This document provides a comprehensive overview of operational amplifiers (op-amps), including their definition, functionality, and characteristics. It discusses the differential amplifier configuration, gain stages, and practical parameters of the IC 741 op-amp, highlighting its features like high input impedance and low output resistance. Various configurations and applications of op-amps are also examined, underscoring their role in amplifying voltage signals in electronic circuits.

1. Integrated Circuits
Introduction to Operational Amplifier (Op-Amp)
Mrunalini Pimpale
Assistant Professor
Electronics and Telecommunication Engineering Department
Dwarkadas J. Sanghvi College of Engineering
Ville Parle-Mumbai
Prof.Mrunalini Pimpale
1

2. Operational Amplifier (Op-Amp)
Prof.Mrunalini Pimpale 2

3. • An operational amplifier (or an op-amp) is an integrated circuit (IC)
that operates as a voltage amplifier. An op-amp has a differential
input. That is, it has two inputs of opposite polarity. An op-amp has a
single output and a very high gain, which means that the output signal
is much higher than input signal.
Prof.Mrunalini Pimpale 3

4. Op-Amp Power Supply Connection
Vout = V1 – V2
Prof.Mrunalini Pimpale
1. Let V1= 5V and V2 = 3V then Vout = 5- 3 = 2V (Differential Mode)
2. Let V1= 5V and V2 = 5V then Vout = 5- 5 = 0V (Common Mode)
3. Let V1= 5V and V2 = 0 then Vout = 5- 0 = 5V (Single ended)
4. Let V1= 0V and V2 = 5V then Vout = 0-5 = -5V
4

5. Prof.Mrunalini Pimpale
Vout = V1 – V2
5

6. Prof.Mrunalini Pimpale 6

7. Prof.Mrunalini Pimpale
7

8. Prof.Mrunalini Pimpale 8

9. • First stage provides most of the voltage gain of op-amp and decides Ri
value
• Second stage is gain stage
• Third stage is level shifting stage:- Due to direct coupling between
first two stages, the input of level shifting stage is an amplified signal
with some non zero dc level. This stage is used to bring that dc level to
ground. In this stage the emitter follower with a constant current
source circuit is used.
• Last stage is a complementary output stage .This stage has
Complementary push pull power amplifier. It increases the magnitude
of the voltage and raises the current supplying capability of op-amp
along with low output resistance.
Prof.Mrunalini Pimpale 9

10. Differential Amplifier
Differential Amplifier is used to amplify the difference between the two
input signals. It is used in many Analog circuits. The input stage of
almost every Op-Amp is differential amplifier
Prof.Mrunalini Pimpale 10

11. Differential Amplifier:
Terminology and qualitative description:
1) Differential input voltage : (Vd)
If inputs (i.e Vin1 and Vin2) to differential amplifiers are such that there exists either amplitude or phase-
difference between them, then such input is known as “ differential input”
𝑉𝑑 = (𝑉𝑖𝑛1 − 𝑉𝑖𝑛2)
2) Differential mode gain: (Ad)
The gain with which differential amplifier amplifies differential input signal (Vd) is known as “ Differential mode gain”
𝐴𝑑 =
(𝑉𝑜1−𝑉𝑜2)
𝑉𝑑
=
(𝑉𝑜1−𝑉𝑜2)
(𝑣𝑖𝑛1−𝑉𝑖𝑛2)
=
𝑉𝑜
𝑉𝑑
Ideally, Ad ∞, Practically it should be large.
𝑉𝑜 = 𝑉𝑜1 − 𝑉𝑜2  Differential output voltage.
3) Common-mode input voltage : (VCM )
If input (i.e Vin1 and Vin2) to differential amplifier are of same magnitude and phase then
Such input is known as “Common mode input voltage”
𝑉𝑐𝑚 =
𝑉𝑖𝑛1+𝑉𝑖𝑛2
2
Prof.Mrunalini Pimpale 11

12. 4) Common- mode gain : (ACM)
The gain with which differential amplifier amplifies common mode input signal is known as “Common mode gain”
𝐴𝑐𝑚 =
(𝑉𝑜𝑢𝑡)
𝑉𝑐𝑚
Ideally, Acm 0, Practically it should be very small.
Differential amplifier is designed to reject noise (common mode input), and to amplify differential mode signal
5) Common mode rejection ratio (CMRR)
 CMRR is a parameter which decides the ability of differential amplifier to reject (common mode signal) and amplify differential
mode signal.
 Mathematically , CMRR is the ratio of differential mode gain (Ad) to the common mode gain (Acm).
𝐶𝑀𝑅𝑅 =
|𝐴𝑑|
|𝐴𝑐𝑚|
𝐶𝑀𝑅𝑅 𝑖𝑛 𝑑𝑏 = 20 𝑙𝑜𝑔10
|𝐴𝑑|
|𝐴𝑐𝑚|
 Ideally, CMRR should be infinite (i.e Ad  ∞ and Acm  0 ) and practically it should be very high.
Prof.Mrunalini Pimpale 12

13. Features of Differential Amplifier:
1)High differential gain and low common mode gain.
2) High input impedance and low output impedance
3) High CMRR.
4) High gain.
5) Large Bandwidth
Prof.Mrunalini Pimpale 13

14. Prof.Mrunalini Pimpale 14

15. Configuration of Differential Amplifier
1) Single input Balanced output differential amplifier (SIBO)
2) Single input unbalanced output Differential amplifier (SIUO)
3) Dual input Balanced output Differential amplifier (DIBO)
4) Dual input Unbalanced output differential amplifier (DIUO)
Prof.Mrunalini Pimpale 15

16. Differential Amplifier
Prof.Mrunalini Pimpale 16

17. Single Input Unbalanced Output Single Input balanced Output
Dual Input unbalanced Output
Dual Input balanced Output
Prof.Mrunalini Pimpale 17

18. DC transfer characteristics of MOSFET Differential amplifier
Prof.Mrunalini Pimpale
EMOSFET Differential Amplifier
18

19. Prof.Mrunalini Pimpale 19

20. Prof.Mrunalini Pimpale 20

21. Why we always choose MOSFET DA?
• The maximum differential input signal for the MOSFET differential amplifier is
much larger than BJT differential amplifier.
• The primary reason is that the gain of the MOSFET differential amplifier , as we
will see, is much smaller than the gain of the BJT differential amplifier.
• Many DA are constructed with MOSFET’s since it provides high input
impedances, which helps amplifiers avoid loading of source.
• A MOSFET DA cannot provide high gain but it avoid loading of source.
• Also, MOSFET can be easily fabricated in IC form.
Prof.Mrunalini Pimpale 21

22. Dual input Balanced output Differential
Amplifier
• DC analysis
• AC analysis
Prof.Mrunalini Pimpale 22

23. Prof.Mrunalini Pimpale 23

24. Prof.Mrunalini Pimpale 24

25. Prof.Mrunalini Pimpale 25

26. Prof.Mrunalini Pimpale 26

27. Prof.Mrunalini Pimpale 27

28. Prof.Mrunalini Pimpale 28

29. Prof.Mrunalini Pimpale 29

30. Prof.Mrunalini Pimpale 30

31. Numerical
Prof.Mrunalini Pimpale 31

32. Prof.Mrunalini Pimpale 32

33. Prof.Mrunalini Pimpale 33

34. Prof.Mrunalini Pimpale 34

35. Active load can be used as current mirror circuit. Current mirror means we are copying the
same current from one device to other and main thing is we are controlling the current in
such way the main output current is not disturb , that is the constant
MOSFET Differential Amplifier with Active Load
Prof.Mrunalini Pimpale 35

36. Prof.Mrunalini Pimpale 36

37. Prof.Mrunalini Pimpale 37

38. Prof.Mrunalini Pimpale 38

39. Prof.Mrunalini Pimpale 39

40. MOSFET Differential Amplifier with Swamping
Resistor
• By using external resistors R’E in series with each emitter, the dependence of voltage gain on variations
of r’e can be reduced. It also increases the linearity range of the differential amplifier shows the
differential amplifier with swamping resistor R'E. The value of R'E is usually large enough to swamp the
effect of r’e.
Advantages of the swamping resistors is:
• Input resistance is high
• Increase the linearity range of the differential amplifier
• Minimization of the changes in the transistor parameters due to the temperature
Prof.Mrunalini Pimpale 40

41. Prof.Mrunalini Pimpale 41

42. Prof.Mrunalini Pimpale 42

43. Prof.Mrunalini Pimpale 43

44. Prof.Mrunalini Pimpale 44

45. Prof.Mrunalini Pimpale 45

46. Prof.Mrunalini Pimpale 46

47. Widlar Current Source:-
In basic Current mirror circuit when value of Iref = ID = low , then value of drain resistance
connected need to be increased, which is difficult to fabricate. Hence modifications are done in
the basic current mirror circuit as shown in figure called as WIDLAR Current Source
To avoid drawback of current mirror circuit Widlar Current source is used
Series resistance R2 is placed at source terminal of M2
It is suitable for low value currents
Used for generating low value currents, i.e. Io < IIN
Prof.Mrunalini Pimpale 47

48. Prof.Mrunalini Pimpale 48

49. Prof.Mrunalini Pimpale 49

50. Operational Amplifier
Prof.Mrunalini Pimpale
• An operational amplifier (or an op-amp) is an integrated circuit (IC) that operates as a voltage
amplifier. An op-amp has a differential input. That is, it has two inputs of opposite polarity. An op-
amp has a single output and a very high gain, which means that the output signal is much higher
than input signal. The name “operational amplifier” comes from the fact that they were originally
used to perform mathematical operations such as Addition , subtraction, integration, differentiation,
etc...
50

51. FEATURES:
• Null offset
• Excellent temperature stability
• High input voltage range
• Short circuit protection
• Low power consumption
Prof.Mrunalini Pimpale 51

52. PIN DIAGRAM:
• It is high performance monolithic (active and passive component) operational amplifier.
• It is 8 pin IC in DIP.
Prof.Mrunalini Pimpale 52

53. CHARACTERISTICS OF AN IDEAL OP-AMP
The ideal op-amp should have the following electrical characteristics:
• Infinite Voltage Gain (Av=∞)
• Infinite Input Resistance (Zin= ∞) so that any signal source can drive it and there is no
loading effect of preceding stage.
• Zero Output Resistance so that the output can drive an infinite number of other devices.
• Zero Offset Voltage when input is zero.
• Infinite CMRR (Common Mode Rejection Ratio) so that the output common mode noise
voltage is zero.
• Infinite Bandwidth (BW=∞) so that any frequency signal from 0 to ∞ Hz can be amplified
without attenuation.
• Infinite Slew Rate so that output voltage changes occur simultaneously with input voltage
changes.
Prof.Mrunalini Pimpale 53

54. IDEALAND PRACTICAL PARAMETERS OP-
AMP
Sr.No Characteristics Practical Value Ideal Value
1. Voltage Gain(A) 2x105 ∞
2. Bandwidth(B.W) 1MHz ∞
3. CMRR(ρ) 90dB ∞
4. Input resi Ri 2M ohms ∞
5. Output resi. Ro 75 ohms 0
6. Slew Rate (S) 0.5 V/µs ∞
7. Input offset voltage (Vios) 2mV 0
8. PSRR 150µV/V 0
9. Input bias current IB 50nA 0
10. Input offset current Iios 6nA 0
Prof.Mrunalini Pimpale 54

55. EQUIVALENT CIRCUIT
Vo= Avid=A (v1-v2)
V1 & V2 - Input signals
Av - Voltage Gain
Ri - Input Resistance
R0 - Output Resistance
V0 - Output Voltage
Vd - Differential Input Voltage
Prof.Mrunalini Pimpale 55

56. Prof.Mrunalini Pimpale 56

57. Prof.Mrunalini Pimpale 57

58. TRANSFER CHERECTERISTICS OF OP-AMP
• Transfer Characteristics
Prof.Mrunalini Pimpale 58

59. PARAMETERS OF IC 741
Input Offset Voltage ( Vio)
• The voltage that must be applied between the two input terminals of an op-amp to null the
output as shown in figure. For 741C the maximum value of Vio is 6mv dc.
Input Bias Current (IB)
• Input bias current is the average of the currents that flow into the inverting and non inverting
input terminals of op-amp. In equation IB =(IB1 + IB2)/2
• Range is from 80 nA to 500 nA.
Input Offset Current (Iio)
• The algebraic difference between two biasing currents in to the inverting (IB2) and non
inverting(IB2) terminals. In equation form Iio =/IB1 - IB2/
• It is maximum value 200 nA for 741C.The smaller current shows better performance.
Offset voltage.
• The voltage across input terminals for zero output voltage.
Prof.Mrunalini Pimpale 59

60. PARAMETERS OF IC 741
• Slew Rate (SR)
• The maximum rate of change of output voltage per unit time in input frequency.
S=(dVo/ dt)/max Volts/microsecond
• It indicates how fast the output of op-amp can change in response to changes in input frequency.
High slew rate is desirable, for 741C , SR=0.5V/usec.
• Slew Rate Distortion:
• The picture above shows exactly what happens when the slew rate limitations are not met and
the output of the operational amplifier is distorted.
Prof.Mrunalini Pimpale 60

61. PARAMETERS OF IC 741
• Voltage Gain
• It is the ratio of the output voltage to the input voltage.
Av = Vo / Vd
For 741C op-amp voltage gain is A=200000.
• Common Mode Rejection Ratio (CMRR)
Ability of op-amp to reduce common mode I/p voltage or noise is known as CMRR, and
mathematically given by
CMRR=Ad/Ac
The CMRR should be as large as possible ideally infinite. For 741C CMRR is 90 dB.
• Power Supply Rejection Ratio (PSRR) or SVRR
PSRR=ΔVios /ΔV.
ΔVios: change in I/p offset voltage.
ΔV : change in supply voltage.
For 741C CMRR is150 uv/v.
Prof.Mrunalini Pimpale 61

62. PARAMETERS OF IC 741
• Output Signal swing (Vomax)
The output voltage swing of 741C op-amp is guaranteed to be between -13 and +13 V for RL>2KΩ
is 26 V Peak to peak voltage( undistorted ).The output never exceeds these limits for given supply
voltages +VCC and -VEE.
• Frequency Response:
Curve indicates change in voltage gain with frequency.
“The frequency at which voltage gain falls to unity is unity gain frequency.
• Supply current
For 741C current drawn by the op-amp from the power supply is Is=2.8mA.
Prof.Mrunalini Pimpale 62

63. OPEN-LOOP OP-AMP CONFIGURATIONS
•Inverting amplifier
•V1= 0 . For ideal op-amp, V2 = Vs
• Differential input voltage : Vd = (V1 – V2) = 0 – Vs = -Vs
• Output voltage : VO = AV x Vd = - AvVs
•Negative sign indicates a phase reversal or 180 degree phase shift
Prof.Mrunalini Pimpale 63

64. OPEN-LOOP OPAMP CONFIGURATIONS
• Noninverting amplifier
• V2 = 0 . For ideal op-amp, V1 = Vs
• Differential input voltage : Vd = (V1 – V2) = Vs – 0 = Vs
• Output voltage : VO = AV x Vd = AvVs
• No negative sign indicates absence of phase shift
Prof.Mrunalini Pimpale 64

65. OPEN-LOOP OPAMP CONFIGURATIONS
Differential amplifier.
•Differential input voltage : Vd = (V1 – V2)
• If op-amp is ideal : Vd = (Vs2 – Vs1)
• Output voltage : VO = AV x Vd
Prof.Mrunalini Pimpale 65

66. Limitation of openloop configurations
• The AC gain is not constant, Changes with supply, Changes with h-parameters,
and Age of device.
• The input and output impedances are not according to the requirement of the
basic amplifiers.
• Effect of distortion and noise is more.
• Bandwidth is not sufficiently large.
• These limitations are avoided by providing feedback.
Prof.Mrunalini Pimpale 66

67. VIRTUAL GROUND CONCEPT
• If AV is very large (AV =Vo/Vi ) then Vi will be negligibly small for finite values of Vo.
• The point X is therefore effectively at ground potential and is referred to as a virtual earth
(Ground).
• Since the current drawn by the inverting input is negligibly small, we have that I1  I2.
• We have that the inverting input of the amplifier is effectively at ground potential - i.e. it is a
virtual earth.
Therefore it is possible to write:
1
1
R
V
I s

Prof.Mrunalini Pimpale 67