Research On Multi-mode Multi-band Power Amplifiers For Latest Generation Mobile Terminals

Power amplifier is a key component in radio frequency (RF) front-end modules. Its performance directly affects the communication quality of mobile terminals and their battery life. The mobile communication network has been in the status of coexistence of multi-communication networks since the 3G came to use. At 4th generation (4G), there is a surge of multiple frequency band applications which are required by the communication system. Therefore, the number of power amplifiers to be used increase significantly.Furthermore,the RF front-end module complexity becomes a real challenge. Thus,the study of multi-mode multi-band power amplifiers gets really important. In this work, in order to meet the demand of RF front-end power amplifier ICs for the latest generation 4G(LTE-Advanced) mobile terminal; the research on design of InGaP / GaAs HBT temperature compensation circuit and broadband circuit with high efficiency for multi-mode multi-band power amplifiers is carried out. The main achievements of this work are summarized as follows:(1) The self-heating effect of HBT device and its impact on the temperature stability of active bias circuit were studied for the application of GaAs HBT device in power amplifiers.A modified bias circuit with temperature compensation structure was proposed to improve the performance of the bias current of the temperature stability. The temperature compensation circuit is aimed at stabilizing the reference voltage of the original active bias circuit in order to essentially keep the voltage constant with temperature change. The temperature compensation circuit was achieved by adding a new active mirror circuit structure, which is based on the principle of thermo-electric negative feedback. The simulation result shows that the temperature stability of the bias current is improved appreciably. Its temperature variation is improved from 8.5% to 2.5% at 80 ?.(2) By using the temperature compensation bias circuit, a two-stage high performance amplifier with temperature compensation circuit was successfully designed. The power amplifier adopted an active bias circuit with temperature compensation to optimize the temperature stability and efficiency of the power amplifier. The output matching network contained the Class-F high efficiency harmonic control portion to optimize the output harmonics of the power amplifier in order to improve its efficiency of the power amplifier.The approach to improving the efficiency of the power amplifier also helps the design of high efficiency output matching network. The final measured result shows that the fluctuation of gain was less than ± 2dB with PAE variation 1.5%, ACPR variation 3dBc and quiescent current ± 2.5% over whole temperature range. Its PAE reached 42% at 28dBm linear output power at room temperature.(3) The design of broadband matching network was investigated. The relationship between the bandwidth and efficiency of the LC matching network and the multi-section LC matching network were studied in details. The analyzed result shows that the two-section LC matching network may achieve the highest transmission efficiency. While the second is the three-section LC matching network. For the output matching network, a method of finding the maximum output power matching impedance point of the broadband output matching network was proposed. The method was applied without the help of complex systems such as Load-Pull. In addition, a method of solving the problem of the parasitic parameters from the ground inductance on the laminate and coupling effect between signal paths was also proposed for optimizing the output matching network based on the three-dimensional electromagnetic field simulation. These techniques were used to make sure that the power amplifier can achieve broadband performance.(4) A three-stage wideband MMIC power amplifier working at 4.9GHz ?5.9GHz frequency range was designed successfully by using broadband matching theory. The power amplifier adopted a two-section LC high-efficiency matching structure between the first and second stage, the three-section LC efficient matching network structure between the second and third stage,and a two-section LC high efficiency matching structure at the output stage.The measured result shows that the working bandwidth of the power amplifier reached 1GHz; the gain exceeded 24.5dB, and the gain variation was less than 2dB. The output saturation power (Psat) exceeded 30dBm and the maximum output power Psat reached up to 31.8dBm.(5) A broadband power amplifier with dual power operation mode architecture is presented to improve the efficiency at the power amplifier's back-off region. The power amplifier achieved average power efficiency improvement by using different fundamental impedance values in different output power levels. By using InGaP / GaAs HBT and AlGaAs/ InGaAs pHEMT in a single process, the amplifier circuit and control circuit can be integrated in a single die. In this way, the single chip mode-switching function was achieved.It can improve the amplifier integration effectively.(6) A broadband dual power mode power amplifier working at 2.3GHz ?2.69GHz was implemented. The power amplifier adopted the structure of high and low power mode and improved the efficiency of the power amplifier in the power back-off. A band-gap reference circuit and a simple logic circuit based on the common-emitter structure were used to enable the power amplifier and mode select, respectively. A high efficiency broadband output matching network were also designed by utilizing broadband output matching principle and high efficiency output matching design theory. The measured result shows that the highest efficiency of the amplifier is 38%. This structure can improve the efficiency of the power amplifier at back-off region effectively. The overall performance in the frequency range of 2.3 GHz ?2.69GHz was good enough to meet the requirement of Band 38, Band 40, Band 41 and Band 7 applications. Overall, it achieved the goal of multi-mode multi-band power amplifier design.