ch 3 - feedback.ppt
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CHAPTER 3FEEDBACKAMPLIFIERS
EMT 212/4 Analog Electronc II
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!"tlne
1# Intro$"cton to Fee$%ac&
2# Fee$%ac& A'(l)er Po*t+e , -egat+e
3# A$+antage*/D*a$+antage* o. -egat+e
Fee$%ac&4# Ba*c Fee$%ac& Conce(t
# Cla**)caton o. A'(l)er*
0# Sere* S"nt Con)g"raton
# S"nt Sere* Con)g"raton
# Sere* Sere* Con)g"raton
5# S"nt S"nt Con)g"raton
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Intro$"cton to Fee$%ac&
Fee$%ac& * "*e$ n +rt"all6 all a'(l)er *6*te'#
In+ente$ n 152 %6 Harol$ Blac& engneer n7e*tern Electrc Co'(an6
'eto$* to *ta%l8e te gan o. a'(l)er .or"*e n tele(one re(eater*#
In .ee$%ac& *6*te'9 a *gnal tat * (ro(ortonalto te o"t("t * .e$ %ac& to te n("t an$co'%ne$ :t te n("t *gnal to (ro$"ce a$e*re$ *6*te' re*(on*e#
Ho:e+er9 "nntentonal an$ "n$e*re$ *6*te're*(on*e 'a6 %e (ro$"ce$#
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Fee$%ac& A'(l)er
Feedback* a tecn;"e :ere a (ro(ortono. te o"t("t o. a *6*te'
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Po*t+e Fee$%ac&
Po*t+e .ee$%ac& * te (roce** :en teo"t("t * addedto te n("t9 a'(l)e$agan9 an$ t* (roce** contn"e*#
Po*t+e .ee$%ac& * "*e$ n te $e*gn o.o*cllator an$ oter a((lcaton#
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Po*t+e Fee$%ac&
E?a'(le In a PA *6*te'
get .ee$%ac& :en 6o" ("t te'cro(one n .ront o. a *(ea&er an$ te*o"n$ get* "ncontrolla%l6 lo"$
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-egat+e Fee$%ac&
-egat+e .ee$%ac& * :en te o"t("t **"%tracte$.ro' te n("t#
Te "*e o. negat+e .ee$%ac& re$"ce* tegan# Part o. te o"t("t *gnal * ta&en %ac&to te n("t :t a negat+e *gn#
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-egat+e Fee$%ac&
E?a'(le S(ee$ control
I. te car *tart* to *(ee$ "( a%o+e te$e*re$ *et(ont *(ee$9 negat+e.ee$%ac& ca"*e* te trottle to clo*e9tere%6 re$"cng *(ee$ *'larl69 . te
car *lo:*9 negat+e .ee$%ac& act* too(en te trottle
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Fee$%ac& A'(l)er
Conce(t
Ba*c *tr"ct"re o. a *ngle loo( .ee$%ac& a'(l)er
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A$+antage* o. -egat+eFee$%ac&1# an Sen*t+t6 +araton* n gan *
re$"ce$#
2# Ban$:$t E?ten*on larger tan tat o.
%a*c a'(l)e$#3# -o*e Sen*t+t6 'a6 ncrea*e S- rato#
4# Re$"cton o. -onlnear D*torton
# Control o. I'(e$ance Le+el* n("t an$o"t("t '(e$ance* can %e ncrea*e$ or$ecrea*e$#
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D*a$+antage* o. -egat+eFee$%ac&
1# Crc"t an o+erall a'(l)er gan *re$"ce$ co'(are$ to tat o. %a*ca'(l)er#
2# Sta%lt6 (o**%lt6 tat .ee$%ac&crc"t :ll %eco'e "n*ta%le an$o*cllate at g .re;"ence*#
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Ba*c Fee$%ac& Conce(t
Ba*c con)g"raton o. a .ee$%ac& a'(l)er
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Ba*c Fee$%ac& Conce(t
Te o"t("t *gnal *>
:ere A * te a'(l)caton .actor
Fee$%ac& *gnal *
:ere * te .ee$%ac& tran*.er ."ncton At *"''ng no$e>
Clo*e$loo( tran*.er ."ncton or gan *
.
AS=oS
oS=fbS
fbi SS =S
A
A
S
S
i
o
+==
1fA
11 =>>
A
Athen fAA
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Cla**)caton o. A'(l)er*
Cla**.6 a'(l)er* nto 4 %a*c categore*%a*e$ on ter n("t
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Fee$%ac& Con)g"raton
Series:
connectngconnectng
tete
.ee$%ac&.ee$%ac&
*gnal*gnaln *ere* :tn *ere* :t
tete
n("t *gnaln("t *gnal
+oltage#+oltage#Shunt:
connectngte.ee$%ac&*gnaln *"nt
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Sere* S"nt Con)g"raton
vv
vvf
A
AA
+=1
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Sere* S"nt Con)g"raton
.Lo RR
si RR >>
fbi V=VVvv
v
i
ovf
A
A
V
VA
+==1
:ere + * clo*e$loo( +oltage tran*.er
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Sere* S"nt Con)g"raton
!r
In("t c"rrent
Rif:t .ee$%ac&
A**"'e an$ ?a((le$ to o"t("tter'nal#
!r
In("t c"rrent
Rof:t .ee$%ac&
Input Resistance, Rif Output Resistance, Rof
)( VAVVV vvfbi +=+=V
)1( vv
i
AVV
+=
)1( vvi
i
i
i
AR
V
R
VI
+==
)1( vvii
iif AR
I
VR +==
0=+=+ xvfb VVVV xvVV =
o
vvx
o
vxi
RAV
RVAVI )1( +==
)1( vv
o
x
xof
A
R
I
VR
+==
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Sere* n("t connecton ncrea*e n("t re**tance a+o$ loa$ng e@ect* on te n("t *gnal *o"rce#
S"nt o"t("t connecton $ecrea*e te o"t("tre**tance a+o$ loa$ng e@ect* on te o"t("t *gnal
:en o"t("t loa$ * connecte$#
E;"+alent crc"t o. *"nt *ere* .ee$%ac& crc"t or+oltage a'(l)er
Sere* S"nt Con)g"raton
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For $eal nonn+ertngo(a'( a'(l)er
Fee$%ac& tran*.er."ncton
Sere* S"nt Con)g"raton
-onn+ertng o(a'( * an e?a'(le o.te *ere**"nt con)g"raton#
+==
1
21R
R
V
VA
i
ovf
+
=
1
21
1
R
R
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Sere* S"nt Con)g"raton
E;"+alent crc"t )1(/
1
11
1
221
1
21
1
21
1
vii
i
i
i
if
voi
v
v
v
v
i
ovf
ofb
fbi
ARRV
V
I
VR
R
R
VAVV
RR
RVV
A
A
RR
R
A
A
V
VA
VRR
RV
VV
+===
+
+=
++=
+=
+
+==
+
==
V
VAVvo
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Sere* S"nt Con)g"raton
E?a'(le>
Calc"late te .ee$%ac& a'(l)er gan o.te crc"t %elo: .or o(a'( gan9
A19 R12 G an$ R21# &G#
Sol"ton> A+. 5#555 or 1
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Sere* S"nt Con)g"raton
Ba*c e'tter.ollo:er an$ *o"rce.ollo:ercrc"t are e?a'(le* o. $*cretecrc"t*ere**"nt .ee$%ac& to(ologe*#
vi* te n("t
*gnalerror *gnal *%a*ee'tter/gate
*o"rce +oltage#.ee$%ac& +oltage o"t("t +oltage.ee$%ac&
tran*.er ."ncton9
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Sere* S"nt Con)g"raton
S'all*gnal +oltage gan>
!(enloo( +oltage gan>
Clo*e$loo( n("t
re**tance>
!"t("t re**tance>
e
E
e
E
Em
Em
i
ovf
r
R
r
R
Rgr
Rgr
V
VA
+=
++
+
==11
1
1
e
EEmv
r
RRg
rA =
+=
1
++=++= EmEmif Rgr
rRrgrR
11)1(
Em
E
m
Eof
Rgr
R
rg
rRR
++
=+
=
11
)1(
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S"nt Sere*Con)g"raton
ii
iif
A
AA
+=1
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S"nt Sere*Con)g"raton Ba*c c"rrent a'(l)er :t n("t re**tance9 R
an$ an o(enloo( c"rrent gan9 A#
C"rrent IE * te $@erence %et:een n("t *gnal
c"rrent an$ .ee$%ac& c"rrent#
Fee$%ac& crc"t *a'(le* te o"t("t c"rrent (ro+$e .ee$%ac& *gnal n *"nt :t *gnalc"rrent#
Increa*e n o"t("t c"rrent ncrea*e .ee$%ac&c"rrent $ecrea*e error c"rrent#
S'aller error c"rrent *'all o"t("t c"rrent *ta%l8e o"t("t *gnal#
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S"nt Sere*Con)g"raton. si RR
IAI io=.ee$%ac& c"rrent *>oiIIfb =
In("t *gnal c"rrent>
fbi II += I
ii
i
i
oif
A
A
I
IA
+
==
1
ten IIi
:ere * clo*e$loo( c"rrent tran*.er .
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S"nt Sere*
Con)g"raton
!r
In("t c"rrent
Rif:t .ee$%ac&
Input Resistance, Rif
)( IAIII iifbi +=+=I
)1( ii
i
AII
+=
)1( ii
iiii
A
RIRIV
+==
)1(ii
i
i
iif
A
R
I
VR
+
==
A**"'e I an$ I?a((le$
to o"t("t ter'nal#
Rof:t .ee$%ac&
Output Resistance, Rof
[ ]oiixx
oxiixx
oixx
xi
xifb
RAIVRIAIV
RIAIV
II
IIII
)1()(
)(
0
+==
==
=+=+
( )iio
x
x
of
ARI
VR
+== 1
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S"nt Sere* Con)g"raton
S"nt n("t connecton $ecrea*e n("t re**tance a+o$ loa$ng e@ect* on te n("t *gnal c"rrent *o"rce#
Sere* o"t("t connecton ncrea*e te o"t("t re**tance a+o$ loa$ng e@ect* on te o"t("t *gnal $"e to loa$
connecte$ to te a'(l)er o"t("t#
E;"+alent crc"t o. *"nt *ere* .ee$%ac& crc"t or+oltage a'(l)er
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S"nt Sere* Con)g"raton
!(a'( c"rrent a'(l)er *"nt*ere*con)g"raton#
I .ro' e;"+alent *o"rce o. Ian$ R*#I* neglg%le an$
R*R
a**"'e 1+rt"all6
gro"n$
C"rrent I1>
!"t("t c"rrent>
I$eal c"rrent gan>
fbii II == 'I
FiFfbo RIRI ==V
1/RVo=1I
+=+=
1
1 1R
RIII FifboI
+== 11
R
R
IA F
ii
oI
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S"nt Sere* Con)g"raton
A * o(enloo(c"rrent gan
an$ A**"'e 1* +rt"all6
gro"n$>
I1c"rrent>
!"t("t c"rrent
fbifbi IIII = 'I
)( fbii IIA == IAI io
FfbRI=oV
Clo*e$loo( c"rrent gan>
==
11
1R
RI
R
V Ffb
oI
+=+=
1
1R
RIIII FfbfbfboI
+
+==
1
1
1
R
R
A
A
I
I
F
i
i
i
oifA
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S"nt Sere* Con)g"raton
Co''on%a*e crc"t * e?a'(le o.$*crete *"nt*ere* con)g"raton#
A'(l)er gan> Clo*e$loo(c"rrent gan>
RL
Io
Ii
I
RLIo
Ii
I
Ifb
== iAI/oIi
i
i
oif
A
A
I
IA
+
=
+
==
11
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S"nt Sere* Con)g"raton
Co''on%a*e crc"t :t REan$ RC
RC
Io
RE
Ii
V-V+
RC
Io
RE
Ii
i
E
i
m
E
m
i
oif
AR
r
A
rgR
r
rg
I
IA
+
+
=+
+
==
11
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Sere* Sere*Con)g"raton
gg
g
gfA
AA
+=
1
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Sere* Sere*Con)g"ratonTe .ee$%ac& *a'(le* a (orton o. te
o"t("t c"rrent an$ con+ert* t to a +oltage +oltagetoc"rrent a'(l)er#
Te crc"t con**t o. a %a*c a'(l)er tatcon+ert* te error +oltage to an o"t("tc"rrent :t a gan .actor9 Agan$ tat a* an
n("t re**tance9 R#
Te .ee$%ac& crc"t *a'(le* te o"t("tc"rrent an$ (ro$"ce* a .ee$%ac& +oltage9 .%9
:c * n *ere* :t te n("t +oltage9 #
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Sere* Sere*Con)g"ratonA**"'e te o"t("t * a *ort crc"t9 teo"t("t c"rrent>
VAI go=.ee$%ac& +oltage *>
ozIVfb =In("t *gnal +oltage
fbi VV += V
gz
g
i
ogf
A
A
V
IA
+==1
:ere 8 * a re**tance .ee$%ac& tran*.e
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Sere* Sere*Con)g"raton
A**"'e I an$ I?a((le$
to o"t("t ter'nal#
Rof:t .ee$%ac&
Output Resistance, Rof
[ ]ogzxx
oxzgxx
ogxx
xz
xzfb
RAIV
RIAIV
RIAIV
II
IIII
)1(
)(
)(
0
+==
==
=+=+
( )gzox
x
of
ARI
VR +== 1
!r
In("t c"rrent
Rif:t .ee$%ac&
Input Resistance, Rif
)( VAVVV gzfbi +=+=V
)1( gz
i
AVV
+=
)1( gzi
i
i
i
AR
V
R
VI
+==
)1( gzi
i
iif AR
I
VR +==
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Sere* Sere*Con)g"raton Sere* n("t connecton ncrea*e n("t re**tance
Sere* o"t("t connecton ncrea*e te o"t("tre**tance
E;"+alent crc"t o. *ere* *ere* .ee$%ac& crc"t or+oltage a'(l)er
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Sere* Sere*Con)g"raton
Te *ere* o"t("tconnecton *a'(le*te o"t("t c"rrent
.ee$%ac& +oltage * a."ncton o. o"t("tc"rrent#
A**"'e $eal o(a'(
crc"t an$ neglecttran**tor %a*ec"rrent>
Ei
ogf
Eofbi
RV
IA
RIV
1==
==V
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Sere* Sere*Con)g"raton
A**"'e IEICan$R
( )
( ) Egmgm
i
ogf
Eoigmo
Eoifbi
gmbm
E
fb
o
RArg
Arg
V
IA
RIVArgI
RIVVVV
VArgIrgR
VI
+==
=
==
===
1
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Sere* Sere*Con)g"raton
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Sere* Sere*Con)g"raton
Em
LC
Cm
i
ogf
Emfbi
Emfb
LC
Cmo
Rg
r
RR
Rg
V
IA
Rgr
VVVV
RVg
r
VV
RR
RVgI
++
+
==
++=+=
+=
+=
11
11
)(
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S"nt S"nt Con)g"raton
zz
zzf
A
AA
+=
1
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S"nt S"nt Con)g"raton
Te .ee$%ac& *a'(le* a (orton o. teo"t("t +oltage an$ con+ert* t to a c"rrent c"rrentto+oltage a'(l)er#
Te crc"t con**t o. a %a*c a'(l)er tatcon+ert* te error c"rrent to an o"t("t+oltage :t a gan .actor9 A8an$ tat a*
an n("t re**tance9 R#
Te .ee$%ac& crc"t *a'(le* te o"t("t+oltage an$ (ro$"ce* a .ee$%ac& c"rrent9 I.%9
:c * n *"nt :t te n("t c"rrent9 I#
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S"nt S"nt Con)g"raton
A**"'e te o"t("t * a o(en crc"t9 teo"t("t +oltage>
IAV zo=.ee$%ac& +oltage *>
ogVIfb =In("t *gnal +oltage
fbi II += I
zg
z
i
ozf
A
A
I
VA
+==1
:ere g * a con$"ctance .ee$%ac& tran*.e
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S"nt S"nt Con)g"raton
!r
In("t c"rrent
Rif:t .ee$%ac&
Input Resistance, Rif
)( IAIII zgfbi +=+=I
)1( zg
i
AII
+=
)1( zg
iiii
A
RIRIV
+
==
)1( zg
i
i
iif
A
R
I
VR
+==
A**"'e an$ ?a((le$ to o"t("t
ter'nal#
!r
In("t c"rrent
Rof:t .ee$%ac&
Output Resistance, Rof
0=+=+ xgfb VVVV xgVV =
o
zgx
o
zxi
RAV
RVAVI )1( +==
)1( zg
o
x
xof
A
R
I
VR
+
==
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S"nt S"nt Con)g"raton
E;"+alent crc"t o. *"nt *"nt .ee$%ac&crc"t or
+oltage a'(l)er
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S"nt S"nt Con)g"raton
Ba*c n+ertng o(a'( crc"t * an e?a'(le o.*"nt*"nt con)g"raton#
In("t c"rrent *(lt* %et:een .ee$%ac& c"rrent an$error c"rrent#
S"nt o"t("t connecton *a'(le* te o"t("t+oltage .ee$%ac& c"rrent * ."ncton o. o"t("t+oltage#
2
2
RI
VA
IIwhere
RIV
i
ozf
ifb
fbo
==
=
=
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S"nt S"nt Con)g"raton
A8 * o(enloo(tran*re**tancegan .actor
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S"nt S"nt Con)g"raton
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S"nt S"nt Con)g"raton
+
+
+
==
=
+
+
+
+
+=
=++
F
m
FFFC
F
m
i
ozf
F
oi
F
m
FFC
o
F
oi
F
om
C
o
Rg
RRrRR
Rg
I
VA
R
VI
Rg
RrRRV
R
VV
r
VI
R
VVVg
R
V
111111
1
011111
0
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( )
( )
+=
+
+
+
++
==
=
=
F
z
z
i
ozf
F
Cz
FFF
C
F
Cz
i
ozf
Cm
C
mz
R
A
A
I
VA
R
RrARR
r
R
R
R
RrA
I
VA
Rrg
rR
gA
11
111
11
S"nt S"nt Con)g"raton
!(enloo( tran*re**tance gan .actor A8*
.o"n$ %6 *ettng RF
M"lt(l6 %6
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Fee$%ac& A'(l)er
Input and output Impedances Summary
1# For a *ere* connecton at n("t oro"t("t9 te re**tance * ncrea*e$
%6
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