Introduction to digital design (EEEg4302)

1. Digital Logic Design (EEEg4302)
Chapter 1 : Introduction to Digital Design
AASTU
Department of Electrical and
Computer Engineering
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By Milkias H.

2. Outline
• Chapter 1 : Introduction to Digital Design
• Digital and Analogue Quantities
• Binary digits, Logical levels and Digital wave form.
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3. Digital and Analogue Quantities
• What is signal ?
o In electronics, a signal is an electric current or electromagnetic field used to
convey data (encode message) from one point to another.
• How electric current can be used to encode a messages ?
o By varying the voltage of an electric current.
o A message can be encoded by changing the voltage of an electric current is called
electronic signal.
o The use of electric current for this purpose is called electronics.
• Electronic signals can be analog or digital signals.
o Analog signals : consists of continuously changing voltage in an electric current. It
is a set of continuous values with infinitely small variations. The quantity that has
continuous values is called as the analog quantity.
o Digital signals : consists of rapid pulses of voltage that repeatedly switches the
current off and on. It is a set of discrete values with in instantaneous change
sampled at moments in time and quantized. The quantity that has a discrete set of
values is called as the digital quantity.
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4. Digital and Analogue Quantities
• Why are we changing analog to digital?
The four main advantages of digital.
o Digital data can be processed more efficiently.
o It can be transmitted more efficiently and reliably.
o It can be stored more compactly.
o It can be reproduce with greater accuracy and clarity
o Security
o Cost and so on.
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} Noise (unwanted fluctuation)
affects analog signal
more than the Digital one.

5. Outline
• Chapter 1 : Introduction to Digital Design
• Digital and Analogue Quantities
• Binary digits, Logical levels and Digital wave form
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6. Binary Digits
• Digital electronics involves circuits and systems in which there are two types of
possible states.
• These states are represented by two different voltage levels: HIGH and LOW.
• In digital systems such as computers; combinations of two states, called codes,
are used to represent numbers, symbols, alphabetic characters and other types
of information.
• The two-state number system is called binary and its two digit are called Binary
Digit: 0 and 1.
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7. Binary Digits
Each of the Binary digit '0’ and ‘1’ is called bit (A unit of measurement of information).
• In digital circuits, two different voltage levels are used to represent the two bits.
Generally;
o 1 is represented by the higher voltage (HIGH) and
o 0 is represented by the lower voltage (LOW).
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8. Logic Levels
A logic level is a specific voltage or a state in which a signal can exist. Usually, the
term refers to binary logic in which two levels or states can exist: logic 1 (also called
the high state) and logic 0 (also called the low state).
The voltage used to represent a ‘1’ and ‘0’ are 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 specified maximum value. Likewise for a LOW
voltage levels.
• There can be no overlap between the accepted range of HIGH levels and the
accepted range of LOW levels.
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9. Logic Levels
The voltage values between VH(min) and VL(max) are unacceptable for
proper operation (invalid or uncertain region).
● The voltage values between VH(max) and VH(min) are HIGH.
● The voltage values between VL(max) and VL(min) are LOW.
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10. Digital Waveforms
• Digital waveforms consists of voltage levels that are changing back and forth
between the HIGH and LOW levels or states.
• Usually these waveforms are represented as timing diagrams used to represent
wave behavior relative to time.
• Pulse have two edge
• A leading edge where pulse goes to HIGH from LOW state and falling edge where
pulse revert.
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11. Digital Waveforms
• Sudden transition from one state to other is impractical (ideal). Depending on
practical consideration it will take small amount of time to get from one state to
another.
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Rise Time → time required for pulse to go from LOW level to HIGH.
Fall Time → time required for pulse to go from HIGH level to LOW.
Amplitude → the maximum value of a digital waveform.
Pulse Width → the time gap between the raising edge and falling edge.

12. Digital Logic Design
• Digital logic design is a system in electrical and computer engineering that uses
simple number value to produce input and output operations.
• Digital logics are rooted in binary code.
• This system facilitates the design of electronics circuits that convey information,
including logic gates with functions that include AND, OR and NOT commands.
• The value system translates input signals into specific output. These functions
facilitate computing, robotics and other electronics applications.
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13. Last slide
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