RF MEMS压控振荡器的研制及相位噪声特性研究

利用RF MEMS可变电容作为频率调节元件,制备了中心频率为2 GHz的MEMS VCO器件.RF MEMS可变电容采用凹型结构,其控制极板与电容极板分离,并采用表面微机械工艺制造,在2 GHz时的Q值最高约为38.462.MEMS VCO的测试结果表明,偏离2.007 GHz的载波频率100kHz处的单边带相位噪声为-107 dBc/Hz,此相位噪声性能优于他们与90年代末国外同频率器件.并与采用GaAs超突变结变容二极管的VCO器件进行了比较,说明由于集成了RF MEMS可变电容,使得在RF MEMS可变电容的机械谐振频率近端时,MEMS VCO的相位噪声特性发生了改变.     

低相位噪声宽带LC压控振荡器设计

基于0.13μm CMOS工艺,设计了一款低相位噪声宽带LC压控振荡器。采用开关电容阵列使VCO在达到宽调谐范围的同时保持了低相位噪声。采用可变容阵列提高了VCO频率调谐曲线的线性度。仿真结果表明,在1.2 V电源电压下,电路功耗为3.6 m W。频率调谐范围4.58 GHz-5.35 GHz,中心频率5 GHz,在偏离中心频率1 MHz处相位噪声为-125d Bc/Hz。     

一种用于GPS波段的低相噪VCO设计

设计了一种工作频率为1.8 GHz的低相噪频率可调的LC压控振荡器电路。该压控振荡器采用AMOS管作为变容二极管,提高了频率的调谐范围。为了降低电路的相位噪声,设计中采用了PMOS顶部偏置电路代替底部的NMOS偏置电路,并在电路中串联了一个大电容以滤除电路中的高频噪声。仿真测试结果表明,该电路在1 MHz频偏时其相位噪声为-116.5 dBc/Hz。     

Effect of filter parameters on the phase noise of RF MEMS tunable filters employing shunt capacitive switches

The effect of filter parameters on the phase noise of RF MEMS tunable filters employing shunt capacitive switches is investigated in this article. It is shown that the phase noise of a tunable filter is dependent on the input power, fractional bandwidth, filter order, resonator quality factor, and tuning state. Phase noise is higher for filters with smaller fractional bandwidth. In filters with high fractional bandwidth (>3%), phase noise increases as the input power approaches the power‐handling capability of the filter. In filters with smaller bandwidths, phase noise increases with input power upto a threshold level of input power, but begins to decrease thereafter. The unloaded quality factor of the filter has a noticeable effect on the phase noise of filters with narrow bandwidths. The phase noise changes with the filter tuning state and is maximum when all the switches are in the up‐state position. It is also shown that the phase noise increases with the filter order, due to increase in the number of noisy elements in the filter structure. This article provides a methodology to evaluate the phase noise of a tunable filter and proves that RF MEMS filters are suitable for high performance applications without considerable phase‐noise penalty. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

一种用于铷原子钟的低相位噪声压控振荡器

基于相干布局囚禁(CPT)现象研制的原子钟与传统原子钟相比,能够提供更高的时间精度,且有利于原子钟向微型化、低功耗方向发展。在不同种类的CPT原子钟中,铷原子钟应用最为广泛,而其性能的优劣很大一部分取决于自身内部的用于提供微波信号源的压控振荡器(VCO)。基于此,利用高品质因数的同轴谐振器和Clapp振荡电路,首先根据负阻分析法使电路快速起振,并结合虚拟地技术对电路参数进行优化,完成了一个小体积、低相位噪声的3.035 GHz压控振荡器的设计。其相位噪声为-60.49 d Bc/Hz@300 Hz、-73.08 d Bc/Hz@1 k Hz和-97.48 d Bc/Hz@10 k Hz,压控调节灵敏度为12 MHz/V,输出信号的功率为-1.13 d Bm,满足铷原子钟的应用需求。     

A novel design of RF MEMS dual band phase shifter

In this paper a novel design of RF MEMS dual band phase shifter is presented. The new design is switched-line type phase shifter which has been constructed by distributed MEMS transmission line (DMTL). Since the constant phase of DMTL can be changed, the proposed design has capability for working at two or more frequencies. The performances of the new design are compared with conventional switched-line design that has been constructed by transmission line of coplanar waveguide. The results show the feasibility of the new design and also show the new design reduces the size and loss of the structure compared with conventional switched-line design. The proposed design is unique approach to achieve a dual band phase shifter using MEMS technology which has low loss and weight with high linearity respect to the other technologies. This dual band phase shifter has very small size than the other passive dual band phase shifters.     

A low-voltage lateral MEMS switch with high RF performance

MEMS switches are one of the most promising future micromachined products that have attracted numerous research efforts in recent years. The majority of MEMS switches reported to date employ electrostatic actuation, which requires large actuation voltages. Few are lateral relays and those often require nonstandard post process, and none of them is intended for high-frequency applications. We have developed an electrothermally actuated lateral-contact microrelay for RF applications. It is designed and fabricated on both low-resistivity and high-resistivity silicon substrate using surface micromachining techniques. The microrelay utilizing the parallel six-beam actuator requires an actuation voltage of 2.5-3.5 V. Time response is measured to be 300 /spl mu/s and maximum operating frequency is 2.1 kHz. The RF signal line has a current handling capability of approximately 50 mA. The microrelay's power consumption is in the range of 60-100 mW. The lateral contact mechanism of the microrelay provides a high RF performance. The microrelay has an off-state isolation of -20 dB at 40 GHz and an insertion loss of -0.1 dB up to 50 GHz. The simplicity of this 4-mask fabrication process enables the possibility of integrating the microrelay with other passive RF MEMS components.     

Design and performance analysis of hybrid SPDT RF MEMS switch

Microsystem Technologies - This paper presents the design and simulation of Hybrid type RF MEMS switch for satellite communication application. The Hybrid switch beam is having non-uniform meanders...     

A new design of multi-bit RF MEMS distributed phase shifters for phase error reduction

In this paper, the major source of phase error for multi-bit MEMS distributed phase shifters, the mismatch between adjacent bits, is investigated. A quantitative account of the phase deviation with the effect of mismatch considered is presented by the simulated results as well as theoretically calculated results. A novel multi-bit distributed MEMS phase shifter aimed to eliminate this error source is proposed. The basic concept for the structure is that, by controlling the phase shifter from the unit cell level, performance deterioration resulted from multiple reflection of the signal in the device in the phase state switching process is avoided. To verify the feasibility of the proposed structure, two X-band 5-bit distributed phase shifters are designed and simulated. Compared with the traditional structure, the average phase errors in all phase states of the two are improved by 28.22 and 36.52 % at 10 GHz. The average RMS phase errors in the bandwidth of 1–12-GHz of 56 frequency points are 1.23° and 1.85°. The improvements of the return loss and insertion loss are also exhibited. Furthermore, the aperiodic distributed phase shifter using different unit cells is introduced to demonstrate that the proposed structure can also be used to decrease the number of MEMS switches of multi-bit MEMS distributed phase shifters.     

Design and consideration of wafer level micropackaging for distributed RF MEMS phase shifters

A novel packaging structure which is performed using wafer level micropackaging on the thin silicon substrate as the distributed RF MEMS phase shifters wafer with vertical feedthrough is presented. The influences of proposed structure on RF performances of distributed RF MEMS phase shifters are investigated using microwave studio (CST). Simulation results show that the insertion loss (S₂₁) and return loss (S₁₁) of packaged MEMS phase shifters are −0.4–1.84 dB and under −10 dB at 1–50 GHz, respectively. Especially, the phase shifts have well linear relation at the range 1–48 GHz. At the same time, this indicated that the proposed pacakaging structure for the RF MEMS phase shifter can provide the maximum amount of linear phase shift with the minimum amount of insertion loss and return loss of less than −10 dB.     

Design and performance analysis of double cantilever type capacitive shunt RF MEMS switch

This paper presents a novel structure of capacitance shunt type RF switch for 5G applications. The proposed RF MEMS switch is having Cantilever type designed with optimized dimensions to operate in V-band applications. The electromechanical analysis is done by using the COMSOL tool. The actuation voltage of the proposed switch is 10.5 V with the air gap of 1 µm and gold as a beam material. The proposed switch with the meanders and perforations show the scattering parameters in HFSS software such as insertion loss (S₁₂) of − 0.033 dB and return loss (S₁₁) less than − 48 dB and the isolation (S₂₁) calculated in off-state as − 62 dB at 50 GHz.

     

发展中的RF MEMS开关技术

从驱动方式和机械结构的角度介绍了不同的RF MEMS开关类型,分析了各类MEMS开关的性能及优缺点,分析了MEMS开关在制作和发展中面临的牺牲层技术、封装技术、可靠性问题等关键技术和问题,介绍了MEMS开关的发展现状及其在组件级和系统级的应用,以及对MEMS开关技术的展望。     

Electromechanical model of RF MEMS switches

With the recent rapid growth of Radio Frequency Micro-Electro-Mechanical Systems (RF MEMS) switches, there has developed an emergent requirement for more accurate theoretical models to predict their electromechanical behaviors. Many parameters exist in the analysis of the behavior of the switch, and it is inconvenient for further study. In this paper, an improved model is introduced, considering simultaneously axial stress, residual stress, and fringing-field effect of the fixed-fixed bridge structure. To avoid any unnecessary repetitive model tests and numerical simulation for RF MEMS switches, some dimensionless numbers are derived by making governing equation dimensionless. The electromechanical behavior of the fixed-fixed bridge structure of RF MEMS switches is totally determined by these dimensionless numbers.The supports from the Key Project from the Chinese Academy of Sciences (No. KJCX2-SW-L2), projects from the NSFC (Nos 19928205, No. 50131160739 and No. 10072068), and the National 973 Project (Grant No. G1999033103) are gratefully acknowledged. The authors would like to thanks Prof. Yilong Hao of Institute of Microelectronics, Peking University, for helpful discussion.     

RF micro-electro-mechanical system (MEMS) capacitive switch performance parameters and improvement strategies

Microsystem Technologies - In this review article, the important switch performance parameters such as actuation voltage, capacitance ratio, radio frequency-scattering parameters (RF S-parameters),...     

Design of MEMS switch for RF applications

Components like passive electronically scanned (sub) arrays, T/R modules, reconfigurable antennas etc., in RF applications are in need of MEMS switches for its re-configurability and polarization. This paper presents the analysis, design and simulation of a MEMS switch. The switch proposed in this paper is intended to work in the frequency range of 4–8 GHz. The proposed switch fulfills the switching characteristics concerning the five requirements loss, linearity, high switching speed, small size/power consumption, low pull down voltage following a relatively simple design, which ensures reliability, robustness and high fabrication yield. The switch implemented in this paper is based on the integration mode of operation and widely used in RF applications.     

Cryogenic Performance of RF MEMS Switch Contacts

A series of experiments was performed to characterize RF microelectromechanical system switch performance under variable environmental conditions and cryogenic temperatures. Data were recorded in helium and nitrogen environments to lower stiction failure rates as well as to circumvent switch bouncing arising from low pressure at cryogenic temperatures. Contact resistance values were observed to be lower at cryogenic temperatures but still two orders of magnitude higher than the values predicted for the constriction resistance of gold asperity contacts, consistent with the presence of adsorbed films on the contacts. An asperity-heating model was applied, from which it was deduced that contact voltages can selectively disassociate adsorbed films from the contact surface while not softening the gold asperity contacts. The results are consistent with the reduced mobility of the adsorbed surface films at cryogenic temperatures.$hfill$[2007-0217]      

CMOS环形振荡器相位噪声仿真分析

通过分析环形振荡器的一阶线性模型,得到环形振荡器相位噪声的功率谱的近似表达式.为了分析相位噪声的时域特征,引进谱综合法,并利用快速傅立叶变换(FFT),求出了相位噪声的时域采样信号.并进一步分析了相位噪声的采样信号的自相关序列,发现相位噪声是一个长记忆过程,具有非平稳的特征.采用Yule-Walker功率谱估计法,分析了相位噪声的采样信号的功率谱密度,其仿真结果进一步验证了理论分析结果.     

RF MEMS悬臂梁开关的设计与仿真

利用有限元软件HFSS和ANSYS系统研究了串联MEMS开关的微波性能和力学性能与其结构参数之间的关系,并在此基础上优化出悬臂梁开关的几何结构参数,设计了RF MEMS开关,实验表明：在外施电压为10V左右时,悬臂梁的挠度可达3μm左右,5GHz时,回波损耗小于0．2dB,隔离度大于35dB。     

RF MEMS引线键合的射频性能和等效电路研究

针对一种用键合线连接的简单封装模型进行射频性能的模拟.用HFSS软件对不同长度、不同高度、不同直径以及不同间距的键合线进行模拟,总结出这些参数对键合线射频性能的影响.提出了由顶盖、CPW和键合线组成的简单封装结构的等效电路,并提取参数值.用Mcrowave Office软件对等效电路进行模拟,其S11在6～8 GHz内与HFSS模拟的模型的S11相差2 dB以内,其S21在1～10 GHz内与模型的S21相差0.1 dB以内.