lecture notes

1. Digital Logic
K.V. Rop 1
Chapter 1:
Introduction to Digital Logic
Lecturer: Nelson Bett

2. Introduction
Course outline
ICS 2205 Digital Logic Course Outline.docx

3. Analog vs Digital
+5
V
–5
Ti me
Digital:
• Discrete Levels, less sensitive to noise
• Accuracy related to cost (number of
“bits”)
• Less susceptible to noise
Analog:
• Continuous Values
• Fast, economical, low accuracy
• Susceptible to noise & distortion

4. Digital System
 Digital systems process digital signals which can take only a limited
number of values (discrete steps), usually just two values are used:
the positive supply voltage (+Vs) and zero volts (0V).
 Digital systems contain devices such as logic gates, flip-flops, shift
registers and counters.
 The general purpose digital computer is a best known example of digital
system.
A digital meter can display
many values, but not every
value within its range. For
example the display can show
13.81 and 13.82 but not a value
between them.

5. Disadvantages of Digital Systems
 Use more energy than analog circuits to accomplish the same
tasks, thus producing more heat as well.
 Digital circuits are often fragile, in that if a single piece of digital
data is lost or misinterpreted the meaning of large blocks of
related data can completely change.
 Digital computer manipulates discrete elements of information
by means of a binary code.
 Quantization error during analog signal sampling.

6. Information Representation Signals
 Information variables represented by physical quantities.
 Digital systems
 The variables take on discrete values.
 Two level or binary values are the most prevalent values in digital
systems.
 Binary values are represented abstractly by:
 digits 0 and 1
 words (symbols) False (F) and True (T)
 words (symbols) Low (L) and High (H)
 and words On and Off.
 Binary values are represented by values or ranges of values of
physical quantities

7. Signal Examples over time

9. Application of Logic Circuits
 Computers: The brain, body, and limbs of computer systems –
Everything except peripherals
 Embedded Systems: The brains that control the system (e.g.
avionics, auto electronics, microwaves, etc.)
 Digital Signal Processing (DSP): E.g. in Cellular phones, Digital TVs,
e.t.c