A novel adaptive digital predistortion for wideband power amplifiers with memory effects

In order to provide broadband communication, the signal bandwidth has continuously increased in existing 4G and will keep increasing in upcoming 5G communication systems. Therefore, as the bandwidth of the transmitting signal increases, memory effects arise in high power amplifiers (HPAs). A GaN Doherty HPA is known as the device that can amplify the RF signals with high efficiency. However, the performances of the linearizer are severely degraded due to memory effects in GaN active devices as the bandwidth of the input signal increases. This paper proposes a novel scheme that improves the linearization performance of the digital predistortion (DPD) for wideband transmitting signals with 100 MHz continuous bandwidth and 3.5 GHz GaN Doherty HPA. It is shown that the knowledge of the phase trajectory between adjacent transmitting samples gives an extra degree of freedom for DPD coefficient selection compared with traditional approaches and results in enhancement of the linearization performance. Thus, the proposed DPD based on the memory polynomial is able to compensate for strong nonlinearity with memory in GaN Doherty HPA by considering the phase shift between adjacent transmitting samples. The experimental results obtained for a transmitting signal with 100 MHz continuous bandwidth show that the proposed approach achieves an 8 dB adjacent channel leakage ratio (ACLR) performance improvement over standard memory polynomial DPD.