1
© 2009 A. Ganago
Logic Gates
Many today’s applications require logic
functions such as AND, OR, NOT, etc.
Even a washing machine uses logic such as
“start only if the working cycle is chosen AND
the lid is closed.”
Here we learn about logic operations and
how they can be implemented as diode and
transistor circuits.
1
Logic gates
© 2009 A. Ganago
Digital Circuits Do Logic
Operations on Signals
•
Logic operates with “TRUE” and “FALSE”
•
Mathematically, “TRUE” = “1” and
“FALSE” = “0”
•
In the circuits,
positive logic
means “1”
= HIGH voltage;
“0” = LOW voltage
• Negative logic
means “0” = HIGH
voltage;
“1” = LOW voltage
2
Logic gates
© 2009 A. Ganago
Basic Logic Operations (1)
• NOT
If A (input) is TRUE then C
(output) is FALSE
• AND
If
both
A and B (two inputs) are
TRUE then C (output) is TRUE; if any of
A and B is FALSE, C is FALSE
• OR
If
any
of A and B (two inputs) is
TRUE then C (output) is TRUE
3
Logic gates
© 2009 A. Ganago
Basic Logic Operations (2)
• NAND = NOT(AND)
If
both
A and B
(two inputs) are TRUE then C (output) is
FALSE; if
any
of A and B is FALSE then
C is TRUE
• NOR = NOT(OR)
If
any
of A and B
(two inputs) is TRUE then C (output) is
FALSE; if
both
A and B are FALSE,
then C is TRUE
4
Logic gates
© 2009 A. Ganago
Basic Logic Operations (3)
•
There are many more operations,
including
OR, AND
with three or more
inputs, and other types as well
•
In this course, we cover only the 5
operations listed above:
OR, AND,
NOT, NOR, NAND
5
Logic gates
© 2009 A. Ganago
Basic Logic Operations (4)
•
Logic operations are identified by the
truth tables
•
Each logic operation has its unique truth
table
•
If two operations have identical truth
tables, the operations are identical
6
Logic gates
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
2
© 2009 A. Ganago
Truth Tables (1)
NOT
Input
Output
A
C
0
1
1
0
7
Logic gates
© 2009 A. Ganago
Input
Input
Output
A
B
C
0
0
0
1
0
0
0
1
0
1
1
1
AND
Truth Tables (2)
8
Logic gates
© 2009 A. Ganago
Truth Tables (3)
Input
Input
Output
A
B
C
0
0
0
1
0
1
0
1
1
1
1
1
OR
9
Logic gates
© 2009 A. Ganago
Truth Tables (4)
Input
Input
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '07
 Ganago
 Logic, Gate, Logic gate, A. Ganago

Click to edit the document details