基于温度特性测试的GaN HEMT功率放大器性能退化研究

Research on performance degradation of GaN HEMT power amplifier based on temperature characteristic tests

为了研究氮化镓高电子迁移率晶体管功率放大器在不同环境温度下的性能退化情况,根据我国东、西、南、北4个地区的极端温度、平均温度以及电路的工作温度对其进行了系统的温度特性测试。测试结果显示,随着温度升高,该功率放大器的直流特性和交流特性都出现了不同程度的退化,当温度升高至125℃时,小信号增益较常温减少了1.26 dB,三阶交调点下降了6.03 dBm,输出功率与增益最大差值为1.31 dB。分析可得其主要原因是温度升高直接引起阈值电压正向偏移和二维电子气迁移率下降,进而导致饱和电流减小和膝点电压增加,最终使得输出功率显著减小。为保证电路在不同温度下正常工作,提出了一种温度补偿措施来抵消由温度引起的性能退化,这为电路的可靠性设计提供了重要参考。

[Objective]As advancements in satellite communication,phased array radar,and electronic warfare technologies surge forward,we are ushered into a new era of semiconductor materials and electronic techniques.Gallium nitride(GaN),a third-generation semiconductor material,is emerging as a vital player owing to its excellent characteristics,such as high breakdown field strength,large thermal conductivity,and high electronic saturation drift speed.These qualities make GaN indispensable in microwave,millimeter-wave devices,and RF circuits.The GaN power amplifier(PA),a key module of transceivers,has become a focal point in communication system research.However,its operation in harsh conditions can significantly affect the reliability and stability of the entire communication system.While much of existing research focuses on performance analysis under high-temperature and high-power conditions,less attention has been paid to the reliability of these systems in different environments.This study aims to bridge this gap by examining the performance changes of a GaN PA under extreme temperatures in different regions.[Methods]We carried out a series of temperature tests at extreme,average,and operating temperatures for various regions in China.Ten temperature conditions were selected,namely–40℃,–20℃,0℃,5℃,25℃,35℃,45℃,65℃,85℃,and 125℃,to investigate its RF small signal and large signal output.The PA was placed in a temperature chamber set to each respective temperature for approximately 2.5 until output stability was achieved.A comprehensive test scheme has been designed and executed using a professional test setup.[Results]The results revealed that PA output varied significantly with temperature changes.As the temperature increased,both DC and AC characteristics exhibited a certain degree of degradation.At 125℃,its Ids decreased by 32 mA,and S21 dropped about 1.26 dB.Moreover,its power output(Pout),gain,and Output third-order intercept point(OIP3)decreased by approximately 1.31 dBm,1.31 dB,and 6.03 dBm,respectively.[Conclusions]These findings underscore the significant impact of temperature on PA performance.Rising temperatures can cause a positive shift in threshold voltage and a marked decrease in 2D electron gas mobility.These changes can further lead to a reduction in saturation current and an increase in knee voltage,resulting in substandard performance from the PA.Ultimately,the PA demonstrated abnormal performance,including variations in Pout and gain.These irregularities hinder the device from meeting the application needs of the entire system.Therefore,we proposed a temperature compensation measure designed to offset the performance degradation caused by fluctuating temperatures.This system comprises a temperature sensor,a control unit,and an analog attenuator.Based on the real-time compensation parameters in the temperature compensation table,the control unit can adjust the output of the analog attenuator,modifying its attenuation amount to achieve temperature compensation.This investigation provides valuable insights into the detailed performance variations of PA with changing temperatures,offering important reference points for future PA design and reliability analysis.