Logic Circuit

Logic Gates

Logic Circuits

fan-in

Number of inputs of a gate

Universal Gates

AND, OR, NOT gates are sufficient for building any boolean function.

This is called a complete set of logic.

Other gates may still be used due to

• usefulness (XOR: parity bit generation)
• economical
• self-sufficient (NAND/NOR gates)

NAND as a universal gate


NOR as a universal gate


Implementing SOP and POS

SOP expressions

Sum-of-product expression implementation

Can be implemented using:

1. 2 level AND-OR circuit (first level: AND, second level: OR)
2. 2 level NAND circuit

POS expressions

Product-of-sums expression implementation

Can be implemented using:

1. 2 level OR-AND circuit (first level: OR, second level: AND)
2. 2 level NOR circuit

Programming Logic Array

Programming logic array

Programmable integrated circuit implements sum-of-products circuits (to allow multiple outputs)