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CHAPTER 5

Operational Amplifier

OPERATIONALAMPLIFIER ( OP-AMP )

( Chapter 5 )

Industrial Electronics

DEK 3113

Sumaiya Binti Mashori

October 05, 2010

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 _  _ 

++

1) Op-amp ( Operational Amplifier )high gain DC amplifier to increase signal strength

V+

V -

Non-inverting input

Inverting input

Vs -

Vs+

Vout

The Operational Amplifier The Operational Amplifier 

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i(+), i(-) : Currents into the amplifier on the inverting and non-inverting lines 

respectivelyvid : The input voltage from inverting to non-inverting inputs

+VS , -VS : DC source voltages, usually +15V and ±15V

Ri : The input resistance, ideally infinity

 A : The gain of the amplifier. Ideally very high, in the 1x1010 range.

RO: The output resistance, ideally zero

vO: The output voltage; vO = AOLvid where AOL is the open-loop voltage gain

Ideal OpIdeal Op--Amp Amp+VS

-VS

vid

Inverting

Non-inverting

Output

+

 _ i(-)

i(+)

vO = Advid

RO

 ARi

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Characteristic of Ideal OpCharacteristic of Ideal Op--Amp Amp

1) High input impedance

Zi = Ri = 2) Low output impedance

Zo = Ro = 0

3) Ri = ( assume open cct )

i(-)

i(+)V+

V -

o/c

i(+) = i(-) = 0

4) Ro = 0 ( assume short cct )

V+

V -

s/c

Vout

RO = 0

Vdiff   AOL .Vdiff 

V diff =V + - V - = 0

V +=V - 

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Types Of OpTypes Of Op--Amp Amp

1)Inverting Amplifier2)Non-Inverting Amplifier

 3)Inverting Summing Amplifier4)Non-Inverting Summing Amplifier5)Integrator

6)Differentiator7)Voltage Comparator8)Voltage Follower

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Amplify the input,Vs and invert the value to be negative

value.

+

 _ 

RL

vin

+

 _ 

Rii1

RFiF

Vout

Inverting Amplifier Inverting Amplifier (Vin at(Vin at ± ±veve terminal)terminal)

Derivation: hand written

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Inverting Amplifier Inverting Amplifier (Vin at(Vin at ± ±veve terminal)terminal)

+

 _ 

500

+

 _ 

i1

iF

VoutV+

V-

i-

i+

Example1: Find a) Vo

b) i1

c) Av

0.5V

1k

20k

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Inverting Amplifier Inverting Amplifier (Vin at(Vin at ± ±veve terminal)terminal)

Solution Example1:

Phase shift 180o

Find a) Vo Find b) i1

Find c) Av

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Inverting Amplifier Inverting Amplifier (Vin at(Vin at --veve terminal)terminal)

Exercise1: If we need an amplifier of gain =10, Designthe amplifier using inverting amplifier 

1) Assume

+

 _ 

RL

0.5V+

 _ 

10ki1

iF

Vout

100k

2) Design

V+

V-

i-

i+

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Inverting Amplifier Inverting Amplifier (Vin at(Vin at --veve terminal)terminal)

3) Find Vo 4) Find i1

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NonNon--Inverting Amplifier Inverting Amplifier (Vin at +(Vin at +veve

terminal)terminal)

+

 _ 

RL

vin

+

 _ 

Rii1

iF

Vout

RF

Derivation: hand written

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NonNon--Inverting Amplifier Inverting Amplifier (Vin at +(Vin at +veve

terminal)terminal)

Example1: Vin = 0.5V ; Ri = 1k ; RF = 20k ; RLD = 500

Find a) Vo

b) i1c) Av

Diff polarity

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NonNon--Inverting Amplifier Inverting Amplifier (Vin at +(Vin at +veve

terminal)terminal)

Exercise1: Design using non-inverting amplifier with thegain= 10

1) Assume

+

 _ 

RL+

 _ 

i1

iF

Vout

90k

10k

0.5V

V+

V-

i-

i+

2) Design

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NonNon--Inverting Amplifier Inverting Amplifier (Vin at +(Vin at +veve

terminal)terminal)

3) Find Vo 4) Find i1

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+

 _ 

R3

i1

iF

Vout

Inverting Summing Amplifier Inverting Summing Amplifier 

i2V2

V1

R1

R2

RF

i-

i+

Derivation: hand written

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+

 _ 

i1

iF

Vout

NonNon--Inverting Summing Amplifier Inverting Summing Amplifier 

i2V2

V1

R1

R2

RF

i-

i+

R3i3

Derivation: hand written

2 input to +ve terminal

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+

 _ 

i1

iF

Vout

NonNon--Inverting Summing Amplifier Inverting Summing Amplifier 

i2V2

V1

R1

R2

RF

i-

i+

R4i4

Derivation: try on your own

i3V3

R3 3 input to +ve terminal

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Change square wave to triangle.

+

 _ RiR

iC

Vout

C

Integrator Integrator (phase shifter )(phase shifter )

Vi (t)

Derivation: hand written

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Change triangle to square wave.

+

 _ 

R

iC

iR

Vout

C

Differentiator Differentiator (phase shifter )(phase shifter )

Vi (t)

Derivation: hand written

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Has 2 independent input - output based on relation between

2 input

Function: as Switch

Voltage Comparator Voltage Comparator 

Example: hand written

Vout

 _ 

+

Vin

Vref 

+Vcc

-Vcc

Vout

 _ 

+Vin

Vref 

+Vcc

-Vcc

(1) (2)

Concept:

V-

V+

V-

V+

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For impedance matching.

Negative feedback-for stability

+

 _ 

Vout

Voltage Follower Voltage Follower (unity gain)(unity gain)

Vin

Example: hand written

i-

i+