A common-collector transistor circuit is often used

The distinguishing feature of common-collector configuration, (the circuit is also known as an emitter follower because the emitter voltage follows the base voltage), is that the signal is applied to the base and the output is taken from the emitter.

The emitter follower has high input resistance, low output resistance, and near-unity voltage gain. It is most widely used as an impedance transformer to reduce loading of a preceding signal source by the input impedance of a following stage. It also finds application as a unity-voltage-gain level shift because the dc output voltage is shifted from the dc input voltage by VBE(on).