(i) The OR gate : It is a circuit with two or more inputs and one output in which the output signal is HIGH if any one or more of the inputs is HIGH.
The OR operation represents a logical addition.
Below figure shows the 2-input OR gate logic sym-bol, and the Boolean expression and the truth table for the OR function.
Logic symbol :
Boolean expression :
Y = A + B
Truth table :
| Input |
Output
Y |
| A |
B |
| 0 |
0 |
0 |
| 1 |
0 |
1 |
| 0 |
1 |
1 |
| 1 |
1 |
1 |
The OR gate
(ii) The AND gate : It is a circuit with two or more inputs and one output in which the output signal is HIGH if and only if all the inputs are HIGH simultaneously.
The AND operation represents a logical multiplication.
Below figure shows the 2-input AND gate logic symbol and the Boolean expression and the truth table for the AND function.
Logic symbol:
Truth table:
| Input |
Output |
| A |
B |
| 0 |
0 |
0 |
| 1 |
0 |
0 |
| 0 |
1 |
0 |
| 1 |
1 |
1 |
The AND gate
Boolean expression:
Y = A ∙ B
(iii) The NAND gate : It is a circuit with two or more inputs and one output, whose output is HIGH if any one or more of the inputs is LOW; the output is LOW if all the inputs are HIGH.
Logic symbol :
Boolean Expression :
Y = \(\overline{A.B}\)
Truth table :
| Input |
Output
Y |
| A |
B |
| 0 |
0 |
1 |
| 1 |
0 |
1 |
| 0 |
1 |
1 |
| 1 |
1 |
0 |
The NAND gate
The NAND gate is a combination of an AND gate followed by a NOT gate so that the truth table of the NAND function is obtained by inverting the outputs of the AND gate.
