TON DUC THANG UNIVERSITY
FACULTY OF ELECTRICAL & ELECTRONICS ENGINEERING
DEPARTMENT OF ELECTRONICS & TELECOMMUNICATIONS
ENGINEERING
CHAPTER 3:
LOGIC GATES
DIGITAL SYSTEM DESIGN 1
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ACKNOWLEDGEMENT
The picture content of this slide is from
Thomas L. Floyd, [2015],Digital Fundamentals,
11e. Prentice Hall.
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OUTLINE
1. The inverter
2. The AND gate
3. The OR gate
4. The NAND gate
5. The NOR gate
6. The Exclusive-OR gate
7. Fixed-Function logic
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OBJECTIVES
 Describe the operation of logic gates
 Express the operation of logic gates with
Boolean algebra
 Recognize and use both the distinctive
shape logic gate symbols and the rectangular
outline logic gate symbols of ANSI/IEEE
Standard 91-1984
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OBJECTIVES
 Construct timing diagrams showing the
proper time relationships of inputs and outputs
for the various logic gates
 Comparison between CMOS & bipolar (TTL)
ICs
 Use logic gates in simple applications
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INTRO TO BOOLEAN ALGEBRA
Wikipedia: George Boole. Wikimedia Foundation, Inc. 22 July. 2015. Web 20 Jan. 2016
<https://en.wikipedia.org/wiki/George_Boole>
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INTRO TO BOOLEAN ALGEBRA
 Constants and variables have only two
values: 0 or 1
 Operations of Boolean Algebra:
 AND
 OR
 NOT (complement)
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INTRO TO BOOLEAN ALGEBRA
There are 3 ways to describe a digital circuit:
 Schematic diagram
 The distinctive shape symbol
 The rectangular outline symbol
 Truth table
 Boolean expression
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INVERTER
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AND GATE
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OR GATE
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EXCLUSIVE-OR GATE
Ex-OR gate, XOR gate
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THE COMPLEMENT OF BASIC
LOGIC GATES
 NAND gate
 NOR gate
 XNOR gate
Truth table, Boolean expression, and waveform?
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ENABLE/DISABLE USING
AND GATE
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ENABLE/DISABLE USING
OR GATE
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FIXED FUNCTION LOGIC
 Two major fixed function logic families are
TTL and CMOS.
 A third technology is
combines TTL & CMOS.
BiCMOS,
which
ASSIGNMENT:
 What is CMOS made of?
 What is TTL made of?
 Which one consume less power?
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FIXED FUNCTION LOGIC
 Some common gate configurations:
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SIMPLE APPLICATION
 An OR gate is used to detect exceed of
temperature or pressure and produce
command signal for the system to take
required actions
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SIMPLE APPLICATION
Burglar alarm:
 Switch is closed one input of the NAND gate
is LOW.
 LDR is in the light the other input is LOW.
 Output is HIGH and the buzzer sounds.
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SUMMARY
In this chapter, we have learned:
 the description on the operation of logic
gates
 the operation of logic gates with Boolean
algebra
 different standards of logic gate symbols
 timing diagrams of different logic gates
 the comparison between CMOS & bipolar
(TTL) ICs
 the use of logic gates in simple applications
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HW #3
DIGITAL FUNDAMENTALS 11th edition (borrow
from the library)
 Prob: pg 170 – 174 every even problem
 Prepare chap 4: Boolean algebra simplification
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