An automatic phase adjustment scheme for RF and Cartesian feedback linearizers

Amplifier linearization schemes based on modulation feedback (e.g., Cartesian feedback) require a phase correction circuit to stop instability and limit the level of the out-of-band noise floor. It is shown that the optimum phase corrector setting corresponds to the minimum output power condition of the amplifier. A new and very simple method by which the phase correction circuit is adjusted is described. The scheme uses the supply current to the final stage amplifier as a measure of the output power and minimizes this by using a simple direct search algorithm. Phase correction to within 5/spl deg/ of optimum can be obtained after about 50 iterations. The performance is limited by hysteresis in the supply current feedback signal.