++=
BE II )1( += β
KVL around B-E Loop
KCL around C-B-E Node
KVL around C-E Loop
vBE≈ 0.7V
vBE≈ 0.7VvCC≈ 15V
Ω=+
= kRR
RB 33.311
1
21
VRR
RVV CCB 521
2 =+
=
( ) ARR
VVIEB
BEBB µ
β2.41
1=
++−
= mAII BC 12.4== β
VIRIRVV EECCCCCE 72.6=−−=
100=β
Example of Four-Resistor Bias Circuit
IB
IC
iB swings around Q point
vBE swings around Q point
Typical BJT Circuit (AC Coupled)
Q point is set by Bias Circuit with vBB, RB
To Describe BJT with Characteristic Model 1. Variation around Q point is smaller than that of Q point itself
Small Signal Circuit Model is Required2. iC is dependant on iB or vBE as Described in above Figure
Dependant Current Source Model can be used
Small Signal Model for BJT
Hybrid-π Model
Base : Resistor rπCollector : Voltage Controlled
Current Source
Base : Resistor rπCollector : Current Controlled
Current Source
No Passive Element along Emitter
T Model
Base : Resistor reCollector : Voltage Controlled
Current Source
Base : Resistor reCollector : Current Controlled
Current Source
No Element along Base
ib(t) : Signal current flowing into BaseIBQ : DC current that flows with Zero Signal iB(t) : Total Base current.
( ) ( )tiiti bBQB +=
( ) ( )tvVtv beBEQBE +=
Small-Signal Equivalent Circuit
IBQ
vb(t) : Signal current flowing into BasevBEQ : DC current that flows with Zero SignvBE(t) : Total Base current.
vBEQ
( )
+−=+
T
beBEQESBBQ V
tvvItiI
)(exp)1( α
−
−= 1exp)1(
T
BEESB V
vIi α
−=
T
BEQESBQ V
vII exp)1( α
( )
+≅
=+
T
beBQ
T
beBQBBQ V
tvIV
tvItiI )(1)(exp
BQ
T
IVr =π
( )πr
tvti beB
)(=
( ) ( )titi bC β=CQ
T
IVr β
π =
Define
From Previous Definition of Q point
( ) ( )tiIti bBQB +=
Small-Signal Equivalent Circuit for the BJT
CQ
T
IVr β
π = ( ) ( )titi bC β=
1. Common Emitter
2. Emitter Follower(Common Collector)
Typical BJT Amplification Mode
Output Terminal Choice
B C
E
3. Common Base
Common-Emitter Amplifier
C1, C2 : Coupling Capacitorwithout Affecting DC bias from Input & Output (High Pass Filter)AC signal only Pass
CE : Bypass CapacitorLow Impedance path for AC IEto Ground (Same as C1,C2)
for Midband Frequency
Small Signal Equivalent Circuit
C1 : Coupling Capacitorwithout Affecting DC bias from Input (High Pass Filter) : AC signal only Pass
R1 , R2 : See Four Resistor BiasParallel to Base - Emitter
2121 11
1RR
RRRB +==
21
2
RRRVV CCB +
=
C2,CE: Coupling Capacitorwithout Affecting DC bias from Input (High Pass Filter) : AC only Pass CE : Short Circuit to Ground
RC , RL : See Four Resistor BiasParallel to Collector - Emitter
LCLC RR
RRRTotal 11
1'
+==
npn Transistor Hybrid π Model
Small-Signal ac Equivalent Circuit
CLCLL RR
RRR11
1+
==′21
21 111
RRRRRB +
==
π
βr
RvvA Lo
v′
−==in π
βr
RvvA Co
vo −==in
birvv π== bein bL iRv β'o −=
Open Circuit : RL = 0
Input Impedance & Gains
πrRivZ
B 111
in
inin +
==
Lv
in
Looi R
ZAZvRv
iiA in
inin //
===vi AAG =
Output Impedance
Co RZ =
Using Thevnin Equivalent Circuit without LoadZeroing Voltage Source
Common-Emitter Amplifier
C1, C2 : Coupling CapacitorCE : Bypass Capacitor
Co RZ =πrR
ZB 11
1in +=
Lvi R
ZAA in=
vi AAG =π
βr
RA Lv
′−=
π
βr
RA Cvo −=CLL RRR =′
21 RRRB =
CQ
T
IVr β
π =
Ω== kRZ Co 1
Ω=+
= 53111
1in
πrRZ
B
1.28in −==L
vi RZAA
2980== vi AAG106−=′
−=π
βr
RA Lv
158−=−=π
βr
RA Cvo
Ω==′ 667CLL RRRΩ== kRRRB 33.321Ω== 631
CQ
T
IVr β
π
ssin
insin v
RZZvv 515.0=+
= mVtvvAv sinvo )sin(6.546.54 ω=−==
mVtvin )sin(0.1 ω=
Output Source
Wave form in Common-Emitter Amp
Emitter Followers
C1, C2 : Coupling Capacitor
2121 11
1RR
RRRB +==
ELELL RR
RRR11
1+
==′
( )( ) L
Lv Rr
RA′++
′+=
ββ
π 11
itBitB
i ZRZR
Z =+
=11
1 ( ) Lb
it RrivZ ′++== βπ 1in
Lvi R
ZAA i= vi AAG =
Even though the voltage gain of the emitter follower is less than unity, the current gain and power gain can be large.
Output Impedance
21 1111
RRRR
ss ++=′
( ) ( ) Esx
xo RrRi
vZ11
1++′+
==πβ
Parallel Connection
Darlington Configuration