Oct 122017
 

Op-Amp Voltage follower (Buffer)

To better understand the operation of a Op-Amp Voltage follower (Buffer), we must remember the operation of a Op-Amp non-inverting amplifier. See the diagram below.

Op-Amp Non-inverting amplifier

The Op-Amp Non-inverting Amplifier has a gain given by the formula: 1+ (R2 / R1).

If we make R2 resistor value equal to zero and make the R1 resistor value very large (infinity), we have an amplifier with gain G = 1. This means that the output signal has the same value as the input signal  See the following diagram.

Voltage Follower (Buffer)

Op-Amp Voltage follower (Buffer)

This circuit is a Op-Amp Voltage follower (Buffer).

The buffer has an output that is exactly as the input. This behavior may initially seem useless, but has features that help solve impedance coupling problems.

  • The input impedance of a buffer with an operational amplifier is very high, close to infinity
  • The output impedance is very low, just a few ohms.

If the input impedance is very high, it does not charge the circuit that is sending the signal, and if its output impedance is low, it can deliver a sufficient amount of current to the circuit receiving the signal.

In other words a Buffer requests very little current from the circuit that gives the signal and greatly increases the capacity to delivery current to the circuit that receives the signal.

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