Showing papers on "Prototype filter published in 1997"

Fundamentals of nonlinear digital filtering

Abstract: Nonlinear Signal Processing Signal Processing Model Signal and Noise Models Fundamental Problems in Noise Removal Algorithms Statistical Preliminaries Random Variables and Distributions Signal and Noise Models Estimation Some Useful Distributions 1001 Solutions Trimmed Mean Filters Other Trimmed Mean Filters L-Filters C-Filters (Ll-Filters) Weighted Median Filters Ranked-Order and Weighted Order Statistic Filters Multistage Median Filters Median Hybrid Filters Edge-Enhancing Selective Filters Rank Selection Filters M-Filters R-Filters Weighted Majority with Minimum Range Filters Nonlinear Mean Filters Stack Filters Generalizations of Stack Filters Morphological Filters Soft Morphological Filters Polynomial Filters Data-Dependent Filters Decision-Based Filters Iterative, Cascaded, and Recursive Filters Some Numerical Measures of Nonlinear Filters Discussion Statistical Analysis and Optimization of Nonlinear Filters Methods Based on Order Statistics Stack Filters Multistage and Hybrid Filters Discussion Exercises Bibliography Index

Theory and experiment of novel microstrip slow-wave open-loop resonator filters

Abstract: This paper presents the theory and experiment of a new class of microstrip slow-wave open-loop resonator filters. A comprehensive treatment of capacitively loaded transmission line resonator is described, which leads to the invention of microstrip slow-wave open-loop resonator. The utilization of microstrip slow-wave open-loop resonators allows various filter configurations including those of elliptic or quasi-elliptic function response to be realized. The filters are not only compact size due to the slow-wave effect, but also have a wider upper stopband resulting from the dispersion effect. These attractive features make the microstrip slow-wave open-loop resonator filters promising for mobile communications, superconducting and other applications. Two filter designs of this type are described in detail. The experimental results are demonstrated and discussed.

Reflection and transmission guided-mode resonance filters

Abstract: New reflection and transmission optical filters based on guided-mode resonances in multilayer waveguide gratings are characterized and compared with homogeneous thin-film filters. These guided-mode resonance filters are implemented by integration of diffraction gratings into classical thin-film multilayers to produce high-efficiency filter response and arbitrarily low sidebands extended over a large spectral range. Compared with homogeneous thin-film reflection filters, guided-mode resonance reflection filters require significantly fewer layers for a narrow linewidth and a high peak response to be obtained. The single-grating transmission filters presented have a narrower linewidth than Fabry–Perot filters with an equal number of layers and similar materials while maintaining high peak transmittance and low sidebands.

Application of filter sharpening to cascaded integrator-comb decimation filters

Abstract: A new architecture for the implementation of high-order decimation filters is described. It combines the cascaded integrator-comb (CIC) multirate filter structure with filter sharpening techniques to improve the filter's passband response. This allows the first-stage CIC decimation filter to be followed by a fixed-coefficient second-stage filter, rather than a programmable filter, thereby achieving a significant hardware reduction over existing approaches. Furthermore, the use of fixed-coefficient filters in place of programmable-coefficient filters improves the overall throughput rate. The resulting architecture is well suited for single-chip VLSI implementation with very high data-sample rates. We discuss an example with specifications suitable for use in a wideband satellite communication subband tuner system and for signal analysis.

Clutter rejection filters in color flow imaging: a theoretical approach

Abstract: A general class of linear clutter rejection filters is described, covering the commonly used filter types including FIR/IIR filters with linear initialization, as well as regression filters, where the clutter component is estimated by least square curve fitting. The filter can be described by a complex valued matrix, and a frequency response is defined. However, in contrast to a time invariant filter, the general linear filter may create frequency components which are not present in the input signal. This produces bias in the velocity and velocity spread estimates. It is shown that the clutter filter effect on the autocorrelation estimates can be described by a frequency domain transfer function, but unlike time invariant filters, the transfer function is different for each temporal lag of the autocorrelation function. Using a two dimensional (axial and temporal dimension) model of the received signal, the bias in velocity and velocity spread is quantified, both for the autocorrelation algorithm and the time shift cross-correlation estimator. Theoretical expressions, as well as numerical examples are given.

Hairpin-comb filters for HTS and other narrow-band applications

Abstract: The folded half-wavelength resonators in hairpin-comb filters all have the same orientation, whereas the orientations of the resonators in conventional hairpin-filters alternates. Hairpin-comb filters are shown to have attractive properties for design of compact, narrow-band filters such as are often desired for high-temperature-superconductivity (HTS) and other applications. The results obtained from two- and four-resonator trial HTS-filter designs are discussed. The filters are seen to have very strong stopbands, and their computed and measured performance are found to be in very good agreement.

A simple design method for near-perfect-reconstruction nonuniform filter banks

Abstract: In this correspondence, we propose a simple design method for nonuniform integer-decimated filter banks based on a uniform cosine-modulated filter bank. The resulting distortion and aliasing are comparable to the stopband attenuation of the prototype filter. Examples are given to demonstrate the proposed method.

High-order micromechanical electronic filters

Abstract: Third-order, micromechanical bandpass filters comprised of three folded-beam resonators coupled by flexural mode springs are demonstrated using an IC-compatible, polysilicon surface-micromachining technology. The use of quarter-wavelength coupling beams attached to resonators at their folding-trusses is shown to suppress passband distortion due to finite-mass nonidealities, which become increasingly important on this micro-scale. A balanced, 300 kHz, prototype, three-resonator micromechanical filter is demonstrated with filter Q=590 and stopband rejection greater than 38 dB.

A family of pulse-shaping filters with ISI-free matched and unmatched filter properties

Abstract: The raised-cosine pulse-shaping filter plays an important role in digital communications due to its intersymbol interference (ISI)-free property. The ISI-free property holds after matched filtering is performed. In this letter, we propose a new family of pulse-shaping filters. These filters are ISI free with or without matched filtering. Using these new pulse-shaping filters, the computational load, and therefore the hardware cost in demodulation for modem design, might be reduced in some applications.

Universal current-mode filter with reduced number of active and passive components

Abstract: A new current-mode (CM) universal active filter with single-input and three-outputs (SITO) employing only four CCIIs and a minimum number of passive components is presented. The proposed filter based on an RLC shunt circuit, has a good sensitivity performance and achieves the desired filter characteristics without any component matching.

High-Q micromechanical oscillators and filters for communications

Abstract: With Q's in the tens to hundreds of thousands, micromachined vibrating resonators are proposed as IC-compatible tanks for use in the low phase noise oscillators and highly selective filters of communications systems. To date, LF oscillators have been fully integrated using merged CMOS+microstructure technologies, and bandpass filters consisting of coupled resonators have been demonstrated in the HF range. The performance of fabricated two- and three-resonator filters with center frequencies ranging from 300 kHz to 10 MHz and filter Q's from 100 to 2400 are reported. Evidence suggests that the ultimate frequency range of this high-Q tank technology depends upon material limitations, as well as design constraints-in particular, to the degree of electromechanical coupling achievable in micro-scale resonators.

Diffractive narrow-band transmission filters based on guided-mode resonance effects in thin-film multilayers

Abstract: New possibilities for realization of narrow-band transmission filters are introduced. Guided-mode resonance effects in thin-film multilayer structures incorporating a grating layer are shown to yield high-efficiency bandpass transmission filters. Calculated transmission characteristics for such filters are presented and contrasted with characteristics of corresponding thin-film interference filters.

WLS design of variable frequency response FIR filters

Abstract: This paper extends the Weighted Least Squares method to designing FIR filters capable of changing, in the real-time, one of their frequency response characteristics (group delay, the width of the passband, resonance frequency or any other). The filter coefficients are polynomial functions of the parameter characterising the variable feature. The computations needed in such designs can be kept at low level if the weight function in the performance criterion is separable. The advantages of the proposed approach are illustrated by a design of a Fractional Sample Delay filter with variable delay. If this filter has to meet demanding specifications then the proposed approach provides a cheaper and more effective solution than traditional approaches based on Lagrange interpolation.

A comb filter design using fractional-sample delay

Abstract: In this paper, a new comb filter design method using fractional sample delay is presented. First, the specification of the comb filter design is transformed into that of fractional delay filter design. Then, conventional FIR and allpass filter design techniques are directly applied to design fractional delay filter with transformed specification. Next, we develop a constrained fractional delay filter design approach to improve the performance of the direct design method. Finally, several design examples are demonstrated to illustrate the effectiveness of this new design approach.

Optimized E-plane bandpass filters with improved stopband performance

Abstract: A computer-aided synthesis technique for E-plane bandpass filters with improved stopband performance is developed. An optimization procedure based on equal ripple optimization is adopted. The design of a symmetrical E-plane bandpass filter with improved stopband performance is considered; higher order mode interaction between E-plane discontinuities is included in the design. The predicted filter performance shows improved stopband performance and reduced filter dimensions compared with conventional E-plane bandpass filters. The validity of the method is confirmed by the measurement of a fabricated five resonator E-plane bandpass filter with improved stopband performance.

Continuously tunable photonic radio-frequency notch filter

Abstract: We present a continuously tunable nonrecursive radio-frequency (RF) photonic filter. The filter provides fine tuning through the use of a novel RF phase shifter and coarse tuning using an an optical variable time delay. This architecture permits wide-band continuous tuning of the filter null frequency and is useful in applications such as moving target indication (MTI) in an airborne radar.

Miniature LTCC filters for digital receivers

Abstract: The integration of high quality narrow band pass filters into the low power RF system of advanced radar digital receivers is demonstrated by Low Temperature Cofired Ceramic (LTCC) technology. Using computer aided design, simulations, and yield analysis, strip line LTCC filters were designed with 100% yield to tolerances in materials and manufacturing processes. LTCC materials technology and processes used in the filter development is presented. Sample results of measured filter performances under extreme temperature cycling conditions are presented which demonstrate the excellent potential of the LTCC filter technology.

Parallel-resonator HF micromechanical bandpass filters

Abstract: High frequency, fourth-order, micromechanical bandpass filters, with tunable frequency and bandwidth, and filter Q's in the thousands, are demonstrated in a polysilicon surface micromachining technology. These filters utilize a parallel-resonator architecture, in which properly phased outputs from two or more micromechanical resonators are combined to yield a desired filter spectrum. Design formulas are given for Butterworth, Chebyshev, and Bessel filters, and each of these filter types are demonstrated with center frequencies close to 14.5 MHz and filter Q's ranging from 830 to 1600.

High input impedance voltage-mode lowpass, bandpass and highpass filter using current-feedback amplifiers

Abstract: A new configuration for realising high input impedance lowpass, bandpass and highpass filters simultaneously by using three current-feedback amplifiers, three grounded capacitors, three grounded resistors and one floating resistor is presented. The proposed circuit offers the following features: realisation of lowpass, bandpass and highpass signals from the same configuration, no requirements for component matching conditions, orthogonal control of /spl omega//sub 0/ and Q, the use of grounded capacitors, low active and passive sensitivities and low output impedance.

Multistage adaptive filters for in-phase processing of line-frequency signals

Abstract: The authors describe two adaptive multistage digital filters for 50/60-Hz line-frequency signal processing in zero-crossing detectors and synchronous power systems. These filters combine a median filter with adaptive predictors, either finite-impulse response (FIR)- or infinite-impulse response (IIR)-based, thus making it possible to extract the sinusoidal signals from noise and strong disturbances without phase shifting the primary frequency signal. The median filter is used as a prefilter because it can remove deep commutation notches from the waveform. Adaptation allows the filters to track the exact instantaneous line frequency and avoids the selectivity problem encountered with a fixed filter.

Method and apparatus for high-order bandpass filter with linearly adjustable bandwidth

Abstract: A method and apparatus for linearly adjusting the bandwidth of a high-order bandpass filter. A high-order bandpass filter is formed by cascading together two or more low-order bandpass filters. The bandwidths and center frequencies of each individual low-order bandpass filter is adjusted. The center frequency of some low-order bandpass filters are adjusted so as to achieve linear adjustment of the bandwidth of the high-order bandpass filter.

Q-enhancement of microelectromechanical filters via low-velocity spring coupling

Abstract: A micromechanical filter design technique based on low-velocity coupling of resonators is described that can achieve percent bandwidths less than 0.1% without the need for aggressive, submicron lithography. Using this low-velocity coupling technique, an IC process limited to feature sizes no less than 2 /spl mu/m was utilized to achieve three-resonator micromechanical filters centered at 340 kHz with percent bandwidths as low as 0.1% (filter Q's as high as 800), passband rejections up to 60 dB (the highest reported to date on the micro-scale), and insertion losses less than 1 dB. In addition, two-resonator 7.82 MHz filters were demonstrated with percent bandwidths of 0.2% and comparable insertion losses, all within an area of less than 50/spl times/50 /spl mu/m/sup 2/.

Advanced filter design

Abstract: Classical filter design techniques return only one design from an infinite collection of alternative designs, or fail to design filters when solutions exist. These classical techniques hide a wealth of alternative filter designs that are more robust when implemented in analog circuits, digital hardware, and embedded software. We present (1) case studies of optimal analog and digital IIR filters that cannot be designed with classical techniques, and (2) the formal, mathematical framework that underlies their solutions. We have automated the advanced filter design techniques in software.

Realizable warped IIR filters and their properties

Abstract: Digital filters where unit delays are replaced with frequency dependent delays, such as first order allpass sections, are often called warped filters since they implement filter specifications on a warped non-uniform frequency scale. Warped IIR (WIIR) filters cannot be realized directly due to delay free loops. Specific solutions have been known that make WIIR filters realizable but no general approach has been available so far. In this paper we will explore the generation of such filters, including new filter structures. The robustness and computational efficiency of WIIR filters are studied and most potential applications are discussed.

Microwave filter analysis using a new 3-D finite-element modal frequency method

Abstract: A new finite element modal frequency method is presented and shown to be advantageous for the analysis of microwave filters. The method analyzes a finite-element model of a filter by first computing the eigenmodes of the three-dimensional (3-D) structure. The computed eigenvalues are shown to reliably determine all of the resonant frequencies in a frequency range; the filter design can be changed until the desired resonant frequencies are computed. Finally, the eigenvectors are used as basis functions to compute the frequency response of the filter, thereby achieving a speedup that increases with the number of frequencies analyzed. Two filters analyzed in this paper show speedups ranging from 1.39 to 4.01, and their computed S-parameters agree closely with measurements.

Spectral transposition of a digital audio signal

Abstract: In this spectral transposition system for digital audio signals, the coefficients in an analysis filter are passed directly to the synthesis filter so that the coefficients in both filters match. The single unit delays in either or both of the analysis and synthesis filters are replaced by all-pass filters that provide a non-integer delay or an integer delay where the integer is greater than one. Thereby the transfer function for the analysis filter and/or synthesis filter is compressed/expanded depending on the transfer function of the all-pass filters. Thus, the dominant peaks or formants in the frequency spectrum of the resynthesized audio signal is transported to a user determined frequency range. The delay may be constant or variable over frequency. If the delay is variable over frequency so that it is other than 1.0 in the portion of the spectrum of interest for transposition of the spectral envelope and returns to 1.0 at the ends of the spectrum, the spectral envelope may be compressed or expanded without replication.

Synthesis of reflection-mode prototype networks with dissipative circuit elements

Abstract: A new procedure for synthesising lossy reflection-mode filters is presented. The resultant one-port prototype networks enable any lossless approximation function to be realised with finite Q circuit elements, provided a constant level of passband attenuation may be tolerated. Numerical examples are presented for a second-order Butterworth filter and a fourth-order elliptic function bandstop filter.

Space-frequency balance in biorthogonal wavelets

Abstract: This paper shows how to design good biorthogonal FIR filters for wavelet image compression by balancing the space and frequency dispersions of analysis and synthesis low-pass filters. A quality metric is proposed which can be computed directly from the filter coefficients. By optimizing over the space of FIR filter coefficients, a filter bank can be found which minimizes the metric in about 60 seconds on a high performance workstation. The metric contains three parameters which weight the space and frequency dispersions of the low pass analysis and synthesis filters. A series of biorthogonal, symmetric wavelet filters of length 10 was found, each optimized for different weightings. Each of these filter banks was then evaluated by compressing and decompressing five test images at three compression ratios. Selecting each optimum provides fifteen sets of parameters corresponding to filter banks which maximize the PSNR in each case. The average of these parameters was used to define a 'mean' filter banks which was then evaluated on the test images. Individual images can produce substantially different weightings of the time dispersion at the optimum, but the PSNR of the mean filter is normally close to the optimum. The 'mean' filter also compares favourably with a maximum regularity biorthogonal filter of the same length.

An innovative CAD technique for microstrip filter design

Abstract: An innovative computer-aided design (CAD) technique for efficient and accurate microstrip filter design is presented in this paper. The technique utilizes full-wave electromagnetic (EM) simulation for the individual circuit elements, while interactions between nonadjacent elements are emulated by introducing circuit components to form extra signal paths. Designs can be accomplished with the accuracy of complete circuit EM simulation while keeping the computational efforts at a cascading simulation level which is crucial for design optimization. The technique has clear physical interpretations and is easy to implement. The authors have successfully applied this technique to design several microstrip filters. Very good filter performance was achieved with good correlation between predicted and measured results.

Quasi-static design technique for MM-wave micromachined filters with lumped elements and series stubs

Abstract: This paper describes micromachined, membrane-supported low-pass and bandpass filters which are suitable for microwave and millimeter-wave (MM-wave) application. The designs are realized in coplanar-waveguide (CPW) form using short- and open-end series stubs with integrated metal-insulator-metal (MIM) capacitors, and are compact in lateral and longitudinal dimensions. A computationally efficient analysis has been developed for the design and characterization of the filters. The technique is based on a quasi-static coupled-line (CL) treatment of the series stubs, and uses normal mode impedance parameters, which are calculated with the spectral-domain approach (SDA). Due to the broad TEM-bandwidth of the membrane-supported transmission lines, the method can accurately predict filter responses well into the rejection band. To demonstrate the above claims, the measured and simulated S-parameters of a 0.3 mm /spl times/2.2 mm low-pass filter with a cutoff frequency at 17 GHz, and a second passband at 115 GHz, are presented. The new approach is also used in the design of bandpass filters which exhibit 1.5-2-dB insertion loss and bandwidths around 10%.