In general, amplifiers are used to increase the power of signals. For example, amplifiers can be used to convert low-power radio frequency (RF) signals into larger RF signals for driving the antenna of a transmitter. In such cases, amplifiers may be implemented as part of overall power amplifier used by an RF transmission system.
One measure of amplifier performance is back-off power. In general, the back-off power of an amplifier represents the output power at the point where the highest efficiency is achieved, divided by the maximum output power (P−3 dB), with the back-off power expressed in decibels (dB).
Unfortunately, some previous power amplifier designs have been limited with respect to back-off power. For example, some previous symmetrical power amplifier designs have been limited in their ability to provide arbitrary back-off power. As another example, some previous asymmetric power amplifiers have been required to implement a low power utilization ratio in order to obtain desired high back-off power. Specifically, some previous symmetrical power amplifier designs have been limited to providing back-off power of around 6 dB. Therefore, there remains a need for amplifiers that provide high performance and controllable back-off power.