lect26 OMP AMP

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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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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


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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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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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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=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


= out

+

_


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+nalysis of "n#erting p +mp

+ _

#/

#6

= i

Α(#6 / #/)#o

= f


= 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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+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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+

_

#o

if

+ _

+ _

#i

8d

i/

i6

Buffer +mplifier?8oltage Lollower

+ _

#i

#6

#/

29ui#alent circuit

_ +

Α(#6 / #/)


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+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

lect26 OMP AMP

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