Page 44 - Handout Digital Electronics

LECTURE 6 DIGITAL LOGIC GATES

6.1 Introduction
A logic gate is a physical device that implements a simple Boolean function. Logic gates form the
hardware basis on which digital computers are built. Logic gates are also called logic circuits. The
elementary (basic) logic gates are: NOT, BUFFER, OR, AND, NOR, NAND, EXCLUSIVE OR (XOR)
and Exclusive NOR (XNOR).

6.2 NOT Logic gate

The NOT logic gate is also called an Inventor or Complement, and it produces a 1 at its output for a
zero (0) input and a 0 output for a 1 input, that is, the output is always the opposite or complement of the
input.

Standard symbol

F = A

Truth Table

A F
0 1
1 0

6.3 Buffer

A buffer simply copies its input to its output. A buffer has no logical significance, but it serves an
important practical role as an amplifier, that is, it allows several logical gates to be driven by a single
signal.

Symbol

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