Application of Load-Pull Principle in RF Power Amplifier Design

JasonYoo

Application of Load-Pull Principle in RF Power Amplifier Design [Copy link]

In recent years, due to the advancement of microwave communication technology and the increasing demand for communication bandwidth and mobility, the importance of wireless local area network (WLAN) in people's daily life has greatly increased, and it has driven the industry and academia to invest in the research and development of this system circuit technology and products. Figure 1 shows the wireless local area network technology developed in recent years.

Among them, the 802.11a, g, and HiperLAN communication systems developed by IEEE are the most popular. They all use Orthogonal Frequency Division Multiplexing (OFDM) technology. OFDM is a digital spread spectrum modulation technology that has become the most popular transmission modulation choice in new wireless communication applications. Using OFDM technology can increase bandwidth, reduce noise, improve confidentiality, and solve communication obstacles such as multipath fading.

OFDM technology allows the device to maintain stable and reliable performance in the presence of dynamic and static multipath interference, so it plays a core role in today's wireless communication field. The current application scope of this technology also includes terrestrial digital TV broadcasting and mobile phone networks. Its traditional circuit architecture is shown in the transceiver architecture of Figure 2.

In addition, since OFDM uses BPSK, QPSK, 16QAM and 64QAM modulation methods, it has high requirements for linearity, and the harmonics generated by the modulated signal through the power amplifier will cause nonlinear distortion, seriously affecting the power output, and thus determining the length of the communication distance. In addition, the power consumption of the power amplifier accounts for almost one-third of the entire transceiver, so its efficiency is often an important factor in determining the battery life; and the impedance change and thermal effect during large signal operation have caused the accuracy of the nonlinear model currently provided by the manufacturer to no longer meet the use requirements, which has greatly increased the difficulty of designing RF integrated power amplifiers.

Therefore, we use the load- pull principle to improve the gain compression point to reduce the nonlinear distortion of harmonics and simulate the maximum output power load point of the power amplifier to achieve the design of high power conversion efficiency, high output power, and high linearity RF power amplifier. At the same time, we also use the load-pull measurement system for verification and establish related power component libraries to achieve the research and development goals of circuit modularization.