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Study On Thermal Effect Of RF HBT Power Amplifier

Posted on:2016-12-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H SunFull Text:PDF
GTID:1108330503976445Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
GaAs heterojunction bipolar transistor (HBT) has been widely used in RF power amplifier (PA) design for its outstanding power density, good linearity and superior efficiency at high frequency. In the past few years, there has been a trend of growing integration for power amplifier which generates an increasing power comsumption density. The GaAs material, however, has a poor thermal conductivity. As a result, the power amplifier appears serious thermal effects. The transistor is heated to a high temperature and its’ electrical property is changed correspondingly. Thus, the thermal effects deteriorate the PA’s performance and limit its’ development.There is a strong need to further research on thermal effect mechanism, the related electro-thermal model and circuit design technique. It is of significant importance for the design of RF HBT power amplifiers with excellent performance.This dissertation carries on a detailed study from the point of thermal design for HBT PA integrated circuits, including PA’s heat conduction mechanism, transistor characteristics variation with temperature and electro-thermal coupling effects of paralleled transistors. The internal mechanism of thermal effect is revealed and an accurate distributed electro-thermal model is implemented. An adaptive power cell technique is then proposed to improve both thermal properties and electrical performance. The layout structure is further optimized to implement RF power amplifier chip design with high performance.Several creative works have been done in this dissertation:1 A distributed electro-thermal model is implemented. It reveals a non-uniform temperature distribution along the paralleled transistors. The distribution characteristic depends on heat source values (DC power consumption) and thermal enviroment conditions (transistor location, finger spacing and so on).It provides a theoretical guidence for PA’s thermal design.2、An adaptive power cell technique is proposed. Based on this technology, the transistors appear gradually turning on with an increasing output power. The efficiency is improved for the transistors are operated more efficiently. High efficiency leads to low power consumption and the heat source is decreased as a result. It effectively keeps the temperature from rising and improves the thermal effect.3、Ballast resistors are proposed to implement the adaption power cell technique. The nonlinearity is improved for their negative feedback effect.4、The layout structure is optimizedfor adaptive PA design without electrical modification. The transistors with smaller ballast resistors are located at the boundary while the transistors with larger ballast resistors are located in the center. Furthermore, the finger spacing is designed gradually decreasing from the boundary to the center to reduce and homogenize the temperature.5、A 2.4GHz RF PA is designed and fabricated on AWSC 2μm GaAs technology. With the supply voltage of 5 V, the power amplifier provides a PAE improvement up to 48% with an increase of 5% at an output power of 32 dBm. The IMD3 is improved by lOdB at 25 dBm output power with a frequency spacing of 600KHz. The output power will decrease only 0.5dB when thermal effect occurs, which is much less than the traditional PA.
Keywords/Search Tags:RF power amplifier, thermal effect, GaAs HBT, electro-thermal model, ballast resistor, efficiency, linearity, finger spacing
PDF Full Text Request
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