Trojan Women Τρῳάδες (Trōiades). Peloponnesian War 434-404 BC.
Basic –cutoff frequenciesue.pwr.wroc.pl/wyklad_I/05_BJT_amplifier_CE_CC_CB_cutoff... · 2012. 2....
Transcript of Basic –cutoff frequenciesue.pwr.wroc.pl/wyklad_I/05_BJT_amplifier_CE_CC_CB_cutoff... · 2012. 2....
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BJT ampplifier-cutoff frequencies
Basic –cutoff frequencies
High frequency limits
Low frequency limits
Basic – low/high cutoff frequencies
2
RCf
π21
1 =
f1=100kkHz
AV [dB]
AV=1
=0dB +20dB/decade
RC high pass filterlow cuoff frequency
Low input cutoff frequencies
( ) 11 2
1CrR
finG
in +=
π
Input BJThigh frequencies
RCf
π21
1 =
inG
inbe rR
rUU
+=
3
Low input cutoff frequencies
( ) 1211 ||||2
1CrRRR
fbeBBG
in +=
π
Low input cutoff frequencies
( ) ( ) 221 2
1||2
1CRrCRrR
fLoutCELceC
out +=
+=
ππ
C2
CE
RL
EG ~
RG
RE
+ EC
RB1WY
C1
RB2
WE
RC
mE
GBBbeEinE g
RRRRr
Rr1
||||||
|| 21 ≈
+=β
CE amp BJTlow frequencies
inEEE
rCf
=121
π
EGBBbe
E
E
CRRRr
R
f
+=
βπ ||||
||2
1
211
4
Low frequencies of CE - sum up
EGBBbe
E
E
CRRRr
R
f
+=
βπ ||||
||2
1
211
( ) 1211 ||||2
1CrRRR
fbeBBG
in +=
π ( ) 21 ||2
1CRrR
fLceC
out +=
π
C2
CE
RL
EG ~
RG
RE
+ EC
RB1WY
C1
RB2
WE
RC
( ) ( ) ( )21
21
211 Eoutin ffff ++≈
RLRE
+ EC
C2
RB1
RB2
EG ~
RG
C1WE
WY
( )( ) 121
1
||||||2
1
CRRrRRR
f
inTr
LEbeBBG
in
++
=
44 344 21βπ 2
211 ||||
||||2
1
CRRRRr
rR
f
LGBBbe
ceE
out
++=
βπ
( ) ( )21
211 outin fff +≈
Low frequencies of CC - sum up
( )( ) BGEbeBBB CRRrRR
f||||||2
1
211 βπ +
=
( ) 21 ||2
1CRrR
fLceC
out +=
π
( ) ( ) ( )21
21
211 Boutin ffff ++≈
121
1 ||||2
1
CRRr
RR
fBBbe
EG
in
++=
βπ
Low frequencies of CB - sum up
5
Low frequencies - sum up
f CE CC CB
f1in
X X
f1out
X
f1E(B) NA
f1
EGBBbe
E CRRRr
R
+β
π ||||||2
1
21
( ) 121 ||||21
CrRRR beBBG+π
( ) 2||21
CRrR LceC +π
( )( )( ) 121 ||||||21
CRRrRRR LEbeBBG βπ ++
221 ||||
||2
1
CRRRRr
R LGBBbe
E
++β
π ( ) 2||21
CRrR LceC +π
1||2
1
Cr
RR beEG
+
βπ
( ) ( ) ( )2)(1
21
211 BEoutin ffff ++≈
( )( ) BGEbeBB CRRrRR ||||||21
21 βπ +
Low frequencies - sum up
f CE CC CB
f1in
X X X
f1out
f1E(B) -------( ) EoutCCE CrR ||2
1π
( ) 121
CrR inCEG +π
( ) 221
CRr LoutCE +π
( ) 121
CrR inCCG +π
( ) 221
CRr LoutCC +π ( ) 221
CRr LoutCB +π
( ) 121
CrR inCBG +π
( ) ( ) ( )2)(1
21
211 BEoutin ffff ++≈
( ) BRRinCC CrGL )(2
1
→π
High frequency limits
Low frequency limits
Basic – low/high cutoff frequencies
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RCf
π21
2 =f2=10Hz
AV [dB]
AV=1
=0dB -20dB/decade
RC low pass filter
High input cutoff frequencies
inG
inin rR
rU
+=
( ) ininGin CrR
f||21
2 π=
Input BJThigh frequencies
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High input cutoff frequencies
CceL
Lin RrR
RU
||+=
( ) ( ) outLoutoutLCceout CRrCRRr
f||21
||||21
2 ππ==
Output BJThigh frequencies
rin
rout
( ) ininGin CrR
f||21
2 π= ( ) outLout
out CRrf
||21
2 π=
Output & Inputcutoff frequencies
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The Miller effect
( ) in
in
v
in
vininCCin
sC
V
AsC
VsC
AVV
sC
VII
1||1
1
1||
1
=+
=
=+===
( )1|| += vin ACC
The Miller effect(inverting amp !!!!!!)
( )1|| += vin ACC
+=||1||
v
vout A
ACC
The Miller effect – an example
f – [Hz]
frequency
f2=10Hz
AV [dB]
AV=100dB=
=100000V/V
-20dB/decade
9
C2
CE
RL
EG ~
RG
RE
+ EC
RB1WY
C1
RB2
WE
RC
outrinr beinT rr =
Gin
in
V
outLC
Rr
r
V
k
rRR
LOADmVeff Rgk
+
⋅⋅−= γ
4434421
321||||
be
R
BBin rRRr
B
|||| 21 43421= C
RrCceout RRrr
Cce>>≈= ||
CQ
CEQAce
mbe
T
CQm
I
UVr
gr
Ig
+=
=
=
βϕ
ceoutT rr =
DCAC
CQCEQ
A
T
poIU
VV
mV
ββ
ϕ
≈
−−÷≈
≈
intQ,
30050
26
Summary of CE amp BJTmedium frequencies
( )||1 vbcbeinCE ACCC ++=
be
R
BBin rRRr
B
|||| 21 43421=
Summary of CE BJT ampinput characteristic
( )||1 vbcbeinCE ACCC ++=
be
R
BBinCE rRRr
B
|||| 21 43421=
Summary of CE amp BJTupper cutoff frequency
( ) inCEinCEGin CrR
f||2
12 π
=
10
T
CQm
T
mbcbe
Ig
f
gCC
ϕ
π
=
⋅⋅=+
2
be
R
BBin rRRr
B
|||| 21 43421=
( ) ininGin CrR
f||21
2 π=
( ) ||2
||1 vbcT
mvbcbeinCE AC
f
gACCC +
⋅⋅≈++=
π
Sumary of CE amp BJThigh frequencies
….taking rbb’ into account
( )( ) inbebbBGin CrrRR
f||||2
1
'2 +
=π
….very important for v.h.f.
…..when RG is small and commeasurable with rbb’
parasiticbcoutCE CCC +=
CceoutCE Rrr ||=
Summary of CE BJT ampoutput characteristic
( )( )parabcceCLout CCrRR
f+
=||||2
12 π
11
RLRE
+ EC
C2
RB1
RB2
EG ~
RG
C1WE
WY
⋅+⋅⋅⋅
=
LEcem
bebcBG
in
RRrg
ccRR
f
π2
12
bcT
mbe
CQ
CEQEYce
T
CQm
cf
gc
I
UUr
Ig
−⋅⋅
=
+=
=
π
ϕ
2
0m.cz.dla
kataloguz
pkt.pracy,
30050
26
=
−÷≈
≈
bb'
bc
T
CQCEQ
EY
T
r
c
f
IU
VU
mV
β
ϕ
Sumary of CC amp BJThigh frequencies
inout ff 22 >>
( )( )parabcceLCout CCrRR
f+
=||||2
12 π
Sumary of CB amp BJThigh frequencies
bebe
EG
in
Cr
RR
f
=
βπ ||||2
12
High frequencies - sum up
f CE CC CB
f2in
X X
f2out
X
Just
about
~fT/β <fT ~fT
( ) ( ) 21
21
11
−−− +≈ outin fff
Uwaga: tabela nie uwzględnia rbb’ istotną przy dużych częstotliwościach
( )( ) inbeBGin CrRR
f||||2
12 π
=
( )( )( )parabcbcCLout CCrRR
f+
=||||2
12 π
⋅+⋅⋅
=
LEcem
bebcinCCG
in
RRrg
ccrR
f
π2
12
inout ff 22 >>( )( )( )parabcceCL
out CCrRRf
+=
||||21
2 π
bebe
EG
in
Cr
RR
f
=
βπ ||||2
12
( ) ininGin CrR
f||21
2 π=
( ) outLoutout CRr
f||21
2 π=
( )||1 vbcbein ACCC ++=
T
CQm
T
mbcbe
Ig
f
gCC
ϕ
π
=
⋅⋅=+
2
12
High frequencies - sum up
f CE CC CB
Cin
X X
Cout
X
Just
about
~fT/β <fT ~fT
( ) ( ) 21
21
11
−−− +≈ outin fff
Uwaga: tabela nie uwzględnia rbb’ istotną przy dużych częstotliwościach
parabc CC +
LEcem
bebc RRrg
cc
⋅+
inout ff 22 >> parabc CC +
beC
( ) ininGin CrR
f||21
2 π=
( ) outLoutout CRr
f||21
2 π=
( )||1 Vbcbein ACCC ++=
T
CQm
T
mbcbe
Ig
f
gCC
ϕ
π
=
⋅⋅=+
2
paraC
CE-CC-CB comparison
Para-
meter
configuration
CE CC CB
mbeBBB grRRR /1/|| 21 == β
be
ceLC
r
rRR ||||β−β
beceLE
ceLE
rrRR
rRR
+||||
||||
L
beV u
uA =
L
bI i
iA = β
LceC
ceC
RrR
rR
+−
||||
LceC
ceC
RrR
rR
+−
||||
)(eb
bein i
ur =
)(ec
outout i
ur =
βLE
E
RR
R
+
beB rR ||
ceC rR ||
( )( ) BbeLE RrRR |||| +β Ebe Rr
||
β
( )E
beGB RrRR
||||
+β
(e) – for CB
ceC rR ||
be
ceLC
r
rRR ||||β−
CE-CC-CB general comparison
Para-
meter
configuration
CE CC CB
High(10-200)
<1 High(10-200)
High(10-200)
High(10-200)
<1
Medium(0.5k-5k)
High(10k-1M)
Low(10Ω-500Ω)
Medium(0.5k-5k)
Low(10Ω-500Ω)
Medium(0.5k-5k)
L
beV u
uA =
L
bI i
iA =
)(eb
bein i
ur =
)(ec
outout i
ur =
(e) – for CB
13
C2
RL
EG ~
RG
RE
+ EC
RB1WY
C1
RB2
WE
RC
( )Gininin RrC
fπ2
12 =
0m.cz.dla
kataloguz
pkt.pracy,
30050
26
=
−÷≈
≈
bb'
bc
T
CQCEQ
EY
T
r
c
f
IU
VU
mV
β
ϕ
( ) ( )
E
Cu
ubcEbe
bebein
bcT
mbe
T
CQm
R
Rk
kcRr
rcc
cf
gc
Ig
≈
−+++
=
−⋅⋅
=
=
11
2
β
π
ϕ
( )[ ]121 ++= βEbe
R
BBin RrRRr
B
43421
Sumary of BJT with feedbackhigh frequencies
Sumary cutoff frequencies
RC circuits for high and low cutoff frequencies
( ) ininGin CrR
f||21
2 π=( ) 1
1 21
CrRf
inGin +
=π
Sumary –cutoff frequencies
•RC circuits for high and low cutoff frequencies
•Miller effect
( ) ininGin CrR
f||21
2 π=( ) 1
1 21
CrRf
inGin +
=π
( ) 21 2
1CRr
fLoutCE
out +=
π ( ) outLoutout CRr
f||21
2 π=
14
Problems
• Draw schematic diagram of BJT (transistor as model) amplifier showing cut-off frequencies elements
• Describe Miller effect.• Estimate low- and high-cut off
frequencies for given RC diagram.• Compare high-cut off frequencies for
BJT in CE, CC, CB configurations.