IMD Components Compensation Conditions for Dual-Band Feed-Forward Power Amplifier

This paper presents analysis results of the intermodulation distortion (IMD) components compensation conditions for dual-band feed-forward power amplifier (FFPA) when inputting dual-band signals simultaneously. The signal cancellation loop and distortion cancellation loop of the dual-band FFPA have frequency selective adjustment paths which consist of filter and vector regulator. The filter selects the desired frequency component and suppresses the undesired frequency component in the desired frequency selective adjustment path. The vector regulators repeatedly adjust the amplitude and phase values of the composite components for the desired and suppressed undesired frequency components. In this configuration, the cancellation levels of the signal cancellation loop and distortion cancellation loop are depending on the amplitude and phase errors of the vector regulator. The analysis results show that the amplitude and phase errors of the desired frequency component almost become independent that of the undesired frequency component in a weak non-linearity condition, when the isolation between the desired band and the undesired band given by the filter is more than 40 dB. The amplitude errors of the desired frequency component are dependent on that of the undesired frequency component in a strong non-linear conditions when the isolation level sets as above. A 1-W-class signal cancellation loop and 20-W-class FFPA are fabricated for 1.7-GHz and 2.1-GHz bands simultaneous operation. The experimental results show that the analysis results are suitable in the experimental conditions. From these investigations, the analysis results can provide a commercially available dual-band FFPA. To our best knowledge, this is first analysis results for the dual-band FFPA.