bjt operation modeling - itesobjt operation and modeling dr. josé ernesto rayas sánchez february...
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BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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BJT Operation and Modeling
Dr. José Ernesto Rayas Sánchez
Some figures of this presentation were taken from the instructional resources of the following textbooks:
A. S. Sedra and K. C. Smith, Microelectronic Circuits. New York, NY: Oxford University Press, 2003.
A. R. Hambley, Electronics: A Top-Down Approach to Computer-Aided Circuit Design. Englewood Cliffs, NJ: Prentice Hall, 2000.
R. C. Jaeger, Microelectronic Circuits Design. New York, NY: McGraw Hill, 1997.
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Outline
Simplified physical structure and symbols
Regions of operation
Operation in the active region
Models for the active region
I-V characteristics: iC – vBE , iC – vCE , iC – vCB
Early effect
Models for the cutoff region
Models for the saturation region
Variation of β with IC and temperature
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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Simplified Structure of a BJT and Symbol
NPN Transistor
PNP Transistor
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Regions of Operation of the BJT
Collector-Base Junction (CB)
Forward-biased Reversed-biased
Forw
ard-
bias
ed
Saturation Region (switch on)
Active Region (good amplifier)
Bas
e-Em
itter
Junc
tion
(BE)
Rev
erse
d-bi
ased
Inverted Active Region (poor amplifier)
Cutoff Region (switch off)
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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Operation in the Active Region
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Operation in the Active Region (cont)
EC ii α=
Junction BE behaves as a forward biased diode
Junction CB behaves as a current controlled current source
T
BEV
V
SBB eIi η≈
Typically, 0.970 ≤ α ≤ 0.997
Since BCE iii += then BBC iii βα
α =−
=1
Typically, 32.3 ≤ β ≤ 332.3)1( += βBE ii
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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Models for the Active Region (NPN)
TBE VvSE eIi /
α=
TBE VvSB eIi /
β=
TBE VvSC eIi /=
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Models for the Active Region (NPN)
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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Models for the Active Region (PNP)
TEB VvSE eIi /
α=
TEB VvSB eIi /
β=
TEB VvSC eIi /=
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Models for the Active Region (NPN)
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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I-V Characteristics (iC – vBE)
iB
B C
E
TBE VvS eI /
β
iB iC
iE Considering temperature effects:
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I-V Characteristics (iC – vCE Ideal)
iB
B C
E
TBE VvS eI /
β
iB iC
iE
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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I-V Characteristics (iC – vCE Real)
iB
B C
E
TBE VvS eI /
β
iB iC
iE
iC increases with vCE due to the Early effect
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Early Effect and Early Voltage (VA)
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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NPN BJT Models in the Active Region - Summary
Considering the Early effect:
Neglecting the Early effect:
B C
E
iB iC
iE
⎟⎟⎠
⎞⎜⎜⎝
⎛+
A
CEB V
vi 1βT
BE
Vv
S eI η
β
B C
E
iB iC
iE
0.7V ⎟⎟⎠
⎞⎜⎜⎝
⎛+
A
CEB V
vi 1β
B C
E
T
BE
Vv
S eI η
β
iB iC
iE
BiβBiβ
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PNP BJT Models in the Active Region - Summary
Considering the Early effect:
Neglecting the Early effect:
BiβT
EB
Vv
S eI η
βBiβ
⎟⎟⎠
⎞⎜⎜⎝
⎛+
A
ECB V
vi 1β
B
C
E
T
EB
Vv
S eI η
β
iB
iC
iE
⎟⎟⎠
⎞⎜⎜⎝
⎛+
A
ECB V
vi 1β
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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BJT Models for the Cutoff Region
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BJT Models for the Saturation Region
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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iC-vCE Characteristics
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iC-vCE Characteristics Including Breakdown
Zooming the saturation region
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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Active Region vs Inverted Active Region)
-5V 0V 5V 10V
V
3.0mA
2.0mA
1.0mA
0.0mA
-1.0mA
Collector
Current
RegionSaturation
Cutoff
RegionSaturation
RegionForward-Active
RegionReverse-Active β = 25 β = 5
I = 0 uA
I = 100 uA
I = 80 uA
I = 60 uA
I = 40 uA
I = 20 uA
CE
B
B
B
B
B
B
F R
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iC-vCB Characteristics
BJT Operation and ModelingDr. José Ernesto Rayas Sánchez
February 8, 2007
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Typical Variation of β with IC and Temperature
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Variation of β with IC – An Example