Characterization of dynamics and power handling of RF MEMS using vector measurement techniques

This paper proposes a new method to measure dynamics and power handling of RF microelectromechanical systems (MEMS) devices based on a mobile membrane. The method uses in-phase/quadrature demodulation of an RF signal proportional to the reflection coefficient of the measured device, which contains information of its mechanical properties, such as actuation and release times and instantaneous position of the mobile membrane. Both one-port (capacitors) and two-port devices (switches and extended tuning-range capacitors) can be measured. Its main advantage is the capability of obtaining information from both magnitude and phase variations of the device reflection coefficient to characterize its dynamics and power handling. It is shown that detecting phase is advantageous in high quality factor capacitors, where the magnitude of the reflection coefficient is nearly constant for any position of the mobile membrane. Open-short-load calibration of the system is provided in order to obtain absolute measurements, which are necessary for power-handling characterization. The performances of the proposed method are demonstrated by comparison to systems based on detection of the magnitude of the reflection coefficient. A MEMS capacitor is characterized in terms of dynamics-actuation and release times, and mechanical resonance frequency and in terms of power handling-membrane instantaneous position and phase and tuning range variation.     

惯性冲击对低真空封装的RF MEMS电容开关性能的影响

分析了外界惯性冲击对低真空封装的旁路电容式RF MEMS开关性能的影响.得到了近似计算外界惯性冲击引起位移的解析式.在已知最大容许插入损耗和外部惯性冲击环境条件下,MEMS开关支撑梁的最小机械刚度常数以及外部惯性冲击引起的插入损耗可以根据该式得到.通过RF MEMS电容式开关实例,表明设计低真空封装的RF MEMS电容式开关时应考虑外部环境因素.可见,RF MEMS开关用低真空封装可以减小空气阻尼、改善开关速度和执行电压的同时,开关的性能却容易受外界环境因素的影响.该研究对低真空封装的RF MEMS电容式开关的优化设计很有意义.     

惯性冲击对低真空封装的RF MEMS电容开关性能的影响

分析了外界惯性冲击对低真空封装的旁路电容式RF MEMS开关性能的影响.得到了近似计算外界惯性冲击引起位移的解析式.在已知最大容许插入损耗和外部惯性冲击环境条件下,MEMS开关支撑梁的最小机械刚度常数以及外部惯性冲击引起的插入损耗可以根据该式得到.通过RF MEMS电容式开关实例,表明设计低真空封装的RF MEMS电容式开关时应考虑外部环境因素.可见,RF MEMS开关用低真空封装可以减小空气阻尼、改善开关速度和执行电压的同时,开关的性能却容易受外界环境因素的影响.该研究对低真空封装的RF MEMS电容式开关的优化设计很有意义.     

Nonlinear models for the intermodulation analysis of FET mixers

An accurate, detailed analysis program has been developed for intermodulation distortion (IMD) simulation of FET mixers. This program is very efficient at calculating the IMD from multiple RF inputs. We have proposed a simplified nonlinear model for IMD analysis of FET gate mixers. The accuracy of the simplified model has been verified experimentally using two different MESFET mixers and one HEMT mixer at X band. All the tests show good agreement between measured results and the calculated results for second- and third-order IMD. The simplified model is based on modeling the derivative of the device transconductance by a sum of a Gaussian function and a linear function of the gate voltage. Drain bias dependence is ignored. The advantage of this model is that it can be used for both MESFET and HEMT mixers, and its fitting parameters can be easily determined from a nonlinear characterization of the devices at low frequencies     

电磁驱动RF MEMS开关的研究状况

RFMEMS技术在民用和军事方面有巨大的潜力,作为其核心器件的RFMEMS开关很有希望在雷达和通信领域之中成为关键器件。电磁驱动RFMEMS开关具有工作电压比较低,驱动力大,可以工作在恶劣的环境等优点,使其成为近年来RFMEMS开关研究的一个热点。     

A fully integrated SOI RF MEMS technology for system-on-a-chip applications

In this paper, a silicon-on-insulator (SOI) radio-frequency (RF) microelectromechanical systems (MEMS) technology compatible with CMOS and high-voltage devices for system-on-a-chip applications is experimentally demonstrated for the first time. This technology allows the integration of RF MEMS switches with driver and processing circuits for single-chip communication applications. The SOI high-voltage device (0.7-/spl mu/m channel length, 2-/spl mu/m drift length, and over 35-V breakdown voltage), CMOS devices (0.7-/spl mu/m channel length and 1.3/-1.2 V threshold voltage), and RF MEMS capacitive switch (insertion loss 0.14 dB at 5 GHz and isolation 9.5 dB at 5 GHz) are designed and fabricated to show the feasibility of building fully integrated RF systems. The performance of the fabricated RF MEMS capacitive switches on low-resistivity and high-resistivity SOI substrates will also be compared.     

一种新的用于射频功率放大器的预失真器

研究了一种新的预失真线性化电路,他由2路谐波发生器组成,每个谐波发生器都由2个工作于不同偏置电压下的肖特基二极管、电容、电阻和3 dB电桥耦合器(Hybrid)构成。通过调节二极管的偏置电压,可分别产生IM3或IM5。将此预失真线性化电路用于5 W射频功率放大器中,分别独立地对消IMD3和IMD5。双音测试表明,IMD3和IMD5分别改善了14 dBc和9 dBc。     

Requirements for low intermodulation distortion in GaN-AlxGa1-xN high electron mobility transistors: a modelassessment

A model analysis of the large-signal characteristics of GaN-Al_xGa_1-xN high-electron mobility transistors (HEMTs) with particular emphasis on intermodulation distortion (IMD) and the third-order intercept point. Since the nonlinearity depends critically on the carrier transport behavior, a Monte Carlo (MC) based numerical simulation scheme has been employed. The focus is to identify parameters and their interdependencies with a view of setting optimal limits for enhanced microwave performance. A case is made for increased mole fraction for the barrier layer, reducing the transit length, and introducing a thin AlN interfacial layer for suppressing real space transfer for enhancing the device performance. Finally, high-temperature predictions of the nonlinear behavior and IMD have been made, by carrying out the MC simulations at 600 K. In a process a favorable case is made for the GaN system as a potential candidate for microwave and RF applications at elevated temperatures     

日本近年RF MEMS开关研究的进展

RFMEMS是射频表面微机械系统简称。射频表面微机械系统现在包括滤波器和微型电器元件,如开关,微可变电容和微可变电感。射频开关按驱动原理分有静电,压电,电磁以及热驱动。由于这一研究的高频化和高精度的特点,目前开关的研究集中在静电驱动的方式的研究上,从上市的产品来看,静电驱动是最有希望的RFMEMS的执行机构。静电执行器驱动的RFMEMS开关成为下一代高频通讯中的关键部件。     

Two-Tone and Nine-Tone Excitations in Future Adaptive Predistorted Linearised Basestation Amplifiers of Cellular Radio

Linearisation of a radio basestation amplifier using a third order, a fifth order and a seventh order predistortion scheme is studied. Adaptive predistortion using a third order predistorter improved the amplifier intermodulation distortion (IMD) by between 6.4 dB and 33 dB from the third IMD power level (i.e., maximum power amplitude variation of the IMD), provided by the raw amplifier, as measured by a two tone test. The variation in improvement is due to changes in the input power level. Improvement increases as the input power is backed off from the 1 dB compression point. A fifth order predistorter will give an IMD improvement of 8.7 dB and 48.4 dB if properly adjusted. A seventh order predistorter (with the fifth complex coefficient fixed to zero) will show the best performance, particularly throughout a window (approximately from 1.5 dB to 3 dB away from the 1 dB compression point). The IMD improvement throughout this window within the high input range measures between 9.1 dB to 21.7 dB over that achieved with a fifth order predistorter. For a nine-tone test (with uniformly distributed random phase), a third order predistorter will hardly improve the worst IMD power level, provided by the raw amplifier. A fifth order predistorter, if properly adapted will give an IMD improvement of between 8.8 dB and 41.5 dB from the worst IMD level while a seventh order predistorter will give a close performance to that of a fifth order one. Fixing the predistorter coefficients enables a comparative study of the IMD power level improvement between 5th order fixed and adaptive predistorters, for a nine-tone excitation. A 5th order predistorter with its coefficients fixed to those values obtained for optimum IMD level at a backed-off power input value of 8.5 dB from the 1 dB compression point is found to maintain an IMD power variation better than 55 dB from fundamental power level, throughout the input range, up to the backed-off value.     

A comprehensive analysis of IMD behavior in RF CMOS power amplifiers

This paper presents a comprehensive analysis of nonlinear intermodulation distortion (IMD) behavior in RF CMOS power amplifiers (PAs). Separate analyses are presented for small- and large-signal operation regimes. Especially, a new, simple, large-signal behavioral IMD analysis method is presented that allows the mechanisms dominant for IMD generation to be identified and their individual contributions to be studied. By combining these analyses, typical IMD versus input power characteristics of MOSFET PAs can be predicted and understood for different classes of operation. Various measurements made on a 950-MHz RF CMOS PA are used to demonstrate typical behavior and validate the proposed theory. Prediction of IMD using a standard CMOS transistor model is also evaluated and is shown to give good agreement with the measurements.     

Genetic algorithm optimization of a hybrid analog/digital predistorter for RF power amplifiers

This study presents a genetic algorithm optimization of a hybrid analog/digital predistorter, in order to reduce the intermodulation distortion (IMD) caused by the nonlinear properties of the radio frequency (RF) power amplifier (PA). Designed predistorter based on polynomial work function and the coefficient of the polynomial is optimized in order to reduce IMD by spectrum monitoring. The design procedure and validation of predistorter have been carried out by Agilent-ADS2005A. In order to validate the predistorter two different modulation schemes as CDMA and 16-QAM have been used. Also in order to verifying the linearization a test power amplifier circuit has been examined including Motorola MOSFET MRF9742 showing the nonlinear characteristics with memory. Simulations have been shown that adjacent channel power ratio (ACPR) improvements were acceptable for both CDMA and 16-QAM modulation schemes.     

A 2-bit RF MEMS phase shifter in a thick-film BGA ceramic package

The development of a thick-film hermetic BGA package for a radio-frequency (RF) microelectromechanical systems (MEMS) 2-bit phase shifter is presented. The measured packaged MEMS phase shifter average in-band insertion loss was 1.14 dB with an average return loss of 15.9 dB. The package transition insertion loss was less than 0.1 dB per transition with excellent agreement between simulated and measured results. It was also demonstrated that the RF MEMS phase shift performance could be improved to obtain a phase error of less than 3.3 degrees. The first reported measurements of the average rise and fall times associated with a MEMS circuit (in this case a 2-bit phase shifter) were 26 and 70 /spl mu/s, respectively. The advent of packaged RF MEMS phase shifters will reduce the cost (both design and building) of future phase arrays.     

Improved large-signal GaN HEMT model suitable for intermodulation distortion analysis

In this article, a complete empirical large-signal model of GaN high electron-mobility transistors (HEMTs) is presented. The developed nonlinear model employs differentiable trigonometric function continuously to describe the drain-source current characteristic and its higher order derivatives, making itself suitable for the simulation of intermodulation distortion (IMD) in microwave circuits. Besides, an improved charge-conservative gate charge model is proposed to accurately trace the nonlinear gate-source and gate-drain capacitances. The model validity is demonstrated for different 0.25-µm gate-length GaN HEMTs. The simulation results of small-signal S-parameters, radio frequency (RF) large-signal power performances and two-tone IMD products show an excellent agreement with the measured data.     

Pseudorandom BIST for test and characterization of linear and nonlinear MEMS

In this paper we study the use of the pseudorandom (PR) technique for test and characterization of linear and nonlinear devices, in particular for micro electro mechanical systems (MEMS). The PR test technique leads to a digital built-in-self-test (BIST) technique that is accurate in the presence of parametric variations, noise tolerant, and has high-quality test metrics. We will describe the use of the PR test technique for testing linear and nonlinear MEMS, where impulse response samples of the device under test are considered to verify its functionality. Next, we illustrate and evaluate the application of this technique for linear and nonlinear MEMS characterization.     

Miniature SAW device using MEMS technology

A miniature SAW device is designed and fabricated at 1 GHz for wireless communication system. A 5 μm thin film of ZnO is successfully deposited using RF sputtering technique on plasma-enhanced chemical deposition (PECVD) SiO₂ layer of 1 μm on top of Si wafer under various operating conditions. The c-axis-oriented ZnO film exhibit a sharp diffraction peak corresponding to the (0 0 2) reflection at 2θ=34.42. The fabrication process utilizing the micro-electro-mechanical systems (MEMS) technology of the SAW device is described. Simulation of the RF-SAW filter is performed. Measurements and experimental work are presented for the RF-SAW device.     

RF MEMS技术对小型化雷达的作用

该文采用至上而下的方式,介绍了应用RF MEMS技术的雷达系统,将雷达子系统与RF MEMS技术联系起来,具体分析了应用于雷达的RF MEMS开关、移相器、滤波器和谐振器。同时,文中以开关和移相器为例,讨论了如何提高RFMEMS雷达的性能:修改空气桥形状可以提高RF MEMS收发(T/R)组件的功率处理能力,从而减少雷达相控阵的T/R组件数量;缩短转换时间的RF MEMS移相器能够应用于高速电扫描阵列;蜿蜒型5位分布式MEMS传输线移相器面积仅为5.36mm×4.72mm,相比传统移相器长度降低70%,易于实现雷达阵列的小型化。     

简洁构型与馈电的宽带双极化金属锥阵列天线北大核心CSCD

本文提出了一种宽带双极化金属锥阵列天线。该阵列天线以传统的旋转体天线结构为主体,通过在锥体底部开设四道正交的直通槽,以便在锥状单元内部形成可与地板间构成匹配谐振腔的开放式空腔结构。在阵列中,任意两个相邻的锥状单元之间可形成类似于Vivaldi天线的辐射缝隙结构。馈电采用同轴馈电方式,探针无弯折结构,金属锥体无弯折过孔。每个金属锥状单元独立,可极大简化加工、装配和维护过程。该天线具有两个正交极化,分别由左右和前后相邻单元构成。仿真结果表明,在频率范围为2～8GHz内,阵列大部分有源VSWR小于2,小部分端口有源VSWR小于2.5 (相对带宽为120%)。     

RF/微波无线系统中的MEMS技术

着重论述了RF/微波MEMS元件及其制造技术、封装要求和设计,并在此基础上阐述RF/微波MEMS元件的应用电路和系统。     

Theoretical and experimental study of amplifier linearization basedon harmonic and baseband signal injection technique

This paper presents a novel linearization scheme for RF amplifiers based on simultaneous harmonic and baseband signal injection. In this method, second-order frequency components generated by predistortion circuits are fed to the input of the main amplifier to mix with the fundamental signal for third-order intermodulation distortion (IMD) cancellation. A general and rigorous analytical formulation of baseband, harmonic, and the proposed injection techniques is presented, and from these derived expressions, the optimum conditions for IMD suppression are developed. The result also reveals the practical limitation of the proposed method subject to gain and phase error associated with the RF and baseband circuitry. For comparison purposes, an amplifying system is constructed for the experimental investigation of second-order signal injection approach. Both two-tone and digitally modulated waveforms are employed in these measurements