Showing papers on "Prototype filter published in 1995"

A simple method for designing high-quality prototype filters for M-band pseudo QMF banks

Abstract: Discusses a new method for designing the prototype filters necessary to implement M-band pseudo QMF banks. This method does not rely on the traditional nonlinear optimization used in past work but rather optimizes a single parameter on a convex error surface, consistently delivering the best equiripple filter possible while minimizing the overlapped passband distortion. A very simple algorithm for designing lowpass prototype filters suitable for use in pseudo QMF banks is described. To illustrate the applicability of this algorithm, two different filters are designed, both for such applications as wideband audio coding that require high quality reconstructed signals. >

Synthesis of multiple-ring-resonator filters for optical systems

Abstract: A method for the synthesis of optical filters consisting of a cascade of N-coupled rings is presented. The procedure is based on the definition of a polynomial whose roots are the zeros of the channel-dropping transmittance characteristic and provides directly the ring electrical lengths and the mutual coupling coefficients. A design example of a Chebyshev-type 6-ring bandpass filter is presented.

Linear phase cosine modulated maximally decimated filter banks with perfect reconstruction

Abstract: We propose a novel way to design maximally decimated FIR cosine modulated filter banks, in which each analysis and synthesis filter has a linear phase. The system can be designed to have either the approximate reconstruction property (pseudo-QMF system) or perfect reconstruction property (PR system). In the PR case, the system is a paraunitary filter bank. As in earlier work on cosine modulated systems, all the analysis filters come from an FIR prototype filter. However, unlike in any of the previous designs, all but two of the analysis filters have a total bandwidth of 2/spl pi//M rather than /spl pi//M (where 2M is the number of channels in our notation). A simple interpretation is possible in terms of the complex (hypothetical) analytic signal corresponding to each bandpass subband. The coding gain of the new system is comparable with that of a traditional M-channel system (rather than a 2M-channel system). This is primarily because there are typically two bandpass filters with the same passband support. Correspondingly, the cost of the system (in terms of complexity of implementation) is also comparable with that of an M-channel system. We also demonstrate that very good attenuation characteristics can be obtained with the new system.

High-power HTS microstrip filters for wireless communication

Abstract: The performance of narrowband microstrip filters with low insertion loss and high power-handling capabilities made from YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) high-temperature superconducting (HTS) thin films is presented. Results are shown for two different designs that were chosen to optimize the power-handling capability. Both filters have a 2-GHz center frequency and 5 poles that incorporate coupled resonators with 10-/spl Omega/ internal impedances. They were made on 5-cm-diameter LaAlO/sub 3/ substrates. Both designs use parallel-coupled feed lines to avoid current crowding, The first design includes backward- and forward-coupled filters, has 1% bandwidth, and has handled over 25 watts of input power at 10 K with less than 0.25 dB compression. The second design has 1.2% bandwidth and uses only forward-coupled resonators. The dissipation loss is less than 0.2 dB at 45 K and it has a third-order intercept of 62 dBm. Another similar filter handled 36 watts of power at 45 K with less than 0.15 dB compression across the passband. We have developed a technique to visualize the power dissipation of the filter by observing the bubbles created by the filter when submerged in liquid helium, showing areas with local defects or where the current distribution is at its peak value. We also discuss several planar high-power filter issues, including material selection and fabrication, device configuration trade-offs, filter structure optimization, and design approaches to maximize power-handling capacity.

Poly-phase codes and optimal filters for multiple user ranging

Abstract: A technique is introduced to select poly-phase codes and optimal filters of a pulse compression system that have specific temporal and frequency characteristics. In the particular problem under study, multiple vehicles are assigned unique codes and receiver filters that have nearly orthogonal signatures. Narrowband users, that act as interference, are also present within the system. A code selection algorithm is used to select codes which have low autocorrelation sidelobes and low cross correlation peaks. Optimal mismatched filters are designed for these codes which minimize the peak values in the autocorrelation and the cross correlation functions. An adjustment to the filter design technique produces filters with nulls in their frequency response, in addition to having low correlation peaks. The method produces good codes and filters for a four-user system with length 34 four-phase codes. There is considerable improvement in cross and autocorrelation sidelobe levels over the matched filter case with only a slight decrease in the signal-to-noise ratio (SNR) of the system. The mismatched filter design also allows the design of frequency nulls at any frequency with arbitrary null attenuation, null width, and sidelobe level, at the cost of a slight decrease in processing gain. >

EMI filter design

Abstract: With today’s electrical and electronics systems requiring increased levels of performance and reliability, the design of robust EMI filters plays a critical role in EMC compliance. Using a mix of practical methods and theoretical analysis, EMI Filter Design, Third Edition presents both a hands-on and academic approach to the design of EMI filters and the selection of components values. The design approaches covered include matrix methods using table data and the use of Fourier analysis, Laplace transforms, and transfer function realization of LC structures. This edition has been fully revised and updated with additional topics and more streamlined content. New to the Third Edition Analysis techniques necessary for passive filter realization Matrix method and transfer function analysis approaches for LC filter structure design A more hands-on look at EMI filters and the overall design process Through this bestselling book’s proven design methodology and practical application of formal techniques, readers learn how to develop simple filter solutions. The authors examine the causes of common- and differential-mode noise and methods of elimination, the source and load impedances for various types of input power interfaces, and the load impedance aspect of EMI filter design. After covering EMI filter structures, topologies, and components, they provide insight into the sizing of components and protection from voltage transients, discuss issues that compromise filter performance, and present a goal for a filter design objective. The text also includes a matrix method for filter design, explains the transfer function method of LC structures and their equivalent polynomials, and gives a circuit design example and analysis techniques. The final chapter presents packaging solutions of EMI filters.

Parasitic-capacitance-insensitive current-mode filters using operational transresistance amplifiers

Abstract: A parasitic-capacitance-insensitive MOSFET-C integrator and differentiator using operational transresistance amplifiers are proposed and experimental results demonstrated. The bandwidths of these circuits are also independent of their gains. The required capacitances are smaller than those in previous work. Two new configurations of universal current-mode biquad filters based on these circuits are presented. A second-order bandpass filter constructed using universal biquad filters and another third-order Chebyshev lowpass filter with 0.1 dB passband ripple are breadboarded and the measured results presented.

Design of efficient M-band coders with linear-phase and perfect-reconstruction properties

Abstract: This paper presents a new design technique for obtaining M-band orthogonal coders where M=2/sup i/. The structures obtained using the proposed technique have the perfect reconstruction property. Furthermore, all filters that constitute the subband coder are linear-phase FIR-type filters. In contrast with conventional design techniques that attempt to find a unitary alias-component matrix in the frequency domain, we carry out the design in the time domain, based on time-domain orthonormality constraints that the filters must satisfy. The M-band design problem is reduced to the problem of finding a suitable lowpass filter h/sub 0/(n). Once a suitable lowpass filter is found, the remaining (M-1) filters of the coder are obtained through the use of shuffling operators on the lowpass filter. This approach leads to a set of filters that use the same numerical coefficient values in different shift positions, allowing very efficient numerical implementation of the subband coder. In addition, by imposing further constraints on the lowpass branch impulse response h/sub 0/(n), we are able to construct continuous bases of M-channel wavelets with good regularity properties. Design examples are presented for four-, eight-, and 16-band coders, along with examples of continuous wavelet bases that they generate. >

Design of microwave filters by inverse scattering

Abstract: A new design method for planar microwave filters based on the theory of inverse scattering is presented. The method results in filters with a continuously changing profile, for example a nonuniform microstrip line with continuously varying width. Filters designed by this method are shown to possess some distinct advantages in realization and performance over other common techniques. The design method is presented in detail, and efficient numerical algorithms to solve the design equations that arise are discussed. A wideband 4 pole Chebyshev bandpass filter was designed, constructed, and tested, to prove the design method. This is the first demonstration of a microwave filter designed using inverse scattering. >

A 3 V 12-55 MHz BiCMOS pseudo-differential continuous-time filter

Abstract: The reduction of the supply voltage forces one to develop system and circuit solutions able to achieve the same performance previously obtained with higher supply voltage. In this paper, a second-order low-pass continuous-time filter operating at a 3 V power supply is presented. The prototype filter is implemented using a highly linear pseudo-differential transconductor. The input common-mode signal is canceled at the transconductor level using a feed-forward path. The output common mode voltage is controlled at the filter level using lossy integrators. A prototype cell has been realized in 1.2 /spl mu/m BiCMOS technology. The pole frequency can be tuned in the range 12-55 MHz. A THD of -40 dB is achieved for signals up to 1 V/sub pp/ at 10 MHz. The dynamic range is approximately 60 dB.

Log-domain filters based on LC ladder synthesis

Abstract: A design method is proposed for the synthesis of linear, high-order, continuous-time filters using a unique translinear integrator circuit. Unlike previous attempts at incorporating translinear circuits into filter design, the proposed theory makes explicit use of the exponential nature of the bipolar transistor. This technique is based on the operational simulation of LC ladders. A 5th-order Chebyshev filter is designed, simulated and verified experimentally. The filter shows good amplitude response as well as distortion levels comparable to other filtering schemes.

Optimal design of FIR filters with the complex Chebyshev error criteria

Abstract: We present an improved algorithm for an established filter design problem, the design of an FIR filter that best approximates, in the complex Chebyshev sense, a desired complex-valued frequency response. The algorithm is a variant of the simplex algorithm of linear programming, which has an interpretation as an implicit multiple exchange. It is iterative, robust, and exhibits good convergence speed. Global optimum convergence is guaranteed. Both complex and real-valued impulse responses can be designed with it; the design of complex coefficient filters is new. An example is given for each case. The design of noncausal filters is new. In addition to these new applications, we conjecture that this new algorithm may have important advantages over existing techniques, with respect to the maximum filter length possible, speed and stability of convergence, accuracy, and memory requirements. The ability to design long filters is among the more significant improvements over previous work. Filters of length 1000 have been designed with the new method. >

SPUDT-based filters: design principles and optimization

Abstract: Tremendous work has been done all over the world to overcome the difficult problems of triple transit and insertion loss in SAW filters. Most of research efforts towards low losses have consisted of introducing reflections in the filter designs. Two major classes of low loss filters have emerged during the past 20 years, resonator filters and Single Phase UniDirectional Transducer (SPUDT) filters. This paper reviews the design principles of this second class, including some representative examples of actual devices.

Universal filter using two current-feedback amplifiers

Abstract: A new universal filter using two current-feedback amplifiers is presented. This filter can realise lowpass, bandpass, highpass, notch and allpass filters from the same configuration. It has the following features: orthogonal control of the natural frequency and quality factor by grounded resistors, easy conversion into a voltage-controlled filter, minimum active components, without match components except for allpass applications, low active and passive sensitivities, and cascadability. Experimental results that confirm the theoretical analyses are obtained.

Boundary filters for finite-length signals and time-varying filter banks

Abstract: We examine the question of how to construct time-varying filter banks in the most general M-channel nonorthogonal case. We show that by associating with both analysis and synthesis operators a set of boundary filters, it is possible to make the analysis structure vary arbitrarily in time, and yet reconstruct the input with a similarly time-varying synthesis section. There is no redundancy or distortion introduced. This gives a solution to the problem of applying filter banks to finite length signals; it suffices to apply the boundary filters at the beginning and end of the signal segment. This also allows the construction of orthogonal and nonorthogonal bases with essentially any prescribed time and frequency localization, but which, nonetheless, are based on structures with efficient filter bank implementations. >

New `Planar' waveguide cavity elliptic function filters

Abstract: A new coupling method based on the utilisation of cavity transfonnation properties is established for planar waveguide (H-plane) TE10n/TEn01 mode cavity filters. This method is shown to provide the realisation of elliptic function responses by planar waveguide cavity structures, although these configurations exclusively exhibit magnetic iris couplings. Moreover, the flexibility in the design of arbitrary filter characteristics is essentially extended for this class of filters. The approach is verified by a five-pole pseudo elliptic function filter design for the millimetre wave band.

Current mode universal filter

Abstract: A low sensitvity current mode filter circuit which realises highpass, bandpass and lowpass responses is proposed.

Canonical microstrip filter using square open-loop resonators

Abstract: A configuration for the realisation of canonical microstrip elliptic function narrow-band bandpass filters is proposed. The new filter configuration consists of two identical arrays of microstrip square open-loop resonators, The two resonator arrays are approximately placed on the same plane so as to allow nonadjacent electric and magnetic couplings to be realised and adjusted. A theoretical investigation has confirmed the feasibility.

Narrowband lumped-element microstrip filters using capacitively-loaded inductors

Abstract: Coupling between microstrip resonators decreases very slowly as a function of the resonator separation. Therefore, it is difficult to realize narrowband filters (e.g., <0.1% fractional bandwidth) in reasonably sized microstrip form due to the very weak coupling values required. In this paper, we report a class of lumped-element filters that uses capacitively-loaded inductors to give frequency-dependent inductance values. A novel frequency transformation technique is used in the design process. Using this approach, filter bandwidth is determined by the inductance slope of frequency-dependent inductors, dL/d/spl omega/. Large coupling capacitance, thus small coupling element separations, can still be used in narrowband microstrip filters to keep the filter layout compact. We present a 5-pole, 0.27% bandwidth YBa/sub 2/Cu/sub 3/O/sub 7/ high-temperature superconducting thin film microstrip prototype filter at 900 MHz, which has 1.2 dB insertion loss and 20 dB return loss. It was designed with the coupling capacitors of a 1% bandwidth filter, and then transformed to a 0.27% fractional bandwidth using an appropriate inductance slope parameter, dL/d/spl omega/. Measurement showed good agreement with theory.

Synthesis of fiber-optic delay line filters

Abstract: This paper deals with the synthesis of fiber-optic delay line filters and is organized as follows. We show how filters with negative coefficients can be implemented using positive structures and differential detection at the optoelectronic conversion. This possibility implies that not only lowpass, but bandpass and highpass filters with arbitrary transfer functions may be implemented. Synthesis methods for positive filters based on modified versions of well-known time and frequency domain techniques are presented which take into account the restriction on the positive nature of the filter coefficients. We make use of these results to describe the synthesis procedure for arbitrary filters using fiber-optic structures. Some designs of lowpass, bandpass and highpass filters are presented as examples, and a possible implementation of these structures with a view of future optoelectronic integration is presented. >

Universal filter using unity-gain cells

Abstract: The authors propose the use of both current and voltage followers for implementation of a universal filter. The aim is to show how, by using only unity-gain cells as active components, a universal filter can be obtained with improved performance over classical filters.

Design of multidimensional finite-wordlength FIR and IIR filters by simulated annealing

Abstract: This paper describes a new approach to the design of multidimensional (M-D) finite-wordlength digital filters with specifications in the frequency and spatial domains. The approach is based on stochastic optimization and extends previous work on finite impulse response (FIR) filters in two ways: by inclusion of spatial constraints and by application to the case of infinite impulse response (IIR) filters. The formulation proposed is based on a multiple-term objective function that, in addition to magnitude constraints, also includes step response, group delay and stability constraints. Our attention to these characteristics stems from the application of such filters to video processing that we are actively pursuing. Since filter coefficients are of finite precision and since the objective function is multivariable, nondifferentiable and likely to have multiple minima, we use simulated annealing for optimization. We show numerous examples of the design of practical filters such as channel and luminance/chrominance separation filters used in the NTSC system. We demonstrate the impact of coefficient precision as well as of group delay and step response constraints on filter parameters. >

Effects of reconstruction filters in digital predistortion linearizers for RF power amplifiers

Abstract: The reconstruction filters are a major source of error in digital predistortion linearizers for RF power amplifiers. This paper presents a method that enables these filters to be designed for lowest filter complexity and minimum degradation of the linearizer performance. Furthermore, a method to choose an appropriate sampling rate for the predistorter is presented. Different filter approximations and orders are examined for different amplifier configurations by means of simulation. Of the filters tried, low-ripple Chebyshev and Butterworth filters perform best. It is demonstrated that it is possible to account for reasonable filter misalignment with only a small degradation in performance. It is also shown that the effect on the modulation is small with respect to intersymbol interference. >

Beamformer using coefficient restrained adaptive filters for detecting interference signals

Abstract: In an adaptive array beamformer, a spatial beamforming filter is connected to a sensor array for respectively filtering and summing array signals to produce a first filter output containing a target signal that arrives in a specified direction. First adaptive filters provide transversal-filtering the first filter output to produce a second filter output not containing the target signal, using a first error signal by restraining their tap weight coefficients. The array signals are further coupled to subtractors. Each subtractor detects a difference between the second filter output of the corresponding first adaptive filter and the corresponding sensor signal to derive the first error signal. Second adaptive filters provide transversal-filtering the first error signals of the subtractors to produce third filter outputs, using a second error signal, by restraining their tap weight coefficients. The third filter outputs are summed and subtracted from the first filter output to produce an output of the beamformer, which is supplied as the second error signal to the second adaptive filters

Cascadable current-mode filters using single FTFN

Abstract: A new configuration for realising current-mode filters using a single four-terminal floating nullor (FTFN) is presented. It can realise lowpass, bandpass, highpass, notch and allpass filters from the same configuration. This configuration has a high output impedance, so the synthesised current-mode filters can be cascaded without additional buffers. Moreover, the resultant current-mode filters will be insensitive to the current tracking error of an FTFN. Experimental results that confirm the theoretical analyses are obtained.

Method and apparatus for suppressing acoustic feedback in an audio system

Abstract: A method (FIGS. 6-8) for detecting and attenuating N feedback frequencies in a digitized signal uses a tree structure containing a plurality of staged filters. In a step (602), an array of digital filters (FIG. 8) having N branches (40) is constructed. The array is arranged in a tree structure with each branch (40) having several stages (42, 44, and 46). Many of the N filters are used simultaneously in multiple different branches of the tree structure thus reducing the total number of filters required to detect all N feedback frequencies. Within each branch, N-1 of the N filters are notch filters, and each of the N- 1 notch filters attenuates the digitized signal at one of the N feedback frequencies. The remaining one filter in each of the N branches is a bandpass filter that passes the remaining of the N feedback frequency. Therefore, each branch of the tree passes a unique feedback frequency absent of all other N-1 feedback frequencies.

Switched Capacitor Filters: Theory, Analysis and Design

Abstract: MOS Technology and Sampled Data Filters. Analysis of Switched-Capacitor Networks. Passive Switched-Capacitor Networks. First-Order Active Switched-Capacitor Networks. Second-Order Active SC Filters. Switched-Capacitor Ladder Filters Based on Impedence Simulation. SC Filters Based on Operational Simulation of LC Ladders and on Multiloop Feedback Concepts. Switched-Capacitor N-Path Filters. Practical Considerations in the Design of Switched-Capacitor Networks and Their Applications. Appendices.

Neural network filters for speech enhancement

Abstract: In adaptive noise cancelling, linear digital filters have been used to minimize the mean squared difference between filter outputs and the desired signal. However, for non-Gaussian probability density functions of the involved signals, nonlinear filters can further reduce the mean squared difference, thereby improving the signal-to-noise ratio at the system output. This is illustrated with a two-microphone beamformer for cancelling directional interference. In the case of a single uniformly distributed interference, we establish the optimum nonlinear performance limit. To approximate optimum performance, we realize two nonlinear filter architectures, the Volterra filter and the multilayer perceptron. The Volterra filter is also examined for speech interference. The beamformer is adapted to minimize the mean squared difference, but performance is measured with the intelligibility weighted gain. This criterion requires the signal-to-noise ratio at the beamformer output. For the nonlinear processor, this can only be determined when no target components exist in the reference channel of the noise canceller so that the target is transmitted without distortion. Under these ideal conditions and at equal filter lengths, the quadratic Volterra filter improves the intelligibility-weighted gain by maximally 2 dB relative to the linear filter.

Toward the ideal codirectional Bragg filter with an acousto-optic-filter design

Abstract: We present a novel design scheme based on the Gel'fand-Levitan-Marchenko inverse-scattering method for an acousto-optic tunable filter having an almost-ideal bandpass spectrum. We find that the ideal filter characteristics of flat-top with unity transmission and no side-lobes are in principle asymptotically possible in a properly designed codirectional Bragg filter. We propose physical schemes of achieving such characteristics in the acousto-optic tunable filter design. Filters having this desirable characteristic are of immense importance in improving the crosstalk performance in optical networks employing the wavelength-division-multiplexing scheme. We then discuss design specifics and simulated performances, and present a new optimization formula. >