Digital Waveforms-Digital Electronics I- Lecture 01 Slides-Electronics and Communication Engineering, Slides of Digital Electronics

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EEE130 Digital Electronics I

Lecture #1_

• Digital Waveforms -

By Dr. Shahrel A. Suandi

Digital Waveforms

• Types of pulse: ideal and non-ideal
• Non-ideal pulse
  • Real applications exhibit this characteristic
  • Overshoot and ringing – produced by stray inductive and capacitive effects
  • Droop – caused by stray capacitive and circuit resistance (forming an RC circuit) - Important items: - Rise time - Fall time - Amplitude - Pulse width

Waveform Characteristics

• Series of pulses can be found in digital systems – called as pulse trains
• This can be further classified as periodic and nonperiodic
  • Periodic – repeating the same waveform at a fixed interval, called period (T)
  • Nonperiodic – opposite to periodic, where the waveform does not repeat itself at a fixed interval
• Terms to be remembered (and of course to understand) are
  • Period – total of time that a waveform repeats itself
  • Frequency – rate of how many times a waveform repeats itself
  • Duty cycle – ratio of the pulse width to the period in percentage
• Examples:

Relationships between period,

frequency and duty cycle

• Period:
• Frequency:
• Duty cycle:

T =

f

f =

T

DutyCycle =

tW T

Clock

• Must be periodic!!!
• Used to synchronize all waveforms in digital systems
• Each interval between pulses in clock equals the time for one bit
• It, itself does not carry any information

Timing diagrams

• Using timing diagrams, we may know:
  • The states of all waveforms at any specified time
  • The exact time a waveform changes relative to other waveforms
• In the example below, notice that all three waveforms are HIGH only during bit time 7 and change back to LOW at the end of bit time 7

Serial transfer

• Data are transferred in serial form from

one point to another

• During the time interval from to , the

first bit is transferred

• Slow. Why??
  • The data have to transferred one by one
• Advantage:
  • Requires only one line

t 0 t 1

Parallel Transfer

• Data are transferred in parallel form from

one point to another

• During transfer, all the bits in a group are

sent out on separate lines simultaneously

• Fast. Why??
  • A few bits can be sent at one time
• Disadvantage:
  • Requires a few lines

Basic Logic Operations

• Something about logics:
  • 1850s – Geoge Boolean (Irish logician and mathematician) developed a mathematical system for formulating logic statements with symbols so that problems can be written and solved in a manner similar to ordinary algebra
  • Real world basic example:
    • “The light is on” – we need to think about the bulb‟s condition and the switch. What is all this about?? Let‟s think!!!
• The term “logic” is applied to digital circuits to implement logic functions
• Basic logic operations are NOT, AND and OR

NOT

• One input and one output
• Also known as „inverter‟. Why??
  • The output will always opposite to the input
• Definition:
  • Operation that changes one logic level to the opposite logic level

OR

• Input can be at least two and output is one
• Definition:
  • Operation produces a HIGH output when one

or more inputs are HIGH

What we have learnt today??

• Digital waveforms and the characteristics
• Clock and time diagram
• Data transfer
• Basic logic operations