Digital Electronics
Mr. S.S.Abeywickrama
Department of Physics
University of Ruhuna
Analog vs. Digital
Analog and digital signals are used to transmit information, usually
through electric signals. In both these technologies, the information,
such as any audio or video, is transformed into electric signals. The
difference between analog and digital technologies is that in analog
technology, information is translated into electric pulses of varying
amplitude. In digital technology, translation of information is into
binary format (zero or one) where each bit is representative of two
distinct amplitudes.
Digital electronics
• Analog vs. Digital
•
Deparment of Physics, University of
Ruhuna.
Analog vs. Digital
Analog
Digital
Signal
Analog signal is a continuous signal
which represents physical
measurements.
Digital signals are
discrete time signals
generated by digital
modulation.
Waves
Denoted by sine waves
Denoted by square
waves
Representation
Uses continuous range of values to
represent information
Uses discrete or
discontinuous values to
represent information
Example
Human voice in air, analog
electronic devices.
Computers, CDs, DVDs,
and other digital
electronic devices.
Technology
Analog technology records
waveforms as they are.
Samples analog
waveforms into a limited
set of numbers and
records them.
Uses
Can be used in analog devices only.
Best suited for Computing
Logic Families
basic logic functions are implemented by many different
logic circuits. these circuits can be classified into families
based upon the logic circuit used. Each such families has
its performance determined by there speed, noise
immunity and power dissipation characteristics
• TTL- Transistor Transistor Logic
• CMOS- Complimentary Metal Oxide Semi-Conductors
TTL Logic Family
The transistor-transistor-logic (TTL) family was developed in
the use of transistor switches for logical operations and
defines the binary values as
0 V to 0.8 V = logic 0
2 V to 5 V = logic 1 @5V
TTL is the largest family of digital ICs, but the CMOS family
is growing rapidly. They are inexpensive, TTL draw a lot of
power and must be supplied with +5 volts. Individual gates
may draw 3 to 4 mA.
The low power Schottky versions of TTL chips draw only 20%
of the power, but are more expensive. Part numbers for
these chips have LS in the middle of them.
Logic gates
• Logic gates are fundamental building blocks of
digital electronics
• They perform basic logic operations
• Every logic gate has one or more input
terminals and only one output terminal
• They are come as integrated circuits (ICs)
NOT -Gate
X
Y
Symbol
Logical Expression :
Truth Table:
X
Y
0
1
1
0
OR-Gate
X
Z
Y
Symbol
Logical Expression :
Truth Table:
X
0
0
1
1
Y
0
1
0
1
Z
0
1
1
1
AND-Gate
X
Z
Y
Symbol
Logical Expression :
Truth Table:
X
Y
Z
0
0
1
0
1
0
0
0
0
1
1
1
NOR-Gate
X
Z
Y
Symbol
Logical Expression :
Truth Table:
X
Y
Z
0
0
1
0
1
0
1
0
0
1
1
0
NAND-Gate
X
Z
Y
Symbol
Logical Expression :
Truth Table:
X
Y
Z
0
0
1
0
1
0
1
1
1
1
1
0
XOR-Gate
X
Z
Y
Symbol
Logical Expression :
Truth Table:
X
Y
Z
0
0
1
0
1
0
0
1
1
1
1
0
XNOR-Gate
X
Z
Y
Symbol
Logical Expression :
Truth Table:
X
Y
Z
0
0
1
0
1
0
1
0
0
1
1
1
Transistor based NOT gate
Applications of Gates
•
•
•
•
•
•
•
Encoder and decoder circuits
Arithmetic and logic circuit
Flip-flops
Counters
Registers
Oscillators
Field Programmable Gate Array (FPGA)
Boolean algebra
• OR laws
𝑨+𝟎=𝑨
𝑨+𝟏=𝟏
𝑨+𝑨=𝑨
𝑨+𝑨=𝟏
• AND laws
𝑨. 𝟎 = 𝟎
𝑨. 𝟏 = 𝑨
𝑨. 𝑨 = 𝑨
𝑨. 𝑨 = 𝟎
Boolean algebra
• Laws of complementation
ഥ=𝟏
𝟎
ഥ=𝟎
𝟏
𝒊𝒇 𝑨 = 𝟎 , 𝒕𝒉𝒆𝒏 ഥ
𝑨=𝟏
𝒊𝒇 𝑨 = 𝟏 , 𝒕𝒉𝒆𝒏 ഥ
𝑨=𝟎
ന=𝑨
𝑨
𝑨. 𝑨 = 𝟎
Boolean algebra
• Associative laws
𝑨+𝑩 +𝑪=𝑨+ 𝑩+𝑪 =𝑨+𝑩+𝑪
𝑨. 𝑩 . 𝑪 = 𝑨. (𝑩. 𝑪)
• Commutative laws
𝑨+𝑩=𝑩+𝑨
𝑨. 𝑩 = 𝑩. 𝑨
• Distributive laws
𝑨. 𝑩 + 𝑪 = 𝑨. 𝑩 + 𝑨. 𝑪
𝑨 + 𝑩. 𝑪 = 𝑨 + 𝑩 . (𝑨 + 𝑪)
• Absorptive law
𝑨 + 𝑨. 𝑩 = 𝑨
ഥ + 𝑩 = 𝑨. 𝑩
𝑨. 𝑨
Boolean algebra
De Morgan’s Theorem
ഥ. 𝑩
ഥ
(𝑨 + 𝑩) = 𝑨
ഥ+𝑩
ഥ
(𝑨. 𝑩) = 𝑨