Why Are Digital Circuits Built from NAND Gates?

In the world of digital electronics, circuits are often built using NAND gates, which are known as universal building blocks. This is because logic circuits can be constructed using only NAND gates, even when other gates such as AND, OR, and NOT are needed.

Understanding Universal Gates

NAND and NOR gates are considered as universal gates because any other logic gate can be derived from them. For instance, AND, OR, NOT, and EX-OR gates can all be created using only NAND gates. This capability to represent various gates makes NAND gates particularly useful in minimizing the design complexity and simplifying logic circuit implementation.

NAND Gate Construction and Function

NAND gates are typically constructed with fewer transistors compared to AND gates. This is because the transistors required to build a NAND gate are fewer, which in turn translates to reduced power consumption.

A NAND gate can be thought of as a combination of an AND gate followed by a NOT gate. The truth table for a two-input NAND gate is as follows:

A B NAND(A, B) 0 0 1 0 1 1 1 0 1 1 1 0

Building Basic Gates with NAND Gates

It's important to note that an AND gate can be simulated by making a NAND gate followed by a NOT gate. Similarly, an OR gate can be realized with just a set of NAND gates, as shown below:

The same is true for an AND gate, which can also be created using NAND gates:

NOR Gates as Universal Gates

Interestingly, just like NAND gates, NOR gates can also be used to construct any basic logic gate. This is demonstrated below:

OR gate using NOR gates:

AND gate using NOR gates:

NOT gate using NOR gates:

Conclusion

Due to their versatility, NAND and NOR gates are pivotal in digital circuit design. These universal gates allow for efficient and simplified logic circuit construction, making them essential in modern electronics.

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