Class 12 Physics Semiconductor Electronics Digital electronics

Digital electronics – Introduction

Logic gates

• In digital electronics, we consider only two values of voltage – high represented as 1 and low represented as 0
• Logical gates are electronic circuits
• Just as a gate controls the flow of vehicles, the logical gates controls the flow of information based on the logical relations. Only if the logical relations are satisfied, the digital circuit allows the signal to pass through
• The logic gates are the basic building blocks of digital electronics.
• We can say logic gate is a digital circuit which follows a logical relationship between the input and output
• Some of the basic types of logical gate are – NOT, OR, AND, NOR and NAND. Every gate has a single or multiple input and output
• Every gate is represented by a symbol
• The input and output of the logical gate is represented in the form of a truth table. The truth table considers all possible combinations of the input and shows the respective output in each case

NOT gate

The symbol and truth table for NOT gate is as given below: OR gate

The symbol and truth table for NOT gate is as given below: AND gate

The symbol and truth table for NOT gate is as given below: NOR gate

The symbol and truth table for NOT gate is as given below: NAND gate

The symbol and truth table for NOT gate is as given below: Universal gate

The NAND gate and the NOR gate are called as universal gates as any Boolean function can be implemented without the need to use any other gate. The following diagrams below show NAND gate and NOR gate combinations as NOT, AND and OR gates: .