Name: What are Basic logic gates? | Learn basic digital gates in 6 min | AND, OR and NOT gates | DE.10
Uploaded: 2020-06-07T18:11:16.000Z
Duration: 6 min
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

We begin this session with an example to understand the impact of 0s and 1s in our lives.

Basic passive voice

Suppose you are handed with a will of 1000 dollars.

The money increases if we increase zeroes on the right.

However, if we swap the one to right, the values decreases drastically.

This is numerical significance whereas in smart devices, it has a logical significance.

The values are decisions which can have a high value or logic 1

The decision-making elements are called logic gates.

The decisions are termed as output which are binary variables 0 or 1.

The input to logic gate can be single or multiple.

The output changes for every input combination and it depends upon two things -

Type of logic gate and nature of input variables.

There are numerous gates available, each for a specific decision.

Each of these have a specific symbol and clearly defined behaviour.

There are two major classifications- Basic gates and derived gates.

We will discuss each of them in detail later.

For now, let's concentrate upon the nature of binary input variables.

To study this, let's understand the truth table.

The left hand side, lists all possible combinations of input binary variables

Consider a logic gate with a single input A.

There are 2 input combinations for 1 input variable.

It may happen that A has the value 0 and B takes values

When A is at logic 1, B may have values 0 or 1.

Thus there are 4 input combinations for 2 input variables.

Therefore, n input variables will have 2^n input combinations.

There is a trick to fill the truth table.

We start filling with the leftmost input and will go column by column.

Since we know it will have four input combinations,

Next column with have one zero followed by one one.

Left most column will have 4 zeroes, 4 ones.

Last column will have a series of 0 and 1.

But how do we decide the output for each input?

The type of logic gate decides the output.

Basic logic gates are the fundamental logical operations

These functions are named as AND, OR and NOT.

A and B are two inputs resulting in a single output Y.

The Boolean expression  is read as Y = A and B..

A Boolean expression relates output with the inputs of the logic system

For a 3 input AND gate, the boolean expression is Y=A and B and C.

This way the boolean expression can be written for a multiple input AND gate.

Let's construct the truth table. When both

The output of AND Gate is low when either

Both the inputs A, B need to be at logic 1

You can imagine it as 2 switches in series.

When the circuit is complete, the bulb will glow.

When both the switches are at logic 1, the path is complete and current

flows. AND Gate finds applications in security systems such as burglar's alarm.

Suppose you have to leave the house and keep the house secure.

This turns first input of AND gate as high.

high, the output of AND gate is high which sets the alarm ON.

For two inputs A and B, the Boolean expression

For multiple input, It is simply this way.

when both the inputs are low the output is low

is high for remaining 3 input combinations.

The circuit is complete when either of the inputs is at logic 1 or both at logic 1 which makes the bulb glow.

When a house has a front door and a back door, guests can arrive at any door

In the event, when either the front door or the back door bell is pressed, the

bell rings indicating that the guest has arrived.

The last basic gate is a NOT gate. This gate can only have one input.

As the name suggests, the output is always NOT the input i.e., complement of input.

A complement is denoted by a bar over the variable. The boolean expression for input, A is A bar.

When the input is 0, output is 1 and vice versa

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What are Basic logic gates? | Learn basic digital gates in 6 min | AND, OR and NOT gates | DE.10

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