Talha's Physics Academy
Fundamental Logic Gates: AND, OR, and NOT Gates
Video Lecture: Fundamental Logic Gates
Watch the complete video lecture explaining the definitions, boolean expressions, and truth tables of fundamental logic gates:
1. AND Gate
“The AND gate is a logic gate that produces a high output ($1$) only when all its inputs are high ($1$). If any input is low ($0$), the output is low ($0$).”
Boolean Expressions
- Two Inputs: $X = A \cdot B$
- Three Inputs: $X = A \cdot B \cdot C$
- Four Inputs: $X = A \cdot B \cdot C \cdot D$
Fig: Logic symbols for AND gates.
Truth Tables
i) Two Inputs
| Inputs | Output | |
|---|---|---|
| A | B | X |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
ii) Three Inputs
| Inputs | Output | ||
|---|---|---|---|
| A | B | C | X |
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 |
| 0 | 1 | 0 | 0 |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | 0 | 0 |
| 1 | 1 | 1 | 1 |
iii) Four Inputs
| Inputs | Output | |||
|---|---|---|---|---|
| A | B | C | D | X |
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 1 | 0 |
| 0 | 0 | 1 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 |
| 0 | 1 | 0 | 0 | 0 |
| 0 | 1 | 0 | 1 | 0 |
| 0 | 1 | 1 | 0 | 0 |
| 0 | 1 | 1 | 1 | 0 |
| 1 | 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 1 | 0 | 0 |
| 1 | 0 | 1 | 1 | 0 |
| 1 | 1 | 0 | 0 | 0 |
| 1 | 1 | 0 | 1 | 0 |
| 1 | 1 | 1 | 0 | 0 |
| 1 | 1 | 1 | 1 | 1 |
2. OR Gate
“The OR gate is a logic gate that produces a high output ($1$) when any one or more of its inputs are high ($1$). The output is low ($0$) only when all inputs are low ($0$).”
Boolean Expressions
- Two Inputs: $X = A + B$
- Three Inputs: $X = A + B + C$
- Four Inputs: $X = A + B + C + D$
Fig: Logic symbols for OR gates.
Truth Tables
i) Two Inputs
| Inputs | Output | |
|---|---|---|
| A | B | X |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
ii) Three Inputs
| Inputs | Output | ||
|---|---|---|---|
| A | B | C | X |
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 1 |
| 0 | 1 | 1 | 1 |
| 1 | 0 | 0 | 1 |
| 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 |
iii) Four Inputs
| Inputs | Output | |||
|---|---|---|---|---|
| A | B | C | D | X |
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 1 | 1 |
| 0 | 0 | 1 | 0 | 1 |
| 0 | 0 | 1 | 1 | 1 |
| 0 | 1 | 0 | 0 | 1 |
| 0 | 1 | 0 | 1 | 1 |
| 0 | 1 | 1 | 0 | 1 |
| 0 | 1 | 1 | 1 | 1 |
| 1 | 0 | 0 | 0 | 1 |
| 1 | 0 | 0 | 1 | 1 |
| 1 | 0 | 1 | 0 | 1 |
| 1 | 0 | 1 | 1 | 1 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 0 | 1 | 1 |
| 1 | 1 | 1 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 |
3. NOT Gate (Inverter)
“The NOT gate is a single-input logic gate that performs the complement or inversion operation in digital circuits, turning a high input into a low output and vice versa.”
Boolean Expression
$X = \bar{A}$
Fig: Logic symbol for a NOT gate.
Truth Table
| Input | Output |
|---|---|
| A | X |
| 0 | 1 |
| 1 | 0 |
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