ECE442–JoseSchutt‐Aine 1
ECE442
Solid‐StateDevices&Circuits
Review‐ 2
Jose E. Schutt-Aine
Electrical & Computer Engineering
University of Illinois
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Solid-State Devices and Circuits - Electronic Circuits | ECE 342, Study notes of Microelectronic Circuits
Exam 2 Review Slides Material Type: Notes; Professor: Schutt-Aine; Class: Electronic Circuits; Subject: Electrical and Computer Engr; University: University of Illinois - Urbana-Champaign;
Typology: Study notes
2011/2012
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ECE^442 – Jose
Schutt‐Aine
ECE
Solid
‐State
Devices
&^ Circuits
Review
‐^2
Jose E. Schutt-Aine Electrical & Computer Engineering
University of [email protected]
ECE^442 – Jose
Schutt‐Aine
-^ Methods^ –^
First nethod is to find
R& R^1
from^ E 2
and^ Rth
and^ Ith BQ
-^ Second method is to select
Rto be 10 times to 20 times^2
RtoE^
provide good stability & then select
Rto give proper^1
I^ BQ
Bipolar Biasing Approach
Remark: To keep collector voltage at the middle of theforward active region, use:
min^ max
1 2
2 C^ C
CC
E
CQ
E^ C
V^ V
V
R
V^
⎛^ R^ R
⎞
+=
=^
+⎜
⎟+ ⎝^
⎠
ECE^442 – Jose
Schutt‐Aine
Small-Signal Model
-^ What is a small-signal incremental model?^ –^
Equivalent circuit that only accounts for signal level fluctuations aboutthe DC bias operating points– Fluctuations are assumed to be small enough so as not to drive thedevices out of the proper range of operation– Assumed to be linear– Derives from superposition principle
ECE^442 – Jose
Schutt‐Aine
Hybrid-
π^ Incremental Model for BJTs
r:^ input resistance looking into the base^ π r^ : parasitic series resistance looking into base – ohmic base resistance x g^ : BJT transconductance m r^ =r^ : output collector resistance related to the Early effect oce
ECE^442 – Jose
Schutt‐Aine
Common Emitter (CE) Amplifier
Bias: Choose
R^ & R^1
to set 2
V^ Î VB
is then set. Choose E
R^ to set E^
I~I****. EC
Quiescent point of
V will be determined by out^
R^. Emitter is an AC short. C
ECE^442 – Jose
Schutt‐Aine
Incremental Model for CE Amplifier
1 2 R^ RB
Hybrid-^ R= &
π^ model (ignoring
r^ ) x v^ i in B i R^
R^ r i π =^ =
&
B^
in
Sometimes R
r and R
r π
π
^
rπ^ E
ro
g^ vm^ π
vout R^ C
v^ in
C
R^ B R^ sig
- vπ^ -
R^ L
B i^ i^ + vi -
i^ o
ECE^442 – Jose
Schutt‐Aine Output Impedance^ out
C
o R^
R^ r =^
& , o^
C^ out
C
If r^
R^ R
R
^
^ L
v^ vo
R L o
from which A
A^
⎛^ R^ R
⎞ =^ ⎜
⎟+ ⎝^
⎠
It can be seen that if
R^ >> rsig^
, the gain will be highly dependent on π
β.^ This is not
good because of
β^ variations
(^
)
sig^
v^
m^ C L^
o
If R^
r^ G
g
R^
R^ r
π^
^
^
&^ &
CE Amplifier
ECE^442 – Jose
Schutt‐Aine
CE with External Resistors
ECE^442 – Jose
Schutt‐Aine (^
)^ (^
1 1 )
1
MB^
m^ L^
C E^
B
A^
g^ R^
R^ R
R r^
r π
π β
= −^
+^ +^
& R^ and E^
R^ degrade the gain B^
CE with External Resistors
(^
)^
(^
) (^ 1 )
m^
L^ C
m^
L^ C
out in^
m^ E
E^
B^
E^
B
g r^
R^ R
g r^
R^ R
v v^
g r R
R
r^
R^
R^
r^ R
π
π
π
π
π β
= −^
+^ +
+^
+^ +
&^
(^
) (^
L^ C 1 )
MB
E^
B
R^ R
A^
R^
r^ R^ π
β β
= −^
+^ +
&^ +
ECE^442 – Jose
Schutt‐Aine (^
) (^
)
(^
) (^
)^ (^
) 1
1
1
1 L^ C
L^ C MB
B
E^
B^
E
R^ R
R^ R A^
r^
R
R^
r^ R
R
π
π
β
β
β
β
β
β ⎛^
⎞ ⎜^
⎟+ ⎝^
⎠
= −^
= − +^ +^
+^
+^
& ++ +
& The gain can be written as: (^
)
and since
β^ =α^1
β +
(^
) L^
C
MB
R^ R E^ e
A^
R^
r
CE with External Resistors
(^
)
neglecting
R^ B^1 β +
ECE^442 – Jose
Schutt‐Aine
C MB
R E e
A^
with
R^
α^ r
α
= −^
+^
T 0.
Vr = e IE
=^
=^
0.^
0.^
C^
outQ
I^
mA^
V^
V^
V
⇒^
=^
−^
×^ =
AC analysis:
R^ is shorted and E^
R^ =R^ EE
=100Ω. Since
β^ is not
known, use:
A^ = −^ MB
Example (Cont’) +
A^ =^ −MB
ECE^442 – Jose
Schutt‐Aine
1
o^
m^
E^
m^
E
v v^
g v^
R^
v^ g
R
r^
r
π π
π π
π
⎛^
⎞^
⎛^
⎞
=^
+^
=^
⎜^
⎟^
⎜^
⎟
⎝^
⎠^
⎝^
⎠
Emitter Follower
1
in^
B b^
o^
E^
m^
B v
v^
v^
R i^
v^
v^
v R^
g^
R r^
π r
π
π^
π
π
π
⎛^
⎞
=^
+^
+^
=^
+^
+^
⎜^
⎟ ⎝^
⎠ Incremental model
circuit
ECE^442 – Jose
Schutt‐Aine
(^
in^
B^
E
r^
r^
R^
R
π
=^
+^
+^
Emitter Follower – Input Impedance
(^
1
/^
1 / / B^
E^ m
in in
v b
R^ r
R
g^
r
v r^
i^
v^ r π
π
π
π^ π ⎡^
⎤
+^
+^
⎣^
⎦
=^
=
ECE^442 – Jose
Schutt‐Aine
20
Emitter Follower – Output Impedance
o B
v B i^
r^
R π = −^
o^
o^
o^
m^ o^
o
o^
m E
B^ E
B^
B
v^
v^
v^ g r v
v
i^
g vR
r^ R
R r^
R^ r
R π
π^ π
π
π
=^ −
+^
=^ +
+^
+^
[^
]^ (^
)
1
1
1 (^ 1)
m o^ o^
o^
B^ E
E^
B^
B^
E^
B
g i^ v^
v^ r^
R^ R
R^ r^ R
r^
R^
R^ r^
R
π
π
π
π β
⎡^
⎤
=^
+^
+^
=^
+^ +
⎢^
⎥ +^
+^
⎣^
⎦