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Logical Circuits

• Fundamentals
  • Propositional calculus
  • Semiconductors
  • MOSFETs
  • CMOS
• Circuits
  • Identity
  • NOT
  • AND
  • NAND
  • OR
  • XOR
  • XNOR
• Credits
• Sources

OR (Disjunction)

Introduction

The OR gate has two OR-combined input terminals.
If at least one of the input terminals is true, the output will also be true.
This means that the output Z will be HIGH (1), if input-terminal A or input-terminal B is HIGH (1). The output Z will also be HIGH (1), if both input-terminals are HIGH (1). Otherwise the output Z will be LOW (0).

Example

claim: Emilia works as a babysitter or at the till.
(If Emilia doesn't work, the claim will be false.)

If...	the claim will be...
Emilia doesn't work,	False
Emilia works as a babysitter,	True
Emilia works at the till,	True
Emilia works both as a babysitter and at the till,	True

claim (Z) = Emilia works as a babysitter (A) or at the till (B).

A	B	Z
No babysitter	No till girl	False
No babysitter	Till girl	True
Babysitter	No till girl	True
Babysitter	Till girl	True

Z = Emilia works as a babysitter OR at the till.
1: Emilia has one or more jobs / true
0: Emilia doesn't work / false

Truth table

Z = A OR B

A	B	Z
0	0	0
0	1	1
1	0	1
1	1	1

Functional equation

Electronic Symbol

Exercises

Propositional calculus with words:

claim: Tomorrow it will snow or it'll be warmer than 30 degrees.

If it won't snow tomorrow although it will be -2°C cold, the claim will be __________.
false
If it will be 36°C warm tomorrow, the claim will be __________.
true
If it will snow tomorrow and temperature will be 32°C, the claim will be __________.
true

Specials

It is possible to build this gate just from NAND gates:
A OR B = (A NAND A) NAND (B NAND B)

CMOS implementation