Tuning in to RF MEMS

RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.     

A reconfigurable high ultimate rejection inductorless band‐pass filter by the use of N‐path passive mixers

In this paper, a band‐pass filter with a tunable bandwidth and the center frequency is introduced, which employs N‐path and N × M‐path passive mixer structures, for multiband multistandard wireless receivers. The center frequency of the proposed filter is tunable from 0.1 to 1 GHz, while its bandwidth is also adjustable from 6% to 34% of the center frequency at 100 MHz. The passband ripple is reduced by applying a Miller compensation technique, resulting in a worst‐case ripple of only 1.6 dB over the entire tuning range. An additional eight‐path filter is also utilized at the input of the circuit, which highly improves the out‐of‐band rejection of the filter as well as its out‐of‐band linearity. The noise figure and the input return loss are, respectively, better than 5 and 10 dB, and depending on the desired center frequency, the total power consumption of the proposed filter varies from 41 to 70 mW.     

Bandwidth extension,linearity enhancement,and cost reduction techniques for continuous‐time channel‐select filters

Achieving a wide bandwidth in a conventional active‐RC filter requires large power consumption and is often accompanied by significant performance degradation. In this paper, a new structure to implement active‐RC continuous‐time filters and also a new frequency compensation scheme for the operational amplifiers that are the main building blocks of active‐RC filters are proposed. Exploiting these techniques increases the maximum possible bandwidth with lower power consumption in comparison with the conventional architectures, reduces die area, and enhances the dynamic range. The effectiveness of these methods has been verified by analysis and simulation of the conventional and proposed filters under identical conditions. Both the analytical investigations and extensive simulation results prove that the adopted techniques improve the performance of continuous‐time filters considerably in terms of bandwidth and linearity while reducing the die area. Simulations have been carried out in a standard 90‐nm CMOS process by using Advanced Design System (ADS), and the proposed filter features 11.08‐dB spurious‐free dynamic range improvement and 5.9 times bandwidth enhancement. Also, the total on‐chip capacitance is made 2.4 times smaller by using the new biquad structure. Copyright © 2016 John Wiley & Sons, Ltd.     

An electronically tunable RC active filter

An RC active filter with embedded FET switches is presented for the realization of a general second order filter. The filter consists of minimal number of capacitors, two differential input dual output operational amplifiers, fixed resistors and resistors connected as potential dividers. The network has low Q and ω₀ sensitivities; further, the finite bandwidth of the operational amplifiers has negligible effect on the Q of the filter. The introduction of FET switches in the network results in frequency scaling and consequently, the possibility of electronically tuning it. In addition, by switching the FETs by pulses of very low duty cycle, it is possible to obtain subaudio filters using resistive and capacitive components of smaller values than required for a conventional filter. Experimental results pertaining to the band-pass case are also included.     

14 GHz Tunable Filters Base on Ferroelectric Films

Two new types of microwave four-pole tunable waveguide filters containing planar (Ba,Sr)TiO₃ film ferroelectric capacitors are presented. The frequency tuning of the filters is due to the variation of ferroelectric capacitance with applied dc voltage. The parameters of the K_u-band filters are the following: 1 dB bandwidth is ～0.9%, the range of tuning is 350 MHz and 260 MHz, insertion losses are not more than 4.7 dB and 3 dB respectively.     

Tunable optical narrowband filter using a gain-coupled phase-shift-controlled distributed feedback laser

In this paper, we have proposed and analyzed a new tunable optical narrowband filter using gain-coupled phase-shift-controlled distributed feedback (GC-PSC-DFB) laser diode. Coupled-mode equations are solved by using the transfer matrix method (TMM). The GC-PSC-DFB filters offer a stable single-mode bandpass output, similar to that obtained with phase-shifted index-coupled structures. However, GC structures do not suffer from the severe longitudinal spatial hole burning (SHB) that occurs in high-coupling quarter-wave-shifted DFB filters. This SHB can cause multimoded behavior for high-input signal power. Various filter parameters such as wavelength tuning range, side-mode suppression ratio (SMSR), and channel gain deviation have been investigated and discussed. Our results show that the GC DFB structures offer a wider tuning range of 23.3 /spl Aring/ compared with the similar index-coupled DFB structures with nearly steady bandwidth of 12 GHz, while maintaining 41.8-dB constant gain.     

Reconfigurable planar filters

Electronically reconfigurable or tunable microwave filters are attracting more attention for research and development because of their increasing importance in improving the capability of current and future wireless systems. For instance, emerging ultrawideband (UWB) technology requires the use of a wide radio spectrum. However, the frequency spectrum as a resource is valuable and limited, so the spectrum is always being used for several purposes, which means it is full of unwanted signals when an operation such as a UWB wireless system is concerned. In this case, existing undesired narrowband radio signals, which vary from place to place and from time to time, may interfere with the UWB system's range. A solution for this is to introduce an electronically switchable or tunable narrow rejection band (notch) within the passband of a UWB bandpass filter. Such an electronically reconfigurable filter is also desired for wideband radar or electronic warfare systems. This paper discusses the development of electronically reconfigurable filter types.     

Ferroelectric thin film and broadband satellite systems

There are several microwave applications where tunable ferroelectric devices could play a key role in improving system performance, or they could provide the key technology that enables a system to be deployed. This article focuses on the Ka-band phased array antennas, but tunable filters, oscillators, and switches could also utilize these materials     

Tunable optical transversal filters based on a Gires-Tournois interferometer with MEMS phase shifters

We present tunable optical filters based on a modified Gires-Tournois interferometer. The back reflection plane of the interferometer is replaced with a one-dimensional micromirror array for phase modulation. Using Gaussian beam optics, we show that the transfer function of the device has the form of the transversal filter in digital signal processing. The design and analysis techniques of conventional digital filters can, therefore, be adapted to tunable optical filters. Both the amplitude and phase of the transfer function can be controlled by reconfiguring the micromirrors. Application examples in dispersion compensation and variable bandwidth bandpass filtering are discussed and experimentally demonstrated.     

Effect of dc biasing on YBCO/STO/LAO tunable microstrip filters

Abstract

One of the critical design aspects in ferroelectric tunable microstrip filters is choosing the right bias configuration, for large tunability as well as to maintain the filter's passband characteristics. This work is based on strontium titanate (STO) ferroelectric thin-film based tunable microstrip filters for cryogenic temperature applications. Large tunability factors have been demonstrated in YBCO/STO/LAO two-layered microstrip filters when operated at or below 77 K. The effect of the dc electric field (primarily responsible for tuning) and critical design parameters such as the insertion loss, frequency tunability, return loss, and bandwidth of superconductor/ferroelectric/dielectric microstrip tunable K-band microwave filters is discussed in this work.     

Properties of Tunable Filters with Ferroelectric Capacitors

The range of a tunability of the filter with ferroelectric capacitor is determined by the commutation quality factor (CQF), which takes into account both the tunability of the capacitor under biasing voltage and the loss factor. For effective tuning, the CQF should be high enough (more than 1000). The main goal of the tunable filter synthesis is to provide non-degrading filter performance while tuning, and particularly to keep the same fractional bandwidth. Two different approaches to the tunable filter design are suggested and discussed: the image parameter method and insertion loss method. For both methods the filter structure is suggested and analyzed.     

A dual-mode tunable bandpass filter for GSM,UMTS, WiFi,and WiMAX standards applications

This paper presents a dual-mode tunable bandpass filter (BPF) for global system for mobile communication, universal mobile telecommunications system, wireless fidelity, and worldwide interoperability for microwave access standard applications. The proposed filter consists of a stepped-impedance resonator, single resonator, and coupled line, which are loaded with varactors. The center frequency and bandwidth of the proposed filter can be tuned with tuning varactors. Furthermore, the measurement results show that the BPF can be tuned over the frequency range of 1.8 to 2.5 GHz. Moreover, the bandwidth can be changed at each certain frequency. Furthermore, using PIN diodes, a bandstop filter is added to the tunable BPF to reduce the out-of-band frequencies around the desired frequencies. The values of LC equivalent circuits are calculated, and the results are compared with those obtained from the layout of the proposed structure. Finally, the measurement results justify the simulation results.     

Magnetically Tunable Microwave Filters based on YBCO/YIG/GGG Heterostructures

Superconducting, monolithic magnetically tunable microwave filters have been designed and fabricated demonstrating high tuning ranges (up to 19%) at a center frequency of 10 GHz. These filters are based on fully epitaxial YBa₂Cu₃O₇ (YBCO) thin films grown by pulsed laser deposition onto liquid-phase epitaxy yttrium iron garnet (YIG) layers on gadolinium iron garnet (GGG) substrates. Mechanisms resulting in variations of the bandwidth and insertion losses upon tuning are analyzed and understood in terms of the material properties of YIG and GGG.     

Thermal noise and radiation pressure in MEMS Fabry-Perot tunablefilters and lasers

In this paper, we examine thermal noise and radiation-pressure effects in MEMS tunable Fabry-Perot etalons. We show that thermal noise causes a jitter in the center wavelength in very high finesse etalons. In turn, the jitter causes an effective increase in the time-averaged filter bandwidth. Radiation pressure is of little consequence in conventional Fabry-Perot etalons, but it can give rise to nonlinearities and hysteresis in the tuning response of high-finesse MEMS filters. We develop models of noise and optical nonlinearities and compare the models with a series of measurements on commercial tunable high-finesse MEMS Fabry-Perot etalons     

基于人工神经网络的有源电力滤波器控制方法的研究

提出了一种适用于控制有源电力滤波器的人工神经网络方法,该方法采用两个前馈网络构成控制器,基中一个用于获取电力系统负荷欲补偿的三相有害电流,另一个用于获取控制主电路导通状态的开关模型。最后给出和分析了仿真结果。     

High-Q tunable dielectric resonator filters

Tunable dielectric resonator filters can potentially address wireless and satellite applications that require very high Q values (4,000 and up) with a limited tuning range (less than 15%). Such high Q requirements cannot be met by any other known non-superconductor tunable filter technology at the present time. The intent of this paper is to provide newcomers and end users with the current status and prospective of using dielectric resonators for tunable filters. It is an enabling technology for high-Q tunable filter applications. A key challenge, however, is to increase the tuning range without degrading the Q value. While several techniques have been reported to demonstrate the feasibility of tuning dielectric resonators, the tunable dielectric resonator filter technology is still in its infancy. Very limited research effort has been dedicated to explore the potential for improving the tuning range. Most of the work reported thus far has focused on the use of TE_01delta modes and standard shape resonators demonstrating a narrow tuning range. We believe that the tuning range can be increased while maintaining reasonably high Q values by exploring the use of other modes and by the use of non-standard-shape dielectric resonators.     

改进的有源电力滤波器滞环电流控制策略

针对滞环电流控制开关频率不固定、频率范围大从而产生较大损耗的问题,以提高控制精度、减少开关损耗为目标,提出一种有源电力滤波器随机变环宽滞环电流跟踪控制方法。该方法针对电力系统负荷的特点,产生预置变环宽函数,能够较合理地给出滞环宽度,并引入随机函数,将开关频率范围拉宽,使电流频谱分布范围更宽,从而降低谐波畸变率,减少开关损耗。仿真及实验结果均证明了其可行性,可在保持总控制精度的同时有效降低总开关损耗,同时具有良好的补偿性能。     

Generation and classification of single amplifier filters

A unified approach is presented for generating configurations for circuits containing one operational amplifier together with RC elements and capable of realizing a general second-order voltage transfer function. Systematic application of the generation procedure leads to various single amplifier biquads with the known circuits, as well as some new ones, obtained as special cases. The insight gained from the generalized approach as well as the results of a general sensitivity analysis (including the effects of the amplifier limited bandwidth) offer a method for categorizing and classifying single amplifier filters. The different filter classes are illustrated and compared with the aid of extensive design tables. General equations for the effect of the amplifier limited bandwidth are also given.     

Analysis and design of highly linear triode‐mode based OTA and its application to a wide tunable Gm‐C filter

In this paper, a new highly linear operational transconductance amplifier (OTA) based on triode‐mode input transistors is introduced. An analysis based on theoretical relations and simulation results is presented that aims to obtain the best operating points of triode‐mode and cascode transistors to achieve the highest linearity. The proposed analysis is utilized to design a linear pseudo‐differential OTA, benefiting a linear common mode feedforward and an appropriate common mode feedback circuit. The common mode feedforward circuit is also regulated in the same manner as main the transconductor to stabilize the output common mode voltage during tuning action and achieve higher common mode rejection ratio. Proposed OTA is used to implement a tunable low‐power linear Gm‐C filter. The cutoff frequency of the filter is tunable from 2.7 to 44 MHz while its power consumption changes from 3.5 to 8.5 mW in the entire tuning range. By applying input voltages up to 1.1 Vp‐p, the filter's IM3 remains less than −48 dB for various cutoff frequencies. The proposed OTA and filter are simulated in 0.18‐μ m CMOS technology with Hspice simulator. Copyright © 2017 John Wiley & Sons, Ltd.