Download Digital Hardware Systems Digital Systems vs. Analog systems

Introduction
CS3402
Digital Logic Design
Reading Assignment: Chapters 0 & 1
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Digital Hardware Systems
Electronic systems:
• Digital Systems vs. Analog systems
• Digital vs. Analog Signals
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0
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Time
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Digital:
only assumes discrete values
Analog:
values vary over a broad range
continuously
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Digital Hardware Systems
Advantages of Digital Systems
• Analog systems: slight error in input yields large error in output
• Digital systems are more accurate and reliable:
 can deal better with degraded signals
• Digital signals are generally easier to process
• Current general purpose computers are digital
• Real life signals (e.g. human voice) are analog
• Interface circuits (i.e. sensors & actuators) are often analog
• Digital signals are generally used as an approximation to real
analog signals
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Binary Digital Systems
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High
Noise
margin
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Low
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time
• The simplest digital systems are binary digital systems
– only two discrete values
» easier to decode
– rigorous mathematical foundation based on logic & Boolean
algebra
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Digital Hardware Systems
Digital Binary Systems
• Two discrete values:
high voltage, high current flowing, ON, TRUE, YES, "1"
low voltage, low current flowing, OFF, FALSE, NO, "0"
• Advantage of binary systems:
• rigorous mathematical foundation based on logic & Boolean Algebra
• Math. Logic allows to reason about the truth of a set of
statements
IF( the garage door is open) AND ( the car is running)
THEN the car can be backed out of the garage
• “the garage door is open”, “the car is running”, “the car
can be backed out of the garage” are logical propositions
that can be TRUE or FALSE.
• AND is a logical operator: The two preconditions must be
True for the conclusion to be true
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Digital Hardware Systems
• Boolean Algebra
– Deals with logical propositions/statements and their
logic values: A logical statement can be either TRUE or
FALSE ( 0 or 1).
– provides algebraic formulation of how to combine logic
values.
» Logic operators
• At the hardware level:
– Each logical statements is represented with an
electrical signal.
– The logic value of a statement is represented with the
signal’s voltage level
Example:
High voltage level => Statement is True
Low voltage level => Statement is False
– Logic operators are represented with Logic Gates
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Digital Hardware Systems
Boolean Algebra and Logical Operators
Three basic Logical Operations: AND, OR, NOT
X
Y
X AND Y
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T
T
F
T
F
T
F
F
F
T
X
Y
Low
Low
High
High
X
Y
X AND Y
X
0
0
1
1
0
1
0
1
0
0
0
1
0
0
1
1
Y
0
1
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Low
High
Low
High
X OR Y
0
1
1
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X AND Y
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Low
Low
High
X
NOT X
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1
1
0
Any Boolean function can be realized using AND, OR and NOT
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Digital Hardware Systems
Hardware Systems and Logical Operators
IF the garage door is open
AND the car is running
THEN the car can be backed out of the garage
door open?
Low/0
Low/0
High/1
High1
car running?
Low/0
High/1
Low/0
High/1
Door Open
back out car?
Low/0
Low/0
Low/0
High/1
Back out car
Car running
AND gate
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Digital Hardware Systems
• Logic gates are the standard building blocks used to build primitive
logic operations
• Digital Technologies:
• Electron Tube technology
– Electron tubes, resistors and capacitors
– interconnected with copper wire
• Discrete Transistor technology
• Resistor-Transistor Logic (RTL)
• Diode-Transistor Logic (DTL)
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Integrated Circuits (ICs)
• Integrated circuit technology
» Uses conducting, non-conducting, and semi-conducting (i.e.
“sometimes conducting” ) materials
» the basic component: Transistor (electrically controlled
switch)
» An Integrated Circuit (IC): a device (a chip) that contains from
few to several million transistors
=> Small size, low power consumption, high speed
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Integrated Circuits (ICs)
Two Main IC Technologies:
• Bipolar
– Transistor-Transistor Logic(TTL):
Medium Power Consumption, Medium Speed
• SSI, MSI
– Emitter Coupled Logic (ECL):
High Power Consumption, High Speed
• SSI, MSI, LSI
• CMOS:Complementary Metal-Oxide-Silicon
Low Power Consumption, Medium Speed
• VLSI
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Integrated Circuits (ICs)
• Scales of integration
– Small Scale integrated Circuits (SSI)
» ICs with 1 to 10 gates
» Independents gates
– Medium Scale integrated Circuits (MSI)
» ICs with 10 to 100 gates
» IC performs one standard function (e.g. decoder,
Multiplexer, counter, adder, etc.)
– Large Scale integrated Circuits (LSI)
» ICs with 100 to 1000s of gates
» IC performance relatively complex functions (e.g. an
ALU, a memory device, etc.)
– Very-Large Scale integrated Circuits (VLSI)
» Ics with 1000s to millions of gates
» Processors, Memories, etc.
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» CMOS technology
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Digital Hardware Systems
CMOS Technology
Transistor : basic electrical switch
Gate
Drain
Sourc e
three terminal switch: gate, source, drain
when voltage between gate and source exceeds a certain threshold
the switch is conducting or "closed"
=> electrons flow between source and drain
when voltage is removed, the switch is "open" or
non-conducting
=> connection between source and drain is broken
Control
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Switch
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Digital Hardware Systems : Switches
A transistor can be represented as a switch
A switch connects two points under a control signal.
Normally Open
when the control signal is 0 (false), the switch is open
when it is 1 (true), the switch is closed
Normally Closed
when control is 1 (true), switch is open
when control is 0 (false), switch is closed
True
Control
Closed
Switch
True
Control
False
Normally Open
Switch
Open
Switch
False
Normally Closed
Switch
Open
Switch
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Closed
Switch
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Implementation of AND and OR Functions with Switches
A
B
The output is True if and only if
False
A AND B are True.
output
=> this circuit realizes the AND
function
True
Abstract Representation:
A
OR
Output
B
AND gate
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Implementation of AND and OR Functions with Switches
A
B
False
Output is True iff A is True OR
B is True (or both are True)
output
=> The circuit realizes the OR
function
True
Abstract Representation:
A
Output
B
OR gate
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• Semi-conductor material => Transistors
• Transistors => Logic Gates
• Gates => any switching function
– Arithmetic: Adders, Multipliers, Dividers, etc.
– Logic
» ALU
– Storage Devices: registers, memory
– Control Devices
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Digital Systems Design Hierarchy
System-level
microprocessors, storage units,
buses.
Register-level
registers, adders, multipliers,
control units, etc.
Gate-level
AND, OR, NOT, EX-OR gates
counters, multiplexers,
decoders, laches, etc.
Transistor-level
Transistors, diodes, resistors,
capacitors, etc.
This course is about logic design, not system design (processor
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architecture), not circuit design
(transistor level)
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Course Coverage
• Binary Number Systems and Codes
• Boolean Algebra
• Analysis, Synthesis, and
implementation of Combinational
Circuits
• Analysis, Synthesis, and
implementation of Sequential Circuits
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