Analog & Digital Integrated Circuits - Material (Short Answers)

Analog & Digital IC’s S.MATHANKUMAR, AP/EEE TWO MARK QUESTIONS WITH ANSWERS

DEPARTMENT OF BIOMEDICAL ENGINEERING 1

Subject Name ANALOG AND DIGITAL IC’s

Objective SHORT QUESTIONS WITH ANSWERS

UNIT - I PART – A

1. Define virtual short.

The differential input voltage Vd between the noninverting and inverting input

terminals is essentially zero and the input current of the op-amp is always zero.

2. What is differential amplifier?

The differential amplifier amplifies the difference between two input voltage

signals.

3. Define slew rate.

The maximum rate of change of output voltage with respect to time is called slew

rate of op-amp. The slew rate equation is, S=2πfVm in V/Sec

(Or)

The slew rate is defined as the maximum rate of change of output voltage caused

by a step input voltage and is usually specified in V/µs. Slew rate of 741 IC is

0.5V/µS.



4. List the important characteristics of an ideal op-amp.

Characteristics of an ideal operational amplifier:

S.NO Characteristics Symbol Values

1. Open loop voltage gain AOL ∞ (infinity)

2. Input impedance Ri ∞ (infinity)

3. Output impedance Ro 0 (zero)

4. Zero offset voltage Vo 0 (zero)

5. Band width BW ∞ (infinity)

6. CMMR ρ ∞ (infinity)

7. Slew rate S ∞ (infinity)

8. Power Supply Rejection Ratio PSRR 0 (zero)

5. Define CMRR of an Op – Amp.

Definition of CMRR:

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

(Or)

Common Mode Rejection Ratio (CMRR) is defined as the ratio of difference

mode gain to common mode gain. It‟s ideal value is infinity, and it is given by,

CMRR = | Ad| / |Ac|

Where, Ad is difference mode gain and

Ac is common mode gain.

6. Differentiate Average & peak detector.

It is sometimes necessary to measure the maximum positive excursion (peak

value) or negative excursion (valley value) of a waveform over a given time

period. There may also be a requirement to capture and hold some maximum value

of a positive or negative pulse. A circuit that performs this function is a peak

detector.



7. Mention some of the linear and non linear applications of Op - Amp.

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.

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.

8. Draw the integrator circuit using Op - Amp.

An op – amp acts as an Integrator

9. Define precision diode.

Precision diode is the diode which is placed in the feedback loop of an op-

amp which is capable of rectifying input signals of the order of millivolts.

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.



10. What is hysteresis?

The graph indicates that once the output changes its state, it remains there

indefinitely until the input voltage crosses any of the threshold voltage levels.

This is called hysteresis of Schmitt trigger. The hysteresis is also called dead band

or dead zone.

11. Draw the circuit diagram of Astable vibrator.

Astable Multivibrator Circuit Diagram Using the 555 Timer

12. What is meant by filters? What are the types?

Filter is a frequency selective circuit that passes signal of specified band of

frequencies and attenuates the signals of frequencies outside the band.

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.



13. Define PSRR of an Op - Amp.

Definition of PSRR:

Power Supply Rejection Ratio (PSRR) is defined as the change in op-amp‟s input

offset voltage due to variations in supply voltage. It is expressed in microvolt per

volt or in db.

(Or)

PSSR is Power Supply Rejection Ratio. It is defined as the change in the input

offset voltage due to the change in one of the two supply voltages when other

voltage is maintained constant. Its ideal value should be zero.

14. Write down the applications of precision diode.

Essentially a precision diode can be used in all the application circuits of

conventional p-n diodes (except power applications) to allow for low –

level processing.

Rectifiers

Limiters

Clamping circuits

15. What is Peak detector?

A peak detector is a circuit which notes and remembers the peak positive or

negative value of an input signal for an infinite period of time until it is rest.

16. Draw the circuit diagram of triangular generator.



17. Write short notes on Schmitt trigger and List out the applications.

Schmitt trigger is a generic name of threshold circuits with positive feedback having

a loop gain > 1.

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.

(Or)

Schmitt trigger is an inverting comparator with positive feedback. It converts an

irregular-shaped waveform to a square wave or pulse, and is called as squaring circuit.

Schmitt trigger devices are typically used in open loop configurations for noise

immunity and closed loop negative feedback configurations to implement bistable

regulators, triangle/square wave generators, etc.

Applications:

Squaring circuit

Sine-to-Square comparator

Amplitude comparator

As flip flops

18. What are the limitations of integrated circuits?

The integrated circuits have few limitations also, as listed below:

In an IC the various components are part of a small semi-conductor chip

and the individual component or components cannot be removed or

replaced, therefore, if any component in an IC fails, the whole IC has to be

replaced by the new one.

Limited power rating as it is not possible to manufacture high power (say

greater than 10 Watt) ICs.

Need of connecting inductors and transformers exterior to the semi-

conductor chip as it is not possible to fabricate inductors and transformers

on the semi-conductor chip surface.

Operations at low voltage as ICs function at fairly low voltage.

http://en.wikipedia.org/wiki/Positive_feedback#In_electronics

http://en.wikipedia.org/wiki/Loop_gain

http://en.wikipedia.org/wiki/Open_loop

http://en.wikipedia.org/wiki/Closed_loop

http://en.wikipedia.org/wiki/Negative_feedback

http://en.wikipedia.org/wiki/Relaxation_oscillator



Quite delicate in handling as these cannot withstand rough handling or

excessive heat.

Need of connecting capacitor exterior to the semi-conductor chip as it is

neither convenient nor economical to fabricate capacitances exceeding

30pF. Therefore, for higher values of capacitance, discrete components

exterior to IC chip are connected.

High grade P-N-P assembly is not possible.

Low temperature coefficient is difficult to be achieved.

Difficult to fabricate an IC with low noise.

Large value of saturation resistance of transistors.

Voltage dependence of resistors and capacitors.

The diffusion processes and other related procedures used in the fabrication

process are not good enough to permit a precise control of the parameter

values for the circuit elements. However, control of the ratios is at a

sufficiently acceptable level.

19. Draw the Op – Amp symbol and state its important terminals.



20. State the advantages of voltage follower.

Very large input resistance, of the order of MΩ.

Low output impedance, almost zero. Hence it can be used to connect high

impedance source to a low impedance load, as a buffer.

It has a large bandwidth.

The output follows the input exactly without a phase shift.

21. When inverting amplifier is called phase inverter?

When the gain of the inverting amplifier is unity and it is used to change the phase

of the input produce the output then it is called phase inverter.

22. Draw the circuit diagram of subtractor.

Basic differential amplifier used as a Subtractor

23. List the applications of differentiator circuit.

In the wave shaping circuits to detect the high frequency components in the

input signal.

As a rate – of – change detector in the FM demodulators.

It is used in wave shaping circuits to detect the frequency in an input signal.

It is also used as rate of change detector in modulations.



24. State the applications of V to I converter and I to V converter.

Applications of V to I converter

Low voltage d.c. voltmeter

Low voltage a.c. voltmeter

Diode tester and match finder

Zener diode tester

Applications of I to V converter

Photodiode detector

PhotoFET detector

25. Draw the circuit diagram of full wave rectifier using Op - Amp.

Full wave rectifier using op-amp

26. List out the applications of an instrumentation amplifier and what are the

requirements of instrumentation amplifier?

Applications of an instrumentation amplifier ☼Temperature controller ☼Data acquisition systems

☼Temperature indicator ☼Light intensity meter

☼Analog weight scale

Requirements of instrumentation amplifier

☼It should be finite, accurate and stable ☼Easy gain adjustment

☼High input impedance ☼Low output impedance

☼High CMRR ☼Low power consumption



☼Low thermal drift ☼High slew rate

27. State the applications of monostable multivibrator.

☼Frequency divider ☼Missing pulse detector

☼Pulse width modulation ☼Pulse position modulation

☼Linear ramp generator

28. What is clamper circuit? How clamper circuits are classified?

A clamper is an electronic circuit that prevents a signal from exceeding a

certain defined magnitude by shifting its DC value. The clamper does not

restrict the peak-to-peak excursion of the signal, but moves it up or down by

a fixed value.

Based on which point of the wave D.C. is inserted the clamper circuits are

classified into.

Negative clamper.

Positive clamper.

29. List the applications of Log amplifiers.

Analog computation may require functions such as ln x, 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

http://en.wikipedia.org/wiki/Electronic_circuit



UNIT – II PART – A

1. Define phase comparator.

A phase detector or phase comparator is a frequency mixer, analog multiplier or

logic circuit that generates a voltage signal which represents the difference in

phase between two signal inputs. It is an essential element of the phase-locked

loop (PLL).

2. Define lock in range.

The range of frequencies over which the PLL can maintain locked with the

incoming signal is called the lock in range.

(Or)

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.

3. Define capture range.

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

is called capture range.

(Or)

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.

4. List out the typical applications of Phase Locked Loop.

Frequency multiplication

Frequency division

Frequency translation

AM detection

FM detection.

http://en.wikipedia.org/wiki/Frequency_mixer

http://en.wikipedia.org/wiki/Analog_multiplier

http://en.wikipedia.org/wiki/Digital_logic

http://en.wikipedia.org/wiki/Phase-locked_loop

http://en.wikipedia.org/wiki/Phase-locked_loop



5. Define voltage controlled oscillator.

The voltage controlled oscillator is defined as the one in which the frequency of

the output signal (Vo) is controlled by the control voltage (Vc).

6. What is monotonicity?

The converter is said to have good monotonicity if it does not miss any step

backward when stepped through its entire range by a counter.

7. Draw the blocks of PLL.

8. Write the operation of Voltage to Frequency ADC.

Voltage-to-frequency analog-to-digital converters use an input voltage to an

output pulse train with a frequency proportional to the input voltage. Output

frequency is determined by counting pulses over a fixed time interval and the

voltage is inferred from the known relationship.

Voltage-to-frequency analog-to-digital conversion has a high degree of noise

rejection, because the input signal is effectively integrated over the counting

interval. Voltage-to-frequency conversion is commonly used to convert slow and

often noisy signals. It is also useful for remote sensing applications in noisy

environments. The input voltage is converted to a frequency at the remote location

and the digital pulse train is transmitted over a pair of wires to the counter. This

eliminates the noise that can be introduced in the transmission of an analog signal

over a long distance.



9. Define counter ramp ADC.

A delta-encoded ADC or counter-ramp has an up-down counter that

feeds a digital to analog converter (DAC). The input signal and the DAC both go

to a comparator. The comparator controls the counter.

The circuit uses negative feedback from the comparator to adjust the

counter until the DAC's output is close enough to the input signal. The number is

read from the counter. Delta converters have very wide ranges and high resolution,

but the conversion time is dependent on the input signal level, though it will

always have a guaranteed worst-case.

10. What is pull- in time?

The total time taken by the PLL to establish lock 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.

11. Define resolution of DAC.

It is the smaller change in voltage which may be produced at the output or input of

the converter.

(Or)

This is defined as the smallest possible change in the analog output voltage. Its

value depends on the number of bits in the digital input applied to DAC.

12. State advantage of R- 2R ladder type DAC.

Easier to build, as only two values of resistors are needed.

It is possible to increase the no. of bits just by adding more sections of same

R/2R values.

http://en.wikipedia.org/wiki/Counter

http://en.wikipedia.org/wiki/Digital_to_analog_converter

http://en.wikipedia.org/wiki/Feedback



13. Which is the fastest ADC and why?

A pipeline ADC generally several flash ADCs in series. Because of this you have

a latency due to each flash. Plus you have to have op-amps in a pipeline ADC and

compensating the op-amps limits the speed of the ADC. A flash ADC will be the

fastest ADC you can have, but for it to have the same resolution as a 10-12 bit

pipeline, it will consume a lot more area, input capacitance, and possibly more

power. But the benefit is that the output data will be available usually 1/2-1 clock

cycle later instead of several clock cycles later in a pipeline.

A Flash ADC is the fastest ADC in terms of speed but it has added disadvantage

that we have to compromise on power verse resolution. Pipelined ADC comes

second in terms of power.

14. List out the advantages of DAC.

Simple to construct

Economic

15. Define amplitude modulation.

The amplitude of high frequency carrier wave is varied in accordance with the

message signal.

16. List out the disadvantages of ADC.

Accuracy & stability of this ADC depends on the resistors

A wide range of resistors required

Finite resistance of the switches may disturb the currents.

17. Give the specification of DAC.

☼Resolution ☼Linearity ☼Accuracy

☼Monotonic ☼Setting time ☼Stability

☼Temperature ☼Speed



18. What are the different types of ADC?

Flash type converter

Counter type converter

Tracking type converter

Successive approximation type converter.

19. What is linear error?

The linear error is defined as the amount by which the actual output differs from

the ideal straight line output characteristics of DAC.

20. Define 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. 10µ s

depending on word length & type circuit used.

(Or)

It is a comparison of actual output voltage with expected output. It is expressed in

percentage. Ideally, the accuracy of DAC should be, at worst, ±½ of its LSB.

21. What are the stages through which PLL operates?

Free running

Capture

Phase lock

22. Where is the successive approximation type ADC used?

The Successive approximation ADCs are used in applications such as data

loggers & instrumentation where conversion speed is important.



23. Listout the advantage and draw backs of dual slop ADC.

Advantages:

For accurate measurement of slowly varying signals, such as thermocouples

and weighing scales.

It provides excellent noise rejection of ac signals whose periods are integral

multiples of the integration time T.

Disadvantages:

Long conversion time.

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

of dual slope ADC.

24. Write the two problems associated with DM.

Problems associated with DM: Slope overload

Granular noise

25. Define Voltage to Frequency conversion factor.

Voltage to Frequency conversion factor is defined as,

Ky = Δf0 / ΔVC = 8f0 / VCC

Where, ΔVC is the modulation voltage required to produce the frequency shift Δfo.



UNIT – III PART – A

1. Define radix.

Total numbers available in a number system is called base or radix.

(Or)

The number of values that a digital (one character) can assume is equal to the base

of the system. It is also called as the radix of the system.

2. What are the number systems?

Decimal number system

Binary number system

Octal number system

Hexadecimal number system

3. Define the following: minterm and maxterm.

Minterm

The „n‟ variables forming an AND term, with each variable being primed or

unprimed, provide in 2n

possible combinations, called Minterm or Standard

Products. Each individual term in standard SOP form is called minterm.

Maxterm

The „n‟ variables forming an OR term, with each variable being primed or

unprimed, provide in 2n

possible combinations, called Maxterm or Standard

Sums. Each individual term in standard POS form is called maxterms.

4. What is meant by prime implicant?

A prime implicant is a group of minterms which cannot be combined with any

other minterm or groups.



5. Convert the given binary (1101010110)10 into gray code.

The most significant bit (MSB) in the Gray code is the same as the

corresponding MSB in the binary number.

Going from left to right, perform an EX-OR operation between the adjacent

pair of binary code bits to get the next code bit.

Binary : 1 1 0 1 0 1 0 1 1 0

Gray : 1 0 1 1 1 1 1 1 0 1

Gray code : 1011111101

6. Distinguish between 1’s and 2’s complements.

In 1's complement, a negative number is represented by taking all the bits in the

positive number and inverting them: 0's become 1's, 1's become 0's.

The 2‟s complement of a binary number is obtained by adding 1 to the 1‟s

complement of that number.

Therefore , 2’s complement = 1’s complement + 1

7. Define the terms disjunction and conjunction.

Disjunction

A coordinate construction that uses a disjunctive conjunction (usually or or either .

. . or) to indicate a contrast. The items on either side of the disjunctive conjunction

are called disjunctions.

Logical disjunction is an operation on two logical values, typically the values of

two propositions, that produces a value of false if and only if both of its operands

are false. More generally a disjunction is a logical formula that can have one or

more literals separated only by ORs. A single literal is often considered to be a

degenerate disjunction.

http://grammar.about.com/od/c/g/coordterm07.htm

http://grammar.about.com/od/c/g/conjuncterm.htm

http://grammar.about.com/od/d/g/disjunctterm.htm

http://en.wikipedia.org/wiki/Logical_operation

http://en.wikipedia.org/wiki/Logical_value

http://en.wikipedia.org/wiki/Proposition

http://en.wikipedia.org/wiki/Literal_%28mathematical_logic%29



Conjunction

In logic and mathematics, a two-place logical operator and, also known as logical

conjunction, results in true if both of its operands are true, otherwise a value of

false.

The analogue of conjunction for a (possibly infinite) family of statements is

universal quantification, which is part of predicate logic.

8. What are the logic gates?

Logic gates are the basic elements that make up a digital system. The electronic

gate is a circuit that is able to operate on a number of binary inputs in order to

perform a particular logical function.

There are three basic logic gates each of which performs a basic logic function,

they are called NOT, AND and OR.

The three basic logic gates can be combined to provide more complex logical

functions. Four important logical functions are NAND, NOR, XOR and XNOR.

9. Define SOP and POS.

Sum Of Products

The logical sum of those fundamental products that produce output 1‟s in the truth

table. The corresponding logic circuit is an AND – OR circuit or equivalent

NAND – NAND circuit.

Product Of Sum

The logical product of those fundamental sums that produce output 0‟s in the truth

table. The corresponding logic circuit is an OR - AND circuit or equivalent NOR –

NOR circuit.

http://en.wikipedia.org/wiki/Logic

http://en.wikipedia.org/wiki/Mathematics

http://en.wikipedia.org/wiki/Logical_operator

http://en.wikipedia.org/wiki/Infinite

http://en.wikipedia.org/wiki/Universal_quantification

http://en.wikipedia.org/wiki/Predicate_logic



10. What do you meant by LSB and MSB?

The binary digits (0 and 1) are also called as bits. Thus binary system is a two bit

system.

The leftmost bit in a given binary number with the highest weight is called as

Most Significant Bit ( MSB ) whereas the rightmost bit in a given number with the

lowest weight is called as Least Significant Bit ( LSB ).

11. How will you find 2’s complement of a binary number?

i) Find 1‟s complement by replacing 0 by 1 and 1 by 0.

ii) Then add 1 to the 1‟s complement.

12. What are the alphanumeric codes?

ASCII ( American Standard Code for Information Interchange )

EBCDIC ( Extended Binary – Coded – Decimal Interchange Code )

Five bit Baudot Code ( Hollerith Code )

13. Convert the given gray code (1011011101) into binary code.

The most significant bit (MSB) in the binary code is the same as the corresponding

bit in the gray code.

To obtain the next binary digit, perform an EX-OR operation between the bit just

written down and the next gray code bit.

Gray : 1 0 1 1 0 1 1 1 0 1

Binary : 1 1 0 1 1 0 1 0 0 1

Binary code : 1101101001



14. Define karnaugh maps.

The Karnaugh map is a graphical representation of a truth table that can be used

to reduce a logic circuit to its simpliest terms.

A Karnaugh map or k map is a pictorial form of truth table, in which the map diagram is

made up of squares, with each squares representing one minterm of the function.

15. Write the truth table of AND, OR and NAND gates.

Truth table of AND Truth table of OR Truth table of NAND

16. What is meant by excess 3 decimal numbers?

The excess – 3 code is a modified form of binary number. It is obtained by simply

adding „3‟ to a decimal number.

For example, to encoded the decimal number „4‟ into an excess 3 code, first add 3.

i.e. 4+3=7.

17. Define the law of Boolean algebra.

De Morgan suggested two theorems that form important part of Boolean algebra.

They are,

1) The complement of a product is equal to the sum of the complements.

(A.B)' = A'+B'

2) The complement of a sum term is equal to the product of the

complements.

(A+B)' = A'.B'

A

B

AB

AB

0 0 0 1

0 1 0 1

1 0 0 1

1 1 1 0

A B AB

0 0 0

0 1 0

1 0 0

1 1 1

A B A+B

0 0 0

0 1 1

1 0 1

1 1 1



18. What is meant by universal gates?

A universal gate is a gate which can implement any Boolean function without

need to use any other gate type.

The NAND and NOR gates are universal gates.

In practice, this is advantageous since NAND and NOR gates are economical and

easier to fabricate and are the basic gates used in all IC digital logic families.

NAND and NOR both are called as universal gate. You can built any circuit or

design using either NAND or NOR, this will be so flexible to fabricate any circuit

in a single chip

19. What is Multivariable Theorem?

In the multivariable theorem, the multiple inputs (x,y and z) can be either a logic 0

or a logic 1.

Example:

x+ (y+z) = (x+y) +z = x+y+z (associative law)

x (yz) = (xy) z = xyz (associative law)

20. Convert (25)10 to binary.

25

14 – 1

7 – 0

3 – 1

1 – 1

2510 = 111012



21. What are the types of karnaugh map?

A Karnaugh map provides a pictorial method of grouping together expressions

with common factors and therefore eliminating unwanted variables. The Karnaugh

map can also be described as a special arrangement of a truth table.

Minimization Technique 2-Variable K-Map Grouping/Circling K-maps 3-Variable K-Map 4-Variable K-Map 5-Variable K-Map Inverse Function

22. Write the truth table of X-OR and X-NOR.

Truth table of X-OR Truth table of X-NOR

23. Distinguish between Boolean addition and Binary addition.

Boolean addition

Let us begin our exploration of Boolean algebra by adding numbers together:

The first three sums make perfect sense to anyone familiar with elementary

addition. The last sum, though, is quite possibly responsible for more confusion

A B AB

0 0 0

0 1 1

1 0 1

1 1 0

A B AB

0 0 1

0 1 0

1 0 0

1 1 1



than any other single statement in digital electronics, because it seems to run

contrary to the basic principles of mathematics. Well, it does contradict principles

of addition for real numbers, but not for Boolean numbers. Remember that in the

world of Boolean algebra, there are only two possible values for any quantity and

for any arithmetic operation: 1 or 0. There is no such thing as "2" within the scope

of Boolean values. Since the sum "1 + 1" certainly isn't 0, it must be 1 by process

of elimination.

Binary addition

These are computed without regard to the word size, hence there can be no sense

of "overflow." Work through the columns right to left, add up the ones and express

the answer in binary. The low bit goes in the sum, and the high bit carries to the

next column left.

Adding binary numbers is a very simple task, and very similar to the

longhand addition of decimal numbers. Unlike decimal addition, there is little

to memorize in the way of rules for the addition of binary bits:

0 + 0 = 0

1 + 0 = 1 & 0 + 1 = 1

1 + 1 = 10 & 1 + 1 + 1 = 11

24. What is meant by multilevel gates networks?

Maximum number of gates cascaded in series between an input and output is

the number of levels of gates.

Example: sum of products form is a two level gate network.

We do not count inverter gates.

The number of levels can be increased by factoring the sum of products

expression for AND-OR network, or by multiplying out some terms in the

product of sum expression for OR-AND network.



25. What are the drawbacks of K –map method?

It is a manual technique. We cannot use computers for K – map solution.

Minimization is extremely complicated as the number of variables exceeds 6.

The simplification process depends heavily on human user‟s abilities.

26. State De Morgan’s law.

De Morgan's laws are rules relating the logical operators "and" and "or" in terms

of each other via negation. With two operands A and B:

27. What is the number of bits in ASCII code? What is the need for ASCII code?

ASCII is abbreviated from American Standard Code for Information

Interchange. It is a seven bit code.

This code allows the manufacturer to standardize I/O hardware such as

keyboards, video displays and so on.

28. Simplify : A AB A B

http://en.wikipedia.org/wiki/Logical_operator

http://en.wikipedia.org/wiki/Logical_conjunction

http://en.wikipedia.org/wiki/Logical_disjunction

http://en.wikipedia.org/wiki/Logical_negation



UNIT – IV PART – A

1. Define half adder.

A half-adder is a combinational circuit that can be used to add two bits. It has two

inputs that represent the two bits to be added and two outputs, with one producing

the SUM output and the other producing the CARRY.

2. What do you meant by Encoder?

An encoder is a combinational circuit that converts binary information from 2n

input lines to a maximum of „n‟ unique output lines. The general structure of

encoder circuit is

3. List out the basic types of PLD.

PROM - Programmable Read Only Memory

GAL - Generic Array Logic

PLA - Programmable logic arrays

PAL - Programming Array Logic

Structured ASIC

CPLD - Complex Programmable Logic Devices

FPSC - Field Programmable System Chip

EPLD - Erasable Programmable Device

FPOA - Field Programmable Object Array

Mask-Programmable Gate Array (MPGA)

FPGA - Field Programmable Gate Array

http://www.fpgacentral.com/pld-types/prom-programmable-read-only-memory

http://www.fpgacentral.com/pld-types/gal-generic-array-logic

http://www.fpgacentral.com/pld-types/pla-programmable-logic-arrays

http://www.fpgacentral.com/pld-types/pal-programming-array-logic

http://www.fpgacentral.com/pld-types/structured-asic

http://www.fpgacentral.com/pld-types/cpld-complex-programmable-logic-devices

http://www.fpgacentral.com/pld-types/fpsc-field-programmable-system-chip

http://www.fpgacentral.com/pld-types/epld-erasable-programmable-device

http://www.fpgacentral.com/pld-types/fpoa-field-programmable-object-array

http://www.fpgacentral.com/pld-types/fpga-field-programmable-gate-array



4. Define full adder.

A full adder is a combinational circuit that forms the arithmetic sum of three

Input bits. It consists of 3 inputs and 2 outputs.

Two of the input variables, represent the significant bits to be added. The third

input represents the carry from previous lower significant position.

The block diagram of full adder is given by,

5. What is PLA? How its differ from ROM?

The most flexible PLD is the programmable logic array (PLA), where both the

AND and OR arrays can be programmed. The product term in the AND array may

be shared by any OR gate to provide the required sum of product implementation.

A PLA or PAL (programmable array logic) device is like a baby FPGA which can

be programmed to perform basic logic functions. Tens to hundreds of gates on a

PAL can be connected to perform simple logic functions. A PAL is often read

only, in that after programming you have to perform a complete erase to update it.

A ROM does not perform logic functions, but stores data. A type of ROM might

be EPROM, erasable programmable read only memory.

You can use a ROM as a logic device, by implementing a simple logic table

lookup. Like a truth table. However, it is somewhat wasteful and expensive to do

this compared to actually using a PAL or even a CPLD/FPGA.



6. Define half subtractor.

A half-subtractor is a combinational circuit that can be used to subtract one binary

digit from another to produce a DIFFERENCE output and a BORROW output.

The BORROW output here specifies whether a „1‟ has been borrowed to perform

the subtraction.

7. What is meant by decoder?

A decoder is a combinational circuit that decodes the binary information on „n‟

input lines to a maximum of 2n unique output lines.

The general structure of decoder circuit is

8. Differentiate sum and carry.

The sum output is 1 when any of inputs (A and B) is 1 and the carry output is 1

when both the inputs are 1.

9. What is meant by a full subtractor? Draw a full subtractor circuit.

A full subtractor performs subtraction operation on two bits, a minuend and a

subtrahend, and also takes into consideration whether a „1‟ has already been

borrowed by the previous adjacent lower minuend bit or not.



As a result, there are three bits to be handled at the input of a full subtractor,

namely the two bits to be subtracted and a borrow bit designated as Bin. There are

two outputs, namely the DIFFERENCE output D and the BORROW output Bo.

The BORROW output bit tells whether the minuend bit needs to borrow a „1‟ from

the next possible higher minuend bit.

10. Draw the logic diagram of half – adder.

11. Write a design procedure of combinational circuits.

The Design of the combinational circuits starts from the verbal outline of the

problem and ends in a logic circuit diagram or a set of Boolean functions from

which the logic diagram can be easily obtained.

Steps:

Determine Number of inputs and number of outputs to the system and assign

names to the input and output variables.

Setup a truth table which specifies the output(s) as a function of the input

variables.

Drive the Algebraic Expression for the outputs.

Drive simplified algebraic expressions for the output functions using K-maps,

the Tabulation method, or other similar procedures.

Draw the circuit diagram.



12. Differentiate decoder and encoder.

13. What is the similar between a half adder and a half subtractor?

In this both half adder and subtractor produce a same output for sum and difference.

14. What do you meant by Comparator?

A comparator is a circuit which compares a signal voltage applied to one input of

an op-amp with known reference voltage at other input. It is basically an op-amp

with output + (Vsat).



15. Define Multiplier.

A multiplexer is a digital switch which allows digital information from several

sources to be routed into a single output line.

The basic multiplexer has several data-input lines and a single output line. The

selection of a particular input line is controlled by a set of selection lines.

Normally there are 2n input lines and n selection lines.

16. What is meant by multiple bit adders?

A multi-bit adder adder does not require much more circuitry. The only

improvement that it must have over the 1-bit adder is that it has to account for the

carry bit coming from the previous bit addition. The change is that after the first

adder, there needs to be another one (since we are adding the carry bit in addition

to the regular two bits). Since there can be only one carry bit for the operation, and

both of the adders can yield a carry bit, both carry bits need to be OR'ed together

to be taken into account.

17. Write short notes on ROM.

A Read-only memory (ROM) is essentially a memory device in which permanent

binary information is stored. The binary information must be specified by the

designer and is then embedded in the unit to form the required interconnection

pattern. Once the pattern is established, it stays within the unit even when power is

turned OFF and ON again.

There are four types.

Masked ROM,

Programmable ROM (PROM)

Erasable ROM (EPROM)

Electrically Erasable ROM (EEROM)



18. Define propagation delay.

Speed of operation expressed interms of propagation delay. It is defined as the

time taken for the output of a gate to change after the inputs have charged. It is

measured in „ns‟.

19. What is PAL? How it differs from ROM and PLA?

The PAL consists of a programmable array of AND gates that connects to a fixed

array of gates. This structure allows any sum - of – products (SOP) logic

expression with a defined number of variables to be implemented.

20. What is meant by Combinational circuits?

A combinational circuit consists of logic gates whose outputs at anytime are

determined directly from the present combination of inputs, without regard to

previous inputs.

21. Draw the logic diagram of BCD to Excess 3 code converter.



22. Write the truth table of Full – adder.

23. What is meant by binary decoder?

A binary decoder has „n‟ bit binary input and a one activated output out of 2n

outputs. A binary decoder is used when it is necessary to activate exactly one of 2n

outputs based on an n – bit input value.

24. What are the difference between decoder and demultiplexer?

Decoder:

It is a digital device that converts coded information into another code or

non – coded form. It is a multi – input multi – output logic circuit. The number of

outputs is greater than the number of inputs (n:2n).

Demultiplexer:

Demultiplex means “one into many”. A demultiplexer is a combinational

logic circuits with one input many outputs. But applying control signal, we can

steer the input signal to one of the output lines.



25. Write short notes on priority encoder.

A priority encoder is an encoder that includes the priority function. The operation

of the priority encoder is such that if two or more inputs are equal to 1 at the same

time, the input having the highest priority will take precedence.



UNIT – V PART – A

1. What is sequential circuit?

The Circuits whose outputs depend not only on the present input value but

also the past input value are known as sequential logic circuits.

The mathematical model of a sequential circuit is usually referred to as a

sequential machine.

2. Define flip-flop.

Flip-Flops are synchronous bistable devices (has two outputs Q and Q‟). An

edge-triggered Flip-Flop changes state either at the positive edge (rising edge)

or at the negative edge (falling edge) of the clock pulse and is sensitive to its

inputs only at this transition of the clock.

3. What is shift registers?

A register capable of shifting its binary information in one or both

directions is called shift register. The logical configuration of a shift register

consists of a chain of flip-flops in cascade, with the output of one flip-flop

connected to the input of the next flip-flop. All flip-flops receive common

clock pulses, which activate the shift from one stage to the next.

4. List out the various types of flip-flop.

All flip-flops can be divided into four basic types.

SR flip - flops

JK flip - flops

D flip - flops

T flip - flops



5. Define metastability.

A state which exists between either "valid" digital logic states {an undefined

voltage}.

(Or)

Whenever there are setup and hold time violations in any flip-flop, it enters a

state where its output is unpredictable: this state is known as metastable state

(quasi stable state); at the end of metastable state, the flip-flop settles down to

either '1' or '0'. This whole process is known as metastability.

6. Write the specifications of shift register IC’s

Voltage at Any Pin : - 0.3V to VCC +0.3V

Operating Temperature Range : -55°C to +125°C

Storage Temperature Range : -65°C to +150°C

Absolute Maximum VCC : 18V

Power Dissipation

Dual-In-Line : 700 mW

Small Outline : 500 mW

Operating VCC Range : 3V to 15V

Lead Temperature (Soldering, 10 sec.): 260°C

7. List the function of asynchronous inputs.

The memory commonly used in asynchronous sequential circuits is

time-delayed devices, usually implemented by feedback among logic

gates.

Thus, asynchronous sequential circuits may be regarded as

combinational circuits with feedback.



8. What is meant by trigger?

The state of a flip-flop is switched by a momentary change in the input

signal. This momentary change is called a trigger and the transition it

causes is said to trigger the flip-flop.

9. Derive the characteristic equation of T flip flop.

Characteristic equation of T flips flop:

Characteristic equation: Qn+1= TQn’+ T’Qn

10. What is universal shift register?

The register operates in any of the modes, like SISO, SIPO, PISO, PIPO or

bidirectional. If a register can be operated in all the five possible ways, it is

known as universal shift register.

(Or)

A register which is capable of shifting data both to the right and left is called a

bi-directional shift register. A register that can shift only one direction is called

a uni-directional shift register. If the register has shift and parallel load

capabilities, then it is called a shift register with parallel load or universal shift

register.



11. Draw a block diagram of sequential circuit.

12. Derive the characteristic equation of SR flip flop.

13. Write the specifications of counter IC’s.

Specification

* Logic Base Number : 4516

* Logic IC Function : Binary Up/Down Counter

* Package/Case : 16-DIP

* Supply Voltage Min : 3V

* Supply Voltage Max : 20V

* Operating Temperature Range : -55°C to +125°C



14. Define a register and shift register.

Register

Memory elements capable of storing one binary word. It consists of a group of

Flip-flops, which store the binary information.

Shift Register

A register capable of shifting its binary information in one or both directions is

called shift register.

15. Write down the 74194 IC specifications.

Logic Base Number : DM54194

Logic IC Function : 4- bit bidirectional universal Shift Register

Supply Voltage : 7V

Input Voltage : 5.5V

Package/Case : 16-DIP

Operating Free Air Temperature Range: -55°C to +125°C

Storage Temperature Range: -65°C to +150°C

16. What are the applications of flip-flop?

Counters

Frequency dividers

Shift registers

Storage registers

17. What is meant by synchronous circuit?

Synchronous sequential circuits change their states and output values at

discrete instants of time, which are specified by the rising and falling

edge of a free-running clock signal.

18. Define clock period.

Clock period is the time between successive transitions in the same

direction, that is, between two rising and two falling edges.



19. What is meant by state table?

A table, which consists time sequence of inputs, outputs and flip-flop states, is

called state table. Generally it consists of three section present state, next state

and output.

20. Draw a logic diagram of counters.

Decade counter Logic diagram

Logic diagram of a 3-bit binary counter

21. What is meant by state diagram?

A graphical representation of a state table is called a state diagram.

In the state diagram, a state is represented by a circle and the transition

between states is indicated by directed line connecting the circles. There is no

difference between a state table and a state diagram except in the manner of

representation.



22. Draw the state diagram of JK flip flop.

23. What is meant by asynchronous circuit?

In asynchronous sequential circuits, the transition from one state to

another is initiated by the change in the primary inputs; there is no

external synchronization.

24. Derive the characteristic equation of JK flip flop.

Characteristic equation of JK flips flop:

Characteristic Equation: Qn+1= JQ’+ K’Q

25. What are the bistable elements? It is a circuit having two stable conditions (states). It can be used to store

binary symbols.

Analog & Digital Integrated Circuits - Material (Short Answers)

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