A positive feedback pilot system for a wide bandwidth feedforward amplifier

The positive feedback pilot system described in [1] for controlling the second loop of a feedforward (FF) compensated power amplifier (PA) is improved for use in wide bandwidth applications. The log-detector and limiter are replaced with an automatic level controller (ALC) making the control of the pilot shut-off threshold more precise. A multi-pilot frequency optimization is proposed, which when combined with the pilot shut-off feature, allows for wide bandwidth cancellation of distortion without introducing discernible pilot residuals in the output signal. Test results on a feedforward power amplifier show that the multi-pilot optimization improves the wide bandwidth cancellation by 5 dB over that of a single pilot.