1. OPERATIONAL AMPLIFIER
Module 3
OPERATIONAL AMPLIFIER

2. Brainstorming Session….
What does an AMPLIFIER do?

3. What is an IC?

4. Integrated Circuits

5. Inside an IC

6. OP-Amp is an amplifier IC

7. 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.

8. 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

9. 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.

10. OP-AMP BLOCK DIAGRAM - V + V Output Differential Amplifier
Figure 1 Op Amp Block Diagram
Inverting Input (- VIN)
+ V
- V
Output
Noninverting Input (+ VIN)
Differential Amplifier
Voltage Amplifier
Output Amplifier

11. 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)

12. OP-AMP CHARACTERISTICS
Very high input impedance
Very high gain
Very low output impedance
OP-AMP is a differential, voltage amplifier with high gain.

13. 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)

14. The 741 Op-amp
The most common op-amp is the 741 IC.

15. Figure : Op Amp packages
Packaging Types
Figure : Op Amp packages
(b) OPA547FKTWT
DIP SMT package
(a) Op Amp 741
8-pins DIP package
(c) TO-5 metal can
8-Leads package

16. OP-AMP pins identification
Figure 3 Op Amp pins Identification 1 2 3 4 5 6 7 8
+VCC
-VEE - +
741
b) Notched Package
a) Dot marked Package

17. What are these pins? http://www.quia.com/pp/200743.html 7. +VCC
Figure 4 Op Amp pins Description 1 2 3 4 5 6 7 8
1. Offset Null
-VEE
8. N / C
6.Output
741
7. +VCC
3. Noninverting Input +VIN
2. Inverting Input –VIN
5.Offset Null

18. 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

19. Symbol of OP-AMP - + Figure 5 Op Amp Schematic Symbols -VIN +VIN VOUT
+VS
-VS
(a) Without power connection
(b) With power connection

20. Most Op Amps require dual power supply with common ground
Positive Supply (+15V) to pin7 Negative Supply (-15V) to pin4
Figure 6 Dual Supply Voltages connection
-VIN + -
+VIN
VOUT
+VS
-VS 7 4
Common Ground

21. Some Op Amps work on single supply also
Figure 7 Single Supply Voltages connection
-VIN + -
+VIN
VOUT
-VS 7 4
+VS
(a) Single Positive Voltage
(b) Single Negative Voltage

22. Advantage of dual power supply
Using dual power supply will let the op amp to output true AC voltage. 0V
+15V
-15V
Output
Figure 8a Op Amp powered from Dual supply
+30V
Figure 8b Op Amp powered from Single supply
30 V

23. What is dual power supply?
Single Power Supply
Figure 18 Dual Power Supply
Common
+15V
–15V

24. How can you make a dual power supply using two 9V batteries?
What is the voltage between + of first battery and – of second battery?

25. Operational Amplifier
Single-Ended Input
+ terminal : Source
– terminal : Ground
0o phase change
+ terminal : Ground
– terminal : Source
180o phase change
Ref:080114HKN
Operational Amplifier

26. Operational Amplifier
Double-Ended Input
Differential input
0o phase shift change
between Vo and Vd
Qu: What Vo should be if,
Ans: (A or B) ?
(A)
(B)
Ref:080114HKN
Operational Amplifier

27. Common-Mode Operation
Same voltage source is applied
at both terminals
Ideally, two input are equally
amplified
Output voltage is ideally zero
due to differential voltage is
zero
Practically, a small output
signal can still be measured
Note for differential circuits:
Opposite inputs : highly amplified
Common inputs : slightly amplified
 Common-Mode Rejection
Ref:080114HKN
Operational Amplifier

28. Common-Mode Rejection Ratio (CMRR)
Differential voltage input :
Common voltage input :
Common-mode rejection ratio:
Output voltage :
Note:
When Gd >> Gc or CMRR 
Vo = GdVd
Gd : Differential gain
Gc : Common mode gain
Ref:080114HKN
Operational Amplifier

29. Operational Amplifier
Op-Amp Properties
Infinite Open Loop gain
The gain without feedback
Equal to differential gain
Zero common-mode gain
Pratically, Gd = 20,000 to 200,000
(2) Infinite Input impedance
Input current ii ~0A
T- in high-grade op-amp
m-A input current in low-grade op-amp
(3) Zero Output Impedance
act as perfect internal voltage source
No internal resistance
Output impedance in series with load
Reducing output voltage to the load
Practically, Rout ~ 
Ref:080114HKN
Operational Amplifier

30. Ideal Vs Practical Op-Amp
Open Loop gain A 
105
Bandwidth BW
10-100Hz
Input Impedance Zin
>1M
Output Impedance Zout
0  
Output Voltage Vout
Depends only on Vd = (V+V)
Differential mode signal
Depends slightly on average input Vc = (V++V)/2 Common-Mode signal
CMRR
10-100dB
Ref:080114HKN
Operational Amplifier

31. OP-AMP CONFIGURATIONS
Figure Types of Feedback
(a) No Feedback (open loop comparator circuit)
(b) Negative Feedback
(c) Positive Feedback

32. 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(

33. 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)

34. Examples of Negative Feedback Applications: A) Inverting Amplifiers
1.Summing Amplifier 2.Differentiator 3.Integrator B) Non Inverting Amplifiers 1. Voltage Follower

35. Ideal Op-Amp Applications
Analysis Method :
Two ideal Op-Amp Properties:
The voltage between V+ and V is zero V+ = V
The current into both V+ and V termainals is zero
For ideal Op-Amp circuit:
Write the kirchhoff node equation at the noninverting terminal V+
Write the kirchhoff node eqaution at the inverting terminal V
Set V+ = V and solve for the desired closed-loop gain
Ref:080114HKN
Operational Amplifier

36. Operational Amplifier
Inverting Amplifier
Kirchhoff node equation at V+ yields,
Kirchhoff node equation at V yields,
Setting V+ = V– yields
Notice: The closed-loop gain Vo/Vin is dependent upon the ratio of two resistors, and is independent of the open-loop gain. This is caused by the use of feedback output voltage to subtract from the input voltage.
Ref:080114HKN
Operational Amplifier

37. 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.
Where;
VO = Output voltage
VIN = Input voltage
AI = Inverting Gain VO
VIN RF
RIN

38. Noninverting Amplifier
Kirchhoff node equation at V+ yields,
Kirchhoff node equation at V yields,
Setting V+ = V– yields or
Ref:080114HKN
Operational Amplifier

39. 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. VO
VIN RF R1
Figure 11 Closed-Loop Noninverting Amplifier Circuit
Where;
VO = Output voltage
Vin= Input voltage= Vf
ANI = Noninverting Gain

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

41. Operational Amplifier
Multiple Inputs
Kirchhoff node equation at V+ yields,
Kirchhoff node equation at V yields,
Setting V+ = V– yields
Ref:080114HKN
Operational Amplifier

42. Summing Amplifier (Adder) : the inputs are added and the sum is inverted . If all resistors are of equal value, then Vo = -(V1 + V2+ V3)
Figure 14 Summing Amplifier V1 VO V2 V3 0V R1 R2 R3 RF

44. Operational Amplifier
Inverting Integrator
Now replace resistors Ra and Rf by complex components Za and Zf, respectively, therefore
Supposing
The feedback component is a capacitor C, i.e.,
The input component is a resistor R, Za = R
Therefore, the closed-loop gain (Vo/Vin) become:
where
What happens if Za = 1/jC whereas, Zf = R?
Inverting differentiator
Ref:080114HKN
Operational Amplifier

45. Integrator (the input is integrated with respect to time)
Figure 15 Inverting Op-Amp as Integrator R C
VIN VO

46. Operational Amplifier
Op-Amp Integrator
Example:
Determine the rate of change
of the output voltage.
Draw the output waveform.
Solution:
(a) Rate of change of the output voltage
(b) In 100 s, the voltage decrease
Ref:080114HKN
Operational Amplifier

47. Differentiator (the input is differentiated with respect to time)
Figure 16 Inverting Op-Amp as Differentiator C R
VIN VO

48. Op-Amp Differentiator
Ref:080114HKN
Operational Amplifier

49. Voltage Follower (Non Inverting)
It is a non inverting amplifier with gain=1
So the output is the same as input.
VIN VO
Figure 17 Voltage Follower

50. Positive Feedback is used in oscillators
Astable Multivibrator (Relaxation Oscillator) VO R2 R3 R1 C1
Figure 13 Astable Multivibrator

51. Offset Null Adjustment (practical)
Figure 22 Offset Null adjustment
-VS
N/C VO
+VS
VIN = 0
A741 1 2 3 4 5 6 7 8 V

52. offset voltage can 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.

53. Practical-Summing Amplifier

54. Results Table Vo = - (V1 + V2 )