Overview
This lecture introduces the three basic logic gates—AND, OR, and NOT—explaining their function as building blocks for digital systems and circuits.
Transistors as Switches
- Transistors act as switches to represent digital signals in circuits.
- Digital circuits use switches to process and transmit binary information.
Logic Gates in Digital Systems
- Logic gates are fundamental components for building digital systems.
- All digital systems can be constructed using three basic logic gates: AND, OR, and NOT.
AND Gate
- The AND gate outputs 1 only when both inputs are 1.
- Switch analogy: Bulb glows (output is 1) only if both switches A and B are ON.
- Symbol: A flat-ended shape with two inputs and one output.
- Mathematical notation: F = A·B or F = AB (dot implies AND).
OR Gate
- The OR gate outputs 1 if at least one input is 1.
- Switch analogy: Bulb glows if either switch A or B or both are ON.
- Symbol: A curved shape with two inputs and one output.
- Mathematical notation: F = A + B (plus implies OR).
NOT Gate
- The NOT gate (inverter) outputs the opposite of the input.
- If input A is 0, output F is 1; if input A is 1, output F is 0.
- Symbol: Triangle with a circle on the output end.
- Mathematical notation: F = NOT A, F = AÌ…, or F = A'.
Key Terms & Definitions
- Transistor — A semiconductor device that acts as an electronic switch in circuits.
- Logic Gate — A circuit element that performs a basic logical function (AND, OR, NOT) on input signals.
- AND Gate — Outputs 1 only if all inputs are 1.
- OR Gate — Outputs 1 if at least one input is 1.
- NOT Gate — Outputs the inverse of the input.
Action Items / Next Steps
- Review the operation and symbols of AND, OR, and NOT gates.
- Prepare for discussion on VHDL programming related to logic gates.