Wideband Digital Predistortion Using Spectral Extrapolation of Band-Limited Feedback Signal

With the ever increasing demands for higher data rate, wider bandwidth is required for improving the throughput. This trend, however, imposes design challenges for the digital predistortion (DPD) in many aspects. In order to sample the broadband power amplifier (PA) output signal, it requires the use of high-speed analog-to-digital converters (ADCs), which tend to be the most expensive components in a transmitter with DPD. The sampling speed of the ADC for conventional DPD has to be several times of the original signal bandwidth in order to cover the out-of-band intermodulation components caused by nonlinear PA. In this paper, a novel technique, which allows the use of low-speed ADCs by introducing spectral extrapolation to the band-limited feedback signal, is proposed. This allows efficient implementation of DPD for very wideband signals. Experimental results demonstrate that the bandwidth of the acquisition path can be even less than the bandwidth of original signal applying the proposed technique. In addition, satisfactory linearization performance has been achieved employing wideband signals up to 160 MHz bandwidth.