Compact VDTA-based current-mode electronically tunable universal filters using grounded capacitors

This paper presents a compact current-mode three-input single-output (TISO) type universal filter. Only one voltage differencing transconductance amplifier (VDTA) and two grounded capacitors are employed in the proposed filter. The circuit can realize lowpass, bandpass, highpass, bandstop and allpass biquadratic filter outputs by connecting the appropriate inputs, and offers electronic control of the natural angular frequency (ω₀) and quality factor (Q) by means of adjusting the transconductance gain of the VDTA. In addition, by slight modification of the proposed scheme, another more useful TISO construction with orthogonal ω₀–Q tuning has been obtained. Both the discussed universal filters have been shown to have low incremental active and passive sensitivities. To demonstrate the performances of the filters and verify the theoretical analysis, computer simulations are accomplished with the PSPICE program.     

MEMS tunable resonant leaky mode filters

A tunable double-grating resonant leaky mode microelectromechanical-type element is introduced. A significant level of tunability is demonstrated by adjusting mechanically the structural symmetry of the grating profile. Tuning is also possible by variation of the thickness of the resonant layer. For a particular example silicon-on-insulator structure treated, it is shown that the resonance wavelength can be shifted by /spl sim/300 nm with a horizontal movement of /spl sim/120 nm within the 1.4-1.7-/spl mu/m wavelength band. Additionally, the reflectance can be varied from /spl sim/10/sup -3/ to 1 at central wavelength of 1.55 /spl mu/m with a vertical movement of /spl sim/200 nm. These results demonstrate new possibilities in design of tunable optical devices.     

A probabilistic design optimization for MEMS tunable capacitors

This paper presents a design optimization method for MEMS parallel-plate capacitors under fabrication uncertainties. The objective of the optimization problem is to maximize the production yield considering the fabrication tolerances. The method utilizes aspects of the advanced first-order second-moment (AFOSM) reliability method in probabilistic design to find a linearized feasible region for performance functions and uses an analytical double-bounded-probability distribution function (DB-PDF) to approximate the distribution of random variables. Then, it attempts to place the tolerance box in such a way that the portions of the box with higher yield lies in the feasible region. The yield is directly estimated using the joint cumulative distribution function (CDF) over the tolerance box requiring no numerical integration and saving considerable computational complexity for multidimensional problems. For this reason, any arbitrary distribution can be considered for random parameters and the problem is not restricted to normality assumptions. Numerical examples, verified by Monte-Carlo simulations, demonstrate that optimal designs significantly increase the yield. The advantage of the proposed design optimization method is that the yield can be maximized in early design stages without tightening tolerances or increasing the fabrication cost and complexity. The application of the presented method is not limited to tunable capacitors and can be extended to other MEMS devices.     

Miniature and tunable millimeter-wave lowpass filter with MEMS switch

In this paper, fully monolithic tunable millimeter-wave filters with tapped-line feedings are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass filters were designed, fabricated, and tested. The cascaded CPW-based periodic structures, with low-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. The measured results of the reconfigurable low-pass filter show the 3-dB cutoff frequency change from 19 to 11 GHz with very small change in the average insertion loss from 1.3 to 1.9 dB. The chip size of the low-pass is 4.0 mm × 1.6 mm.     

Quality of ferroelectric capacitors used in tunable microwave filters

The problem of determining the quality of ferroelectric capacitors from measured characteristics of tunable microwave bandpass filters has been solved. The quality of ferroelectric capacitors based on barium-strontium-titanate (BST) thin films, used in four filters tunable over a frequency range of 1.8 to 4.3 GHz, have been determined.     

Current-mode electronically tunable biquadratic filters consisting of only CCCIIs and grounded capacitors

In this paper, a current-mode (CM) analog filter for simultaneously realizing high output impedance low-pass, band-pass and high-pass analog responses besides high output impedance notch and all-pass analog filter responses with interconnection of the relevant output currents, is presented. Also, two CM filters for simultaneously providing high output impedance universal filter responses are derived from the proposed one. All of the introduced CM topologies employ a canonical number of only grounded capacitors without requiring any resistors, and do not need critical component matching conditions. All of the developed circuits have low input impedance and high output impedance resulting in easy cascadability with other CM ones. Frequency dependent non-ideal gain and parasitic impedance effects on the performance of the presented first filter are investigated as examples. In order the show the performance of the filter and verify the theory, simulations are accomplished with SPICE program.     

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.     

Voltage tunable capacitors using high temperature superconductorsand ferroelectrics

In this paper we report the construction of both slot capacitors on bulk substrate and thin film interdigital capacitors using YBa₂ Cu₃O_7-δ (YBCO) and Ba_xSr _1-xTiO₃. Slot capacitors made on bulk Ba_x Sr_1-xTiO₃ (BST) yielded variations in capacitance of more than 6 to 1 at 86 K with a peak electric field strength of 25 kV/cm. With a metal organic deposition (MOD) grown Ba_xSr_1-xTiO₃ 300-nm overcoat on a YBCO thin film, an interdigital capacitor on LaAlO₃ substrate yielded an approximate tuning range of 10% for peak field of 66 kV/cm over temperatures ranging from 50 K to 120 K     

Effect of etch holes on the capacitance and pull-in voltage in MEMS tunable capacitors

Microelectromechanical systems (MEMS) tunable capacitors, switches or actuators are widely applied in wireless communication systems. In the fabrication process etch holes are used to release the sacrificial layer with relatively large structures, which obviously affects the performance of devices. However, most researchers neglect this effect during their designing of the capacitors, switches or actuators. This article presents the theoretical calculation of the capacitance of tunable capacitors with etch holes, and analyses the deviation of the capacitance and pull-in voltage with different parameters such as the length of the plates w, the length of the etch holes w _h, the air gap between the two plates d, and the number of the etch holes. To validate the theory in this article, a tunable capacitor was fabricated by surface micromachined technology. The theoretical results compare well with the experimental results.     

Integrated acoustooptic tunable filters using weighted coupling

A detailed theory and experimental results are presented on weighted-coupling integrated acoustooptic tunable filters (IAOTF). A low-sidelobe-level single-stage IAOTF in which the weighted coupling was facilitated by focused surface acoustic waves along an interaction length of 6.0 mm has been realized on a Y-X LiNbO₃ substrate, 8 mm in length. The measured performances of this weighted-coupling IAOTF at the optical center wavelength of 1.31 μm include a peak mode conversion at the acoustic center frequency of 214.6 MHz, a wavelength tuning range of 110 nm, a -3 dB optical bandwidth of 4.1 nm, and a switching rise time of 0.965 μs. Sidelobe levels below -21.4 dB have been accomplished at the mode-conversion efficiency of 15 percent and an RF drive power of 160 mW     

Miniature high selectivity filters using grounded spiral resonators

A novel miniature high selectivity filter designed using a metamaterial resonator based on four grounded spirals (ForeS) is presented. This enables extreme size reduction together with high out-of-band rejection and low insertion loss. A fabricated third-order filter has overall dimensions of lg/4 by lg/15, a 3 dB bandwidth of 3.7% at 1.63 GHz, insertion loss of 23 dB, attenuation greater than 75 dB in the lower stopband and greater than 40 dB up to 2.6 times the centre frequency.     

Miniature surface-acoustic-wave filters

An introduction to Surface-Acoustic-Wave (SAW) devices-their operation, advantages, and applications--is presented. The process of design and realization of high-performance SAW filters is examined from initial specifications to final device operation. Several techniques drawn from a variety of disciplines illustrate the implementation of finite impulse response SAW frequency functions. Material properties, transducer weighting, and computer-aided design are treated. An example of the design and testing of a 321-MHz 0.35-percent bandwidth, 65-dB sidelobe, 15-dB insertion loss filter is presented.     

Miniature broadband bandpass filters using double-layer coupled stripline resonators

A novel double-layer coupled stripline resonator structure is introduced to realize miniature broadband bandpass filters. Filters with relative bandwidth up to 60% and size less than /spl lambda//8/spl times//spl lambda//8/spl times/h (/spl lambda/ is wavelength at the midband frequency; h is the substrate height, which is much smaller than /spl lambda//8) can be fulfilled using such resonators. Two possible filter configurations are proposed in this paper: combline and interdigital. The filter synthesis procedure follows the classical coupling matrix approach that generates very good initial responses. Optimization by the mode-matching method and fine tuning in Ansoft's High Frequency Structure Simulator are combined to improve the filter performance. Two filter design examples are given to validate the feasibility. Low temperature co-fired ceramic (LTCC) technology is employed to manufacture the filters. Experimental results of the two manufactured filters are presented. The effects of LTCC manufacturing procedure on the filter performance are also discussed.     

Miniature low-pass EMI filters

This paper describes miniature ceramic feedthru type electromagnetic interference (EMI) filters. Electrically, the devices function as low-pass filters with a 3-dB cutoff frequency in the low-megahertz range. The filters are mechanically rugged and in many applications can be placed in the I/O connector or substituted for the existing feedthrus. The monolithic distributed filter covered in the paper behaves as a section of transmission line at all frequencies and is essentially free of undesired resonances. The theory of lossy transmission line is used to show that with a distributed dissipative filter, the effect of terminating impedances is dramatically reduced. The effect of operating environment on the electrical characteristics is also presented.     

Analysis and modeling of liquid-crystal tunable capacitors

Three different configurations of liquid-crystal tunable capacitors were investigated, including fractal structures, comb structures, and square structures. The tuning ranges of the fractal structures, the comb structures, and the square structures at 4 GHz from 0 to 5 V were found to be 8.81%, 7.17%, and 11.85%, respectively. The square structures have the largest tuning ranges mostly because of the uniform electric fields dominated. The Q-values of the fractal structures, the comb structures, and the square structures at 4 GHz with an operation voltage of 5 V were 68.2, 98.3, and 31.0, respectively. Compared to the other two structures, the square structures perform the highest inductive effects, leading to the lowest Q-values. In addition, the liquid crystals with different chiral doping concentrations were injected into the capacitor structures to investigate the impact of different liquid crystals on the tunable capacitors. The threshold voltages (V/sub th/) increase as the chiral doping concentrations enlarge. The steepness of the C-V curves increases as the chiral doping concentrations reduce. Furthermore, a liquid-crystal capacitor model was developed to qualitatively illustrate the performance of the liquid-crystal tunable capacitors. The model prediction and the measurement results were highly correlated.     

A photonic wavelength-division switching system using tunable laserdiode filters

A photonic wavelength-division switching system using semiconductor tunable wavelength filters is proposed. A switching system using wavelength switches and multistage switching networks is discussed. A crucial point in developing this switching system is to achieve a large number of wavelength-division channels. The potential of 100 wavelength-division channels in such switching systems is estimated, based on InP optical integrated circuits. A wavelength network synchronization which permits the network to utilize such a large number of wavelength-division channels without wavelength misalignment and drift is proposed. An eight-channel wavelength-division switching experiment, using phase-shift-controlled distributed feedback laser diodes as tunable wavelength filters, is reported     

Integrated wavelength-selective optical MEMS switching using ring resonator filters

An integrated optical microelectromechanical system (MEMS) switch that provides wavelength selectivity is described. The switching mechanism is based on moving a MEMS actuated optically absorbing membrane into the evanescent field of a high-index-contrast optical ring resonator. By controlling the loss, and thus, the cavity quality factor, the resonant wavelength is switched between the drop and through ports.     

Microwave characteristics of liquid-crystal tunable capacitors

This letter investigates the microwave characteristics of the liquid crystal tunable capacitors for the first time. With the dielectric anisotropy properties, the liquid crystal capacitors present very different characteristics compared to the semiconductor or MEMS tunable capacitors. A quality factor of 310 with a control voltage of 5 V was achieved at 4 GHz. A tuning range of 25.3% for the control voltages from 0 to 5 V was obtained at 5 GHz. The results demonstrate the potential applications of liquid crystals as dielectric materials for capacitors with high quality factors and wide tuning ranges at high frequencies, particularly suitable for the future flexible electronics with transparent substrates.     

Simple implementation of sampled-data filters using current multipliers, switches and capacitors

An approach is discussed for a simple implementation of sampled-data filters. The implementation uses m.o.s. current multipliers, switches and capacitors and is useful for the design of integrated m.o.s. analogue filters. Compared with other approaches, the filters designed with this method require smaller area, use no operational amplifiers and have no consumption of d.c. static power. An example is presented showing good agreement between experimental and theoretical results.     

Miniature tunable Airy beam optical meta-device

Tunable Airy beams with controllable propagation trajectories have sparked interest in various fields,such as optical manipulation and laser fabrication.Existing research approaches encounter challenges related to insufficient compactness and integration feasibility,or they require enhanced tunability to enable real-time dynamic manipulation of the propagation trajectory.In this work,we present a novel method that utilizes a dual metasurface system to surpass these limitations,significantly enha...