The voltage or source follower is a unity-gain, noninverting amplifier with no resistor in the feedback loop (see Figure 2-19). The output is exactly the same as the input. The voltage follower has a high input impedance which is equal to the operational amplifier intrinsic input impedance.
The function of the voltage follower circuit is identical to a emitter follower for a bipolar transistor or a source follower on an FET transistor. The main purpose of the circuit is to buffer the input signal from the load. The input impedance is high and the output impedance is low