Spur-Free Harmonic Cancelation Digital Predistortion for HF Transmitters

High frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) is always faced with the problem of harmonics because of the nonlinearity of the PA. With the previous harmonic cancellation digital predistortion (HC-DPD) scheme, harmonics and the fundamental components, as a whole, are modeled with a uniform memory polynomial (MP) model. Although the harmonics can be well canceled, unwanted spurs can be generated when the nonlinearity order of the MP model exceeds the critical point because of the limited sampling rate. In this letter, a spur-free HC-DPD (SF-HC-DPD) scheme is proposed to suppress the spurs. Without increasing the sampling rate, a novel anti-aliasing MP (AA-MP) model is proposed. With the energy-saving linearization technique, the signal quality and robustness of HF communication can be greatly improved. Measurement results show that the harmonic-to-fundamental power ratio, the adjacent channel power ratio (ACPR), and the error vector magnitude (EVM) performances were all improved by nearly 20 dB. In addition, the unwanted spurs can be suppressed for being below -80 dBc, which is more than 26 dB better than the HC-DPD scheme with the MP model.