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ECE- 1551
DIGITAL LOGIC
LECTURE 1: INTRODUCTION AND BASICS
Assistant Prof. Fareena Saqib
Florida Institute of Technology
Spring 2016, 01/12/2016
Introduction to Digital Systems and Applications
 Digital is derived from the way the operations are performed.
 Applications of digital systems:






Computer systems
Television
Communication systems
Radar
Navigation
Medical Instrumentation
Analog and Digital Systems
 Most natural quantities that we see are analog and vary continuously. Analog
systems can generally handle higher power than digital systems.
 Digital systems can process, store, and transmit data more efficiently but can only
assign discrete values to each point.
Temperature
(°F)
100
95
90
85
80
75
70
Time of day
1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
A .M .
P.M .
Analog and Digital Systems Cont.
 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 data
Digital-to-analog
converter
Linear amplifier
Analog
reproduction
of music audio
signal
Speaker
Sound
waves
Binary Digits and Logic Levels
 Digital electronics involves circuits and systems
that have only two possible states, which are
represented by two different voltage levels called
HIGH and LOW.
The voltages represent
numbers in the binary system.
 In binary, a single number is called a bit (for
binary digit). A bit can have the value of either a
0 or a 1, depending on if the voltage is HIGH or
LOW.
VH(max)
HIGH
VH(min)
Invalid
VL(max)
LOW
VL(min)
Digital Pulse and Waveforms
 A pulse is a transition from one voltage level to another. A positive going pulse is
one that goes from a normally LOW logic level to a HIGH level and then back again.
HIGH
HIGH
Rising or
leading edge
LOW
Falling or
trailing edge
t0
(a) Positive–going pulse
t1
Falling or
leading edge
LOW
Rising or
trailing edge
t0
t1
(b) Negative–going pulse
 Digital waveforms change between the LOW and HIGH levels. Digital waveforms are
made up of a series of pulses.
Volts
Period, T
Amplitude (A)
Time
Pulse
 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
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.
f 
1
T
T
1
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?
T
1
1

 313 ps
f 3.2 GHz
Periodic Pulse Waveforms
 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
Amplitude (A)
Pulse
width
(tW)
Time
Period, T
Timing Diagrams
 A timing diagram is used to show the relationship between two or more digital
waveforms,
Clock
A
B
C
Syllabus
 Has been posted on canvas.
Next Class
 Study Number Systems