The NOT Gate (Inverter)

The simplest logic gate changes a 0 into a 1 and a 1 into a 0.

1️⃣

One input

A NOT gate receives one binary input, either 0 or 1.

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Opposite output

The output is always the opposite of the input.

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Virtual Lab

At the end, experiment with a real NPN transistor inverter.

Click Next to begin.

Binary Values

0 and 1

Digital circuits use two states. A 0 usually represents LOW or OFF. A 1 usually represents HIGH or ON.

0

or

1

A NOT gate receives one of these values as its input.

Core Concept

the opposite value

NOT means opposite. If the input is 0, the output is 1. If the input is 1, the output is 0.

0

→

NOT

→

1

Input 0 becomes output 1.

Interactive Truth Table

try it

Toggle the input. The output and truth table update immediately.

Input switch

INPUT = 0

OUTPUT = 1

Input	Output
0	1
1	0

Why It Is Called an Inverter

same meaning

To invert means to reverse or change something into its opposite. That is exactly what the NOT gate does.

Input 0 becomes Output 1.

Input 1 becomes Output 0.

NOT gate and inverter are two names for the same logical operation.

Inside the Circuit

transistor switching

A transistor can act like an electronic switch. Turning that transistor on or off creates the inverted output.

Input LOW → transistor OFF → output HIGH.

Input HIGH → transistor ON → output LOW.

The transistor does the physical switching that produces the NOT operation.

Explore the Real Circuit

shared external SVG

Select a component from the list. Every SVG element belonging to that component is highlighted in the actual NPN inverter schematic.

Could not display npn-inverter-schematic.svg.

Power supply

The 9 V source supplies electrical energy to the circuit and establishes the voltage between the power rail and the 0 V return.

This lesson and the Virtual Lab use the same shared schematic design.

Virtual Lab

hands-on experiment

Use the interactive NPN inverter simulation to toggle the input, watch current flow, and compare the result with the truth table.

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NPN Transistor Inverter

Experiment with the actual circuit behavior. The simulation opens as a separate page and uses the shared SVG schematic file.

Knowledge Check

three questions

Select an answer for each question.

1. How many inputs does a NOT gate have?

2. If the input is 1, what is the output?

3. What is another name for a NOT gate?

Choose an answer to receive immediate feedback.

Summary

lesson complete

✅ A NOT gate has one input and one output.

✅ The output is always the opposite of the input.

✅ A NOT gate is also called an inverter.

✅ An NPN transistor can provide the switching action.

🎉 Congratulations!

lesson complete

🏆

You completed the NOT Gate lesson!

✅ You learned what a NOT gate does.

✅ You understand why it is called an inverter.

✅ You explored the truth table.

✅ You examined a real transistor implementation.

✅ You completed the virtual lab.

Continue with more Digital Logic Basics lessons.