Overview What is Op- Amp History Where it is used What does it do Op-Amp block diagram Inputs of Op-Amp Closed loop configuration Positive feedback Negative feedback

1. Operation Amplifire

2. Hello!
Nabila Tabassum
2015-2-50-029
Musharrat Zabin
2015-2-50-
Raihana Taherin
2015-2-50-
Taslima Yasmin
2015-2-50-

3. Overview
• What is Op- Amp
• History
• Where it is used
• What does it do
• Op-Amp block diagram
• Inputs of Op-Amp
• Closed loop configuration
• Positive feedback
• Negative feedback

4. What is Op-Amp??

5. “
An operational amplifire(op-amp) is a
DC-coupled high gain electronic voltage
amplifire.

6. ◇ Direct- coupled high gain amplifire usually consist of one
or more operation amplifire
◇Output stage is generally a push-pull or push-pull
complimentary symmetry pair.
◇Op-amps are differential amplifires, and their output
voltage is propotional to the difference of the two input
voltage.
◇The two input voltage terminals are called inverting and
non inverting and labbeled with + and -

7. Basic Diagram

8. History

9. “
First developed by Jhon R. Raggazzine
in 1947 with vacuum tube.
In 1968 FAIRCHILD introduces the op-
amp that was to become the industry
standard.

10. John R. Raggazzini David Farchild

11. What does an Op-
Amp do?
◇Performs many
different “operations”
• Addition/Subtraction
•Integration/Differentia
tion
•Buffering
•Amplification

12. Op-Amp
Block
Diagram

14. Differential
amplifire stage
◇ Provides differenial inputs for the
op-amp
◇ Provides DC gain
◇ Has very high input impedance
◇ Draws negligible input currents
◇ Enables users to utilize ideal op-
amp equations for circuit
analysis
Differenti
al stage
Voltage
gain stage
Output
stage

15. High gain voltage
amplifier
◇Provides the “gain” of the amplifier
◇Gains up the differential signal
from input and conveys it to the
output stage Differenti
al stage
Voltage
gain stage
Output
stage

16. Low impedance
output stage
◇Delivers current to the load
◇Very low impedance output stage
(to minimize
Differenti
al stage
Voltage
gain stage
Output
stage

17. Inputs of
Op-Amp

18. ◇Two inputs terminals
• Positive input (non-inverting)
• Negative input (inverting)
◇Can be used in three different
input modes
• Differential input mode
• Inverting mode
• Non Inverting mode

19. Differential Input Mode
◇Both input terminals are used
◇Input signals are 180 degree
out of phase
◇Output is in phase with non
inverting input

20. Inverting mode
◇Non inverting mode is grounded
(connected to mid supply)
◇Signal is applied to the inverting input
◇Output is 180 degree out of phase
with input

21. Non inverting mode
◇Inverting input is grounded
◇Signal is applied to the non
inverting input
◇Output is in phase with
input

22. CONFIGURATION OF
OP-AMP
◇Open loop configuration
In open loop configuration , there is no feedback from
output to input.
The differential signal present between the inputs will
be amplified by it’s open loop gain.(Av=2×105)
Therefore even for very small magnitude of differential
voltage output will reach positive or negative saturation

23. Why is OP-AMP not used
as an amplifier in the open
loop configuration?
◇Due to very open loop gain, distortion is introduced in the
amplified output signal.
◇The open loop gain does not remain constant but varies with
temperature and power supply as well due to mass production
technique.
◇The bandwidth of an OP-AMP is very small almost equal to
zero. For this reason the open loop OP-AMP is not used in
practice as an amplifier.

24. Close loop configuration
◇In close loop configuration , a feedback is
introduced i.e. a part of output is fed back to
input
The feedback can be following two types
1. Positive feedback/regenerative feedback
2. Negative feedback/degenerative
feedback

25. Positive feedback
◇If feedback signal and the input signal are in phase
with each other then it is called as the positive
feedback.
It is used in application such as oscillators and
Schmitt trigger or regenerative comparators.

26. Negative feedback
◇If the signal fed back to the input and
the original input signal are 180 degree
out of phase, then it is called as
negative feedback
In application of on op-amp as an
amplifier the negative feed back is used

27. Advantages of
negative feedback
◇It stabilizes the gain
◇Reduces the distortion
◇Increases the bandwidth
◇Reduces the effects of variations in temperature and supply
voltage on the output of op-amp
The only disadvantage of negative feedback is low gain

28. Characteristics of
non ideal op-amp
◇Infinite input impedance(about 2Mohm)
◇Low output impedance(about 200 ohm)
◇Very large voltage gain at low frequency
◇Thus,small changes in voltages can be amplified byusing an op-amp
◇Infinte bandwidth(all frequencies are amplified by same factor
◇Infinite Common-mode rejection ratio
◇Infinite Power supply rejection ratio.

29. Characteristics of
ideal op-amp
 Finite open-loop gain that causes gain error
Finite input impedance
Non zero output impedance
Finite CMRR
Common-mode input resistance
Finite bandwidth
Finite power supply rejection ratio.

30. Comparison of ideal and practical
OP- AMP
characteristics Practical value Ideal value
Voltage gain 2 ×105 ∞
Input resistance 2MΩ ∞
Output resistance 75Ω 0
Bandwidth 1 MHz ∞
CMRR 90 dB ∞
Slew rates 0.5V/µs ∞
PSRR 150µV/V 0
Input offset voltage 2mV 0
Input bias current 50 nA 0
Input offset current 6 nA 0

31. ◇Op-amp is an universal amplifier.
◇Voltage comparators.
◇Precision rectifiers
◇ Anologe to digital converters.
◇ Digital to analogue converters.
◇Filters.
◇Diffrentiators and integrators.
◇ Voltage and current regulator.
◇ Analogue to computers.
Advantages of an
op-amp

32. Disadvantages of
an op-amp
◇Most op-amp are designed to for lower power
operation.
◇For high output is desired then the op-amp specifically
designed for that purpose must be seen.
◇Most commercial op-amp shuts off when the load
resistance is below a specific level.

33. Thanks!
Any questions?