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L07 February 05 1
EE 4345 - SemiconductorElectronics Design ProjectSpring 2002 - Lecture 07
Professor Ronald L. [email protected]
http://www.uta.edu/ronc/
L07 February 05 2
Lab schedule
• As announced last week, plan toattend your lab session (Tu or Th at230 to 500 PM) this week foradditional Cadence instruction.
• Topics to be covered– schematic capture of a circuit– making a symbol– simulating a circuit
L07 February 05 3
Bipolar junctiontransistor (BJT)• The BJT is a
‘silicon sandwich’p+np- or n+pn-
• npn For. ActiveBJT action when
VBE > 0 andVBC < 0
p n p
E B C
VEB VCB
Charge neutralRegion
Depletion Region
General bias ona pnp transistor
L07 February 05 4
npn BJT currents(F A region, ©RLC)
IC =JCAC
IB=-(IE+IC )
JnE JnC
IE =-JEAE
JRB=JnE-JnC
JpE
JGC
JRE JpC
L07 February 05 5
Ebers-Moll(npn injection model)
C
E
B
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expt
BC
R
S
R
ECV
VII
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t
BC
t
BES
ECCCCT
VVV
VI
III
exp
exp
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expt
BE
F
S
F
CCV
VII(common-emitter)
L07 February 05 6
E-M modelequations
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1exp1exp
1exp1exp
1
and ,1
defining ,0
1exp1exp
1exp1exp
t
BC
R
S
t
BE
F
S
t
BCS
R
S
t
BES
F
SB
R
RR
F
FFECB
t
BCCSR
t
BEESE
t
BEESF
t
BCCSC
VVI
VVI
VVII
VVIII
III
VVI
VVII
VVI
VVII
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SCSRESF III ����
L07 February 05 7
Ebers-Moll Model(npn bipolar jctn. tran. w/o inj.)
CSRESFS
CSRESF
III
1*NR
expII , 1*NF
expII
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BC
t
BEV
VV
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E
B
C
�RIR �FIF
� IF RI �
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� IB(Common base)
L07 February 05 8
IC npn BJT(*Fig 9.2a)
L07 February 05 9
npn BJT regionsof operation
VBE
VBC
ForwardActive
ReverseActive Saturation
Cutoff
L07 February 05 10
npn FA BJT minoritycarrier distribution (Fig 9.4*)
L07 February 05 11
npn RA BJT minoritycarrier distribution (Fig 9.11a*)
L07 February 05 12
npn cutoff BJT mincarrier distribution (Fig 9.10a*)
L07 February 05 13
npn sat BJT minoritycarrier distribution (Fig 9.10b*)
L07 February 05 14
Defining currents inFA mode npn BJT (Fig 9.13*)
L07 February 05 15
Non-ideal effectsin BJTsº Base-width modulation (FA: xB
changes with changes in VBC)º Current crowding in 2-dim base�High-level injection (minority carriers
g.t. dopant - especially in the base).�Emitter Bandgap narrowing for NE -->
density of states at cond. band. edge�Junction breakdown at BC junction
L07 February 05 16
npn Base-width modulation(Early Effect) Fig 9.15*
xnqDJ nn
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BC
B
BBC
BB
BC
BBjC
BC
j
Vx
xJ
VJ
xJ
xJ
VxAqNC
VQ
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L07 February 05 17
Base-width modulation(Early Effect, cont.)
Fig 9.16*
ACEB
jC
CE
B
jC
B
BC
B
BCB
VVI
QC
VI
AqNC
xJ
VxA
xJ
VI
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L07 February 05 18
Emitter currentcrowding in baseFig 9.21*
L07 February 05 19
Interdigitated basefixes emitter crowdingFig 9.23*
L07 February 05 20
Effect of HLI innpn base region Figs 9.18 and 9.19*
L07 February 05 21
Ebers-Moll Model(Neglecting G-R curr)
(Fig. 9.30*) N
nqD
,aB
2inB
CSRESFeffBW
II ����
L07 February 05 22
Hybrid-piCircuit model
Fig 9.33 Semiconductor Physicsand Devices, 2nd ed., by Neamen,Irwin, Boston, 1997.
L07 February 05 23
Hybrid-picircuit model• Adapted from inj. model version of E-M
model with parasitic rb, rc, re, and CSubst
• C-E branch is linking current• B-E branch is the reduced B-E diode
with diffusion (for and rev) resistanceand capacitance and junction cap.
• B-C branch is the reduced B-C diodewith diffusion (for and rev) resistanceand capacitance and junction cap.
L07 February 05 24
References
* Semiconductor Physics & Devices, byDonald A. Neamen, Irwin, Chicago,1997.