Linear Integrated Circuits

1. Unit- I - BASICS OF OPERATIONAL AMPLIFIERS
EC3451 - Linear Integrated Circuits

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4. Advantages of integrated circuits
1. Miniaturization and hence increased equipment
density.
2. Cost reduction due to batch processing.
3. Increased system reliability due to the elimination of
soldered joints.
4. Improved functional performance.
5. Matched devices.
6. Increased operating speeds.
7. Reduction in power consumption
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5. Basic processes involved in fabricating Monolithic
ICs
1. Silicon wafer (substrate) preparation
2. Epitaxial growth
3. Oxidation
4. Photolithography
5. Diffusion
6. Ion implantation
7. Isolation technique
8. Metallization
9. Assembly processing & packaging
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6. AIC– Module 1

7. Silicon wafer (substrate) preparation
• A wafer, also called a slice or substrate,
is a thin slice of semiconductor material,
such as a crystalline silicon, used in
electronics for the fabrication of
integrated circuits and in photovoltaics
for conventional, wafer-based solar cells.
• The wafer serves as the substrate for
microelectronic devices built in and
over the wafer and undergoes many micro
fabrication process steps such as doping or
ion implantation, etching, deposition of
various materials, and photolithographic
patterning. Typical wafer
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8. Photolithography
The process of photolithography makes it possible to produce microscopically small
circuit and device pattern on si wafer.
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9. OP-AMP
• An operational amplifier (often op-amp or opamp) is a DC-coupled
high-gain electronic voltage amplifier with a differential input and,
usually, a single-ended output.
• In this configuration, an op-amp produces an output potential (relative
to circuit ground) that is typically hundreds of thousands of times larger
than the potential difference between its input terminals.
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10. • Operational Amplifier is represented schematically below:
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11. INTERNAL CONNECTION OF OP-AMP
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12. AIC– Module 1

13. BLOCK DIAGRAM OF OP-AMP
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14. Current mirror and current sources
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Q1 & Q2 – Identical or Matched Transistors

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19. Improved Current Source Circuit
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High resistance Current
Sources

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21. WILSON CURRENT SOURCE
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Current sources as Active loads
The current source can be used as an active load in both analog and digital IC‘s.
The active load realized using current source in place of the passive load (i.e. a
resistor) in the collector arm of differential amplifier makes it possible to achieve high
voltage gain without requiring large power supply voltage.

26. Differential Amplifier
• A differential amplifier is a type of electronic amplifier that amplifies the
difference between two input voltages but suppresses any voltage common
to the two inputs.
• It is an analog circuit with two inputs and and one output in which the
output is ideally proportional to the difference between the two voltages.
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29. Real time Example
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Constructed using Emitter Biased
Circuits

31. Dual- Input, balanced output Differential
amplifier
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34. AIC– Module 1

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D.C. Analysis - Differential Amplifier

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Collector Voltage

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A.C. Analysis - Differential Amplifier - Ad, Ac, Ri, Ro

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Substitute Ib Vaue

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To improve diferential mode
gain
Current mirror has high a.c.
resistance
Current mirror circuit acting as
load provides high a.c resistance

50. OP-AMP
• An operational amplifier (often op-amp or opamp) is a DC-coupled
high-gain electronic voltage amplifier with a differential input and,
usually, a single-ended output.
• In this configuration, an op-amp produces an output potential (relative
to circuit ground) that is typically hundreds of thousands of times larger
than the potential difference between its input terminals.
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51. • Operational Amplifier is represented schematically below:
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52. INTERNAL CONNECTION OF OP-AMP
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53. Ideal Op-amp Characteristics
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54. GENERAL OPERATIONAL-AMPLIFIER STAGES
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INPUT STAGE OPERATIONAL-AMPLIFIER
Q1 to Q4 – Part of Differential amplifier inputs
Q5, Q6,Q8,Q9 – Current Source
Q7 – Supplies Base current

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Intermediate Stage –
Differential Amplifier –
Additional Gain

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Class AB or Class B Push-Pull
Amplifier used as output stage
Level Shifting operation

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Q14 & Q20 – Complementary Emitter
Follower
Q18 & Q19 _ Darlington Pair
Q15 & Q21 – Active Current Limiting

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60. DC Characteristics of Op-Amp
• Input bias current
• Input offset -current
• Input offset voltage
• Thermal drift
Note:
The op-amp input is made up of differential amplifiers, which can be
made of BJT or FET.
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Input bias current

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66. Input offset voltage
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In spite of the use of the above compensating techniques, it is found
that the output voltage may still not be zero with zero input voltage
[Vo ≠ 0 with Vi= 0].
This is due to unavoidable imbalances inside the op-amp and one may
have to apply a small voltage at the input terminal to make output
(Vo) = 0.

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Total Output offset voltage

68. Thermal drift
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 Bias current, offset current, and offset voltage change with
temperature.
 A circuit carefully nulled at 25ºC may not remain. So when the
temperature rises to 35ºC. This is called drift.
 Offset current drift is expressed in nA/ºC.
 These indicate the change in offset for each degree Celsius change in
temperature.

69. AC Characteristics of Op-Amp
• Frequency Response
• Slew Rate
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Frequency Response
The variation in operating frequency will cause variations in gain
magnitude and its phase angle.
The manner in which the gain of the op-amp responds to different
frequencies is called the frequency response

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The op-amp gain decreases (roll-off) at higher frequency what reasons to decrease
gain after a certain frequency reached.
There must be a capacitive component in the equivalent circuit of the op-amp.
For an op-amp with only one break (corner) frequency all the capacitors effects can
be represented by a single capacitor C.

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From the phase characteristics that the phase angle is zero at frequency f = 0. At the
corner frequency f1 the phase angle is -45 (lagging and an infinite frequency the phase
angle is -90 .
 It shows that a maximum of 90 phase change can occur in an op-amp with a single
capacitor C.
Zero frequency is taken as the decade below the corner frequency and infinite
frequency is one decade above the corner frequency.

73. Stability of Op-amp
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74. Frequency Compensation
• The Network System formed to compensate the unstable system is
called compensating network
• Modifies the rate of change of gain and phase of op-amp
• Methods
• External Compensation
• Internal Compensation
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External Compensation

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A’

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A’

79. Voltage Sources
• A voltage source is a circuit that produces an output voltage V0,
which is independent of the load driven by the voltage source, or the
output current supplied to the load.
• The voltage source is the circuit dual of the constant current source
• Methods
1.Using the impedance transforming properties of the transistor, which
in turn determines the current gain of the transistor
2. Using an amplifier with negative feedback.
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81. Voltage References
• The circuit that is primarily designed for providing a constant voltage
independent of changes in temperature is called a voltage reference
Properties of a Voltage Reference
• Reference voltage must be independent of any temperature change.
• Reference voltage must have good power supply rejection which is as
independent of the supply voltage as possible
• the circuit should have low output impedance
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84. Configurations of Op-amp
• Open Loop
• Closed Loop
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Closed Loop

86. in
f
in
in
f
out
R
R
A
V
R
R
V 



The Inverting Amplifier
86

87. Analyzing the Inverting Amplifier
inverting input (-):
non-inverting input (+):
1)
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88. :
:
)
1


Inverting Amplifier Analysis
in
f
in
out
f
out
in
in
B
A
A
f
out
B
in
B
in
R
R
V
V
R
V
R
V
V
V
V
R
V
V
R
V
V
R
V
i














0
)
3
0
:
:
)
2
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89. g
f
in
g
f
out
R
R
A
V
R
R
V












1
1
The Non-Inverting Amplifier
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90. Analysis of Non-Inverting Amplifier
g
f
in
out
g
g
f
in
out
out
g
f
g
in
B
A
out
g
f
g
B
in
A
R
R
V
V
R
R
R
V
V
V
R
R
R
V
V
V
V
R
R
R
V
V
V












1
)
3
:
:
)
2
Note that step 2 uses a voltage divider to find the
voltage at VB relative to the output voltage.
:
:
)
1


90

91. MOSFET Operational Amplifiers – LF155 and
TL082
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