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Chapter 8
Feedback andOscillator Circuits
Spring 2016
4th Semester Mechatronics
SZABIST, Karachi
CH 8
Feedbackand
Oscillators
5/8/16 09:21:39 AM
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Fall 2016
ME-2401
Electronic Circuitesi!n
3rd Semester (Mechatronics)SZABIST, Karachi
2
5/8/16 09:21:39 AM CH 8
Feedbackand
Oscillators
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Cha"ter Contents
• Feedback Concept
• Feedback Connection Types
• Feedback Circits
• !sci""ator !peration
• !sci""ator Types
#
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Feedbackand
Oscillators
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4
FeedbackConcept
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Feedbackand
Oscillators
db k
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Feedback $m"li%er&
Feedback Conce"t '
5/8/16 09:21:39 AM
CH 8
Feedbackand
Oscillators
• A connection o o!tp!t "ac# to the inp!t
• $o%iti&e an' negati&e ee'"ac#(or)ar' a*p+ier-% gain
• (ee'"ac#net)or#
• $ro&i'e%re'!ce' portiono the o!tp!t a%ee'"ac# to the
inp!t *i.er
F db k
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Feedback $m"li%er&
Feedback Conce"t 6
5/8/16 09:21:39 AM
CH 8
Feedbackand
Oscillators
The eect% o negati&e ee'"ac# on an a*p+ier:
i%a'&antage
• o)er gain
A'&antage%
• igher inp!t i*pe'ance
• More %ta"+e gain
• I*pro&e' re!enc4 re%pon%e
• o)er o!tp!t i*pe'ance
•
e'!ce' noi%e• More +inear operation
F db k
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(
Feedback
Connection
Types
5/8/16 09:21:39 AM CH 8
Feedbackand
Oscillators
F db k
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Feedback Connection )*"es&
Feedback Conce"t 8
5/8/16 09:21:39 AM CH 8
Feedbackand
Oscillators
1 7o+tage%erie% ee'"ac#
2 7o+tage%h!nt ee'"ac#
3 !rrent%erie% ee'"ac#
!rrent%h!nt ee'"ac#
onnection to 7o!tp!t a%inp!t to ee'"ac#net)or#
$art o the o!tp!t c!rrentI
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Feedback Connection )*"es&
Feedback Conce"t +
5/8/16 09:21:0 AM CH 8
Feedbackand
Oscillators
7o+tage%erie% ee'"ac#
7o+tage%h!nt ee'"ac#
!rrent%erie% ee'"ac#
!rrent%h!nt ee'"ac#
Feedback
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10
Efects oFeedback
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Feedbackand
Oscillators
Feedback
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Feedback Connection )*"es&
Feedback Conce"t 11
5/8/16 09:21:0 AM CH 8
Feedbackand
Oscillators
•
=ain
• Zi
• Z<
• (re!enc4 i%tortion
• >oi%e an' non+inear 'i%tortion
• Ban')i'th
Feedback
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,olta!e Series Feedback&
Eect o. Feedback /ith ain 12
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Feedbackand
Oscillators
•
(or &o+tage%erie% ee'"ac#, the o!tp!t &o+tage i% e' "ac# in%erie% to the inp!t
• The ee'"ac# gain i% gi&en "4:
Feedback
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,olta!e Shunt Feedback&
Eect o. Feedback /ith ain 1#
5/8/16 09:21:0 AM CH 8
Feedbackand
Oscillators
• (or a &o+tage%h!nt ee'"ac# a*p+ier, the o!tp!t &o+tage i% e'"ac# in para++e+ )ith the inp!t
• The ee'"ac# gain i%gi&en "4
Feedback
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Current Series Feedback&
Eect o. Feedback /ith ain 14
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Feedbackand
Oscillators
• (or a c!rrent%erie% ee'"ac# a*p+ier, a portion o the o!tp!tc!rrent i% e' "ac# in %erie% )ith the inp!t
• The ee'"ac# gain i%gi&en "4
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Feedback
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Eect o. Feedback /ith ain 16
5/8/16 09:21:0 AM CH 8
Feedbackand
Oscillators
• The ee'"ac# gain i%
gi&en "4
)able
141
)able142
Feedback
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Eect o. Feedback /ith ain 1(
5/8/16 09:21:0 AM
Eam"le 141&
eter*ine the &o+tage gain, inp!t, an' o!tp!t i*pe'ance )ith
ee'"ac# or &o+tage %erie% ee'"ac# ha&ing A # − 100, $i # 10 #Ω,
$o # 20 #Ω or ee'"ac# o β:
?a@ − 01
?"@− 05
CH 8
Feedbackand
Oscillators
Feedback
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Eects o. Feedback 18
5/8/16 09:21:0 AM CH 8
Feedbackand
Oscillators
Fre3uenc* istortion /ith Feedback&
•
I the ee'"ac# net)or# i% p!re+4 re%i%ti&e, then the gain)ith ee'"ac# )i++ "e +e%% 'epen'ent on re!enc4&ariation%, e&en i the a*p+ier net)or# i% not p!re+4re%i%ti&e
• I the ee'"ac# inc+!'e% re!enc4 'epen'entco*ponent% ?capacitor% an' in'!ctor%@, then the
re!enc4 re%pon%e o the a*p+ier )i++ "e aecte'
Feedback
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1+
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Feedbackand
Oscillators
oise and on linear istortion&
• The ee'"ac# net)or# re'!ce% noi%e "4 cance++ation
• The pha%e o the ee'"ac# %igna+ i% oten oppo%ite the pha%e othe inp!t %igna+
• >on+inear 'i%tortion i% a+%o re'!ce' %i*p+4 "eca!%e the gain i%re'!ce'
• The a*p+ier i% operating in *i'range an' not at the e.tre*e%
Eects o. Feedback
Feedback
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20
5/8/16 09:21:0 AM CH 8
Feedbackand
Oscillators
ain Stabilit*&
• =ain ca+c!+ation% )ith ee'"ac# are oten "a%e' on e.terna+re%i%ti&e e+e*ent% in the circ!it
• B4 re*o&ing gain ca+c!+ation% ro* interna+ &ariation% o β an'g*, the gain "eco*e% *ore %ta"+e
Eam"le 142&I an a*p+ier )ith gain o 1000 an' ee'"ac# o 01 ha% a gain
change o 20 '!e to te*perat!re, ca+c!+ate the change in gain o
the ee'"ac# a*p+ier
Eects o. Feedback
Feedback
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21
Practical
FeedbackCircuits
5/8/16 09:21:0 AM CH 8
andOscillator
s
Feedback
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22
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andOscillator
s
5ractical Feedback Circuits&
Feedback Circuits
Eam"le 14#&
a+c!+ate the gain )itho!t an' )ith ee'"ac# or the (T a*p+iercirc!it o (ig1C, )here : $1D 80 #Ω, $2D 20 # Ω, $o# 10 # Ω, $% D10 #Ω, an' &m
D 000 µS
,olta!e-Series Feedback
2Feedback
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2#
5/8/16 09:21:0 AM CH 8
andOscillator
s
5ractical Feedback Circuits&
Feedback Circuits
Eam"le 144&
a+c!+ate the a*p+ier gain o the circ!it o (ig 18, )here : $1D
18 #Ω an' $2D 200 Ω
,olta!e-Series Feedback /ith o"-am"
' i
' s
'
' o
2Feedback
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24
5/8/16 09:21:0 AM CH 8
andOscillator
s
5ractical Feedback Circuits&
Feedback Circuits
Current-Series Feedback&
2Feedback
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2'
5/8/16 09:21:0 AM CH 8
andOscillator
s
5ractical Feedback Circuits&
Feedback Circuits
Current-Series Feedback&
Eam"le 14'&
a+c!+ate the a*p+ier-% &o+tage gain:
2Feedback
d db k i i
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26
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andOscillator
s
5ractical Feedback Circuits&
Feedback Circuits
,olta!e Shunt Feedback&
2Feedback
d db k Ci i
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2(
5/8/16 09:21:0 AM CH 8
andOscillator
s
5ractical Feedback Circuits&
Feedback Circuits
,olta!e Shunt Feedback&
Eam"le 146&
a+c!+ate the &o+tage gain )ith an')itho!t ee'"ac# )ith g* D 5 *S:
H ) k 2
Feedbackd
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eadin!&
1 S!**ar42 !ation%
5roblems&
3 e+e&ant
Home )ask 28
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andOscillator
s
. 2+Feedback
d
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e.erences
1 Bo+e%ta'
2 $a4nter
3 Ei#ipe'ia
ph4%ic%ani*ation%co*
2+andOscillator
s