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Module 3. OPERATIONAL AMPLIFIER. Brainstorming Session…. What does an AMPLIFIER do?. What is an IC?. Integrated Circuits. Inside an IC. OP-Amp is an amplifier IC. What can you do with Op amps?. You can make music louder when they are used in stereo equipment.

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Module 3

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Module 3

Module 3

OPERATIONAL AMPLIFIER


Brainstorming session

Brainstorming Session….

What does an AMPLIFIER do?


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  • What is an IC?


Integrated circuits

Integrated Circuits


Inside an ic

Inside an IC


Op amp is an amplifier ic

OP-Amp is an amplifier IC


What can you do with op amps

What can you do with Op amps?

  • You can make music louder when they are used in stereo equipment.

  • You can amplify the heartbeat by using them in medical cardiographs.

  • You can use them as comparators in heating systems.

  • You can use them for Math operations like summing, integration etc.


Op amp operational amplifier

OP-AMP (operational amplifier)

  • An OP-AMP is an integrated circuit (IC) used for amplification of signals.

  • It is the most widely used analog IC.

  • It is used in control systems, instrumentation, signal processing etc


Operational amplifier

Operational Amplifier

  • The Operational Amplifier or "op-amp" is an amplifier with two inputs and one output. One input is the inverting input and the other is a non inverting input.


Op amp block diagram

Inverting Input (- VIN)

+ V

Output

Differential Amplifier

Voltage Amplifier

Output Amplifier

Noninverting Input (+ VIN)

- V

Figure 1 Op Amp Block Diagram

OP-AMP BLOCK DIAGRAM


Op amp has 3 stage amplifier circuits

OP-AMP HAS 3 –STAGE AMPLIFIER CIRCUITS

  • First Stage : Differential Amplifier -it gives the OP-AMP high input impedance (resistance)

  • Second Stage: Voltage Amplifier – it gives high gain

  • Third Stage : Output Amplifier (Emitter Follower) – gives low output impedance (resistance)


Op amp characteristics

OP-AMP CHARACTERISTICS

  • Very high input impedance

  • Very high gain

  • Very low output impedance

    OP-AMP is a differential, voltage amplifier with high gain.


Op amp is a differential voltage amplifier with high gain why

OP-AMP is a differential, voltage amplifier with high gain. Why????

  • Differential Amplifier: Because it amplifies the difference between 2 voltages

  • Voltage Amplifier: Because input and output are voltages

  • High Gain Amplifier: Because the voltage gain is very high (> 100,000)


The 741 op amp

The 741 Op-amp

The most common op-amp is the 741 IC.


Packaging types

(c) TO-5 metal can

8-Leads package

(a) Op Amp 741

8-pins DIP package

(b) OPA547FKTWT

DIP SMT package

Figure : Op Amp packages

Packaging Types


Op amp pins identification

741

1

1

8

8

+VCC

+VCC

-

-

2

7

2

7

3

6

3

6

+

+

-VEE

-VEE

4

5

4

5

b) Notched Package

a) Dot marked Package

Figure 3 Op Amp pins Identification

OP-AMP pins identification


What are these pins

1. Offset Null

1

8. N / C

8

741

2. Inverting Input –VIN

7. +VCC

2

7

3. Noninverting Input +VIN

3

6

6.Output

5.Offset Null

-VEE

4

5

Figure 4 Op Amp pins Description

What are these pins?

http://www.quia.com/pp/200743.html


What are these pins1

What are these pins?

  • Pin 1 and Pin 5 : Offset null input, are used to remove the Offset voltage.

  • Pin 2: Inverting input (-VIN), signals at this pin will be inverted at output Pin 6.

  • Pin 3: Non-inverting input (+VIN), signals at pin 3 will be processed without inversion.

  • Pin 4: Negative power supply terminal (-VEE).

  • Pin 6: Output (VOUT) of the Op-Amp

  • Pin 7: Positive power supply terminal (+VCC)

  • Pin 8: No connection (N\C), it is just there to make it a standard 8-pin


Symbol of op amp

+VS

-VIN

-

-VIN

VOUT

-

+VIN

VOUT

+

+VIN

+

-VS

(a) Without power connection

(b) With power connection

Figure 5 Op Amp Schematic Symbols

Symbol of OP-AMP


Most op amps require dual power supply with common ground

+VS

-VIN

-

7

VOUT

+VIN

4

+

Common Ground

-VS

Figure 6 Dual Supply Voltages connection

Most Op Amps require dual power supply with common ground

Positive Supply (+15V) to pin7

Negative Supply (-15V) to pin4


Some op amps work on single supply also

+VS

-VIN

-

7

VOUT

+VIN

4

+

-VIN

-

VOUT

7

+VIN

4

+

-VS

(a) Single Positive Voltage

(b) Single Negative Voltage

Figure 7 Single Supply Voltages connection

Some Op Amps work on single supply also


Advantage of dual power supply

+15V

+30V

30 V

30 V

Output

Output

0V

-15V

0V

Figure 8a Op Amp powered from Dual supply

Figure 8b Op Amp powered from Single supply

Advantage of dual power supply

Using dual power supply will let the op amp to output true AC voltage.


What is dual power supply

–15V

+15V

Common

Figure 18 Dual Power Supply

Single Power Supply

Single Power Supply

What is dual power supply?


How can you make a dual power supply using two 9v batteries

How can you make a dual power supply using two 9V batteries?

What is the voltage between + of first battery and – of second battery?


Op amp configurations

(a) No Feedback (open loop comparator circuit)

(b) Negative Feedback

(c) Positive Feedback

Figure Types of Feedback

OP-AMP CONFIGURATIONS


Feedback

Feedback

  • No feedback : Open loop (used in comparators)

  • Negative feedback : Feedback to the inverting input (Used in amplifiers)

  • Positive feedback : Feedback to the non inverting input (Used in oscillators(


Op amp as a comparator compares 2 voltages and produces a signal to indicate which is greater

+VS

–VIN

VO

+VIN

–VS

VO

+VS

+VIN –VIN

0

+VIN = –VIN

+VIN –VIN

–VS

(a) Comparator Circuit

(b) Comparator Output

OP AMP as a Comparator (compares 2 voltages and produces a signal to indicate which is greater)


Applications of comparators

Applications of Comparators

  • Analog to digital converters (ADC)

  • Counters (e.g. count pulses that exceed a certain voltage level).

  • Cross Over Detectors


Op amps with negative feedback

OP-AMPS WITH NEGATIVE FEEDBACK

The two basic amplifier circuits with negative feedback are:

  • The non-inverting Amplifier.

  • The inverting Amplifier

    (Note: Negative feedback is used to limit the gain)


Non inverting amplifier

Where;

VO = Output voltage

Vin= Input voltage= Vf

ANI = Noninverting Gain

RF

R1

VIN

VO

Figure 11 Closed-Loop Noninverting Amplifier Circuit

NON-INVERTING AMPLIFIER

  • The input signal is applied to the non-inverting input (+VIN). The output is fed back to the inverting input through resistor RF.


Problem

Problem:

  • Calculate the gain of a non inverting amplifier if Rin=3K and Rf=30K. If Vin=4mV, calculate the output voltage.


Inverting amplifier

RF

RIN

VIN

VO

Where;

VO = Output voltage

VIN = Input voltage

AI = Inverting Gain

INVERTING AMPLIFIER

  • The input signal is applied through a series input resistor RI to the inverting input. Also, the output is fed back through RF to the same input. The noninverting input is grounded.


Examples of negative feedback applications a inverting amplifiers

Examples of Negative Feedback Applications:A) Inverting Amplifiers

1.Summing Amplifier

2.Differentiator

3.Integrator

B) Non Inverting Amplifiers

1. Voltage Follower


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R1

RF

V1

R2

V2

VO

R3

V3

0V

Figure 14 Summing Amplifier

Summing Amplifier (Adder) : the inputs are added and the sum is inverted . If all resistors are of equal value, thenVo = -(V1 + V2+ V3)


Integrator the input is integrated with respect to time

C

R

VIN

VO

Figure 15 Inverting Op-Amp as Integrator

Integrator (the input is integrated with respect to time)


Differentiator the input is differentiated with respect to time

R

C

VIN

VO

Figure 16 Inverting Op-Amp as Differentiator

Differentiator (the input is differentiated with respect to time)


Voltage follower non inverting

Figure 17Voltage Follower

VO

VIN

Voltage Follower (Non Inverting)

  • It is a non inverting amplifier with gain=1

  • So the output is the same as input.


Positive feedback is used in oscillators

R1

C1

VO

R2

R3

Figure 13 Astable Multivibrator

Positive Feedback is used in oscillators

  • Astable Multivibrator (Relaxation Oscillator)


Offset null adjustment practical

8

7

6

5

A741

1

3

4

2

VO

V

+VS

N/C

Figure 22Offset Null adjustment

-VS

VIN = 0

Offset Null Adjustment (practical)


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  • offset voltagecan be defined as the slight amount of voltage that appears at the output when the voltage differential (ΔVIN) between the input pins is 0 V.


Practical summing amplifier

Practical-Summing Amplifier


Results table v o v 1 v 2

Results TableVo = - (V1 + V2 )


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