Digital baseband injection techniques to reduce spectral regrowth in power amplifier

Two novel injection techniques reduce adjacent channel power ratio (ACPR) in a nonlinear power amplifier (PA). The first injects two ‘brick-wall’ signals covering the adjacent channel bandwidths. All the injected sub-frequencies have the same amplitude but different phases. Tuning these phases, we plot the output signal to determine the appropriate sub-frequency amplitudes and phases to reduce ACPR. The second technique injects cubic products of the original signals, covering the adjacent channels. Both techniques, considered in theory and practice, can reduce spectral regrowth by nearly 30dB. The first is conceptually simple while the second is more practical for embedding into a predistorter.