The changes in these components also cause changes in amplitude and frequency. Output power is another consideration in the use of oscillators. Generally speaking, high power is obtained at some sacrifice to stability. The buffer provides isolation between the oscillator and the load to prevent changes in the load from affecting the oscillator. If the oscillator stage must develop high power, efficiency becomes important.
Many oscillators use class C bias to increase efficiency.
Other types of oscillators may use class A bias when a high efficiency is not required but distortion must be kept at a minimum. Other classes of bias may also be used with certain oscillators. An amplifier can be made into a sine-wave oscillator by providing regenerative feedback through an RC network. The RC network also acts as the frequency-determining device. For the circuit to produce regenerative feedback, the RC network must provide a 180-degree phase shift of the collector signal.