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Electronics Components: How to Use an Op Amp as a Unity Gain Amplifier

A unity gain amplifier is an electronic amplifier circuit that doesn’t amplify. In other words, it has a gain of 1. The output voltage in a unity gain amplifier is the same as the input voltage.

You may think that such a circuit would be worthless. After all, isn’t a simple piece of wire a unity gain circuit? Sure, but a unity gain amplifier provides one important benefit: It doesn’t take any current from the input source. (Remember, that’s one of the Golden Rules of the ideal op amp.)

Therefore, it completely isolates the input side of the circuit from the output side of the circuit. Op amps are often used as unity gain amplifiers to isolate stages of a circuit from one another.

Unity gain amplifiers come in two types: voltage followers and voltage inverters. A follower is a circuit in which the output is exactly the same voltage as the input. An inverter is a circuit in which the output is the same voltage level as the input but with the opposite polarity.

If you think about it for a moment, you might be able to come up with the circuit for unity gain followers and inverters on your own. The formula for calculating the gain of both an inverting amplifier and a noninverting amplifier requires you to divide R2 by R1, so all you have to do is choose resistor values that will result in a gain of 1.

Configure an electronic unity follower

A unity gain follower is simply a noninverting amplifier with a gain of 1. The formula for calculating the value of a noninverting amplifier is this:

image0.jpg

To create a unity gain follower, you just omit R2 and connect the output directly to the inverting input. Because R2 is zero, the value of R1 doesn’t matter, because zero divided by anything equals zero. So R1 is usually omitted as well, and the V input isn’t connected to ground.

image1.jpg

Configure an electronic unity inverter

The formula for calculating gain for an inverting amplifier is this:

image2.jpg

In this case, all you have to do is use identical values for R1 and R2 to make the amplifier gain equal to 1. Here is a unity gain inverter circuit using 1 k resistors.

image3.jpg
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