Patent attributes
A pilot generation and detection system within a feed forward power amplifier that uses positive feedback to create a narrow bandwidth limit cycle is disclosed. The pilot system adjusts its frequency automatically to keep a desirable phase relationship between the pilot generation and detection. As a result, quadrature modulation/detection of the pilot used in prior approaches to ensure reliable estimates of the detected pilot power is unnecessary. This reduces the cost of the system. In addition, the pilot system turns the pilot amplitude ‘on’ or ‘off’ as needed. When the alignment of the second loop is good, the positive feedback will not have sufficient gain to maintain a limit cycle. As a result, the pilot will turn off when the second loop has converged. The pilot will return automatically as a by-product of the positive feedback if the second loop alignment degrades. Turning off the pilot when the second loop has converged reduces the pilot spurs appearing at the output of the feed forward amplifier. In addition, turning off the pilot reduces the power in the error amplifier, which in turn, allows the transistor size to be reduced.
