A power amplifier system can be configured to provide amplification to a radio frequency signal associated with a first frequency band and to output an amplified radio frequency signal. The system can include a bandpass filter arranged in a feedback loop with respect to the power amplifier and configured to pass through a portion of the amplified radio frequency signal corresponding to a second frequency band. A first shifter can be positioned in the feedback loop, and an output of the feedback loop can provide negative feedback to an input of the power amplifier.