badass tutorial 1 circuits analog digital beginning

8/12/2019 BADASS Tutorial 1 Circuits Analog Digital Beginning

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Ms sandhya Rani Dash

UNIT 1: INTRODUCTION TO DIGITAL CIRCUITS AND SYSTEMS

Structure

1.1 Introduction1.2 Objectives1.3 Signal and its Types1.4 Electronic Circuits and System1.5 Use of Digital Systems

1.5.1 Advantages of digital system

1.5.2 Limitations of digital system

1.6 Design of Digital System

1.6.1 System design

1.6.2 Logic design

1.6.3 Circuit design

1.6.4 Digital Computer

1.7 Multibit Representation of Signals

1.8 Unit Summary

1.1IntroductionDigital systems, in todays world, have great impact on the modern society. Many scientific,industrial, commercial advances have become possible due to the digital systems. Digital

systems like computers, communication systems, digital voltmeters, counters have become animportant part of our life. The operation of these systems based on the principle of digital

techniques.

In digital systems, the data is usually in binary states(0&1),which is processed and storedelectrically to prevent errors due to noise and interfering signals , electronic amplifiers are used

to amplify electrical signals .This types of signals are continuous signals and can have any valuewithin a specified range, called analog signal. On the other hand the electrical signals which have

two discrete values (0 or 1) or levels (low or high) are called the digital signals.

This unit discus about the analog and digital signals, the advantages and limitations of analogand digital systems. The block diagram and functions of a digital computer is also explained

here. Representation of signals by the binary bits is also introduced in this unit. Attempt has beentaken to present the basic concepts used in design and development of digital systems with the

introduction to the principles of digital computer as an example. Multi bit representation ofsignals, different number system and inter conversion of one system to another is explained for

analysis and design of a digital system.


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1.2ObjectivesAfter going through this module you would be able to

i) Define digital systems and analog systemsii) Appreciate the relevance of digital system over analog systemsiii)Explain the basic design of a digital systemiv)Understand the functioning of a digital system (digital computer)

1.3Signal and its TypesWhat is a Signal?

Any thing that carries information is called a signal. It can also be defined as any physical

quantity that varies with time, space or any

other independent variable.For Example:

The variation of temperature /atmosphericpressure of a location

The motion of a particle with respect tospace

Types of Signal

Signals are of two types.

1. Analog or Continuous valued signal2. Digital or Discrete value signal

Analog Signals

Signal that continuously varies with time between two defined intervals is called Analog Signal.

It represents some physical quantities which are analogues to the real quantity.In most of thetimes the variations correspondence to that of the original signal.

For Example

In a transistor radio receiver the receiver receives modulated signals which are analog in nature.These signals are processed by analog circuits and the output obtained is also in analog form

An Analog signal can take on any value across a continuous range of voltage, current or other

metric. It can have an infinite number of values.


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Digital Signals

The electrical signal which has two discrete levels/values is called a digital signal. It consists ofnumber of pulses or digits with discrete levels or values which represents the magnitude of signal

at an instant of time. The value of each pulse is constant. However, there is an abrupt change

from one digit to the next.

The two discrete value of a digital signal can be specified as one of two possibility such as 1 or

0/High or Low/True or False and so on

1.4Electronic Circuits/SystemsWhat is a System?

A system is a physical device that performs an operation on signal

For Example

There are two types of electronic circuits/system

1. Analog circuit/system2. digital circuit/system

Analog Circuit/System

An electronic circuit/system meant to process analog signals is called analog circuit/system. The

voltage and current in an analog circuit/system vary continuously through a given range.

Examples of Analog Devices are: An amplifier, A TV receiver, electric motors, Signalgenerators etc.

Digital Circuits/Systems

An electronic circuit/system meant

to process digital signals is calledanalog circuit/system. Digital

circuits have two discrete voltagelevels. The voltage levels assume a

finite number of distinct values.

Examples of Digital Devices are: Calculators, Digital watch, Refrigerators, Washing machines

etc.Digital circuits are invariably constructed with integrated circuits (IC). An IC is a small silicon

semi conductor crystal called a chip which contains electric components such as transistors,diodes, registers, and capacitors


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As the voltage levels in a digital circuit are switched from one value to another, therefore, thedigital circuits are also called as switching circuits.

Each digital circuit is governed by a set of logic rules, so digital circuits are also called as Logic

circuits

Characteristics of a Digital System

Store, process and manipulation of discrete elements of information through the use of electricpulses which represents binary digits 0 and 1

1.6Use of Digital SystemsDigital systems are commonly used in different aspects such as; i) Computations and data

processing; ii) control systems; iii) communications and measurements etc.

1.6.1 Advantages of digital system

Why do we go for digital system?

The followings are certain important advantages digital system over analog system

Easy to design Easy to store information More versatile High accuracy and precision Less prone to noise Can be fabricated by IC chips

Because of the above mentioned advantages there is wide spread use of digitalsystem/techniques.

1.6.2 Limitations of digital system

The major limitation of digital system is that The Real World Is Analog. Therefore, there is nodigital signal in the real world. Most of the physical quantities are analog in nature. So we have

to process and express these analog quantities digitally. That is to make a digital approximationto an analog quantity. Therefore, first the analog form is converted to digital form and then

processed using digital techniques. The resultant is obtained in analog form for interpretation.Such conversions leads to increase the time of processing and therefore the system become more

complex. However, the limitations are outweighed by number of advantages of digitaltechniques.


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Self Check Exercise -1

Answer the following questions (Q. No. 1-10) selecting most appropriate alternatives given

under each question.

No.1 Which one of the following systems isanalog

i) Electronic Calculatorii) Pressure gaugeiii) Electric Switchiv) An electronic counter used to count

persons entry on exhibition

No.2 Which one of the following systemsis digital

i) Thermometerii) Transistor radio receiveriii) Signal generatoriv) Refrigerator

No.3 Integrated circuits arei) Analogii) Digitaliii)Both analog and digitaliv)Mostly analog

No.4 The rate of change of digital signalbetween high and low level is

i) Very fastii) Fastiii)Slowiv)Very Slow

No.5 Digital circuits mostly used

i) Diodesii) Bipolar transistorsiii) Diode and bipolar transistorsiv) Bipolar Transistors and FETs

No.6 Logic status can only be ----- and 0

i) 3ii) 2iii) 1iv) 0

No.7 Which of these devices have twostates

i) Lampii) Punched Cardiii) Magnetic Tapeiv) All of the above

No.8 The operation of a digital systemcan be performed by using

i) Switchedii) Amplifiersiii) Rectifiersiv) Oscillators

No.9 The devices commonly used formaking digital circuits are

i) Mechanical switchedii) Relaysiii) Vacuum tubesiv) Semiconductor Devices

No.10 The binary electrical switch is ------------- device

i) Analogii) Digitaliii) Both analog and digitaliv)None of the above

Answer the following questions in 50-60 words

11. State the advantages of digital systems over the analog systems? What is the chief limitation

to the use of digital techniques?


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12. Why are digital circuits also called

a) logic circuits, and b) switching circuits

1.7 Design of Digital System

Let us first consider the following block diagram of a digital system

As discussed in 1.5.2 we know that analog signal is a naturally occurring phenomenon in most of

the real life situations. We have to convert the analog domains to digital domains for betterinterpretation

Block diagram of a digital system is shown above where an analog interface is first fed to ananalog to digital converter which converts the analog form into a digital form and then subjected

to process, using digital techniques. The results of processing is again converted back to get ananalog out put through a digital to analog converter for interpretation.

Let us discuss the design of a digital system under different stages such as; i) system design; ii)

logic design; and iii) circuit design.

1.7.1 System design

A digital system comprised of many subsystems and each subsystem has specific characteristics.

For Example:The system design of a digital computer is based on the

- Number and types of memory unit- Arithmetic units

- Input and output devices- Interconnection and control of these subsystems

Let us look at the hierarchic of a digital system as presented below

A

D

C

D

A

CDigital

System

Analog

In putsAnalog

Out puts


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Any digital system has the same hierarchy as explained above.

1.7.2 Logic design

There are numbers of basic logic building blocks. Each block performs a particular function.

The interconnection between basic logic blocks (to perform a specific function) is called Logic

Design

For Example

-Determining the inter conversion of logic gates and flip flops

-This is required to perform binary addition

1.7.3 Circuit design

Interconnection of certain specific components such as resistors, diodes, capacitors, transistors

etc. to form a gate, flip flop or any other building block is called Circuit Design

1.7.4 Digital Computer

The general purpose digital computer is the best known example of a digital system. It is asystem hardware that performs arithmetic operations, manipulates data and makes decision with

greater speed and accuracy. the computer has to given a set of instructions called a programwhich guides it at each step of its operation .Program are placed in the computers memory unit

Functional

Blocks

System Design

Subsystems Modules

Basic UnitsCircuitsDevices &

Com onents


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in binary coded form with each instruction having a unit code. The computer takes theseinstruction codes from memory and performs the operation.

Functional units of a digital computer

Though there are several types of computer system but each system has the same functionalunits. All the units function together to carry out the instructions as per the programme. Let ussee the internal structure of a digital computer and their interconnections

Input device & control The programme and data prepared by the user are fed into the

memory unit by means of inputdevice.

For example: Key board, magnetic tape, punch card reader etc

Memory Unit The memory unit stores programmes, data received from the

input units and also the results of arithmetic and logicoperations received from the arithmetic and logic unit. It also

supplies information to output device

Control unit The control unit supervises the flow of information between

the various units. It retrieves the instruction one by one fromthe programme. For each instruction the control unit informs

the processor to execute the operation specified by theinstruction

Arithmetic and logic

unit

All arithmetic calculations and logical decisions are performedin this unit. The processor manipulates the data as specified by

the programme. The results of this unit is then sent to thememory to be stored there

Input

Unit

Arithmetic &

Logic Unit

Control

Unit

Output

Unit

MEMORY

UNIT


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Output device An output device receives the result of computations and printsout, displaces, or otherwise presents information to the user.

For Example: Printer

1.8 Multibit Representation of Signal

We know that a digital signal can have only two possible levels.

i.e, High and Low/On and Off/true/False

Each level can be presented by the binary digits 1 and 0. The binary number system can be usedfor the analysis and design of a digital system. The accuracy and precision of a digital system can

be improved by increasing the number of levels. i.e., by adding more switches.

For Example

Let us consider two voltage levels 0 to 5 v. These two voltage levels can be represented by the

binary digits 0 and 1 and the switch indicates off and on respectively.

Binary 0 represents 0v (the switch is OFF)

1 represents 5v (the switch is ON)

A signal of two levels (i.e. 0v & 5v) can be represented by a single switch

If a given range of signal is divided into four levels (i.e. 0v, 1.25v, 2.5v, 3.75v & 5v), it can be

represented by a combination of two switchesFor more accuracy the number of levels needs to be increased and therefore, depending upon the

number of levels the signal can be represented by different number of switches.

For Example

The symbols and the respective switches for a four level signal can be represented as

SYMBOLS SWITCH 1 SWITCH

00 OFF OFF

01OFF ON

10 ON OFF

11 ON ON

This is called the binary representation of numbers


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Self Check Exercise-2

Answer the following questions (Q. No. 13-19) selecting most appropriate alternatives given

under each question.

No. 13 Numbers are stored and

transmitted inside a computer in

i) Binary formii) ASC II code formiii)Decimal formiv)Alphanumeric form

No. 14 Which part of the computer

perform arithmetic calculations

i) ALUii) Registeriii) Logic Busiv) None of the above

No.15 Memories are used in the digital

system to store

i) Instructionsii) Dataiii) Intermediate and final resultsiv) All of the above

No.16 A train of pulse is a -------------

signal

i) Analogii) Digitaliii) Both analog and digitaliv) None of the above

No.17 How many levels are used torepresent a digital signal?

i) Twoii)

Threeiii) Four

iv) Five

No.18 The high voltage levelrepresents logic____

i. 0ii.

1iii. Both 1&0

iv. None of the aboveNo.19 The low voltage level representsthe logic_____

i. 0ii. 1

iii. Both 1&0iv. None of the above

No. 20 Registers are used in digital

circuits fori)Storage of informationii) Transmission of information

iii) Storage & Transmission ofinformation

iv) None of the above

Answer the following questions in 50-60 words

21. Name the five major functional units of a digital computer.

22. What are the two voltages normally used to represent binary digits 0& 1?


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1.9 Unit summary

This unit explains the basic concepts of analog and digital signals. The basic features of analog

and digital systems, their advantages and limitations have been given briefly. The block diagram

and functional unit s of a computer and representation of the signals with the binary bits (0&1)

have also been clearly explained in this unit.

Answers to Self check Exercise

1) (ii) 2) (iv) 3) (iii) 4) (i) 5) (iii) 6) (iii) 7) (iv) 8) (i) 9) (iv) 10) (ii)

11.The advantages of digital systems over the analog systems are:

Digital systems are more versatile, easier to design, less affected by noise, more accurate and

precise than analog systems.

The chief limitation to the use of digital techniques is that, real world isnt digital, it is

analog.

12. Digital circuit is called logic circuits, because each type of digital circuit obeys a certain set

of logic rules.

Digital circuit are called switching circuits, because the voltage level in a digital circuit

are assumed to be switched from one value to another instantaneously.i.e the transition time

is assumed to be zero.

13) (i) 14) (i) 15) (iv) 16) (ii) 17) (i) 18) (ii) 19) (i) 20) (i)

21. The five major functional units of a digital computer are:

Input unit, memory unit, control unit, arithmetic & logic unit , output unit (all details are

explained at section 1.7.4)

22. The two voltages normally used to represent binary digits 1& 0 are, HIGH & LOW. The

binary digit 1 represents the HIGH voltage and the binary digit 0 represents the LOW

voltage. The switching circuits, in which there are only two voltage levels, are easier to

design.


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References

Hall, D. V. (1989) Digital Circuits and Systems; McGraw-Hill International Editions; Singapore

Jain, R. P. (2007) Modern Digital Electronics; Third Edition; Tata McGraw-Hill PublishingCompany Limited; New Delhi

Kumar, A. A. (2004) Fundamentals of Digital Circuits; Seventh Edition; Eastern EconomyEditions; Prentice- Hall India Pvt. Ltd; New Delhi

Mano, M. M. (2006) digital Logic and Computer Design; Second Edition; Eastern Economy

Editions; Prentice- Hall India Pvt. Ltd; New Delhi

Srinivasan, P. ( 2007) National Programme Technology Enhanced Learning Video Lectures onIntroduction to Digital Circuits and System. Lecture I & II

Unit End Exercise

1. What do you mean by the term signal? Distinguish between analog and digital signal with real

life experiences.

2. Distinguish between analog and digital circuits. Explain with relevant examples of each.

3. Explain the design of a digital system.

4. Functional applicability of digital systems are more relevant in the real world. Explain with

suitable example.

5. Illustrate various functions of digital logic.

badass tutorial 1 circuits analog digital beginning

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