Research On Efficiency And Linearization Techniques Of Broadband Power Amplifiers

With the rapid development of modern wireless communication technology,the transmission rate of information is developing in a faster direction,and the bandwidth is developing in a wider direction.However,in order to cope with the transmission of high information capacity,modulation methods are becoming more and more complex,resulting in a higher peak-to-average ratio of the signal and a narrower available frequency band.As mentioned above,modern wireless communication requires a new transmitter structure.The power amplifier plays a decisive role in the transmitter and will affect the performance of the entire transmission system.For the power amplifier,its bandwidth,efficiency,and linearity are three factors that affect each other and limit each other.Then,based on broadband power amplifiers,equalization linearity,efficiency and other indicators are important directions for scientific and technological research.In order to meet the above scientific research needs,the main work of this paper is divided into the following three parts:First,the performance indicators,types,and linearization techniques of the power amplifier are introduced.The traditional linear power amplifier is difficult to achieve good linearity and high efficiency at the same time.The Doherty power amplifier commonly used in base stations is based on the theory of active load traction,and its fallback efficiency can reach78.5%.Therefore,this paper makes a theoretical analysis of the Doherty power amplifier.Secondly,this paper investigates in detail the factors limiting the bandwidth of Doherty power amplifiers.Under the theoretical support of the two-point matching method,the quarter-wavelength line is cancelled and the load impedance modulation point is advanced before the signal synthesis network.In order to avoid the effect of parasitic phase shift on the broadband high-order output matching circuit,a low-order impedance conversion method is used to design a symmetrical Doherty power amplifier that operates in the 1.8GHz-2.8GHz and has a relative bandwidth of 43%.DC analysis simulation,stability simulation,small-signal S-parameter simulation,large-signal harmonic simulation,and parameter optimization are performed on the overall circuit in the ADS software.The actual product is processed,and the thermal feasibility simulation is performed.After the debugging is completed,the saturated output power can reach 44.9d Bm-46 d Bm,the saturation drain efficiency can reach 53%-66%,the back-drain efficiency can reach 46%-57% and the saturation gain is greater than 8.1d B.Combined with digital pre-distortion technology,at an output power of 38 d Bm and an efficiency of 52%,the AC LR index meets-48 d Bc for three carriers with a carrier bandwidth of20 MHz and peak-to-average amplification compared to a 7.5d B LTE signal.Finally,this thesis studies the analog predistortion,which is also a predistortion technology,like digital predistortion.The analog predistortion is suitable for high frequency and wide bandwidth situations.Based on the non-linear characteristics of Schottky diodes,the linear index improvement of the analog predistorter structure in series analog predistorter structure,parallel diode predistorter structure,single diode analog predistorter structure,and antiparallel diode is compared.Finally,this paper designs an analog predistorter based on a parallel reverse diode pair reflective structure to achieve a maximum gain expansion range of10 dB and a maximum phase compression range of 32° in 13.75GHz-14.5GHz.