The Research Of Linearization Techniques On Envelope Tracking Power Amplifiers

With the development of wireless communication system and modern signal processing, envelope tracking power amplifier(ETPA)with its linearization technique is becoming a hot spot of research and digital predistortion has gradually become the main linearization technology for ETPA. The ETPA linearization techniques, especially the predistortion techniques is researched in this theis which consists of three parts. First, the characteristics of the ETPA is researched, then the design of digital predistortion based on FPGA(Field Programmable Gata Array) is discussed, and last, digital predistortion is applied to ETPA. The main work and innovations are summarized as follows:First, the characteristics of fixed bias power amplifier and the envelope amplifier is studied, three kinds of envelope shaping method and two kinds of envelope bandwidth reduction is analyzed, the effects of non-ideal factors such as time delay, minimum drain bias voltage and envelope bandwidth on ETPA are discussed and fractional delay compensation for time delay is carried on.Second, digital predistortion based on FPGA for the power amplifier part of ETPA is implemented, the key technologies to implement the digital predistortion such as the finite word length effect, look-up table and Cordic algorithm is discuss, the influence of channel distortion on digital predistortion are analyzed, the non-ideal factors for DACs, reconstruction filter and quadrature modulator are compensated, and the test of two-tone signal completed. IM3 is improved 12 d B for two-tone with bandwidth 1MHz, and 22 d B is improved after channel equalization.Third, Dual-Input amplifier architecture is discussed for ETPA, three kinds of ETPA are designed based on max PAE, equal gain compression and equal gain, digital predistortion method based on vector decomposition is analyzed in detail, ADS and Matlab joint simulation system is constructed and simulation of two-tone signal and WCDMA signal is carried on for the above mentioned three kinds of ETPA. For ETPA with max PAE, IM3 is respectively improved 43 d B and 38 d B for two-tone with bandwidth 2MHz and 5MHz and ACPR is improved 40 d B for single carrier WCDMA and 30 d B for four carriers WCDMA. For ETPA with equal gain compression, IM3 is respectively improved 37 d B and 36 d B for two-tone with bandwidth 2MHz and 5MHz and ACPR is improved 33 d B for single carrier WCDMA and 23 d B for four carriers WCDMA. For ETPA with equal gain, IM3 is respectively improved 36 d B and 34 d B for two-tone with bandwidth 2MHz and 5MHz and ACPR is improved 26 d B for Single carrier WCDMA and 22 d B for four carriers WCDMA.The experiment and simulation show that the channel equalization method can further improve the linearity of the power amplifier and digital predistortion method based on vector decomposition can well improve the linearity of ETPA.