Digital Logic Design

(DLD)

CHAPTER ONE
Introduction to Digital System

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Introduction
• Most of the Electronic device consists of two
Integrated system
1. Hardware
2. Software
• Hardware : Circuit that executes the program
commands.
• Software : program that control hardware to
execute user wishes.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
Digital Logic design(DLD)

• Digital logic design is a system in Electrical

and computer Engineering that uses simple
number value to produce input and output
operations.
• DLD used in :- To develop hardware
Circuit board
microchip processor
Integrated circuits (IC)

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 1.1. Introduction to Digital system
Ø A system is a set of related components that work as a whole to achieve a
goal. A system contains inputs, behavior and outputs.

Ø Components are electronics blocks – digital, analog, or mixed signal

Ø Digital systems are designed to store, process, and communicate
information in digital form.
Ø They are found in a wide range of applications, including process
control, communication systems, digital instruments, and consumer
products.
Ø The digital computer, more commonly called the computer, is an
example of a typical digital system.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 1.1. Introduction to Digital system
Digital systems can process, store, and transmit data more
efficiently but can only assign discrete values to each point.
Digital Circuitry
v The fundamental of digital computer
v Automated control system
Example : Modern home digital circuitry controls
Appliance
Alarms
Heating systems

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Ø Digital circuitry includes the Area of
Automated Machine control
Energy Monitoring and control
Inventory management
Medical Electronics
Music
Ø Digital Electronics :
Evolved from the principle that Transistor circuitry could
easily be fabricated and designed to the output one of the two
Voltage level.
5 volt which is represented High
0 volt low
Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Digital Versus Analog system
v Digital system operates on discrete digits that represents
Number ,letters and symbols.
v They deal strictly with ON and OFF states
Ø Analog System : Measure and responds to continuously
Varying Electrical or Physical magnitude.
Ø Analog device are integrated Electronically into system to
continuously monitor and control variables :-
Temperature
Pressure
Velocity and Position

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Digital representation of Analog Quantities
Most natural quantities that we see are analog and vary
continuously. Analog systems can generally handle higher
power than digital systems.

Analog signal –Continuously variable electrical or physical

quantity (continuous motion of signal).
Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
Why do we need to use digital representation in a world
that is naturally Analog ?

• Answer –If we want an Electronic Machine to:-

Interpret
Communicate
process
Store analog Information
It is much easier for machine to handle it if we first
converted the information to a digital format.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 The Advantage of Digital over Analog

vDigital representation has certain advantages over analog

representation in electronics applications.
vFor one thing, digital data can be processed and
transmitted more efficiently and reliably than analog
data.
vAlso, digital data has a great advantage when storage is
necessary.
vNoise (unwanted voltage fluctuations) does not affect
digital data nearly as much as it does analog signals.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Analog and Digital Systems

Many systems use a mix of analog and digital electronics to

take advantage of each technology.
A typical CD player accepts digital data from the CD drive
and converts it to an analog signal for amplification.
CD drive

10110011101 Digital-to-analog Linear amplifier

Digital data converter Analog
reproduction
of music audio Speaker
signal
Sound
waves

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
The process of converting analog sound to digital and then
back to analog.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Binary Digits

v Each of the two digits in the binary system, 1 and 0, is called a bit,
which is a contraction of the words binary digit.
v In digital circuits, two different voltage levels are used to represent
the two bits. Generally, 1 is represented by the higher voltage,
which we will refer to as a HIGH, and a 0 is represented by the
lower voltage level, which we will refer to as a LOW.
positive logic HIGH =1 and LOW = 0
Negative logic 1 is represented LOW=1 and High= 0
v Groups of bits (combinations of 1s and 0s), called codes, are used
to represent numbers, letters, symbols, instructions, and anything
else required in a given application.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Logic Levels
Ø The voltages used to represent a 1 and a 0 are called logic levels.
Ideally, one voltage level represents a HIGH and another voltage level
represents a LOW. In a practical digital circuit, however, a HIGH can
be any voltage between a specified minimum value and a specified
maximum value. Likewise, a LOW can be any voltage between a
specified minimum and a
specified maximum. There can be no overlap between the accepted
range of HIGH levels and the accepted range of LOW levels
VH(max)
Ø In binary, a single number is HIGH
called a bit (for binary digit). VH(min)
(Binary 1)
A bit can have the value of Invalid
either a 0 or a 1, depending VL(max)

on if the voltage is HIGH or LOW

(Binary 0)
LOW. VL(min)

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Digital Waveforms
Ø Digital waveforms consist of voltage levels that are changing
back and forth between the HIGH and LOW levels or states.
Ø A positive going pulse is one that goes from a normally LOW
logic level to a HIGH level and then back again.
Ø The negative-going pulse is generated when the voltage goes
from its normally HIGH level to its LOW level and back to
its HIGH level. Digital waveforms are made up of a series of
pulses.
HIGH HIGH
Rising or Falling or Falling or Rising or
leading edge trailing edge leading edge trailing edge

LOW LOW
t0 t1 t0 t1

(a) Positive–going pulse (b) Negative–going pulse

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Pulse Definitions

Actual pulses are not ideal but are described by the rise time,
fall time, amplitude, and other characteristics.

Overshoot
Ringing
Droop
90%
Amplitude tW
50%
Pulse width

10%
Ringing

Base line Undershoot

tr tf
Rise time Fall time

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Periodic Pulse Waveforms
Periodic pulse waveforms are composed of pulses that repeats
in a fixed interval called the period. The frequency is the rate
it repeats and is measured in hertz.
1 1
f  T
T f

The clock is a basic timing signal that is an example of a

periodic wave.
What is the period of a repetitive wave if f = 3.2 GHz?
1 1
T   313 ps
f 3.2 GHz

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Pulse Definitions

In addition to frequency and period, repetitive pulse waveforms

are described by the amplitude (A), pulse width (tW) and duty
cycle. Duty cycle is the ratio of tW to T.
Volts

Pulse
width
Amplitude (A)
(tW)

Time
Period, T

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Timing Diagrams

A timing diagram is used to show the relationship between

two or more digital waveforms,
Clock

A diagram like this can be observed

directly on a logic analyzer.

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 Serial and Parallel Data

Data can be transmitted by either serial transfer or parallel

transfer.

1 0 1 1 0 0 1 0
t0 t1 t2 t3 t 4 t5 t6 t7
Computer Modem

1
Computer Printer
0

0
t0 t1

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved
 End of Chapter one
Thank you !!

Floyd, Digital Fundamentals, 10th ed © 2009 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved