NOORUL ISLAM COLLEGE OF ENGG, KUMARACOIL.

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGG.

SUBJECT CODE: EC 1254

SUBJECT NAME: Linear Integrated circuits

Prepared by,

Y.Ireaneus Anna Regani (Asst.Prof/ECE)

E.P.Kannan (Sr. Lect/ECE)

NOORUL ISLAM COLLEGE OF ENGINEERING, KUMARACOIL

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EC1254– LINEAR INTEGRATED CIRCUITS

(Fourth semester ECE)

UNIT-I CIRCUIT CONFIGURATION FOR LINEAR ICs

2 marks questions

1.Mention the advantages of integrated circuits.

*Miniaturisation and hence increased equipment density.

*Cost reduction due to batch processing.

*Increased system reliability due to the elimination of soldered joints.

*Improved functional performance.

*Matched devices.

*Increased operating speeds.

*Reduction in power consumption.

2.Write down the various processes used to fabricate IC’s using silicon planar

technology.

*Silicon wafer preparation.

* Epitaxial growth

*Oxidation.

*Photolithography.

*Diffusion.

*Ion implantation.

*Isolation.

*Metallisation.

*Assembly processing and packaging.

3.What is the purpose of oxidation?

*SiO2 is an extremely hard protective coating and is unaffected by almost all

reagents.

*By selective etching of SiO2, diffusion of impurities through carefully defined

windows can be accomplished to fabricate various components.

4.Why aluminium is preferred for metallization?

*It is a good conductor.

*it is easy to deposit aluminium films using vacuum deposition.

*It makes good mechanical bonds with silicon.

*It forms a low resistance contact.

5. What are the popular IC packages available?

Metal can package.

Dual-in-line package.

Ceramic flat package.

6. Define an operational amplifier.

An operational amplifier is a direct-coupled, high gain amplifier consisting of

one or more differential amplifier. By properly selecting the external components, it can

be used to perform a variety of mathematical operations.

7.Mention the characteristics of an ideal op-amp.

* Open loop voltage gain is infinity.

*Input impedance is infinity.

*Output impedance is zero.

*Bandwidth is infinity.

*Zero offset.

8.What happens when the common terminal of V+ and V- sources is not grounded?

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.

9.Define input offset voltage.

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.

10. 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.

11. Define CMRR of an op-amp.

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

12.What are the applications of current sources?

Transistor current sources are widely used in analog ICs both as biasing

elements and as load devices for amplifier stages.

13. Justify the reasons for using current sources in integrated circuits.

*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.

14. What is the advantage of widlar current source over constant current source?

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.

15.Mention the advantages of Wilson current source.

*provides high output resistance.

*offers low sensitivity to transistor base currents.

16.Define sensitivity.

Sensitivity is defined as the percentage or fractional change in output current

per percentage or fractional change in power-supply voltage.

17.What are the limitations in a temperature compensated zener-reference source?

A power supply voltage of atleast 7 to 10 V is required to place the diode in the

breakdown region and that substantial noise is introduced in the circuit by the

avalanching diode.

18.What do you mean by a band-gap referenced biasing circuit?

The biasing sources referenced to VBE has a negative temperature co-efficient

and VT has a positive temperature co-efficient. Band gap reference circuit is one in

which the output current is referenced to a composite voltage that is a weighted sum

of VBE and VT so that by proper weighting, zero temperature co-efficient can be

achieved.

19.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.

20. What is the need for frequency compensation in practical op-amps?

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.

21.Mention the frequency compensation methods.

*Dominant-pole compensation

*Pole-zero compensation.

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

*noise immunity of the system is improved.

*Open-loop bandwidth is reduced.

23.Define slew rate.

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.

24.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.

25.What causes slew rate?

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.

16 marks questions

1.Explain in detail the fabrication of ICs using silicon planar technology.

Ans:

*Silicon wafer preparation.

* Epitaxial growth

*Oxidation.

*Photolithography.

*Diffusion.

*Ion implantation.

*Isolation.

*Metallisation.

*Assembly processing and packaging.

2.Design an active load for an emitter-coupled pair(differential amplifier) and

perform a detailed analysis to find its differential mode gain and the output

resistance.

Ans:

Output voltage, Vo=Vcc –VBE(on) + 2VA(eff) tanh(Vid / 2VT)

Gain , Avd = 1 / ( VT/VAN + VT/VAP )

Output resistance,Ro = ronpn || ropnp

3.Design a Widlar current source and obtain the expression for output current.Also

prove that widlar current source has better sensitivity than constant current

source.

Ans:

For Widlar current source, VT ln( Ic1/ Ic2 ) = Ic2 R2

Sensitivity is defined as the percentage or fractional change in output current

per percentage or fractional change in power-supply voltage.

For constant current source sensitivity is unity because the output current is directly

proportional to supply voltage. The sensitivity of a widlar current source is better

compared to constant current source because the output current has a logarithmic

dependence on power supply voltage.

4. Explain the supply independent biasing technique using VBE as the reference

voltage.Also, find the dependence of its output current on temperature.

Ans:

The output current is given by, Iout = VBE1 / R2 = (VT /R2) ln ( Iref / Is1 )

(Circuit diagram, self-biasing VBE reference circuit, start-up circuit to avoid zerocurrent

state)

Temperature co-efficient, TCF = ˜9BE1/ VBE1 ˜7 -- ˜5 5 ˜7

5.Explain supply independent biasing using zener-referenced bias circuit.

Also,design a temperature compensated zener-reference source.

Ans:

The output current is given by, Iout = VZ / R2

(Circuit diagram, self-biasing zener bias reference circuit, temperature compensated

zener reference source )

6.Obtain the frequency response of an open-loop op-amp and discuss about the

methods of frequency compensation .

Ans:

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. 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.

Frequency compensation methods:

*Dominant-pole compensation

*Pole-zero compensation.

UNIT II : APPLICATIONS OF OP – AMPS

2 Marks Questions:

1.Mention some of the linear applications of op – amps :

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.

2.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.

3.What are the areas of application of non-linear op- amp circuits?

” industrial instrumentation

” Communication

” Signal processing

4.What is the need for an instrumentation amplifier?

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.

5.List the features of instrumentation amplifier:

” high gain accuracy

” high CMRR

” high gain stability with low temperature co-efficient

” low dc offset

” low output impedance

6.What are the applications of V-I converter?

” Low voltage dc and ac voltmeter

” L E D

” Zener diode tester

7.What do you mean by a precision diode?

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 millivolt.

8.Write down the applications of precision diode.

” Half - wave rectifier

” Full - Wave rectifier

” Peak – value detector

” Clipper

” Clamper

9.List the applications of Log amplifiers:

” 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

10.What are the limitations of the basic differentiator circuit?

” At high frequency, a differentiator may become unstable and break

into oscillations

” The input impedance decreases with increase in frequency , thereby

making the circuit sensitive to high frequency noise.

11.Write down the condition for good differentiation :-

For good differentiation, the time period of the input signal must be

greater than or equal to Rf C1

T > R f C1

Where, Rf is the feedback resistance

Cf is the input capacitance

12.What is a comparator?

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 .

13.What are the applications of comparator?

” Zero crossing detector

” Window detector

” Time marker generator

” Phase detector

14.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.

15.What is a multivibrator?

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.

16.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.

17.What is an astable multivibrator?

Astable multivibrator is a free running oscillator having two quasi-stable

states. Thus, there is oscillations between these two states and no external signal are

required to produce the change in state.

18.What is a bistable multivibrator?

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 an second trigger is

applied . Thus, it requires two external triggers before it returns to its initial state

19.What are the requirements for producing sustained oscillations in feedback

circuits?

For sustained oscillations,

” The total phase shift around the loop must be zero at the desired

frequency of oscillation, fo. ie, $% RU °

” At fo, the magnitude of the loop gain | A b | should be equal to unity

20.Mention any two audio frequency oscillators :

” RC phase shift oscillator

” Wein bridge oscillator

21.What are the characteristics of a comparator?

” Speed of operation

” Accuracy

” Compatibility of the output

22.What is a filter?

Filter is a frequency selective circuis filter

” Band reject filter.

16 marks questions:

1.Discuss the need for an instrumentation amplifier? Give a detailed analysis for the

same.

Ans:

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.

Circuit diagram, instrumentation amplifier with transducer bridge,

Analysis, Expression for out put voltage.

2.Explain the operation of the Schmitt trigger.

Ans:

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.

Circuit diagram, Analysis.

Expression for upper and lower threshold voltages with and without Vref.

Hysterisis width.

Waveforms.

3.Discuss in detail the operation of Astable multivibrator.

Ans:

Astable multivibrator is a free running oscillator having two quasi-stable states.

Thus, there is oscillations between these two states and no external signal are required to

produce the change in state.

Circuit diagram, Analysis.

Expression for time period , 7 5& OQ –

Waveforms.

Circuit for asymmetric square wave generator.

4. Discuss in detail the operation of Monostable multivibrator.

Ans:

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.

Circuit diagram, Analysis.

Expression for time period , T = RC ln ( 1 + VD / Vsat ) / ( 1 –

Waveforms.

5. What are the requirements for producing sustained oscillations in feedback

circuits?Discuss any two audio frequency oscillators.

Ans:

For sustained oscillations,

” The total phase shift around the loop must be zero at the desired

frequency of oscillation, fo. ie, $% RU °

” At fo, the magnitude of the loop gain | A b | should be equal to unity.

RC phase shift oscillator: Circuit diagram,Derive the condition for frequency of

oscillation.

Gain,Av >= - 29

Wein bridge oscillator : Circuit diagram,Derive the condition for frequency of

oscillation.

Gain, Av = 3

UNIT – 3 :ANALOG MULTIPLIER AND PLL

2 marks questions

1.Mention some areas where PLL is widely used:

*Radar synchronisation

*satellite communication systems

*air borne navigational systems

*FM communication systems

*Computers.

2.List the basic building blocks of PLL:

*Phase detector/comparator

*Low pass filter

*Error amplifier

*Voltage controlled oscillator

3.What are the three stages through which PLL operates?

*Free running

*Capture

*Locked/ tracking

4.Define lock-in range of a PLL:

The range of frequencies over which the PLL can maintain lock with the incoming

signal is called the lock-in range or tracking range.It is expressed as a percentage of the

VCO free running frequency.

5.Define capture range of PLL:

The range of frequencies over which the PLL can acquire lock with an input signal

is called the capture range. It is expressed as a percentage of the VCO free running

frequency.

6.Define Pull-in time.

The total time taken by the PLL to establish lok is called pull-in time.It depends

on the initial phase and frequency difference between the two signals as well as on the

overall loop gain and loop filter characteristics.

7.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.

8.Give the classification of phase detector:

*Analog phase detector

*Digital phase detector

9.What is a switch type phase detector?

An electronic switch is opened and closed by signal coming from VCO and the

input signal is chopped at a repetition rate determined by the VCO frequency.This type of

phase detector is called a half wave detector since the phase information for only one half

of the input signal is detected and averaged.

10.What are the problems associated with switch type phase detector?

*The output voltage Ve is proportional to the input signal amplitude.This is

undesirable because it makes phase detector gain and loop gain dependent on the input

signal amplitude.

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11.What is a voltage controlled oscillator?

Voltage controlled oscillator is a free running multivibrator operating at a set

frequency called the free running frequency.This frequency can be shifted to either side

by applying a dc control voltage and the frequency deviation is proportional to the dc

control voltage.

12.On what parameters does the free running frequency of VCO depend on?

*External timing resistor,RT

*External timing capacitor,CT

*The dc control voltage Vc.

13.Give the expression for the VCO free running frequency.

fo = 0.25 / RT CT

14.Define Voltage to Frequency conversion factor.

Voltage to Frequency conversion factor is defined as,

.Y Io 9c= 8fo /Vcc

ZKHUH 9c is the modulation voltage required to produce the frequency shift Io

15.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.

16.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.

17.Mention some typical applications of PLL:

· Frequency multiplication/division

· Frequency translation

· AM detection

· FM demodulation

· FSK demodulation.

18.What is a compander IC? Give some examples.

The term companding means compressing and expanding.In a communication

system, the audio signal is compressed in the transmitter and expanded in the receiver.

Examples : LM 2704- LM 2707 ; NE 570/571.

19.What are the merits of companding?

*The compression process reduces the dynamic range of the signal before it is

transmitted.

*Companding preserves the signal to noise ratio of the original signal and avoids

non linear distortion of the signal when the input amplitude is large.

*It also reduces buzz,bias and low level audio tones caused by mild interference.

20.List the applications of OTA:

OTA can be used in

· programmable gain voltage amplifier

· sample and hold circuits

· voltage controlled state variable filter

· current controlled relaxation oscillator.

16 marks

1. Briefly explain the block diagram of PLL and derive the expression for Lock

range and capture range.

Block diagram of PLL

Explanation for each block.

Derivation for capture range and lock range.

2. With a neat functional diagram, explain the operation of VCO. Also derive

an expression for fo.

Internal diagram for VCO IC.

Explanation

Derivation for fo.

3. Analyse the Gilbert’s four quadrant multiplier cell with a neat circuit

diagram.Discuss its applications.

Circuit diagram

Analysis

Expression for output current

Applications.

4. In detail dicuss the applications of PLL:

AM detection

FM demodulation

FSK demodulation

Frequency multiplication/division.

UNIT IV – A/D AND D/A CONVERTERS

2 marks questions

1. List the broad classification of ADCs.

1. Direct type ADC.

2. Integrating type ADC.

2. List out the direct type ADCs.

1. Flash (comparator) type converter

2. Counter type converter

3. Tracking or servo converter

4. Successive approximation type converter

3. List out some integrating type converters.

1. Charge balancing ADC

2. Dual slope ADC

4. 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.

5. Explain in brief the principle of operation of successive Approximation 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.

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

i. The integrating type of ADC’s do not need a sample/Hold circuit at the

input.

ii. It is possible to transmit frequency even in noisy environment or in an

isolated form.

7. 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.

8. What is the main drawback of a dual-slop ADC?

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

of dual slope ADC.

9. State the advantages of dual slope ADC:

It provides excellent noise rejection of ac signals whose periods are

integral multiples of the integration time T.

10. Define conversion time.

It is defined as the total time required to convert 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

11. Define resolution of a data converter.

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.

12. Define accuracy of converter.

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.

13. What is settling time?

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.

14. 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.

15. What is meant by linearity?

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.

16. What is monotonic DAC?

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

digital input.

17. What is multiplying DAC?

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 give by

V(t)=Vin &RV IW

Then, Vo(t)=Vom&RV IW º)

18.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.

19.Define sample period and hold period.

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.

20.What is meant by delta modulation?

Delta modulation is a technique capable of performing analog signal

quantisation with smaller bandwidth requirements. Here, the binary output

representing the most recent sampled amplitude will be determined on the basis of

previous sampled amplitude levels.

16 marks

1. What is integrating type converter?Explain the operation of dual slope ADC:

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.

Functional diagram of Dual slope ADC.

Explanation, Derivation.

2. Explain the princresenting the most recent sampled amplitude will be determined on the basis of

previous sampled amplitude levels.

Functional diaaagram

Operation.

UNIT V – SPECIAL FUNCTION ICs

2 mark questions

1.Mention some applications of 555 timer:

*Oscillator

*pulse generator

*ramp and square wave generator

*mono-shot multivibrator

*burglar alarm

*traffic light control.

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

*missing pulse detector

*Linear ramp generator

*Frequency divider

*Pulse width modulation.

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

*FSK generator

*Pulse-position modulator

4.What is a voltage regulator?

A voltage regulator is an electronic circuit that provides a stable dc voltage

independent of the load current, temperature, and ac line voltage variations.

5.Give the classification of voltage regulators:

*Series / Linear regulators

*Switching regulators.

6.What is a linear voltage regulator?

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 continous voltage drop taking place across the series pass transistor.

7.What is a switching regulator?

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

continously.This gives improved efficiency over series regulators.

8.What are the advantages of IC voltage regulators?

*low cost

*high reliability

*reduction in size

*excellent performance

9.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.

10.What is the purpose of having input and output capacitors in three terminal IC

regulators?

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.

11. 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 millivolts or as a percentage of the output

voltage.

12.Define load regulation.

Load regulation is defined as the change in output voltage for a change in load

current. It is expressed in millivolts or as a percentage of the output voltage.

13.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.

14.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 continous power dissipation by the transistor

as it operates in the linear region.

15.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.

16.What is an opto-coupler IC? Give examples.

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

device.Examples for opto-coupler circuit : LED and a photo diode,

LED and photo transistor,

LED and Darlington.

Examples for opto-coupler IC : MCT 2F , MCT 2E .

17. Mention the advantages of opto-couplers:

*Better isolation between the two stages.

*Impedance problem between the stages is eliminated.

*Wide frequency response.

*Easily interfaced with digital circuit.

*Compact and light weight.

*Problems such as noise, transients, contact bounce,.. are eliminated.

18.What is an isolation amplifier?

An isolation amplifier is an amplifier that offers electrical isolation between its

input and output terminals.

19.What is the need for a tuned amplifier?

In radio or TV receivers , it is necessary to select a particular channel among all

other available channels.Hence some sort of frequency selective circuit is needed that

will allow us to amplify the frequency band required and reject all the other unwanted

signals and this function is provided by a tuned amplifier.

20.Give the classification of tuned amplifier:

(i) Small signal tuned amplifier

*Single tuned

*Double tuned

*Stagger tuned

(ii) Large signal tuned amplifier.

16 marks

1.What is 555 timer? What are the features of 555 timer? Explain the monostable mode in

detail?

Features of 555

Description about 555

Circuit diagram

Derivation for frequency.

2.Explain the Astable mode of operation using 555 timer.

Description about 555

Circuit diagram

Derivation for frequency.

3.In detail dicuss the 723 IC general purpose voltage regulator.

Functional diagram

Low and high voltage regulation using 723

Features of 723.

4.Explain the operation of switching regulators.Give its advantages.

Functional diagram

Operation

Output waveforms.

Advantages.

5.Explain the functional diagram of LM 380 power amplifier.

Introduction

Internal diagram

Operation

Features.

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DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGG.

SUBJECT CODE: EC 1254

SUBJECT NAME: Linear Integrated circuits

Prepared by,

Y.Ireaneus Anna Regani (Asst.Prof/ECE)

E.P.Kannan (Sr. Lect/ECE)

NOORUL ISLAM COLLEGE OF ENGINEERING, KUMARACOIL

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EC1254– LINEAR INTEGRATED CIRCUITS

(Fourth semester ECE)

UNIT-I CIRCUIT CONFIGURATION FOR LINEAR ICs

2 marks questions

1.Mention the advantages of integrated circuits.

*Miniaturisation and hence increased equipment density.

*Cost reduction due to batch processing.

*Increased system reliability due to the elimination of soldered joints.

*Improved functional performance.

*Matched devices.

*Increased operating speeds.

*Reduction in power consumption.

2.Write down the various processes used to fabricate IC’s using silicon planar

technology.

*Silicon wafer preparation.

* Epitaxial growth

*Oxidation.

*Photolithography.

*Diffusion.

*Ion implantation.

*Isolation.

*Metallisation.

*Assembly processing and packaging.

3.What is the purpose of oxidation?

*SiO2 is an extremely hard protective coating and is unaffected by almost all

reagents.

*By selective etching of SiO2, diffusion of impurities through carefully defined

windows can be accomplished to fabricate various components.

4.Why aluminium is preferred for metallization?

*It is a good conductor.

*it is easy to deposit aluminium films using vacuum deposition.

*It makes good mechanical bonds with silicon.

*It forms a low resistance contact.

5. What are the popular IC packages available?

Metal can package.

Dual-in-line package.

Ceramic flat package.

6. Define an operational amplifier.

An operational amplifier is a direct-coupled, high gain amplifier consisting of

one or more differential amplifier. By properly selecting the external components, it can

be used to perform a variety of mathematical operations.

7.Mention the characteristics of an ideal op-amp.

* Open loop voltage gain is infinity.

*Input impedance is infinity.

*Output impedance is zero.

*Bandwidth is infinity.

*Zero offset.

8.What happens when the common terminal of V+ and V- sources is not grounded?

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.

9.Define input offset voltage.

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.

10. 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.

11. Define CMRR of an op-amp.

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

12.What are the applications of current sources?

Transistor current sources are widely used in analog ICs both as biasing

elements and as load devices for amplifier stages.

13. Justify the reasons for using current sources in integrated circuits.

*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.

14. What is the advantage of widlar current source over constant current source?

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.

15.Mention the advantages of Wilson current source.

*provides high output resistance.

*offers low sensitivity to transistor base currents.

16.Define sensitivity.

Sensitivity is defined as the percentage or fractional change in output current

per percentage or fractional change in power-supply voltage.

17.What are the limitations in a temperature compensated zener-reference source?

A power supply voltage of atleast 7 to 10 V is required to place the diode in the

breakdown region and that substantial noise is introduced in the circuit by the

avalanching diode.

18.What do you mean by a band-gap referenced biasing circuit?

The biasing sources referenced to VBE has a negative temperature co-efficient

and VT has a positive temperature co-efficient. Band gap reference circuit is one in

which the output current is referenced to a composite voltage that is a weighted sum

of VBE and VT so that by proper weighting, zero temperature co-efficient can be

achieved.

19.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.

20. What is the need for frequency compensation in practical op-amps?

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.

21.Mention the frequency compensation methods.

*Dominant-pole compensation

*Pole-zero compensation.

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

*noise immunity of the system is improved.

*Open-loop bandwidth is reduced.

23.Define slew rate.

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.

24.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.

25.What causes slew rate?

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.

16 marks questions

1.Explain in detail the fabrication of ICs using silicon planar technology.

Ans:

*Silicon wafer preparation.

* Epitaxial growth

*Oxidation.

*Photolithography.

*Diffusion.

*Ion implantation.

*Isolation.

*Metallisation.

*Assembly processing and packaging.

2.Design an active load for an emitter-coupled pair(differential amplifier) and

perform a detailed analysis to find its differential mode gain and the output

resistance.

Ans:

Output voltage, Vo=Vcc –VBE(on) + 2VA(eff) tanh(Vid / 2VT)

Gain , Avd = 1 / ( VT/VAN + VT/VAP )

Output resistance,Ro = ronpn || ropnp

3.Design a Widlar current source and obtain the expression for output current.Also

prove that widlar current source has better sensitivity than constant current

source.

Ans:

For Widlar current source, VT ln( Ic1/ Ic2 ) = Ic2 R2

Sensitivity is defined as the percentage or fractional change in output current

per percentage or fractional change in power-supply voltage.

For constant current source sensitivity is unity because the output current is directly

proportional to supply voltage. The sensitivity of a widlar current source is better

compared to constant current source because the output current has a logarithmic

dependence on power supply voltage.

4. Explain the supply independent biasing technique using VBE as the reference

voltage.Also, find the dependence of its output current on temperature.

Ans:

The output current is given by, Iout = VBE1 / R2 = (VT /R2) ln ( Iref / Is1 )

(Circuit diagram, self-biasing VBE reference circuit, start-up circuit to avoid zerocurrent

state)

Temperature co-efficient, TCF = ˜9BE1/ VBE1 ˜7 -- ˜5 5 ˜7

5.Explain supply independent biasing using zener-referenced bias circuit.

Also,design a temperature compensated zener-reference source.

Ans:

The output current is given by, Iout = VZ / R2

(Circuit diagram, self-biasing zener bias reference circuit, temperature compensated

zener reference source )

6.Obtain the frequency response of an open-loop op-amp and discuss about the

methods of frequency compensation .

Ans:

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. 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.

Frequency compensation methods:

*Dominant-pole compensation

*Pole-zero compensation.

UNIT II : APPLICATIONS OF OP – AMPS

2 Marks Questions:

1.Mention some of the linear applications of op – amps :

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.

2.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.

3.What are the areas of application of non-linear op- amp circuits?

” industrial instrumentation

” Communication

” Signal processing

4.What is the need for an instrumentation amplifier?

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.

5.List the features of instrumentation amplifier:

” high gain accuracy

” high CMRR

” high gain stability with low temperature co-efficient

” low dc offset

” low output impedance

6.What are the applications of V-I converter?

” Low voltage dc and ac voltmeter

” L E D

” Zener diode tester

7.What do you mean by a precision diode?

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 millivolt.

8.Write down the applications of precision diode.

” Half - wave rectifier

” Full - Wave rectifier

” Peak – value detector

” Clipper

” Clamper

9.List the applications of Log amplifiers:

” 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

10.What are the limitations of the basic differentiator circuit?

” At high frequency, a differentiator may become unstable and break

into oscillations

” The input impedance decreases with increase in frequency , thereby

making the circuit sensitive to high frequency noise.

11.Write down the condition for good differentiation :-

For good differentiation, the time period of the input signal must be

greater than or equal to Rf C1

T > R f C1

Where, Rf is the feedback resistance

Cf is the input capacitance

12.What is a comparator?

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 .

13.What are the applications of comparator?

” Zero crossing detector

” Window detector

” Time marker generator

” Phase detector

14.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.

15.What is a multivibrator?

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.

16.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.

17.What is an astable multivibrator?

Astable multivibrator is a free running oscillator having two quasi-stable

states. Thus, there is oscillations between these two states and no external signal are

required to produce the change in state.

18.What is a bistable multivibrator?

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 an second trigger is

applied . Thus, it requires two external triggers before it returns to its initial state

19.What are the requirements for producing sustained oscillations in feedback

circuits?

For sustained oscillations,

” The total phase shift around the loop must be zero at the desired

frequency of oscillation, fo. ie, $% RU °

” At fo, the magnitude of the loop gain | A b | should be equal to unity

20.Mention any two audio frequency oscillators :

” RC phase shift oscillator

” Wein bridge oscillator

21.What are the characteristics of a comparator?

” Speed of operation

” Accuracy

” Compatibility of the output

22.What is a filter?

Filter is a frequency selective circuis filter

” Band reject filter.

16 marks questions:

1.Discuss the need for an instrumentation amplifier? Give a detailed analysis for the

same.

Ans:

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.

Circuit diagram, instrumentation amplifier with transducer bridge,

Analysis, Expression for out put voltage.

2.Explain the operation of the Schmitt trigger.

Ans:

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.

Circuit diagram, Analysis.

Expression for upper and lower threshold voltages with and without Vref.

Hysterisis width.

Waveforms.

3.Discuss in detail the operation of Astable multivibrator.

Ans:

Astable multivibrator is a free running oscillator having two quasi-stable states.

Thus, there is oscillations between these two states and no external signal are required to

produce the change in state.

Circuit diagram, Analysis.

Expression for time period , 7 5& OQ –

Waveforms.

Circuit for asymmetric square wave generator.

4. Discuss in detail the operation of Monostable multivibrator.

Ans:

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.

Circuit diagram, Analysis.

Expression for time period , T = RC ln ( 1 + VD / Vsat ) / ( 1 –

Waveforms.

5. What are the requirements for producing sustained oscillations in feedback

circuits?Discuss any two audio frequency oscillators.

Ans:

For sustained oscillations,

” The total phase shift around the loop must be zero at the desired

frequency of oscillation, fo. ie, $% RU °

” At fo, the magnitude of the loop gain | A b | should be equal to unity.

RC phase shift oscillator: Circuit diagram,Derive the condition for frequency of

oscillation.

Gain,Av >= - 29

Wein bridge oscillator : Circuit diagram,Derive the condition for frequency of

oscillation.

Gain, Av = 3

UNIT – 3 :ANALOG MULTIPLIER AND PLL

2 marks questions

1.Mention some areas where PLL is widely used:

*Radar synchronisation

*satellite communication systems

*air borne navigational systems

*FM communication systems

*Computers.

2.List the basic building blocks of PLL:

*Phase detector/comparator

*Low pass filter

*Error amplifier

*Voltage controlled oscillator

3.What are the three stages through which PLL operates?

*Free running

*Capture

*Locked/ tracking

4.Define lock-in range of a PLL:

The range of frequencies over which the PLL can maintain lock with the incoming

signal is called the lock-in range or tracking range.It is expressed as a percentage of the

VCO free running frequency.

5.Define capture range of PLL:

The range of frequencies over which the PLL can acquire lock with an input signal

is called the capture range. It is expressed as a percentage of the VCO free running

frequency.

6.Define Pull-in time.

The total time taken by the PLL to establish lok is called pull-in time.It depends

on the initial phase and frequency difference between the two signals as well as on the

overall loop gain and loop filter characteristics.

7.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.

8.Give the classification of phase detector:

*Analog phase detector

*Digital phase detector

9.What is a switch type phase detector?

An electronic switch is opened and closed by signal coming from VCO and the

input signal is chopped at a repetition rate determined by the VCO frequency.This type of

phase detector is called a half wave detector since the phase information for only one half

of the input signal is detected and averaged.

10.What are the problems associated with switch type phase detector?

*The output voltage Ve is proportional to the input signal amplitude.This is

undesirable because it makes phase detector gain and loop gain dependent on the input

signal amplitude.

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11.What is a voltage controlled oscillator?

Voltage controlled oscillator is a free running multivibrator operating at a set

frequency called the free running frequency.This frequency can be shifted to either side

by applying a dc control voltage and the frequency deviation is proportional to the dc

control voltage.

12.On what parameters does the free running frequency of VCO depend on?

*External timing resistor,RT

*External timing capacitor,CT

*The dc control voltage Vc.

13.Give the expression for the VCO free running frequency.

fo = 0.25 / RT CT

14.Define Voltage to Frequency conversion factor.

Voltage to Frequency conversion factor is defined as,

.Y Io 9c= 8fo /Vcc

ZKHUH 9c is the modulation voltage required to produce the frequency shift Io

15.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.

16.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.

17.Mention some typical applications of PLL:

· Frequency multiplication/division

· Frequency translation

· AM detection

· FM demodulation

· FSK demodulation.

18.What is a compander IC? Give some examples.

The term companding means compressing and expanding.In a communication

system, the audio signal is compressed in the transmitter and expanded in the receiver.

Examples : LM 2704- LM 2707 ; NE 570/571.

19.What are the merits of companding?

*The compression process reduces the dynamic range of the signal before it is

transmitted.

*Companding preserves the signal to noise ratio of the original signal and avoids

non linear distortion of the signal when the input amplitude is large.

*It also reduces buzz,bias and low level audio tones caused by mild interference.

20.List the applications of OTA:

OTA can be used in

· programmable gain voltage amplifier

· sample and hold circuits

· voltage controlled state variable filter

· current controlled relaxation oscillator.

16 marks

1. Briefly explain the block diagram of PLL and derive the expression for Lock

range and capture range.

Block diagram of PLL

Explanation for each block.

Derivation for capture range and lock range.

2. With a neat functional diagram, explain the operation of VCO. Also derive

an expression for fo.

Internal diagram for VCO IC.

Explanation

Derivation for fo.

3. Analyse the Gilbert’s four quadrant multiplier cell with a neat circuit

diagram.Discuss its applications.

Circuit diagram

Analysis

Expression for output current

Applications.

4. In detail dicuss the applications of PLL:

AM detection

FM demodulation

FSK demodulation

Frequency multiplication/division.

UNIT IV – A/D AND D/A CONVERTERS

2 marks questions

1. List the broad classification of ADCs.

1. Direct type ADC.

2. Integrating type ADC.

2. List out the direct type ADCs.

1. Flash (comparator) type converter

2. Counter type converter

3. Tracking or servo converter

4. Successive approximation type converter

3. List out some integrating type converters.

1. Charge balancing ADC

2. Dual slope ADC

4. 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.

5. Explain in brief the principle of operation of successive Approximation 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.

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

i. The integrating type of ADC’s do not need a sample/Hold circuit at the

input.

ii. It is possible to transmit frequency even in noisy environment or in an

isolated form.

7. 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.

8. What is the main drawback of a dual-slop ADC?

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

of dual slope ADC.

9. State the advantages of dual slope ADC:

It provides excellent noise rejection of ac signals whose periods are

integral multiples of the integration time T.

10. Define conversion time.

It is defined as the total time required to convert 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

11. Define resolution of a data converter.

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.

12. Define accuracy of converter.

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.

13. What is settling time?

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.

14. 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.

15. What is meant by linearity?

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.

16. What is monotonic DAC?

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

digital input.

17. What is multiplying DAC?

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 give by

V(t)=Vin &RV IW

Then, Vo(t)=Vom&RV IW º)

18.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.

19.Define sample period and hold period.

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.

20.What is meant by delta modulation?

Delta modulation is a technique capable of performing analog signal

quantisation with smaller bandwidth requirements. Here, the binary output

representing the most recent sampled amplitude will be determined on the basis of

previous sampled amplitude levels.

16 marks

1. What is integrating type converter?Explain the operation of dual slope ADC:

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.

Functional diagram of Dual slope ADC.

Explanation, Derivation.

2. Explain the princresenting the most recent sampled amplitude will be determined on the basis of

previous sampled amplitude levels.

Functional diaaagram

Operation.

UNIT V – SPECIAL FUNCTION ICs

2 mark questions

1.Mention some applications of 555 timer:

*Oscillator

*pulse generator

*ramp and square wave generator

*mono-shot multivibrator

*burglar alarm

*traffic light control.

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

*missing pulse detector

*Linear ramp generator

*Frequency divider

*Pulse width modulation.

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

*FSK generator

*Pulse-position modulator

4.What is a voltage regulator?

A voltage regulator is an electronic circuit that provides a stable dc voltage

independent of the load current, temperature, and ac line voltage variations.

5.Give the classification of voltage regulators:

*Series / Linear regulators

*Switching regulators.

6.What is a linear voltage regulator?

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 continous voltage drop taking place across the series pass transistor.

7.What is a switching regulator?

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

continously.This gives improved efficiency over series regulators.

8.What are the advantages of IC voltage regulators?

*low cost

*high reliability

*reduction in size

*excellent performance

9.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.

10.What is the purpose of having input and output capacitors in three terminal IC

regulators?

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.

11. 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 millivolts or as a percentage of the output

voltage.

12.Define load regulation.

Load regulation is defined as the change in output voltage for a change in load

current. It is expressed in millivolts or as a percentage of the output voltage.

13.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.

14.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 continous power dissipation by the transistor

as it operates in the linear region.

15.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.

16.What is an opto-coupler IC? Give examples.

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

device.Examples for opto-coupler circuit : LED and a photo diode,

LED and photo transistor,

LED and Darlington.

Examples for opto-coupler IC : MCT 2F , MCT 2E .

17. Mention the advantages of opto-couplers:

*Better isolation between the two stages.

*Impedance problem between the stages is eliminated.

*Wide frequency response.

*Easily interfaced with digital circuit.

*Compact and light weight.

*Problems such as noise, transients, contact bounce,.. are eliminated.

18.What is an isolation amplifier?

An isolation amplifier is an amplifier that offers electrical isolation between its

input and output terminals.

19.What is the need for a tuned amplifier?

In radio or TV receivers , it is necessary to select a particular channel among all

other available channels.Hence some sort of frequency selective circuit is needed that

will allow us to amplify the frequency band required and reject all the other unwanted

signals and this function is provided by a tuned amplifier.

20.Give the classification of tuned amplifier:

(i) Small signal tuned amplifier

*Single tuned

*Double tuned

*Stagger tuned

(ii) Large signal tuned amplifier.

16 marks

1.What is 555 timer? What are the features of 555 timer? Explain the monostable mode in

detail?

Features of 555

Description about 555

Circuit diagram

Derivation for frequency.

2.Explain the Astable mode of operation using 555 timer.

Description about 555

Circuit diagram

Derivation for frequency.

3.In detail dicuss the 723 IC general purpose voltage regulator.

Functional diagram

Low and high voltage regulation using 723

Features of 723.

4.Explain the operation of switching regulators.Give its advantages.

Functional diagram

Operation

Output waveforms.

Advantages.

5.Explain the functional diagram of LM 380 power amplifier.

Introduction

Internal diagram

Operation

Features.

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