Buffer amplifier and its importance

A voltage buffer, also known as a voltage follower, or a unity gain amplifier, is an amplifier with a gain of 1. It’s one of the simplest possible op-amp circuits with closed-loop feedback.

Even though a gain of 1 doesn’t give any voltage amplification, a buffer is extremely useful because it prevents one stage’s input impedance from loading the prior stage’s output impedance, which causes undesirable loss of signal transfer. The input impedance of the op-amp buffer is very high: close to infinity. And the output impedance is very low: just a few ohms. This means we can use buffers to help chain together sub-circuits in stages without worrying about impedance problems. The buffer gives benefits similar to those of the emitter follower with transistors, but tends to work more ideally.

A voltage gain of 1 means that if the input voltage goes up by ΔV , then the output voltage is also designed to go up by the same ΔV .

An op-amp can be configured as a voltage buffer by:

1. Connecting the input signal to the non-inverting (+) input, and

2. Connecting the output directly back to the inverting input (-) with a wire

How this works

As we know that the op-amp will change its output voltage until the two inputs are the same. We now have the first opportunity to see how that works because this circuit has closed-loop feedback from the op-amp’s output back to one of its inputs.

1. Suppose the input voltage is suddenly higher than the output.

2. The op-amp will see a higher voltage on its non-inverting input than its inverting input (V+>V-) , and so the output voltage will start to increase.

3. The circuit is configured so that this increased output voltage loops back from the output, through the wire connecting the output to the inverting input.

4. The voltage at the inverting input increases.

5. Once the inverting input voltage rises to meet the non-inverting input voltage, the output will stop increasing.

6. And the output is now equal to the non-inverting input voltage.

Now since the output voltage is what we were getting at the input, but the loading is on the op-amp instead of the input signal.