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Chapter 8

Feedback andOscillator Circuits

Spring 2016

4th Semester Mechatronics

SZABIST, Karachi

CH 8

Feedbackand

Oscillators

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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 '

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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

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Feedbackand

Oscillators

F db k


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Feedback Connection )*"es&

Feedback Conce"t 8

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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 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 Conce"t 11

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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#

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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&


5/8/16 09:21:0 AM CH 8

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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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+

5/8/16 09:21:0 AM CH 8

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

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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

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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


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


Feedback Circuits

Current-Series Feedback&

2Feedback


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2'

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andOscillator

s


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


Feedback Circuits


2Feedback

d db k Ci i


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2(

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andOscillator

s


Feedback Circuits


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

5/8/16 09:21:0 AM CH 8

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

abdulsaeed 2026 12664 3-ecd11 feedback-oscillator-w14

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