4.1.8. Logic Gates

Logic gate basically we are having some standard gates and here in this particular course we are going to see in the gate level only, how those particular gates are implemented.

Logic gates are the fundamental building blocks of digital circuits. They perform basic logical functions that are essential for digital circuits. In this course, we are focusing on the conceptual understanding of these gates rather than their physical implementation.

Think of logic gates as the simple switches in your home that control lights. Just like flipping a switch changes whether a light is on or off, logic gates change the output based on their inputs.

First gate is NOT gate. What is that NOT? It says that if my input is high then output is low and output is input is low output is high. [...] So, if voltage level falls below this particular level generally we say that this is your low signals and when voltage level goes above some certain value we say that this is high level.

There are several types of logic gates including NOT, AND, OR, NAND, NOR, XOR, and XNOR. Each gate has a specific function in how it processes the inputs to produce the output. For instance, a NOT gate inverts the input signal: if the input is high (1), the output is low (0), and vice versa. Other gates like AND require all inputs to be high for the output to be high.

Imagine a traffic signal as a logic gate. A NOT gate would be like a traffic light that shows green when the stop signal is off and red when it’s on. An AND gate would be like a situation where two traffic lights need to be green at the same time for vehicles to go.

So, basically the behaviour of digital circuit can be represented with the help of truth table. Here, I am having 2 input a and b. So, when both the inputs are high then output is high otherwise output is 0.

A truth table is a mathematical table used to determine if a compound statement is true or false based on the possible truth values of its components. In the case of a 2-input AND gate, a truth table would show that the output only is true when both inputs are true.

Think of a truth table like a recipe that shows you the final dish (output) based on different ingredients (inputs) you use. If you have both sugar and flour (the two inputs), you can bake a cake (the output). If you miss one ingredient, you won’t get a cake.

Again the digital logic circuit can be categorized into two different categories one is your combinational circuit and second one is your sequential circuit.

Combinational circuits are those where the output is determined solely by the current inputs, without any memory. Conversely, sequential circuits have memory and the outputs depend on both current inputs and past inputs (previous outputs). This distinction is crucial in designing complex circuits.

Consider a vending machine. A combinational circuit is like a simple calculator that provides change based only on the bill inserted (the current input). In contrast, a sequential circuit is like a bank that keeps track of your balance over time, influencing what you can withdraw (considering past transactions).

Along with that, we are having another terms called universal gates. So, NAND and NOR are treated as universal gates, Why you say these are the universal gates? Any digital logic circuit can be implemented with the help of only NAND gate or only NOR gate.

NAND and NOR gates are unique because any digital circuit can be constructed using just these two types of gates. This makes them fundamental components in digital design, allowing for the creation of a variety of functions and circuits.

Think of universal gates like a multi-tool. Just as a multi-tool can serve various functions like cutting, screwing, and opening bottles, NAND and NOR gates can perform any logical operation needed to build a complex digital circuit.

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