analysis of bjt circuits
Post on 04-Apr-2018
240 Views
Preview:
TRANSCRIPT
-
7/29/2019 Analysis of BJT circuits
1/14
EE2603-01 1
Analysis of BJT circuits (8.1 8.8)
o BJT amplifier parameter r e
o CE amplifierso CE with R E amplifiers
o EF amplifiers
o CB amplifiers
-
7/29/2019 Analysis of BJT circuits
2/14
EE2603-01 2
BJT amplifier parameter r e
RE
R2
RC
VCC
0.7
I C
+
-
+-
R1
VB+
-I C RE
b
BJT amplifier
CeC
EB
CECBC
BB
21B21
1CCBB
ImV26rfindto)2(fromIFind
)2(7.0RR
IRI7.0RI
V
)1(R//RR,RR
RVV
=
++=++=
=+
=
-
7/29/2019 Analysis of BJT circuits
3/14
EE2603-01 3
Example: Find I C and r e
0.2K
15k
VCC=12V
I C8.2k
b=100
47k
=====
++=++==
===
+=
+
=
7.3mA03.7
mV26ImV26rmA03.7
k313.0V2.2)mA(I
7.0k2.0100k37.11
)mA(I7.0RR
I9.2V
k37.1115//47R,V9.24715
1512RR
RVV
CeC
CEB
CBB
B21
1CCBB
-
7/29/2019 Analysis of BJT circuits
4/14
EE2603-01 4
Types of BJT amplifiersVCC
RC
RL
R i CCCB
v i R2
R1
RE
vo
VCC
RL
R i
CC
CB
v i R2
R1
RE
vo
(a) common emitter (CE)
VCC
RC
RL
CE
R i CCCB
v i R2
R1
RE
vo
(c) emitter follower (EF)
VCC
RC
RLR i
CC
CEv i
R2
R1
RE
vo
CB
(d) common base (CB)
(b) common emitter (CE) with R E
(a) Common Emitter (CE)High AV and low Ri
(Voltage amplifications)
(b) Common Emitter (CE) with R ELow AV and high R i
(Stability applications)
(c) Emitter Follower (EF)Very low Ro and high R i
( Buffer applications)
(d) Common Base (CB)Very low Ri and high A V
(High Frequency applications)
-
7/29/2019 Analysis of BJT circuits
5/14
EE2603-01 5
1. CE amplifiers
VCC
RC
RL
CE
R i
CC
CB
v i R2
R1
RE
vo
R in
Rov in
iiniLB
C
E
io
vo
When the input to the amplier is at Base and the output of the amplier is at Collector, Emitter becomes common to both input
and output and the amplier is Common Emitter ( CE) amplier
-
7/29/2019 Analysis of BJT circuits
6/14
EE2603-01 6
CE amplier analysis
RC RL
Ri
vi R2R1RE
vo
Rin Rovin
iiniL
io
vo
RC RL
Ri
vi br eRB
vo
Rin Ro
vin
iin iLio
vo
ibC
B
E
bib
e
L C
e b
L C b
in
o v r
R // R
r i
R // R i
v
v
A =
==
Voltage gain
e B in
in in r // R i
v R ==Input resistance
C o
o o R i v R ==Output resistance
L
in v
L
in in
o
in in
L o
in
L i R
R A
R
R v v
R v
R v
i
i A =
===
Current gain
VCC
RC
RL
CE
R i
CC
CB
v i R2
R1
RE
vo
R in
Rov in
iin iLB
C
E
io
vol First replace VCC with ac ground and all capacitors short , replace BJT with its equivalent circuit, Calculate Av ,Ri, Ro , Ai, from the equivalent circuit l CE amplier has the following ac circuit properties
-
7/29/2019 Analysis of BJT circuits
7/14
EE2603-01 7
Example:
0.2K
15k
VCC=12V
8.2k
b=100
47k VOVin
ROR in
10k
I in I L
=====
++=++
==
===
+=
+
=
7.3mA03.7
mV26ImV26rmA03.7
k313.0V2.2)mA(I
7.0k2.0100
k37.11)mA(I7.0RR
I9.2V
k37.1115//47R,V9.24715
1512RR
RVV
CeC
CEB
CBB
B21
1CCBB
) 8.121k037.0
k10//k2.8r
R//Rri
R//RivvA
e
LC
eb
LCb
in
ov ===
==Voltage gain
k36.07.3100//k37.11r//Ri
vR eB
in
inin ==== Input resistance
k2.8Ri
vR C
o
oo ===Output resistance
38.4k10
k36.08.121
R
RA
R
Rvv
Rv
Rv
i
iA
L
inv
L
inin
o
in
in
L
o
in
Li =
==
===Current gain
.amplifierCEfolowingtheofII
A,vvA,
iv
R,RFindin
Li
in
ov
in
inino
===
-
7/29/2019 Analysis of BJT circuits
8/14
EE2603-01 8
2. CE with R E amplifiers
The amplier is Common Emitter ( CE) amplier but the Emitter capacitor CE is removed .
VCC
RC
RL
R i
CC
CB
v i R2
R1
RE
vo
R in
Ro
v in
iiniLB
C
E
io
vo
-
7/29/2019 Analysis of BJT circuits
9/14
EE2603-01 9
( ) E R e r L R // C R
E R e r b i L R // C R b i
in v o v
v A +
=
+
==
Voltage gain
CE with RE amplier analysis
RC RL
R i
v i R2R1RE
vo
R in Rov in
iiniL
io
vo
RC RL
Ri
vibr e
RB
vo
Rin Ro
vin
iin iLio
vo
ibC
B
Ebib
RE
( ( )E R e r // B R b i
E R b i e r b i // B R in i in v
in R +=+
==
Input resistance
C o
o o R
i
v R ==Output resistance
L
in v
L
in in
o
in in
L o
in
L i R
R A
R
R v v
R v
R v
i
i A =
===Current gain
l First replace VCC with ac ground and all capacitors short , replace BJT with its equivalent circuit, Calculate Av ,Ri, Ro , Ai, from the equivalent circuit l CE with RE amplier has the following ac circuit properties
-
7/29/2019 Analysis of BJT circuits
10/14
EE2603-01 10
3. EF amplifiers
When the input to the amplier is at Base and the output of the amplier is at Emitter, then Collector becomes common to both input and output and the amplier is Common Collector ( CC)amplier or Emitter Follower ( EF) amplier
VCC
RL
R i
CC
CB
v i R2
R1
RE
vo
RoR in
v in
iin
iL
-
7/29/2019 Analysis of BJT circuits
11/14
EE2603-01 11
EF amplier analysis
RL
R i
v i R2R1RE
vo
R in Ro
v in
iin
iL
( ) [ ]+=
+=
==
) R // R ( r // R
i ) R // R ( r i
// R
i v
// R i v
// R R
i B e E
b
i B e b E
b
o E
o
o E o
[ ] 1 ) R // R ( r R // R
) R // R ( r i R // R i
v v
A L E e
L E
L E e b
L E b
in
o v =
+
=
+
==
First replace VCC with ac ground and all capacitors short ,replace BJT with its equivalent circuit, Calculate Av ,Ri, R
o, A
i, from the equivalent circuit
EF amplier has the following ac circuit properties
[ ]( )L R // E R e r // B R b i
L R // E R b i e r b i // B R
in i in v
in R
+=
+
==
L
in v
L
in in
o
in in
L o
in
L i R
R A
R
R v v
R v
R v
i
i A =
===
RE
R i
v ibr eRB
vo
R in Ro
v in
i in
iL
ib CB
E
bib
RL
io
RE
R i br eRB
vo
Ro
ib
E
bib
io +
-
+
-
-
+
Voltage gain
Input resistance
Output resistance
Current gain
-
7/29/2019 Analysis of BJT circuits
12/14
EE2603-01 12
4. CB amplifiers
When the input to the amplier is at Emitter and the output of the
amplier is at Collector, then Base becomes common to both input and output and the amplier is Common Base ( CB) amplier
VCC
RC
RLR i
CC
v iR2
R1
RE
vo
R in Ro
v in
ie
iin
iL
CB amplier without CB
-
7/29/2019 Analysis of BJT circuits
13/14
EE2603-01 13
RCR i
v iR2
R1RE
vo
R in Ro
v in
ie RL
CB
Eiin
iL
CB amplier analysis
RCRB
RE
vo
R in Ro
v in
ie RL
ib bibbr e
B C
E
iL
iin
[ ] +=
+
==
e B
L C
e B b
L C b
in
o
v r R
R // R
r R i
R // R i
v
v A
Voltage gain
+=
+
==
e B
E
b
e B b E
e
in E in
r R
// R
i
r R i // R
i
v // R R
Input resistance
C o R R = Output resistance
L
inv
inin
Lo
in
Li R
RA
R
v
Rv
i
iA ===Current gain
l First replace VCC with ac ground and all capacitors short , replace BJT with its equivalent circuit, Calculate Av ,Ri, Ro , Ai, from the equivalent
circuit l CB amplier has the following ac circuit properties
-
7/29/2019 Analysis of BJT circuits
14/14
EE2603-01 14
VCC
RC
RLR i
CC
v i
R2
R1
RE
vo
CB
R in Ro
v in
ieiin
iL
Ef ect of Base capacitor CB
L
inv
inin
Lo
in
Li R
RA
Rv
Rv
i
iA ===
e
L C
in
o v r
R // R
v
v A ==
C o R R =
e E in r // R R =
Voltage gain
Input resistance
Output resistance
Current gain
CB amplier with CB
If CB is connected in the Base circuit, RB is shorted by zero reactance of the capacitance . By substituting RB = 0 in the previous formula, we will have the followings :
top related