Operational Amplifier(Phe-10) (1)

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Differential Amplifiers



Two matched transistors form a

differential amplifier

input

0 V

-V EE +0.7 VConstantcurrent= I 1+I 2

I 1 I 2

V C 1=V CC -I 1R 2 V C 2=V CC -I 2R 4



Transisterized

Differential AmplifierDouble endedinput - double

ended outputdiff. amp:

v out =A (v 1-v 2)v 1 v 2

v out

- +



● Single endedoutput

Non-inverting

input

Invertinginput

Single Ended Differential Amplifier (commonly used in op-amps)



Op Amp stages with pin-outs of IC741

2

4

7

6

3





Op amp Voltage Level Detector

V OUT +

-V REF

V IN = +V SAT for V IN >V REF

= -V SAT for V IN <V REF



Important features of Op Amp1. High open loop gain (ideally infinite)

which implies that even the smallest

difference between the two inputsresults into saturated output voltage

2. High input impedance (ideally infinite)

implies that there is no currentflowing into the input of an op amp



Virtual GroundThese two conditions give rise to VIRTUALGROUND, where the voltages at both theinputs are maintained at exactly same level.

To achieve this condition, a feedback circuitbetween the output and the inverting inputterminal of the op amp is necessary.

This results into many applications of op amp,which qualify it to be OPERATIONAL: adder, subtractor, multiplier, divider etc.



Op amp Applications



IntroductionThe operational amplifier or op-amp is acircuit of components integrated into one chip.

A typical op-amp is powered by two dc voltages and has an inverting(-) and a non-inverting input (+) and an output.

An op amp is an electronic device which provides a voltage output based on the voltageinput



Basic op-amp

Op-amp has two inputs that connect to two terminal and one output





Operational Amplifiers

• The output of the op amp is given by the following equation:

Vd = E1 – E2

and Vo = AVOL(Vd)

• AVOL is called the open-loop voltage gain because itis the gain of the op amp without any external feedback fromoutput to input





What do they really look like?



IC Circuit



Operational Amplifiers



Operational Amplifiers An ideal op-amp has infinite gain and

bandwidth , we know this is impossible.

However, op-amps do have:

very high gain

very high input impedance(Z in = ∞)

very low output impedance (Z out = 0)

wide bandwidth.



Application in op-amp

• There are 2 types of application in op-amp

– Linear application

– Non-linear application

• Linear application is where the op-amp operate in linearregion:

– Assumptions in linear application:

• Input current, Ii = 0

• Input voltage: V+=V-

• Feedback at the inverting input



• Non-linear application is where the op-amp operate innon-linear region

• By comparing these two input voltages: positive inputvoltages, V+ and negative input voltage, V- where:

VO = VCC if V+ > V-

VO = -VEE if V+ < V-


Application in op-amp







Summary of op-amp behavior

V o = A(V + - V )

V o /A = V + - V

Let A infinity

then,

V +

- V

0



V + = V

I + = I = 0

Seems strange, but the input terminals to anop-amp act as a short and open at the same time

Summary of op-ampbehavior



To analyze an op-amp circuit for linearoperation

•Write node equations at + and - terminals

(I i =I + = I - = 0)

•Set V + = V -

•

Solve for V o



Analysis of inverting amplifier

I 1

I f

I i

V 0 I i 0

I 1

I f I i

V s V

R1

V V o

R f

V V 0

V o

V s

R f

R1

V o

R f

R1

V s



Application:Non-invertingamplifier



Non-inverting configuration

1

2

21

21

21

1

0;

0:

;0

:

R

R

V V

R

V V

R

V V V insert

R

V V

R

V so

I while I I I

KCLuse

V V V

io

oiii

o

i

i

i

Vi

I 1

I 2

I i





Summing Amplifier

V 1

V 2

V 3

R1

R2

R3

R f

This circuit is call

a weighted summe

3

3

2

2

1

1

3

3

2

2

1

1

3

3

2

2

1

1

321

;0

:

;0

:

0

R

V

R

V

R

V

RV

R

V

R

V

R

V

R

V V insert

R

V V

R

V V

R

V V

R

V V so

I while

I I I I I

KCLuse

V V

f o

f

o

f

o

i

Rf i R R R

A li ti U it F ll (P ik t



Application: Unity Follower(PengikutVoltan)

1V V

O



Exercise 1

Find V O ?



Exercise 2

Find V 2 and V 3 ?



Exercise 3

Find V O ?



Exercise 4

Find V O ?



Application:Difference amplifier

)(21

2

4V V

R

RV O

43

21

R R

R R



Application:Instrumentation Amplifier

2 R

Buffer (Penimbal)

2 R

1 R

1 R

A R

B R

A R

Difference amplifier

12

1

22

1 V V R

R

R

RV

B

A

O

2 R



Application:Integrator

Feedback component = capacitor : Integrator

I I C

dt t v RC

t v

dt

t dvC

R

t v

I I I

io

i

C i

)(1

)(

)(0

)(0

sC

1

C j

1X

:impedancecetanCapaci

C



Application:Differentiation

dt

t dv RC t v

Rt vV

dt t dvC

I I

io

oi

RC

)()(

)()(



• Non-linear application is where the op-amp operate innon-linear region

• By comparing these two input voltages: positive inputvoltages, V+ and negative input voltage, V- where:

VO = VCC if V+ > V-

VO = -VCC if V+ < V-


Recall: Non-linear application in op-amp



Non-linear application:Comparator

N li li ti



Non-linear application:Comparator

V o (V)

10

-5

t

V S (V)

t

Compare V + and V -

V +=0

V -=V S

When:V S >0,V +>V - so V o=10V V S <0,V +<V - so V o=-5V (b) Output Voltage of Comparator

(a) Input Voltage of Comparator



Non-linear applicationSchmitt Trigger

-

+

O

f

V R R

RV

1

1

Positive Feedback

N li li ti



V V

V t V V and V V stateinitialwith

V V V and R Rassume

V R R

RV

S

o

EE CC f

O

f

5.7)15(2

1

sin1015

151

1

1

Non-linear applicationSchmitt Trigger

V o (V)

15

-15

t

V S (V)

t

7.5

-7.5

V o (V)

V S (V)-7.5 7.5 -10 10

15

-15

(a) Transfer Characteristic of Schmitt Trigger

(c) Output Voltage of Schmitt Trigger

(b) Input Voltage of Schmitt Trigger



Common Mode Rejection Ratio

(CMRR)• It is the ability of an op amp to reject the

signal which is present at its both inputssimultaneously i.e. the common modesignal

• CMRR = AOL / ACM , where ACM is commonmode voltage gain defined by V out / V CM

• Ideally CMRR is infinite• For IC 741 it is 90 dB



Slew Rate

• Maximum rate of change of outputvoltage (when typically a step voltage isgiven at the input terminal)

StepInput

V out

t

dV out / dt



Slew Rate (cont…)

• Slew rate is caused by the finite responsetime of the circuit elements of an op amp

• It limits the highest possible frequency ofoperation

V in

V out

ExpectedVoltage

t





Input Offset Voltage

• Small voltage needed to be appliedbetween INV and NI terminals to getzero output voltage

• Ideally it should be 0 V (CM operation)

Output Offset Voltage • Under common mode operation, output

voltage should be zero, but due to

mismatch is devices it is non-zero(Can be corrected by applying voltagebetween Pins 1 and 5 of IC 741)

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Operational Amplifier(Phe-10) (1)

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