Author: M Abo Bakar Aslam

Universal Gates - NAND and NOR Gates

In digital electronics, universal gates are logic gates capable of implementing any Boolean function without needing other gate types. Among all logic gates, NAND and NOR gates are called universal gates because every digital circuit can be constructed using only NAND or only NOR gates.


These feature makes these two gates (NAND and NOT Gates) essential in combinational logic circuits, VLSI design, and computer architecture. Engineers prefer universal gates for cost-effective, compact, and reliable digital system design. It is because of that Integrated Circuits (ICs) are designed by Transistors and Transistors are easy to construct by both NAND and NOR Gates.

1. Why NAND and NOR Are Called Universal Gates

The universality of NAND and NOR gates comes from their ability to reproduce the basic logic operations: NOT, AND, and OR. Once these three are available, any complex Boolean expression can be implemented. This makes NAND and NOR highly valuable in logic circuit implementation, IC fabrication, and optimization of hardware systems.

Key Benifits

  1. Reduce hardware complexity
  2. Lower manufacturing cost
  3. Improve circuit reliability
  4. Widely used in digital electronics and microprocessors

As there are three basics (AND, OR and NOT Gates) that are used to construct all other gates. So we construct these gates by both NAND and NOR Gates

2. Implementing Logic Gates Using NAND

2(a). NOT Using NAND

Creating Logic of NOT Gate using NAND Gate
Figure 1: Creating Logic of NOT Gate using NAND Gate

2(b). AND Using NAND

Creating Logic of AND Gate using NAND Gate
Figure 2: Creating Logic of AND Gate using NAND Gate

2(c). OR Using NAND

Creating Logic of OR Gate using NAND Gate
Figure 3:Creating Logic of OR Gate using NAND Gate

3. Implementing Logic Gates Using NOR

3(a). NOT Using NOR

Creating Logic of NOT Gate using NOR Gate
Figure 4: Creating Logic of NOT Gate using NOR Gate

3(b). AND Using NOR

Creating Logic of AND Gate using NOR Gate
Figure 5: Creating Logic of AND Gate using NOR Gate

3(c). OR Using NOR

Creating Logic of OR Gate using NOR Gate
Figure 6: Creating Logic of OR Gate using NOR Gate