Logic Gates and Truth Tables
AND Gate
Symbol: A · B
Outputs 1 only if both inputs are 1.
| A | B | AND |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
OR Gate
Symbol: A + B
Outputs 1 if at least one input is 1.
| A | B | OR |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
XOR Gate
Symbol: A ⊕ B
Outputs 1 if inputs are different.
| A | B | XOR |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
XNOR Gate
Symbol: A ⊙ B
Outputs 1 if inputs are the same.
| A | B | XNOR |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
NAND Gate
Symbol: (A · B)'
Inverse of AND gate.
| A | B | NAND |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NOR Gate
Symbol: (A + B)'
Inverse of OR gate.
| A | B | NOR |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
NOT Gate
Symbol: A'
Outputs the opposite of the input.
| A | NOT |
|---|---|
| 0 | 1 |
| 1 | 0 |
BUFFER Gate
Symbol: A
Outputs the same value as the input.
| A | BUFFER |
|---|---|
| 0 | 0 |
| 1 | 1 |
Negative OR Gate
A negative OR gate behaves logically identical to a NAND gate. Its output is low (0) only when all inputs are high (1); otherwise, the output is high (1). This occurs because a negative OR gate is functionally an OR gate with all its inputs inverted.
Truth Table (2-Input)
| Input A | Input B | Output |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Voltage Level Interpretation
In terms of voltage levels, if High (H) represents logical 1 and Low (L) represents logical 0:
- The output is L only when both inputs are H.
- The output is H for all other input combinations (L/L, L/H, H/L).