6. Fundamental Logic Gates: AND, OR, NOT

Logic gates are the basic building blocks of any digital circuit. They are electronic devices that implement Boolean algebra functions.

1. The AND Gate

• Function: Performs logical multiplication.
• Symbol: (A D-shape symbol)
• Equation: $Y = A \cdot B$

If we model inputs A and B as switches, the AND gate is like two switches in series: the light (Y) only turns on if BOTH switches are closed (1).

2. The OR Gate

• Function: Performs logical addition.
• Symbol: (A curved shield symbol)
• Equation: $Y = A + B$

Modeling with switches, the OR gate is like two switches in parallel: the light (Y) turns on if EITHER switch (or both) is closed (1).

3. The NOT Gate (Inverter)

• Function: Performs complementation.
• Symbol: (A triangle with a circle (bubble) at the output)
• Equation: $Y = \overline{A}$

The bubble on the output is standard notation for inversion. The NOT gate has only one input.

Summary: Truth Tables

Truth tables systematically list all possible input combinations and their resulting outputs for a given circuit.