What is an op amp?

An op amp is an integrated circuit. It is a collection of other electronic components, transistors, resistors and capacitors combined into a circuit that forms a building block.

There are many types of devices with different specifications for different applications.

The thing they have in common is that they have two inputs and an output. One is a non inverting input marked with a + symbol on the diagram and the other is the inverting input marked with a – symbol on the diagram.

They also come in single, dual and quad versions in a single package.

Having a op amp as an integrated circuit saves a lot of components and space and having dual and quad versions saves even more.

What is an op amp?

Op amp circuits

Inverting amplifier

This is one of the most common configurations of this device. It’s used in lots of audio applications. With a low impedance input its idea to amplify the output of microphones and guitars amongst other things.

The low impedance also means it’s less prone to pick up.

Non inverting amplifier

In some ways similar to the inverting amplifier. With A high input impedance it’s ideals for the input stages of audio amplifiers. If the input and output are connected together it will work as a voltage follower or buffer.

Summing amplifier

This is another common configuration. It is widely used when you need to combine different signals together. I’ve used it on a voltage controlled filter circuit. There are various different control voltages that are combined by an op amp configured as a summing amplifier and then fed to the voltage control input.

If you’ve ever had problems combining audio signals try a summing amplifier. I once tried to mix some audio signals together but because of differing levels and impedance’s when I altered one level it affected the others. A summing amplifier stopped this problem.

Comparator

As a comparator the output will go high or low depending on the state of the inputs.

Although not ideal as comparators, they can do the job. Particularly if you need a comparator in your circuit and you have an unused device in a dual or quad package.

Filter

You can also easily configure them as filters. The frequencies can be widely altered for all types. In a high pass filter the frequencies above will be passed while the ones below will be rolled off.

A low pass is exactly the opposite and will the higher frequencies being filtered out.

A band pass will filter out low and high frequencies letting the band between the high and low frequencies through.

The band reject or notch filter is the opposite to the band pass and will reject a band of frequencies.

Oscillator

Although not that common it can also be configured as an oscillator. Although there are better ways and IC’s if that’s primarily what you want but if you only want something simple and you have an unused op amp in a multiple device it’s ideal.

What is an op amp used for?

Op amps are very widely used for many things. Its probably harder to find circuits were they are not used. They are commonly used in audio circuits. They can function in various modes depending on how they are connected, but one of their most common uses is to amplify a signal. This is why is almost impossible to find and audio circuit that doesn’t contain at least one.

Dual power supplies

As you may have noticed most op amp circuits use a dual power supply. This is so the output can go negative as well as positive. There are ways around this however. You can connect two resistors in series across a single supply as a voltage divider and use the middle as the zero volt reference.

I prefer not to do this for two reasons. First if you do this you effectively half the supply voltage and so the peak to peak output voltage.

If you were to use 9 volts as an example the divider would be effect + and – 4.5 volts. This is in theory as in practice the output can’t fully go to the output voltage but is less.

Secondly you have to add coupling capacitors to block the voltage. You will have to calculate these depending on the frequency of the signal through the op amp.

So now you can see why I prefer to just use a dual rail power supply, It’s easier.

What is an op amp – final thoughts

An op amp is one of the most used integrated circuits. As you can see they are tremendously useful and versatile. From oscillators to filters, amplifiers to audio effect processors, they are all packed with op amps.

If you want more specific information check out my post How to use an op amp as this contains some practical experiments that will help learn about them a lot more than just reading will.

You may also like my related posts How to test an op amp and Are all op amps the same.