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EE201 Lecture 26 P. 1
Op Amp Basics
The operation amplifier is a high gain amplifier.
Traditionally used to perform math “operations”, the
op amp has many uses (e.g feedback). Below is atypical package for an op amp.
pinout designations
1. ffset null !. "n#erting input
$. %onin#erting input &. neg. power supply
'. ffset null . utput
. pos. power supply *. no connection
+ Signetics a&1
operational amplifier
(courtesy -ikipedia)
1
!
$
&
*
'
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EE201 Lecture 26 P. 2
e#ice/le#el diagram of operational amplifier
ur interests0
1. "ntroduce basics of operational amplifiers
!. se circuit elements de#eloped in 232 !41 to
model characteristics of op amp.
http://upload.wikimedia.org/wikipedia/commons/e/e0/OpAmpTransistorLevel_Colored_Labeled.svg
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p +mp 5ymbol and %otation
+
_ #6
#/
#out
%onin#erting
"n#ertingutput
EE201 Lecture 26 P. 3
7ositi#e power
supply
%egati#e power
supply
%ote0 only ' terminal leads are important
and of those, we will primarily use $
(in#erting, nonin#erting, and output)
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EE201 Lecture 26 P. 4
p +mp 3urrent 8ariables
+ _ io
#5/
+
_
+
_
#56
i6 (i p)
i/ (in)
i56
i5/
p +mp 8oltage 8ariables
+
_
#/ (#n)#o
+
_
#5/
+
_
+
_ +
_ #56#6 (# p)
+
_
%ote0 %egati#e and positi#e power supplies do not ha#e to be e9ual
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EE201 Lecture 26 P. 5
Because the op amp is a high gain #oltage
amplifier, we are interested in the #oltage transfer
characteristics of the de#ice, as shown below.
The output #oltage is plotted as a function of the
difference in input potential.
(#6 / #/)
#sat
slope:Α
#out
/#sat
;inear
region
7ositi#e
5aturation
region
%egati#e
5aturation
region
" """""
;arge gain de#ice
+ : 14& / 14
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p +mp /#5/?+
+(#6 / #/) /#5/?+ @ (#6 / #/) @ #56?+
#sat : #56 (#6 / #/) A #56?+#o :
Typical op amp parameters0
+ : 14& C #56?/ : 14 8 (#6 / #/) : D1 m8
+ll attributes of #o aresatisfied by dependent source model
+
_
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EE201 Lecture 26 P. 7
=edrawing figure on p. '
+ _
#/
#6
= in
i/
Α(#6 / #/) #o
i6
= out
Euestion0 how does the op amp know it isoperating in its linear regimeF
%egati#e feedbackG 3onnect the output
#oltage to the in#erting input terminal. This
causes input potential difference to decrease.
+
_
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p +mp with negati#e feedback
+
_
#/
#6
= in
Α(#6 / #/) #o
= f
EE201 Lecture 26 P. 8
= out
+
_
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+nalysis of "n#erting p +mp
+ _
#/
#6
= i
Α(#6 / #/)#o
= f
EE201 Lecture 26 P. 9
= s
= o
+ _
#s
a
b
5trategy0 perform H3; analysis at nodes “a”
and “b”, then sol#e for #o as a function of #s.
+
_
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EE201 Lecture 26 P. 11
+nalysis of nonin#erting p +mp
+ _
#/
#6
= i
Α(#6 / #/)#o
= f
= g = o
+ _
#s
a
b
5trategy0 perform H3; analysis at nodes “a”
and “b”, then sol#e for #o as a function of #s.
= s+
_
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EE201 Lecture 26 P. 13
+
_
#o
if
+ _
+ _
#i
8d
i/
i6
Buffer +mplifier?8oltage Lollower
+ _
#i
#6
#/
29ui#alent circuit
_ +
Α(#6 / #/)
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EE201 Lecture 26 P. 14
+nalyMe e9ui#alent circuit
#o : + (#6 / #/)
#i : #6 #o : #/
=elating #o to #i,
#o : + (#i / #o)
#o : K+ ? (+ 6 1)J #i ≈ #i
#o
is said to NfollowO #i
. This is called a
v!ta"e #!!$er. This circuit %u##ers or
is!ates #o from #i, so that circuits connected
to the output are not ad#ersely affected by
input circuitry. + wire directly connecting
outputs and inputs would not ser#e this