Albert Teen
Electricity

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Logic Gates

Logic Gates

Logic Gates

This lesson looks at the different types of logic gates, including the action of NOT, AND, OR, NAND and NOR gates.

A digital signal operates at two levels, high or low. What else can we call them?

A logic gate is a digital electronic component that gives a particular output, depending on the input. We will look at this in more detail in this lesson.

Let's look at the output of logic gates first. What do you think 1 means?

1

So depending on what you put into a logic gate, you will get a different output.

If the output is that the logic gate produces a signal, it is known as a 1. If the output is that the logic gate does not produce a signal, it is known as a 0.

There are different types of logic gates: NOT, AND, OR, NAND, and NOR. Let's first have a look at what we actually mean when we say "not", "and" and "or".

1

Have a look at this sentence: "I have a cat AND a dog." Pick all the options that are true if this sentence is true.

2

Have a look at this sentence: "It is NOT the case that I have a dog." Pick all the options that are true if this sentence is true.

3

Have a look at this sentence: "My cousin has a cat OR a dog." Pick all the options that could be true.

4

Look at this sentence again: "My cousin has a cat OR a dog." Is the sentence true if the cousin owns both a cat AND a dog?

1

So if we say NOT...

we are only talking about 1 input, for example "dog". If it's NOT a dog, then it's true. Otherwise it's false.

2

If we say AND...

we are talking about 2 inputs, for example "cat' and 'dog". If it's BOTH a cat and a dog, then it's true. Otherwise it's false.

3

If we say OR...

we are talking about 2 inputs, for example "cat" and "dog". If just one of them is a cat or a dog or if there is both a cat and a dog, then it's true. Otherwise, it's false.

1

Logic gates work in the same way. This logic gate only gives the output 1 if both inputs are 1. Which logic gate is that?

A) NOT gate B) AND gate C) OR gate

2

AND logic gates...

only give the output 1 if both input 1 AND input 2 are both 1s.

3

This logic gate only gives the output 1 if the input is 0. Which logic gate is that?

A) NOT gate B) AND gate C) OR gate

4

NOT logic gates...

only give the output 1 if the input is NOT 1 (so only if the input is 0).

5

This logic gate gives the output 1 as long as just one of the inputs is 1. Which logic gate is that?

A) NOT gate B) AND gate C) OR gate

6

OR logic gates...

give the output 1 as long as the first OR the second input is 1.

NAND is also a type of logic gate. What do you think NAND might mean?

1

NAND gates are the opposite of AND gates. What does that mean? Pick the most correct option.

A) NAND gates give output 1 if both inputs are 0. B) NAND gates give output 1 if 1 input is 1. C) NAND gates give output 1 if both inputs are not 1.

2

NOR gates mean NOT OR and they are the opposite of OR gates. What does that mean? Pick the most correct option.

A) NOR gates give output 1 if both inputs are 0. B) NOR gates give output 1 if 1 input is 0. C) NOR gates give output 1 if 1 input is 1.

3

To sum up!

NAND gates will give output 1 whenever an AND gate would give output 0, and NOR gates will give output 1 whenever an OR gate would give output 0.

Which logic gate has a single input and will output a signal if the input is not 1?

1

Which logic gate is this?

Which logic gate has two inputs and will output a signal as long as at least one input is not 1?

Which logic gate has two inputs and will output a signal as long as both inputs are 0?

1

Which logic gate is this?