Dr.N.G.P.

Institute of Technology Electronics and Communication

Engineering

Dr. N.G.P. INSTITUTE OF TECHNOLOGY

Coimbatore-641048

DEPARTMENT OF
ELECTRONICS AND COMMUNICATION ENGINEERING

TWO MARKS WITH ANSWERS

EC8453 / LINEAR INTEGRATED CIRCUITS

REGULATION: 2017

Prepared by

Ms.C.Karthika, AP/ECE

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 Dr.N.G.P. Institute of Technology Electronics and Communication
Engineering
SYLLABUS

EC8453 LINEAR INTEGRATED CIRCUITS

OBJECTIVES:

To introduce the basic building blocks of linear integrated circuits.

To learn the linear and non-linear applications of operational amplifiers.
To introduce the theory and applications of analog multipliers and PLL.
To learn the theory of ADC and DAC.
To introduce the concepts of waveform generation and introduce some special
function ICs.

UNIT I BASICS OF OPERATIONAL AMPLIFIERS 9

Current mirror and current sources, Current sources as active loads, Voltage sources, Voltage References,
BJT Differential amplifier with active loads, Basic information about op-amps – Ideal Operational
Amplifier - General operational amplifier stages -and internal circuit diagrams of IC 741, DC and AC
performance characteristics, slew rate, Open and closed loop configurations.
UNIT II APPLICATIONS OF OPERATIONAL AMPLIFIERS 9
Sign Changer, Scale Changer, Phase Shift Circuits, Voltage Follower, V-to-I and I-to-V converters, adder,
subtractor, Instrumentation amplifier, Integrator, Differentiator, Logarithmic amplifier, Antilogarithmic
amplifier, Comparators, Schmitt trigger, Precision rectifier, peak detector, clipper and clamper, Low-pass,
high-pass and band-pass Butterworth filters.

UNIT III ANALOG MULTIPLIER AND PLL 9

Analog Multiplier using Emitter Coupled Transistor Pair - Gilbert Multiplier cell – Variable
transconductance technique, analog multiplier ICs and their applications, Operation of the basic PLL,
Closed loop analysis, Voltage controlled oscillator, Monolithic PLL IC 565, application of PLL for AM
detection, FM detection, FSK modulation and demodulation and Frequency synthesizing.
UNIT IV ANALOG TO DIGITAL AND DIGITALTO ANALOG CONVERTERS 9
Analog and Digital Data Conversions, D/A converter – specifications - weighted resistor type, R-2R
Ladder type, Voltage Mode and Current-Mode R 2R Ladder types - switches for D/A converters, high
speed sample-and-hold circuits, A/D Converters – specifications - Flash type - Successive Approximation
type - Single Slope type – Dual Slope type - A/D Converter using Voltage-to-Time Conversion - Over-
sampling A/D Converters.

UNIT V WAVEFORM GENERATORS AND SPECIAL FUNCTION ICS

Sine-wave generators, Multivibrators and Triangular wave generator, Saw-tooth wave generator, ICL8038
function generator, Timer IC 555, C Voltage regulators – Three terminal fixed and adjustable voltage
regulators - IC 723 general purpose regulator - Monolithic switching regulator, Switched capacitor filter
IC MF10, Frequency to Voltage and Voltage to Frequency converters, Audio Power amplifier, Video
Amplifier, Isolation Amplifier, Opto-couplers and fibre optic IC.

OUTCOMES: Upon Completion of the course, the students will be able to:
• Design linear and nonlinear applications of op– amps.
• Design applications using analog multiplier and PLL.
• Design ADC and DAC using op– amps.
• Generate waveforms using op – amp circuits.
• Analyze special function ICs.

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Engineering

TEXTBOOKS:
1. D.Roy Choudhry,Shail Jain,“Linear Integrated Circuits”,New Age International Pvt.Ltd.,2000.
2. Sergio Franco,“Design with Operational Amplifiers and Analog Integrated Circuits”,3rd
Edition, Tata McGraw- Hill,2007.

REFERENCES:

1. Ramakant A.Gayakwad,“OP-AMP and Linear ICs”,4th Edition, Prentice Hall/ Pearson

Education,2001.
2. RobertF.Coughlin,Frederick F.Driscoll,“Operational Amplifiers and Linear Integrated
Circuits”, Sixth Edition, PHI, 2001.
3. B.S.Sonde,“System design using IntegratedCircuits”,2nd Edition,NewAge Pub,2001
4. Gray and Meyer,“Analysis and Design of Analog Integrated Circuits”,Wiley International,2005.
5. Michael Jacob, “Applications and Design with Analog Integrated Circuits”, Prentice Hall of
India, 1996.
6. William D.Stanley,“Operational Amplifiers with Linear Integrated Circuits”, Pearson
Education,2004.
7. S.Salivahanan &V.S. Kanchana Bhaskaran, “Linear Integrated Circuits”, TMH,2008.

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Dr.N.G.P. Institute of Technology Electronics and Communication Engineering
EC8453 LINEAR INTEGRATED CIRCUITS

UNIT I BASICS OF OPERATIONAL AMPLIFIERS

Current mirror and current sources, Current sources as active loads, Voltage sources,
Voltage References, BJT Differential amplifier with active loads, Basic information about
op-amps – Ideal Operational Amplifier- General operational amplifier stages -and
internal circuit diagrams of IC 741, DC and AC performance characteristics, slew rate,
Open and closed loop configurations.

1. Define an Integrated circuit.

An integrated circuit(IC) is a miniature, low cost electronic circuit consisting of active
and passive components fabricated together on a single crystal of silicon. The active
components are transistors and diodes and passive components are resistors and capacitors.

2. What is OPAMP?
An operational amplifier is a direct coupled high gain amplifier consisting of one or
more differential amplifiers, followed by a level translator and an output stage. It is a versatile
device that can be used to amplify ac as well as dc input signals & designed for computing
mathematical functions such as addition, subtraction , multiplication, integration &
differentiation.

3. What are the applications of current sources? [APR/MAY 2015]

Transistor current sources are widely used in analog ICs both as biasing elements and as load
devices for amplifier stages.

4. Justify the reasons for using current sources in integrated circuits. [APR/MAY 2016]
 Superior insensitivity of circuit performance to power supply variations and
temperature.
 More economical than resistors in terms of die area required to provide bias currents of
small value.
 When used as load element, the high incremental resistance of current source results in
high voltage
 Gain at low supply voltages.

5. What is the advantage of widlar current source over constant current source?
[NOV/DEC 2017]
Using constant current source output current of small magnitude (microamp range) is not
attainable due to the limitations in chip area. Widlar current source is useful for obtaining
small output currents. Sensitivity of widlar current source is less compared to constant current
source.

6. Define sensitivity. Mention the advantages of Wilson current source. [APR/MAY 2015]
Sensitivity is defined as the percentage or fractional change in output current per percentage
or fractional change in power-supply voltage.
* provides high output resistance.
* offers low sensitivity to transistor base currents.

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7. Draw the pin configuration of IC741. [APR/MAY 2017]

8. List out the ideal characteristics of OPAMP?[NOV/DEC 2015]

( i)Open loop gain infinite
(ii)Input impedance infinite
(iii)Output impedance low
(iv)Bandwidth infinite
(v)Zero offset, ie, Vo=0 when V1=V2=0

9. What are the different kinds of packages of IC741?

a) Metal can (TO)package
b)Dual-in-line package
c)Flat package or flat pack

10. What are the assumptions made from ideal op amp characteristics?
i)The current drawn by either of the input terminals(non- inverting/inverting) is negligible.
ii)the potential difference between the inverting & non-inverting input terminals is zero.

11. Mention some of the linear applications of op – amps: [NOV/DEC 2016]

Adder, subtractor, voltage –to- current converter, current –to- voltage converters,
instrumentation amplifier, analog computation, power amplifier, etc are some of the linear op-
amp circuits.

12. Mention some of the non – linear applications of op-amps:-

Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti –
log amplifier, multiplier are some of the non – linear op-amp circuits.

13. What are the areas of application of non-linear op- amp circuits? [APR/MAY 2016]
i. Industrial instrumentation
ii. Communication
iii. Signal processing

14. What happens when the common terminal of V+ and V- sources is

not grounded? [APR/MAY 2017]
If the common point of the two supplies is not grounded, twice the supply voltage will
get applied and it may damage the op-amp.

15. Define input offset voltage. [NOV/DEC 2015]

A small voltage applied to the input terminals to make the output voltage as zero when
the two input terminals are grounded is called input offset voltage.

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16. Define input offset current. State the reasons for the offset currents at the input of the
op-amp.
The difference between the bias currents at the input terminals of the op-amp is called
as input offset current. The input terminals conduct a small value of dc current to bias the input
transistors. Since the input transistors cannot be made identical, there exists a difference in bias
currents.

17. Define CMRR of an op-amp.[APR 2013 ,NOV 2010,APR2011]

The relative sensitivity of an op-amp to a difference signal as compared to a common –
mode signal is called the common –mode rejection ratio. It is expressed in decibels.
CMRR= Ad/Ac
18. In practical op-amps, what is the effect of high frequency on its performance?
The open-loop gain of op-amp decreases at higher frequencies due to the presence of
parasitic capacitance. The closed-loop gain increases at higher frequencies and leads to
instability.

19. What is the need for frequency compensation in practical op-amps?[NOV 2010]
Frequency compensation is needed when large bandwidth and lower closed loop gain is
desired. Compensating networks are used to control the phase shift and hence to improve the
stability.

20. Mention the frequency compensation methods. [NOV/DEC 2016]

*Dominant-pole compensation, *Pole-zero compensation.

21. What are the merits and demerits of Dominant-pole compensation?

*noise immunity of the system is improved.
*Open-loop bandwidth is reduced.

22. Define slew rate.[APR 2014 ,NOV2010,NOV 2011]

The slew rate is defined as the maximum rate of change of output voltage caused by a
step input voltage. An ideal slew rate is infinite which means that op-amp’s output voltage
should change instantaneously in response to input step voltage.

23. Why IC 741 is not used for high frequency applications?

IC741 has a low slew rate because of the predominance of capacitance present in the
circuit at higher frequencies. As frequency increases the output gets distorted due to limited
slew rate.

24. What causes slew rate? [NOV/DEC 2017]

There is a capacitor with-in or outside of an op-amp to prevent oscillation. It is this
capacitor which prevents the output voltage from responding immediately to a fast changing
input.

25. Define thermal drift. [NOV/DEC 2015]

The bias current, offset current & offset voltage change with temperature. A circuit
carefully nulled at 25oC may not remain so when the temperature raises to 35oC.This is called
thermal drift . Often, offset current drift is expressed in nA/ oC and offset voltage drift in
mV/ oC.

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26. Define supply voltage rejection ratio (SVRR).

The change in OPAMP’s input offset voltage due to variations in supply voltage is
called the supply voltage rejection ratio. It is also called Power Supply Rejection Ratio (PSRR)
or Power Supply Sensitivity (PSS).

27. Draw the Circuit symbol of Ideal Op-amp.

The Ri is equal to ∞W, the voltage across Ri is 0V.

v1 = v2
vd = 0 V

28. Differentiate between ideal inverting and non-inverting op-amp.[NOV2010]

Ideal Inverting amplifier Ideal non-inverting amplifier

1. Voltage gain=-Rf/R1 1. Voltage gain=1+Rf/R1
2. The output is inverted with 2. No phase shift between input and output
respect to input
3. The voltage gain can be 3. The voltage gain is always greater than
adjusted as greater than, equal to one
or less than one
4. The input impedance is R1 4. The input impedance is very large

29. State the Effects of Feedback on Op-amp Circuits.

 Negative feedback reduces gain from A to A/(1 + AB)
 In return for this loss of gain we get consistency, provided that the open-loop gain is
much greater than the closed-loop gain (that is, A >> 1/B)
 Using negative feedback, standard cookbook circuits can be used – greatly simplifying
design
 These can be analyzed without a detailed knowledge of the op-amp itself

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30. State the selection of different packages of IC.

Type Criteria
Metal can 1. Heat dissipation is important
package 2. For high power applications like power amplifiers, voltage
regulators etc.
DIP 1. For experimental or bread boarding purposes as easy to mount
2. If bending or soldering of the leads is not required
3. Suitable for printed circuit boards as lead spacing is more
Flat pack 1. More reliability is required
2. Light in weight
3. Suited for airborne applications

31. What is meant by differential Input resistance?

It is the equivalent resistance measured at either the inverting or non inverting input
terminal with the other input terminal grounded

32. Define Power Supply Rejection Ratio.

PSRR is defined as the ratio of the change in input offset voltage due to the change in
supply voltage producing it, keeping the other power supply voltage constant. It is also called
as power supply sensitivity (PSV)

33. What do you mean by Average temperature coefficient of offset parameters?

The average rate of change of input offset voltage per unit change in temperature is called
average temperature coefficient of input offset voltage or input offset voltage drift.
It is measured in µV/oC. For 741 C it is 0.5 µV/oC
The average rate of change of input offset current per unit change in temperature is called
average temperature coefficient of input offset current or input offset current drift.
It is measured in nA/oC or pA/oC . For 741 C it is 12 pA/oC

34. What is meant by Thermal Voltage Drift?

It is defined as the average rate of change of input offset voltage per unit change in
temperature. It is also called as input offset voltage drift

35. What are the advantages of ICs over discrete circuits?

1. Minimization & hence increased equipment density.
2. Cost reduction due to batch processing.
3. Increased system reliability
4. Improved functional performance.
5. Matched devices.
6. Increased operating speeds
7. Reduction in power consumption

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UNIT II APPLICATIONS OF OPERATIONAL AMPLIFIERS

Sign Changer, Scale Changer, Phase Shift Circuits, Voltage Follower, V-to-I and I-to-V
converters, adder, subtractor, Instrumentation amplifier, Integrator, Differentiator,
Logarithmic amplifier, Antilogarithmic amplifier, Comparators, Schmitt trigger,
Precision rectifier, peak detector, clipper and clamper, Low-pass, high-pass and band-
pass Butterworth filters.

PART-A
1. Classify the Op-Amp circuit based on amplifications.
 Linear op-amp circuits
 Non-linear op-amp circuits

2. List the linear applications of an op-amp. [APR/MAY 2015]

Adder, subtractor, sign/phase changer, V to I converter, C to V converter, Instrumentation
Amplifier, and power amplifier.

3. List the linear applications of an op-amp.

Log amplifiers, Rectifier, peak detectors, Clipper, Clamper, S &H circuit and Multiplier.

4. What does mean for sign changer?

 In the ideal inverting amplifier if Rf=R1,then the gain is Acl=-1.
 Thus the magnitude of output is same as that of input but its sign is opposite to that
of the input. The Vo=-Vin for Rf=R1.

5. Draw the Scale changer Circuit using IC741. [NOV/DEC 2016]

Rf
Ra

Vo
Vin ~ +

6. What is phase shifter Circuits? [APR/MAY 2017]

 The phase shift circuits produce phase shifts that depend on the frequency and
maintain a constant gain.
 These circuits are also called constant-delay filters or all-pass filters.
 That constant delay refers to the fact the time difference between input and output
remains constant when frequency is changed over a range of operating frequencies.
This is called all-pass because normally a constant gain is maintained for all the
frequencies within the operating range.

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7. Draw the voltage follower circuit. [APR/MAY 2015]

8. Define current – series negative feedback amplifier.

Voltage to current converter in which load resistor RL is floating (not connected to
ground).Vin is applied to the non inverting input terminal and the feedback voltage across
R1 devices the inverting input terminal. This circuit is also called as a current – series
negative feedback amplifier.

9. Mention the applications V to I converter. [APR/MAY 2016]

 Low voltage ac and dc voltmeters
 Diode match finders
 LED
 Zener diode testers.

10. What is summing amplifier? [NOV/DEC 2016]

Op-amp may be used to design a circuit whose output is the sum of several input signals.
Such a circuit is called a summing amplifier or a summer. The Inverting Summing
Amplifier and Non-Inverting Summing Amplifier are types of summer.

11. State the function Subtractor.

A basic differential amplifier can be used as a subtractor and its derived from linear
amplifier. If all resistors are equal in value, then the output voltage can be derived by using
superposition principle. To find the output V01 due to V1 alone, make V2 = 0. Similarly
the output V02 due to V2 alone (with V1 grounded) can be written simply for an inverting
amplifier as V 02 =@V 2.Thus the output voltage Vo due to both the inputs can be written
as V o = V 01 + V 02 = V 1@V 2.

12. What is meant by Instrumentation amplifier?[APR 2013] [NOV/DEC 2015]

Instrumentation amplifier is an amplifier that realizes high input impedance and very low
offset and drift voltage values. This configuration is better than inverting or non-inverting
amplifier because it has minimum non-linearity, stable voltage gain and high CMRR
(> 100 dB). This type of amplifier is used at output side of thermocouples, strain gauges
and biomedical probes.
13. What is the need for an instrumentation amplifier?[APR 2011] [APR/MAY 2017]
In a number of industrial and consumer applications, the measurement of physical
quantities is usually done with the help of transducers. The output of transducer has to be
amplified So that it can drive the indicator or display system. This function is performed by
an instrumentation amplifier.

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14. List the features of instrumentation amplifier:

i. High gain accuracy
ii. High CMRR
iii. High gain stability with low temperature co-efficient
iv. Low dc offset
v. Low output impedance.

15. Draw the frequency response of Integrator.

16. What is differentiator? Write the limitations of basic differentiator.[APR 2010]

The circuit that performs mathematical operation of differentiation is known as
differentiator or differentiating amplifier. The output waveform is the derivative of input
waveform.
Basic differentiator using op-amp becomes unstable at high frequency. At high
frequency, a differentiator may become unstable and break into oscillations. It is sensitive
to high frequency noise because of low output impedance at high frequency. By nature a
differentiator is more susceptible to noise in the input than an integrator, since the slope of
the input signal will vary wildly with the introduction of noise spikes.

17. List the applications of Log amplifiers: [APRIL-2011]

Analog computation may require functions such as lnx, log x, sin hx etc. These
functions can be performed by log amplifiers Log amplifier can perform direct dB display on
digital voltmeter and spectrum analyzer Log amplifier can be used to compress the dynamic
range of a signal .

18. Define Log amplifier. [NOV/DEC 2017]

Log amplifier is a non linear op-amp circuits, in which the output voltage produced
proportional to logarithm of input signal.

19. What is a comparator?[MAY 2012,NOV2012]

A comparator is a circuit which compares a signal voltage applied at one input of an
opamp with a known reference voltage at the other input. It is an open loop op - amp with
output + Vsat .

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20. What are the applications of comparator?

1. Zero crossing detectors
2. Window detector
3. Time marker generator
4. Phase detector

21. What is a Schmitt trigger?

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square
wave output. The output of Schmitt trigger swings between upper and lower threshold
voltages, which are the reference voltages of the input waveform.

22. What do you mean by a precision diode? [NOV/DEC 2015]

The major limitation of ordinary diode is that it cannot rectify voltages below the cut –
in voltage of the diode. A circuit designed by placing a diode in the feedback loop of an op –
amp is called the precision diode and it is capable of rectifying input signals of the order of
mill volt.

23. Write down the applications of precision diode.

Half - wave rectifier
Full - Wave rectifier
Peak – value detector
Clipper
Clamper

24. What is meant by clipper?

Clipper is a circuit which shapes the input signal by removing certain part. It is used in
digital computers and communications equipments.

25. Draw the positive clamper circuit.

26. What are the different types of filters?

Based on functions : Low pass filter, High pass filter, Band pass filter, Band
reject filter.
Based on order of transfer function : first, second, third higher order filters.
Based on configuration : Bessel, Chebychev, Butterworth filters.

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27. List out the steps involved for the design of active LPF. [APR/MAY 2016]
o The value of high cut off frequency fH is chosen.
o The value of capacitor C is selected such that its value is ≤1F.
o By knowing the values of fH and C, the value of R can be calculated using


o Finally the values of R1 and Rf are selected depending on the designed
pass band gain by using

28. Draw the high pass filter circuit and characteristics. [NOV/DEC 2017]

29. Draw characteristics of Butterworth filters.

30. What is an active filter?

Adding capacitors to op-amp circuits provides external control of the cutoff frequencies
The op-amp active filter provides controllable cutoff frequencies and controllable gain.
Low-pass filter
High-pass filter
Band pass filter
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31. Write down the condition for good differentiation .

1.For good differentiation, the time period of the input signal must be greater than or
equal to Rf C1
2.T > Rf C1 Where, Rf is the feedback

resistance 3.Cf is the input capacitance

32. What is a comparator? [MAY 2010]

A comparator is a circuit which compares a signal voltage applied at one input of an
op-amp with a known reference voltage at the other input. It is an open loop op - amp with
output + Vsat .

33. Define Bandpass filter. (MAY 2010)

The bandpass filter is the combination of high and low pass filters, and this
allows a specified range of frequencies to pass through.

34. Write transfer function of op amp as an integer. (MAY 2010)

The transfer function of the integer is
│A│=1/ωR1cf

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UNIT III ANALOG MULTIPLIER AND PLL

Analog Multiplier using Emitter Coupled Transistor Pair - Gilbert Multiplier cell –
Variable transconductance technique, analog multiplier ICs and their applications,
Operation of the basic PLL, Closed loop analysis, Voltage controlled oscillator,
Monolithic PLL IC 565, application of PLL for AM detection, FM detection, FSK
modulation and demodulation and Frequency synthesizing.

1. What is an analog multiplier? [APR/MAY 2016]

Analog multiplier is an active network which is produces an output proportional to the
multiplication of two inputs V1 and V2. Based on the input it is divided into two types
voltage multiplier and current multiplier.

2. What is Gilbert multiplier circuit?

There is a linear relationship between the collector current of a silicon junction transistor
and its transconductance (gain) which is given by
dIC / dVBE = qIC / kT,
where IC = the collector current, VBE = the base-emitter voltage, q = the electron charge
(1.60219 × 10–19), k = Boltzmann's constant (1.38062 × 10–23), T = the absolute
temperature.

3. Mention features of the Gilbert Cell. [APR/MAY 2015]

Gilbert Cell has three inconvenient features: (1) its X input is a differential current; (2) its
output is a differential current; and (3) its Y input is a unipolar current—so the cell is only
a two quadrant multiplier.

4. Draw the multipliers with op amps circuit to perform arithmetic functions.

[NOV/DEC 2015]

5. What are the two types of analog multiplier ICs?

a) IC AD 533
b) IC AD 534

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6. Draw the multipliers with op amps circuit to perform division. [APR/MAY 2017]

7. What are the two types of analog multiplier ICs?

a) IC AD 533
b) IC AD 534

8. What is ICAD 533?

It is a multiplier IC by analog devices. It is a low cost IC comprising a
transconductance multiplying element, stable reference and an output amplifier.

9. List the features of ICAD533.

1. Its operation is very simple.
2. Only 4 external adjustments are necessary
3.Maximum 4 quadrant error is below 0.5%

10. What is ICAD 534?

It is a multiplier IC by analog devices. It is the first general purpose multiplier capable
of providing gain up to X100.

11. List the features of IC AD534. [NOV/DEC 2016]

 Adjustable scale factor
 Low noise
 Excellent long time stability

12. List the few applications of IC AD534.

 Multiplier
 Divider
 High quality signal processing

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13. Define PLL. [APR/MAY 2015]
A phase-locked loop (PLL) is an electronic circuit with a voltage- or current-driven
oscillator that is constantly adjusted to match in phase (and thus lock on) the frequency of
an input signal. Phase locked loop (PLL) is a controlled oscillator whose instantaneous
frequency is dynamically adjusted through feedback and filtering

14. What are the major components of PLL?[APR2014]

Three fundamental components: the voltage-controlled oscillator (VCO), the phase
detector (PD), and the amplified loop filter. A PLL is a negative feedback system where an
oscillator-generated signal is phase and frequency locked to a reference signal.

15. Draw the circuit block diagram of basic PLL. [NOV/DEC 2015]

16. List out the common applications of PLL.[APR2013]

PLL can be used to generate a signal, modulate or demodulate a signal, reconstitute a
signal with less noise, or multiply or divide a frequency. PLLs are frequently used in
wireless communication, particularly where signals are carried using frequency modulation
(FM) or phase modulation (PM). PLLs can also be used in amplitude modulation (AM).
PLLs are more commonly used for digital data transmission, but can also be designed for
analog information. Phase-locked loop devices are more commonly manufactured as
integrated circuits (ICs) although discrete circuits are used for microwave.

17. Mention the function of control circuit in PLL

In phase lock, the control circuit, i.e., the PD, amplifier, and filter, continuously adjust the
VCO frequency to match the input frequency.

18. Define duty cycle?

The ratio of high output and low output period is given by a mathematical parameter
called duty cycle. It is defined as the ratio of ON Time to total time.

19. Define VCO.[APR 2010] [APR/MAY 2016]

A voltage controlled oscillator is an oscillator circuit in which the frequency of
oscillations can be controlled by an externally applied voltage. A Voltage-Controlled
Oscillator (VCO) is a circuit that provides a varying output signal (typically of square-wave or
triangular-wave form) whose frequency can be adjusted over a range controlled by a dc voltage

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20. List the features of 566 VCO. [APR/MAY 2015]
 Wide supply voltage range(10-24V)
 Very linear modulation characteristics
 High temperature stability

21. What does mean by PLL?

A PLL is a basically a closed loop system designed to lock output frequency and phase
to the frequency and phase of an input signal.

22. Define lock range.[MAY 2010]

When PLL is in lock, it can trap freq changes in the incoming signal. The range of
frequencies over which the PLL can maintain lock with the incoming signal is called as
lock range. The lock range specifies frequency limits beyond which a “locked” loop will
become “unlocked,” i.e., the output frequency will no longer track the input frequency.

23. Define capture range. [APR/MAY 2017]

The range of frequencies over which the PLL can acquire lock with the input signal is
called as capture range.
24. Define pull-in time.
The total time taken by the PLL to establish lock is called pull-in time.

25. List the applications of 565 PLL.

Frequency multiplier
Frequency synthesizer
FM detector

26. What Does PLL Bandwidth Mean?

 PLL acts as a low-pass filter with respect to the reference.
 Low-frequency reference modulation (e.g.spread-spectrum clocking) is passed to
the VCO clock.
 “Bandwidth” is the frequency at which the PLL begins to lose lock with the
reference (-3dB).
 PLL acts as a high-pass filter wrt VCO noise.

27. Classify the phase detector.

Analog phase detector
Digital phase detector

28. Draw the Connection diagram of VCO. [NOV/DEC 2017]

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29. Draw the block diagram of VCO.

30. For perfect lock, what should be the phase relation between the incoming
signal and VCO output signal?
The VCO output should be 90 degrees out of phase with respect to the input
signal.

31. Define Voltage to Frequency conversion factor.

Voltage to Frequency conversion factor is defined as, Kv = fo / Vc= 8fo /Vcc

Vc is the modulation voltage fo frequency shift.
32. What is the purpose of having a low pass filter in PLL?

*It removes the high frequency components and noise.

*Controls the dynamic characteristics of the PLL such as
capture range, lock-in range,band-width and transient
response.
*The charge on the filter capacitor gives a short- time memory to the PLL

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33. Discuss the effect of having large capture range.

The PLL cannot acquire a signal outside the capture range, but once captured, it will
hold on till the frequency goes beyond the lock-in range.Thus , to increase the ability
of lock range,large capture range is required.But, a large capture range will make the PLL
more susceptible to noise and undesirable signal.

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UNIT IV ANALOG TO DIGITAL AND DIGITAL TO ANALOG CONVERTERS

Analog and Digital Data Conversions, D/A converter – specifications - weighted

resistor type, R-2R Ladder type, Voltage Mode and Current-Mode R 2R Ladder
types - switches for D/A converters, high speed sample-and-hold circuits, A/D
Converters – specifications - Flash type - Successive Approximation type - Single
Slope type – Dual Slope type - A/D Converter using Voltage-to-Time Conversion -
Over-sampling A/D Converters.

1. Name the essential parts of a DAC. [MAY 2010]

• Drive motors
• Analog devices
• Deglitcher
• Filter
2. Write down the drawback of weighted D/A converter. [APR/MAY 2016]
The main disadvantage of binary weighted D/A converter is the requirement of wide
range of resister values.As the length of the binary word is increased .the range of
resister values needed also increases.

3. State the advantages of dual slope ADC [DEC 2009]

It provides excellent noise rejection of ac signals whose periods are
integral multiples of the integration time T.

4. Define accuracy of converter. [MAY 2010]

Absolute accuracy:
It is the maximum deviation between the actual converter output & the
ideal converter output.
Relative accuracy:
It is the maximum deviation after gain & offset errors have been removed.
The accuracy of a converter is also specified in form of LSB increments or % of
full scale voltage.

5. What is settling time? [APR/MAY 2015]

It represents the time it takes for the output to settle within a specified band
±½LSB of its final value following a code change at the input (usually a full scale
change). It depends upon the switching time of the logic circuitry due to internal
parasitic capacitance & inductances. Settling time ranges from 100ns. 10µs
depending on word length & type circuit used.

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6. Where are the successive approximation type ADC’s used?
The Successive approximation ADCs are used in applications such as
data loggers & instrumentation where conversion speed is important.

7. What is the main drawback of a dual-slop ADC?[DEC 2009]

The dual slope ADC has long conversion time. This is the main drawback
of dual slope ADC

8. State the advantages of dual slope ADC(DEC 2009)

It provides excellent noise rejection of ac signals whose periods are integral multiples of
the integration time

9. What are the specifications of D/A converter?

The specifications are accuracy, offset voltage, monotonicity, resolution,
and settling time.

10. What is multiplying DAC? [APR/MAY 2017]

a. digital to analog converter which uses a varying reference voltage VR
is called a multiplying DAC(MDAC). If the reference voltage of a DAC, VR is a
sine wave given by
V(t)=Vin Cos 2 ft
Then, Vo(t)=VomCos(2 ft + 180º)

11. What is monotonic DAC?

A monotonic DAC is one whose analog output increases for an increase in
digital input.

12. List the broad classification of ADCs.

1. Direct type ADC.
2. Integrating type ADC.

13. List out the direct type ADCs. [APR/MAY 2016]

1. Flash (comparator) type converter
2. Counter type converter
3. Tracking or servo converter
4. Successive approximation type converter

14. List out some integrating type converters. [NOV/DEC 2015]

1. Charge balancing ADC
2. Dual slope ADC

15. What is integrating type converter?

An ADC converter that perform conversion in an indirect manner by first
changing the analog I/P signal to a linear function of time or frequency and then to a
digital code is known as integrating type A/D converter.

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16. Explain in brief the principle of operation of successive aproximation ADC.

The circuit of successive approximation ADC consists of a successive

approximation register (SAR), to find the required value of each bit by trial & error. With
the arrival of START command, SAR sets the MSB bit to 1. The O/P is converted into an
analog signal & it is compared with I/P signal. This O/P is low or high. This process
continues until all bits are checked.

17. What are the main advantages of integrating type ADCs?

The integrating type of ADC’s doing not need a sample/Hold circuit at the input.
form. It is possible to transmit frequency even in noisy environment or in an isolated

18. Define conversion time. [APR/MAY 2017]

It is defined as the total time required converting an analog signal into its digital
output. It depends on the conversion technique used & the propagation delay of circuit
components. The conversion time of a successive approximation type ADC is given by
T(n+1)
Where T-clock period ,
Tc---conversion time,
n- no. of bits

19. Define resolution of a data converter.[ NOV 2011 ,NOV 2014]

The resolution of a converter is the smallest change in voltage which may be
produced at the output or input of the converter.
Resolution (in volts)= VFS/2n-1=1 LSB increment. The resolution of an ADC is
defined as the smallest change in analog input for a one-bit change at the output.

20. Explain in brief stability of a converter:

The performance of converter changes with temperature age & power supply
variation. So all the relevant parameters such as offset, gain, linearity error &
monotonicity must be specified over the full temperature & power supply ranges to have
better stability performances.

21. What is meant by linearity? [NOV/DEC 2017]

The linearity of an ADC/DAC is an important measure of its accuracy & tells us
how close the converter output is to its ideal transfer characteristics. The linearity error is
usually expressed as a fraction of LSB increment or percentage of full-scale voltage. A
good converter exhibits a linearity error of less than ±½LSB.

22. What is a sample and hold circuit? Where it is used?

A sample and hold circuit is one which samples an input signal and holds on to its
last sampled value until the input is sampled again. This circuit is mainly used in digital
interfacing, analog to digital systems, and pulse code modulation systems.

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The time during which the voltage across the capacitor in sample and hold circuit
is equal to the input voltage is called sample period. The time period during which the
voltage across the capacitor is held constant is called hold period.

23. Which is the fastest ADC and why? [MAY 2010]

Simultaneous type A/D converter(flash type A/D converter) is the
fastest because A/D conversion is performed simultaneously through a set of
comparators .

24. What are the advantages and disadvantages of R-2R ladder DAC?[MAY 2010]
Advantage:
• Easier to build
• Number of bits can be expanded by adding more sections.
Disadvantage:
• More power dissipation makes heating, which in turns develops
non-linearties in DAC.

25. Give the disadvantages of flash type A/D converter.(MAY 2010)

The simultaneous type A/D converter is not suitable for A/D conversion
with more than 3 or 4 digital output bits. Then (2n-1)comparators are required for
an n-bit A/D converter and the number of comparators required doubles for each
added bit.
26. Define quantization error. [APR/MAY 2015]
In A/D converter the smallest digital step is due to the LSB and it can be
made smaller only by increasing the number of bits in the digital representation.
This error is called quantization error.

27. Define Dither.

It is a very small amount of random noise(white noise) which is added to
the input before A/D conversion to improve the performance of A/D converter.

28. Define Delta modulation. [NOV/DEC 2015]

Delta modulation is a technique in which derivative of the signal is
quantized. The delta modulation shows slope overload for fast input signals and
their performance is dependent on input signal frequency.

29. Define slope overload noise and granular noise. [NOV/DEC 2017]
Slope overload noise is introduced due to the use of a step size delta is too small
to follow some portions of the waveform with a step size.
Granular noise results from using a step size that is too large in parts of the
waveform having a small slope.

30. List out the uses of sigma delta A/D converters.

• High resolution
• Moderate speech applications such as digital audio, digital telephony
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Dr.N.G.P. Institute of Technology Electronics and Communication Engineering

UNIT V WAVEFORM GENERATORS AND SPECIAL FUNCTION ICS

Sine-wave generators, Multivibrators and Triangular wave generator, Saw-tooth

wave generator, ICL8038 function generator, Timer IC 555, IC Voltage regulators –
Three terminal fixed and adjustable voltage regulators - IC 723 general purpose
regulator - Monolithic switching regulator, Switched capacitor filter IC MF10,
Frequency to Voltage and Voltage to Frequency converters, Audio Power amplifier,
Video Amplifier, Isolation Amplifier, Opto-couplers and fibre optic IC.

1. What is a voltage regulator? [MAY 2010]

A voltage regulator is an electronic circuit that provides a stable dc voltage
independent of the load current, temperature, and ac line voltage variations.

2. Give the classification of voltage regulators:

*Series / Linear regulators
*Switching regulators.

3. What is a linear voltage regulator? [APR/MAY 2016]

Series or linear regulator uses a power transistor connected in series between the
unregulated dc input and the load and it conducts in the linear region .The output voltage
is controlled by the continuous voltage drop taking place across the series pass transistor.

4. What is a switching regulator? [NOV/DEC 2016]

Switching regulators are those which operate the power transistor as a high
frequency on/off switch, so that the power transistor does not conduct current
continuously. This give improved efficiency over series regulators.

5. What are the advantages of IC voltage regulators?

*low cost, high reliability, reduction in size and excellent performance.

6. Give some examples of monolithic IC voltage regulators:

 78XX series fixed output, positive voltage regulators
 79XX series fixed output, negative voltage regulators
 723 general purpose regulator.

7. What is the purpose of having input and output capacitors in three terminal IC
regulators?[NOV/DEC 2015]
A capacitor connected between the input terminal and ground cancels the inductive
effects due to long distribution leads. The output capacitor improves the transient
response.

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8. Define line regulation.

Line regulation is defined as the percentage change in the output voltage for a
change in the input voltage. It is expressed in mill volts or as a percentage of the output
voltage.

9. Define load regulation.

Load regulation is defined as the change in output voltage for a change in load current. It
is expressed in mill volts or as a percentage of the output voltage.

10. What is meant by current limiting?

Current limiting refers to the ability of a regulator to prevent the load current from
increasing above a preset value.

11. Give the drawbacks of linear regulators:

The input step down transformer is bulky and expensive because of low line
frequency. Because of low line frequency, large values of filter capacitors are required to
decrease the ripple. Efficiency is reduced due to the continuous power dissipation by the
transistor as it operates in the linear region.

12. What is the advantage of switching regulators?

Greater efficiency is achieved as the power transistor is made to operate as low
impedance switch. Power transmitted across the transistor is in discrete pulses rather than
as a steady current flow. By using suitable switching loss reduction technique, the
switching frequency can be increased so as to reduce the size and weight of the inductors
and capacitors.

13. What is an opto-coupler IC?

Opto-coupler IC is a combined package of a photo-emitting device and a photo-
sensing device.

14. What are the types of opto couplers? [NOV/DEC 2017]

 LED and a photo diode,
 LED and photo transistor,
 LED and Darlington.

15. Give two examples of IC optocouplers? [APR/MAY 2016]
Examples for opto-coupler IC
 MCT 2F
 MCT 2E .

16. Mention the advantages of opto-couplers: [APR/MAY 2017]

 Better isolation between the two stages.
 Impedance problem between the stages is eliminated.

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 Wide frequency response.

 Easily interfaced with digital circuit.
 Compact and light weight.
 Problems such as noise, transients, contact bounce, are eliminated.
17. What is an isolation amplifier?
An isolation amplifier is an amplifier that offers electrical isolation between its
input and output terminals.

18. What are the features of isolation amplifier?

Easy to use ,Ultra low leakage 18 pin DIP package

19. What is LM380?

It is a power amplifier produced by national semiconductor. It is capable of
delivering 2.5 W min, to 8 ohm load.

20. What are the features of MA78s40?[NOV 2011]

 Step up,step down or inverting operation
 Operation from 2.5 to 40 V.
 80Db line and load regulation.

21. What are the applications of 555 Timer? [NOV/DEC 2016]

1. astable multivibrator
2.monostable multivibrator
3.Missing pulse detector
.Linear ramp generator
5. Frequency divider
6.Pulse width modulation
7.FSK generator
8.Pulse position modularor
9. Schmitt trigger

22. List the applications of 555 timer in monostable mode of operation:

1. missing pulse detector
2. Linear ramp generator
3. Frequency divider
4. Pulse width modulation.

23. List the applications of 555 timer in Astable mode of operation:

*FSK generator
*Pulse-position modulator

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24. Define 555IC? [APR/MAY 2015]

The 555 timer is an integrated circuit specifically designed to perform signal
generation and timing functions.

24. List the basic blocks of IC 555 timer?

1. A relaxation oscillator
2. RS flip flop
3. Two comparator
4. Discharge transistor.

25. List the features of 555 Timer? [NOV/DEC 2017]

1. It has two basic operating modes: monostable and astble
2. It is available in three packages. 8 pin metal can , 8 pin dip, 14 pin dip.
3. It has very high temperature stability.

26.What is a multivibrator? [APR/MAY 2017]

Multivibrators are a group of regenerative circuits that are used extensively in
timing applications. It is a wave shaping circuit which gives symmetric or asymmetric
square output. It has two states either stable or quasi- stable depending on the type of
multivibrator.

27. What do you mean by monostable multivibrator?

Monostable multivibrator is one which generates a single pulse of specified
duration in response to each external trigger signal. It has only one stable state.
Application of a trigger causes a change to the quasi-stable state. An external trigger
signal generated due to charging and discharging of the capacitor produces the transition
to the original stable state.

28. What is an astable multivibrator? [APR/MAY 2015]

Astable multivibrator is a free running oscillator having two quasi-stable states.
Thus, there are oscillations between these two states and no external signal is required to
produce the change in state.

29. What is a bistable multivibrator? [NOV/DEC 2015]

Bistable multivibrator is one that maintains a given output voltage level unless an
external trigger is applied. Application of an external trigger signal causes a change of
state, and this output level is maintained indefinitely until a second trigger is applied.
Thus, it requires two external triggers before it returns to its initial state

30. What are the requirements for producing sustained oscillations in feedback
circuits?[APR 2012]
For sustained oscillations,
* The total phase shift around the loop must be zero at the desired
frequency of oscillation, fo. ie
*At fo, the magnitude of the loop gain should be equal to unity
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