Chapter One Flashcards
Analog Quantity VS Digital Quantity
An analog quantity is one having continuous values. Examples:
Temperature, Pressure, Level, Position, Volume, Voltage, Current
A digital quantity is one having a discrete set of values. Examples:
• Digital Watch reading – (Time of the day in minutes/seconds)
• Number of coins
• Energy levels for an electron in an atom.
• Human population of a city (it changes with the time)
• People travel from/to the city
Examples of Digital System»>
– Digital Computer – Handheld Calculator – Digital Watch – Telephone system – Digital audio and video equipment
ADVANTAGES OF DIGITAL OVER ANALOG
- Data Processing and Transmission – more efficient and reliable
- Data Storage – more compact storage and greater accuracy and clarity in
reproduction - Ease of design – In switching circuits, only the range in which the voltage
or current fall is important not the exact values - Accuracy and precision are easier to maintain – In analog systems, voltage
and current signals are affected by temperature, humidity but in digital
systems, info. does not degrade - Easy Programmable operation
- Less affected by noise since exact value is not important in digital
systems - Ease of fabrication on IC chips – analog devices cannot be economically
integrated.
THE LIMITATIONS OF DIGITAL TECHNIQUES?
– The real world is analog
– The analog nature of the world requires a time consuming
conversion process:
1.Convert analog inputs to digital
2.Process (operate on) the digital information
3.Convert the digital output back to analog
POSITIVE LOGIC VS NEGATIVE LOGIC
• Positive Logic HIGH = 1 Low = 0 Logic Levels - The voltages used to represent a 1 and a 0 Ex: For TTL ,HIGH=2V to 5 V LOW=0 V to 0.8 V
• Negative logic
High =0
Low =1
RISE TIME, FALL TIME, PULSE WIDTH IN DIGITAL WAVEFORMS»>
Rise Time – measured from 10% of the pulse amplitude to 90% of the pulse
amplitude
Fall Time - measured from 90% of the pulse amplitude to 10% of the pulse
amplitude
Pulse Width – Time interval between the 50% points on the rising and falling edges
Periodic Vs Non-periodic
• Periodic pulse waveform
One that repeats itself
at a fixed interval,
called a period
• Non-periodic pulse waveform composed of pulses of randomly differing time interval between pulses (pulse width)
Period Vs Frequency
• Frequency (f) is the rate at which it repeats itself
- measured in cycles per second or Hertz (Hz)
• Period (T) is the time required for a periodic
waveform to repeat itself
- measured in seconds
• Relationship between frequency and period
f = 1/T
T = 1/f
WHAT IS Duty Cycle?
Duty cycle is the ratio of the pulse width to the period and expressed as a
percentage Duty cycle = (tw/T)100%
Timing Diagrams
• Timing Diagram- a graph of digital waveforms showing the actual relationship of
two or more waveforms and how each waveform changes in relation to the others
• used to show how digital signals change with time.
• used to compare two or more digital signals.
• The oscilloscope and logic analyzer are used to produce timing diagrams.
• Here waveforms A, B, and C are HIGH only during bit time 7
Serial Transfer VS Parallel Transfer
• Serial Transfer
- Sent one bit at a time along a single conductor
- Advantage: only one line is required
- Disadvantage: It takes longer to transfer a given number of bits
•Parallel Transfer - all the bits in a group are sent out on separate lines at the same time - Advantage: Speed of transfer – more - Disadvantage: More lines are required
Integrated circuits:
– Small Scale Integration (SSI): 1-10 gates
– Medium Scale Integration (MSI): 10-100 gates
– Large Scale Integration (LSI): 100-10,000 gates
– Very Large Scale Integration (VLSI): 10,000- >
100,000,000 gates
LEVELS OF IC
LV.1:
Electronic components, e.g.
transistors,
diodes, resistors, capacitors [Components level]
LV.2:
Functional logic unit, e.g. gates,
NOT, AND, NAND [First IC level (SSI)]
LV.3:
Functional logic unit, e.g.
adders, counters, multiplexers [Second IC level (MSI
and LSI]
LV.4:
More complex functional logic
unit, e.g. microprocessor [Third IC level (VLSI)]
LV.5:
Complex systems, functional units
from levels two through four
Bipolar Families:
Bipolar Families:
• The bipolar families of logic circuits construct, especially from components fabricate bipolar transistor on the chip.
• In the bipolar category there are three basic families called Diode transistor logic(DTL), Transistor Transistor Logic(lTL) and Emitter Coupled Logic (ECL).
• DTL uses diodes and transistor, TTL uses transistors almost exclusively, TTL has become the most popular family in SSI (Small scale integration) and MSI( medium scale integration) chips, while ECL is the fastest logic family which is used for high speed applications.
MOS Families
MOS Families:
• The MOS family fabricates MOS field effect transistor (MOSFETs).
• In the MOS category’ there are three logic families namely PMOS(p-channel MOSFTEs) family, NMOS(n-channel MOSFET) family and CMOS(Complementary MOSFET) family.
• PMOS is the oldest and slowest type. NMOS used for LSI (large scale integration) field for microprocessors and memories.
• CMOS which uses a push pull arrangement of n-channel and p-channel MOSFETs, is extensively used where low power consumption is needed such as in pocket calculators.
