Performance optimizing on multi-function MMIC design

Integration of GaAs BiFET (bipolar-FET) devices to obtain the optimum performance for multiple functions of MMIC design has been achieved. In this study, heterojunction bipolar transistors (HBTs), enhancement mode pseudomorphic HEMTs (E-pHEMTs), and depletion mode pHEMTs are developed for potential applications, including the integration of HBT power amplifier circuitry with pHEMT-based bias control, logic, RF switch, and low-noise amplifier circuitries. Critical processes including gate photolithography and gate recess control are presented and discussed in detail. The enhancement-depletion modes of pHEMT, HBT electrical performance, and uniformity are investigated comprehensively. In addition, power amplifiers and high power switches based on BiFET technology are investigated.     

L波段高效率射频功率放大器的设计与仿真

射频功率放大器是无线通信系统中的重要组成部分,其工作效率直接影响着整个系统的耗能、稳定度和对电源散热装置的要求,提高射频功率放大器的效率,能够节约能源,降低功耗,因此实现射频功率放大器的高效率工作是目前射频功率放大器领域的热点问题之一。本文选用Freescale晶体管MW6S004N,借助ADS2013软件,采用负载牵引技术和源牵引技术得到最佳负载阻抗和最佳源阻抗,并用Smith圆图进行电路的匹配设计,对射频功率放大器进行了仿真和优化。仿真结果表明,在频率为1960MHz的L波段,输入功率为21d Bm时,射频功率放大器的输出功率大于36d Bm,功率附加效率大于50%。这种高效率射频功率放大器适用于WCDMA基站,对基站中高效率功率放大器的设计有着重要的参考价值。     

X-parameter measurement on a GaN HEMT device: complexity reduction study of load-pull characterization test setup

Characterization of power transistors is an indispensable step in the design of radio frequency and microwave power amplifiers. A full harmonic load-pull measurement setup is normally required for the accurate and comprehensive characterization of RF power transistors. The setup is usually highly complex, leading to a relatively high hardware cost and low measurement throughput. This paper presents X-parameter measurement on a gallium nitride(GaN) high-electron-mobility transistor and studies the potential of utilizing an X-parameter-based modeling technique to highly reduce the complexity of the harmonic load-pull measurement setup for transistor characterization. During the X-parameter measurement and characterization, load impedance of the device is tuned and controlled only at the fundamental frequency and is left uncontrolled at other higher harmonics. However,it proves preliminarily that the extracted X-parameters can still predict the behavior of the device with moderate to high accuracy, when the load impedance is tuned up to the third-order harmonic frequency. It means that a fundamental-only load-pull test setup is already enough even though the device is to be characterized under load tuning up to the third-order harmonic frequency, by utilizing X-parameters.     

Highest efficiency, linear X-band performance using InP DHBTs - 48%PAE at 30 dB C/IM3

InP single heterojunction bipolar transistors have previously demonstrated 5-10 dB lower third-order intermodulation products (IM3) compared to GaAs heterojunction bipolar transistors (HBTs) under low voltage (2 V) operation. This paper reports excellent single-tone and two-tone X-band operation, including high two-tone power-added efficiency (PAE), on linear InP double heterojunction bipolar transistors (DHBTs) operated at V_ce=4 V. The InP DHBT demonstrated a 30 dB carrier to third-order intermodulation product (C/IM3) output power ratio simultaneously with 48% two-tone PAE. This is the highest known efficiency of an X-band device under linear (30 dB C/IM3) operation. This is especially significant for microwave power amplifiers for satellite communication transmitters, where lower intermodulation distortion is normally accomplished by backing off in RF drive and output power, thus sacrificing PAE performance     

Analysis of the large-signal characteristics of powerheterojunction bipolar transistors exhibiting self-heating effects

The large-signal microwave characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are modeled using the conventional Gummel-Poon-based bipolar junction transistor (BJT) model and extending it to include self-heating effects. The model is incorporated as a user-defined model in a commercial circuit simulator. The experimental microwave characteristics of HBTs are analyzed using the new model and harmonic balance techniques and the impact of self-heating effects on the device large-signal characteristics is investigated. Use of constant base voltage rather than constant current is more suitable for achieving maximum output power. Self-heating induced by RF drive is reduced under constant base current conditions. Increased thermal capacitance values result in gain enhancement at high power levels     

An experimental study of the effects of harmonic loading onmicrowave MESFET oscillators and amplifiers

This paper reports an extensive experimental investigation of the effects of second harmonic loading on the performance of microwave GaAs MESFET oscillators; and strongly driven amplifiers. The measurement system used is an active load system based on six-port techniques. Harmonic load pull measurements were obtained for the NE72084 MESFET; the measurements show how the second harmonic load can influence the power gain and the power added efficiency in strongly driven amplifiers. The device line characterization technique was combined with the harmonic load pull technique; the measurement results illustrate how the output power and the DC to RF conversion efficiency of an oscillator depend on the choice of the second harmonic load. Amplifier and oscillator circuits have been designed using these measurements; the circuits have been constructed and measured. The results validate the experimental approach used and clearly illustrate the importance of properly selecting the second harmonic load in amplifier and oscillator circuits. Significant improvements in gain, output power and efficiency have been achieved by properly selecting the second harmonic load     

Multiharmonic source-pull/load-pull active setup based on six-port reflectometers: influence of the second harmonic source impedance on RF performances of power transistors

An original measurement system for nonlinear RF power-transistor characterization is presented. This new setup enables the measurement and optimization of output power and/or power-added efficiency (PAE) using active harmonic tuning and six-port reflectometers as vector network analyzers. Two active loops are inserted at both ports of transistors in order to independently control the source and load impedances at the fundamental and at the second harmonic frequency. To the authors' knowledge, this is the only active technique that allows a complete automated multiharmonic load-pull/source-pull measurement system. Experimental results are shown for a commercial GaAs MESFET power transistor at 2 GHz.     

Nonuniform RF Overstress in High-Power Transistors and Amplifiers

Nonuniform light emission from power transistors at 2-3-dB compression levels has been imaged using a microscope- mounted camera. The nonuniformity depends on the device lateral geometry, load impedance, dc and radio frequency (RF) conditions, and the negative gate current, which is a result of the RF-induced impact ionization in the transistors. Numerical simulations demonstrated a nonuniform distribution of the RF overstress in the transistors under the same conditions. The simulations indicate that the nonuniformity in the light intensity may be attributed to the RF-induced voltage overstress. Therefore, the observed light emission may be used as a direct and contactless monitor of the RF-induced overstress in transistors and power amplifiers.     

An introduction to GaAs/GaAlAs HBTs for power applications

This paper presents a brief introduction to GaAs/GaAlAs heterojunction bipolar transistors (HBTs) for microwave and millimetre-wave power applications. The theoretical advantages of the heterojunction are outlined and the benefits of its incorporation in DC, RF and power devices are discussed. The problems inherent in the realization of HBTs in terms of device design, epitaxial material growth and device fabrication are discussed and the performance characteristics for practical devices presented. The paper concludes with a look at state-of-the-art GaAs/GaAlAs HBT performance and its standing with respect to the competing technologies of the metal semiconductor field effect transistor (MESFET) and the high electron mobility transistor (HEMT).     

RFCMOS Unit Width Optimization Technique

In this paper, we demonstrate a unit width ( W_f) optimization technique based on their unity short-circuit current gain frequency (f_T) unilateral power gain frequency (f_MAX)? and high-frequency (HF) noise for RFCMOS transistors. Our results show that the trend for the above figures-of-merit (FOMs) with respect to the W_f change is different; hence, some tradeoff is required to obtain the optimum W_f value. During the HF noise analysis, a new FOM is proposed to study the W_f effect on the HF noise performance. In our experiment, the flicker noise of the transistor is also measured and the result shows that the change in W_f does not affect the noise spectral density at the low-frequency range. This technique enables RF engineers to optimize the transistor's layout and helps to select the optimum Wf for transistors used in specific circuit design such as the low-noise amplifier, voltage-controlled oscillator, and mixer. Furthermore, by using layout optimized transistors in the RF circuit, the optimal circuit's performance can be easily achieved and, thus, greatly reduced the circuit development time. In the aspect of RF device modeling, by knowing the optimum W_f for a particular process or technology, the number of transistors to model is reduced and, hence, greatly shortens the RF modeling development time for existing and future technologies.     

An InGaP/GaAs Merged HBT-FET (BiFET) Technology and Applications to the Design of Handset Power Amplifiers

The last decade has seen GaAs HBTs emerge as the dominant technology in wireless handset power amplifiers. Modern application requirements and size limitations have driven industry leaders towards the co-integration of depletion mode n-FET and GaAs HBT. The merger of Bipolar and FET, or BiFET, gives an additional degree of freedom in the design of advanced power amplifiers independent of a silicon controller. This paper provides an overview of the various techniques that can be used to join the two device technologies and then shows how a merged epitaxial structure, where an FET is formed in the emitter layers of an HBT, combines functional versatility with the high volume manufacturability needed to supply millions of power amplifiers at low cost. A large-signal model of the FET structure is developed which takes into account the unique physics and geometries of the device, including voltage-dependant parameters and charges on all four electrical terminals. Specific handset applications that can benefit or be enabled by BiFET are presented, such as on-off switching, low voltage bias controllers , Auto-Bias power amplifiers, and bias circuits with low or no voltage reference. When npn-only bias circuitry is limited to low voltage reference levels, HBT power amplifiers with BiFET bias stages are shown to have superior RF performance to their npn-only counterparts.     

Performance characterization of III-V power devices

The power performance of GaAs/AlGaAs pseudomorphic high electron mobility transistors (PHEMTs) has been modeled by using the statistical Design of Experiment approach. Empirical models for the small signal gain, output power and power added efficiency have been developed. The “walk-out/in” phenomenon has been observed in the devices as a result of power measurements. The evolution of surface photovoltage spectra after RF power stress indicates accumulation of positive electrical charge in the buffer and the surface layer of the devices.     

Experimental study of AlGaAs/GaAs HBT device design for powerapplications

An experimental study of AlGaAs/GaAs heterojunction bipolar transistor (HBT) device design for optimizing key DC and RF performance parameters relevant to power device applications is reported. The design of the collector, base, and base-emitter junction is investigated for improved power device performance, and novel device structures are presented. Device scaling effects and the extent to which air-bridged interconnect can reduce parasitics in large power devices are also explored. Power HBTs employing some of the optimized design features have achieved a power output of 1.2 W (4 W/mm) with 43% power-added efficiency at 10 GHz     

X-band 0.5, 1, and 2 watt power amplifiers with markedimprovement in power-added efficiency

Very efficient X-band MESFET power amplifiers, showing greater power-added efficiency over a wider bandwidth than any X-band amplifiers of comparable output reported to date, are discussed. The amplifiers were designed with attention given to optimum bias, proper harmonic termination, and efficient power combining. These device and design issues are discussed, and a straightforward design method which achieved the increased levels of efficiency is described     

Nonlinear Eulerian hydrodynamical analysis of helix traveling-wavetubes for harmonic generation and its control

Eulerian hydrodynamics was developed to study the nonlinear problem of second harmonic generation in a helix traveling-wave tube (TWT). A closed-form expression for the second-harmonic component of RF output power was obtained. The method required the specification of the dispersion and interaction impedance characteristics of the helical slow-wave structure (SWS) used in the device, obtainable by the field analysis of the SWS. Care was taken however to restrict the present Eulerian theory to the correct regime, which was found in terms of the RF input power drive and the device interaction length, by validating the theory against the more accurate Lagrangian theory. Within this regime, that was below the saturation level of the device, the effect of the dispersion of the SWS on the second harmonic generated in the device was studied. It was found that, irrespective of whether the dispersion of the SWS is positive or negative, the second harmonic content of the device decreased with the amount of the dispersion. Furthermore, though both the fundamental and the second harmonic content of the device decreased with the distributed loss on the SWS, the second harmonic relative to the fundamental showed a minimum at an optimum value of the distributed loss     

ESD protection design considerations for InGaP/GaAs HBT RF power amplifiers

In order to design a robust electrostatic discharge (ESD) protected RF amplifier in InGaP/GaAs HBTs, a comprehensive assessment of device vulnerability to ESD events in both active transistors and passive components of the HBT technology is presented in this paper. The results include not only the intrinsic HBT's ESD robustness performance, but also its dependence on device layout, ballast resistor, and process. Acknowledging the ESD constraints imposed on InGaP/GaAs HBT technology, a 5.4-6.0-GHz power amplifier (PA) with a compact 2000 V/sub ESD/ (human body model) on-chip ESD protection circuit that has a low loading capacitance of less than 0.1 pF and that does not degrade RF and output power performance is developed for wireless local area network application. A diode triggered Darlington pair is implemented as the ESD protection circuit instead of the traditional diode string. Its operation principle, ESD protection performance, and PA performance are also illustrated in this paper.     

RF Amplifier Design with Large-Signal S-Parameters

High-power UHF transistors have been characterized through the use of large-signal S-parameters. These S-parameters have been used successfully to design UHF power amplifiers. Waveform measurements show that due to the Q of the package parasitic, most class C operated UHF power transistors have nearly sinusoidal waveforms at their package terminals. Experimental evidence presented shows that the large-signal S-parameters are relatively independent of power once the device is turned on. These two observations make it possible to extend modified small-signal S-parameter design techniques to large-signal power amplifiers.     

包络跟踪电源优化设计与仿真

在移动通信3G/4G网络中,包络跟踪技术是提高射频功放效率的核心技术之一。从包络跟踪的相位失真问题入手,以降压变换器为拓扑,提出了以4阶贝塞尔低通滤波器传递函数为整体设计模型的包络跟踪电源设计方法,通过线性补偿控制实现对包络跟踪电源的控制。同时,依据线性控制单元在实际设计中可能遇到的问题,提出了一种更为适合实际应用的线性控制器设计方法。最后,通过软件Pspice对此包络跟踪电源进行仿真验证,以降带宽处理后的单载波1 MHz信道宽度的WCDMA包络信号作为跟踪参考信号,通过软件matlab的simulink仿真对包络跟踪电源进行验证,证明方案实际应用可行。     

推-推压控振荡器的仿真设计

在对构成推-推振荡器的基本振荡单元进行常规奇偶模分析的基础上,采用添加辅助信号源的方法,对合成后的频率调谐特性、输出功率及基波抑制特性进行了仿真模拟。并利用负载牵引法对二次谐波匹配网络进行了优化。根据仿真结果设计的X波段推-推压控振荡器,采用封装硅晶体管及砷化镓变容管,在1GHz调谐带宽内,输出功率2～8dBm。     

Optimum design of a predistortion RF power amplifier for multicarrier WCDMA applications

This paper provides a design guide for optimum design of an RF power amplifier with a predistortion linearizer. For a two-tone signal, three performance degradation factors, higher order terms, amplitude, and phase mismatches are analyzed quantitatively. The results are implemented to the design of optimized predistortion power amplifier for a WCDMA signal application. For the experiments, a 2.4-GHz class-AB power amplifier is fabricated using an LDMOSFET with a 30-W peak envelope power. A simple third-order predistorter is used to measure the relative phases of the harmonics, as well as to linearize the amplifier. The performance of the optimized predistortion power amplifier is excellent for an IS-95 code-division-multiple-access signal. Finally, a method for reducing the memory effects of the amplifier is devised to get a good cancellation performance for a wide-band signal, and the performance degradation caused by the memory effects is analyzed. For a forward-link four-carrier WCDMA signal, the predistortion power amplifier delivers an adjacent channel leakage ratio of -46 dBc at a 4-W average output power with a cancellation of 13.4 dB.