On the calibration of the feedback receiver using reduced sampling rate and its application to digital predistortion of 5G power amplifiers

In this paper, an advanced calibration routine is proposed to determine the frequency response of a feedback receiver over a targeted linearization bandwidth, when only sub-Nyquist (aliased) samples are available. A new approach is then devised to apply a direct learning algorithm along with the proposed receiver calibration routine, and thus linearize a millimeter wave power amplifier (PA), driven by a modulated signal, using digital pre-distortion (DPD) with a reduced feedback sampling rate. The proposed new calibration routine and DPD approach are successfully applied to linearize a PA under test, operating at 24GHz and driven by single carrier 16QAM and carrier aggregated LTE signals of 200MHz modulation bandwidth using a feedback receiver with sampling rates of 2Gsps, 1Gsps and 500Msps. Adjacent channel power ratio of about 49dBc and normalized mean square error of about 2% are obtained at the linearized PA output using the three sampling rates.