Slide điện tử từ trường lecture 4 bipolar junction transistors
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Lecture 04
Bipolar junction
transistors
(BJTs)
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Topics
• Transistor physic operation
• Transistor operation modes
• Transistor current-voltage
characteristics
Transistor=Transfer resistor
Two categories of transistor
1. BJT
2. FET
- MOSFET
- JFET
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In 1947, John Bardeen and Walter Brattain at AT&T's Bell Labs in
the United States observed that when electrical contacts were applied to
a germanium crystal, the output power was larger than the input. Solid
State Physics Group leader William Shockley saw the potential in this,
and over the next few months worked to greatly expand the knowledge
of semiconductors.
The first silicon transistor was produced by Texas Instruments in 1954 .
The first MOS transistor actually built was by Kahng and Atalla at Bell
Labs in 1960 .
•1971 : 4004 : 2 300 transistors
•1978 : 8086 : 29 000 transistors
•1982 : 80286 275 000 transistors
•1989 : 80486 : 1,16 millions de transistors
•1993 : Pentium : 3,1 millions de transistors
•1995 : Pentium Pro : 5,5 millions de transistors
•1997 : Pentium II : 27 Millions de transistors
•2001 : Pentium 4 : 42 millions de transistors
•2004 : Pentium 4 EE : 169 millions de transistors
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Structure of transistor
射極：代號E，寬度居三者之中，參雜濃度最濃。
基極：代號B，寬度最薄，參雜濃度最低。
集極：代號C，寬度最大，參雜濃度適中。
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BJT operation mode
mode
EB junction CB junction
active
forward
reverse
Reverse active
reverse
forward
saturation
forward
forward
cutoff
reverse
reverse
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comparison
• NPN (electrons ) fast than PNP (holes)
• NPN easy to product
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PNP transistor in open circuit
Junction voltage
Vo
JE
+
VEB
−
− VCE
JC
+
+
VCB
−
n po
pno
n po
Minority-carrier concentrations
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NPN transistor (Active mode)
iEn
iEp
iCn
iCp
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1. JE forward-Biased : electrons injected from emitter into base ( iEn ),
holes injected from base into emitter ( iEp ).
2. In base: some electrons combined with holes ( iB2 ),
most of electrons diffused to collector ( iCn ).
3. JC reverse-Biased : electrons swept across the depletion region ( iCn ),
small saturation current in depletion region ( iCp ),
iE = iEn + iEp
iC = iCn + iCp
iEn >> iEp
iB = iEp + iB 2 − iCp
iCn >> iCp
iE = iC + iB
iB 2 = iEn − iCn
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Minority-carrier concentrations
Forward-biased
Reverse-biased
iC = I S e
VBE
VT
Ref. to lecture 02 page24
n p ( 0) = n p 0 e
VBE
AE qni2 Dn
Is =
WN A
VT
Ref. to lecture 02 page22
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Active mode
iC = I S e
iB =
VBE
β iB
VT
iC
iB
β
⇒ iB =
(1 + β )iB
IS
β
e
VBE
VT
iE = iC + iB
⇒ iE =
1+ β
β
iC =
1
α
iC
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NPN transistor (reverse active mode)
JE reverse and JC forward
(Active mode)
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NPN transistor (Ebers_Moll mode) (for four modes)
+
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−
NPN transistor (saturation mode)
JE Forward and JC Forward
VBC
+
+
VBE
−
iC = I S e
VBE
iC ≠ β iB
VT
−
IS
αR
e
VBC
VT
VCE ( sat ) = 0.2V ( Si )
VBE ( sat ) = 0.8V ( Si )
Electronic Switch
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pnp transistor
Exercise
IE
− VCE
IC
+
+
+
+
VEB
−
VCB
−
VL
−
+ VCC
−
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Characteristic in Active mode (for Amplifier)
iC = I S e
VBE
iC = β iB
iE =
1
α
iC
VT
β >> 1
α ≈1
iC = I S e
VEB
VT
iC = β iB
iE =
1
α
iC
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Example 5.1
Consider JBE :
I2
V2 − V1 = VT ln
I1
Ref. to lecture 02 page24
2mA
+ 5V
β = 100
2mA
VBE − 0.7 = VT ln
1mA
⇒ VBE = 0.717V
RC =
10V
= 5kΩ
2mA
I E = I C + I B = 2mA +
2mA
= 2.02
100
VE = −VBE = −0.717
RE =
− 0.717 − (−15)
= 7.07kΩ
2.02
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Exercise 5.11
given
find
VB = +1V , VE = +1.7V
α , β , and VC
10 − 1.7
= 1.66mA
IE =
5k
1
= 0.01mA
IB =
100k
I C = I E − I B = 1.65mA
I C 1.65
β= =
= 165
I B 0.01
α=
β
β +1
= 0.994
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Example : the transistor is work in saturation mode find the minimum β
14V
10 KΩ
1KΩ
VBE ( sat ) = 0.8V
VCE ( sat ) = 0.2V
I C ( sat ) × 1K + 0.2 + ( I C ( sat ) + I B ( sat ) ) × 1K = 14V
1KΩ
I B ( sat ) × 10 K + 0.8 + ( I C ( sat ) + I B ( sat ) ) × 1K = 14V
I C ( sat ) = 6.6mA
I B ( sat ) = 0.6mA
β min =
6 .6
= 11
0 .6
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Example (TTL circuit)
VA and AB =+ 5V
+ 5V
4k
1.6k
130
Q4
VA
VB
Q1
Q2
D1
Q3
1k
Q1 : reverse active
Q2 and Q3 : saturation
Q4 and D1 : cut-off
VA or AB = +0.1~0.2V
Q1 : saturation
Q2 and Q3 : cut off
Q4 : saturation
D1 : on
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Fan out
+ 5V
4k
1.6k
130
4k
Q4
VA
VB
Q1
Q2
+ 5V
Q1
Q2
D1
Q3
1k
Gate A
130
Q4
D1
Q3
1.6k
1k
Gate A = low
Gate B
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+ 5V
4k
1 .6 k
130
Q4
VA
VB
Q1
Q2
D1
high
Q3
1k
+ 5V
4k
1.6k
130
Q4
VA
VB
Q1
Q2
D1
Q3
1k
low
In danger
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Open collector
+ 5V
4k
1.6k
External Rc
VA
VB
Q1
Q2
Q3
1k
+ 5V
4k
VA
VB
Q1
1.6k
Q2
Q3
1k
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Current-voltage characteristics
• iC -- VBE
• iC -- VCB
• iC -- VCE
BJT configurations
• Common-Base (CB)
• Common-Emitter (CE)
• Common-Collector (CC)
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