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# Module 3 PowerPoint PPT Presentation

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.

Module 3

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## Module 3

OPERATIONAL AMPLIFIER

### Brainstorming Session….

What does an AMPLIFIER do?

• What is an IC?

### 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)

• 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

• 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.

Inverting Input (- VIN)

+ V

Output

Differential Amplifier

Voltage Amplifier

Output Amplifier

Noninverting Input (+ VIN)

- V

Figure 1 Op Amp Block Diagram

### 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

• 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????

• 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 most common op-amp is the 741 IC.

(c) TO-5 metal can

(a) Op Amp 741

8-pins DIP package

(b) OPA547FKTWT

DIP SMT package

Figure : Op Amp packages

### Packaging Types

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

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 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

+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

+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

+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

+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.

–15V

+15V

Common

Figure 18 Dual Power Supply

Single Power Supply

Single Power Supply

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

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

(a) No Feedback (open loop comparator circuit)

(b) Negative Feedback

(c) Positive Feedback

Figure Types of 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(

+VS

–VIN

VO

+VIN

–VS

VO

+VS

+VIN –VIN

0

+VIN = –VIN

+VIN –VIN

–VS

(a) Comparator Circuit

(b) Comparator Output

### 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

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)

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:

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

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

1.Summing Amplifier

2.Differentiator

3.Integrator

B) Non Inverting Amplifiers

1. Voltage Follower

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)

C

R

VIN

VO

Figure 15 Inverting Op-Amp as Integrator

### Integrator (the input is integrated with respect to time)

R

C

VIN

VO

Figure 16 Inverting Op-Amp as Differentiator

### Differentiator (the input is differentiated with respect to time)

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.

R1

C1

VO

R2

R3

Figure 13 Astable Multivibrator

### Positive Feedback is used in oscillators

• Astable Multivibrator (Relaxation Oscillator)

8

7

6

5

A741

1

3

4

2

VO

V

+VS

N/C

-VS

VIN = 0