Patent ID: 8594231
Filing Date: 2013-11-26
Classification: H03F

Abstract:
1. A power series digital predistorter for adding to an input signal a distortion compensation component for canceling a distortion component generated in a power amplifier, the power series digital predistorter comprising: a linear transfer path adapted to transfer the input signal with a delay; a distortion generation path comprising: an N-th order distortion generator adapted to generate an N-th order distortion component of the input signal; an N-th order distortion vector adjuster adapted to adjust the amplitude and the phase of the N-th order distortion component; and an N-th order frequency characteristic compensator adapted to divide the output of the N-th order distortion vector adjuster into M bands in a frequency domain and to adjust the amplitude and the phase of the output in each of the M bands; and the distortion generation path outputting the output of the N-th order frequency characteristic compensator as the distortion compensation component, where N is a predetermined odd number equal to or larger than three and M is a predetermined integer equal to or larger than two; a combiner adapted to combine the output of the linear transfer path and the output of the distortion generation path; a distortion observer adapted to observe the distortion component included in the output of the power amplifier, which is adapted to amplify the output of the combiner; and a controller adapted to set adjustment amounts for the amplitude and the phase in each of the M bands in the N-th order frequency characteristic compensator according to an observation result of the distortion observer; wherein the controller comprises: a phase setting unit adapted to collectively set the adjustment amounts for the phases in the M bands in the N-th order frequency characteristic compensator; an amplitude setting unit adapted to collectively set the adjustment amounts for the amplitudes in the M bands in the N-th order frequency characteristic compensator; and a processing control unit adapted to determine whether an index indicating the degree of cancellation of the distortion component generated in the power amplifier satisfies a preset condition, and, if the index does not satisfy the condition, to perform control such that the phase setting unit again collectively sets the adjustment amounts for the phases and the amplitude setting unit again collectively sets the adjustment amounts for the amplitudes; wherein the phase setting unit (a1) collectively sets initial adjustment amounts for the phases in the M bands in the N-th order frequency characteristic compensator; (a2) records in each of the M bands a combination of the adjustment amount for the phase in each of the M bands, set in the N-th order frequency characteristic compensator, and a distortion component observed in each of the M bands by the distortion observer when the N-th order frequency characteristic compensator adjusts the phase according to the adjustment amount; (a3) changes step of changing the adjustment amount for the phase in each of the M bands by a preset offset in each of the M bands; (a4) repeats L (a5) calculates coefficients a in each of the M bands by using the combination recorded in (a2) in each of the M bands; (a6) calculates an adjustment amount, −a (a7) collectively sets the adjustment amounts for the phases in the M bands calculated in (a6), in the N-th order frequency characteristic compensator.