What is a Voltage Follower?

The voltage follower is another handy type of amplifier that has a gain of 1.0 (or very close to 1.0 .) This is also called a unity gain amplifier. Why do we need an amplifier that does not increase or decrease the signal level? The reason is that we can buffer a weak current source signal to obtain the same signal level out, but with a strong source that reproduces the original source voltage signal within the bandwidth capability of the amplifier with very good accuracy.
How does it work? Remember the non-inverting amplifier discussed in the previous two articles posted here? If you look back at the previous article and at fig. 1 in this article, you will note that R1 has been removed from the circuit and R2 has been replaced with a short circuit (or sometimes with a relatively low value such as 1000 ohms.) The gain of the non-inverting amplifier was given as

G = ( R1 + R2 ) / R1

In the case of our voltage follower amplifier you can think of R1 as being a very high value and R2 as a very small value. So the gain of the voltage follower is, for example with R2 = 1000:

Gvf = (N + 1000 ) /N

where N is a very large value. In the limit as N approaches an infinite value, the value of R2 at even 1000 ohms is not very significant, so Gvf approaches 1.0 as N becomes larger and larger. Or if we just set R2 = 0 , then we have Gvf = N / N = 1.0.

Note also that we don't have to worry about common mode noise with this circuit unless the external traces are long.

So now we know about the voltage follower. The supply voltage connections are not shown but will be discussed in later articles.