Frequency Response Of Filter Research Articles

Open-end discontinuity model of graphene nanoribbon transmission line in the terahertz band

Recently, attention has been focused on the design of GNR (Graphene Nanoribbon) based devices in the Terahertz band. Considering the effects of discontinuity in the structure of these devices is necessary as an inevitable factor in order to adjust the device response in the desired specifications. In this paper, open-end GNR transmission line, as one of the most important discontinuities in waveguide structures, is studied and modeled in detailed for the first time. This discontinuity effect is analysed using fullwave simulation in the form of an additional length added to the end of the line. Then it is expressed by simple mathematical expressions for a broad parameter range and its lumped element model is extracted. The obtained formula with a relative error of less than 10% is consistent with the results of fullwave simulation and it is also consistent with behavioral analysis of the structure.Finally, a bandstop filter is designed and simulated using quarter-wavelength open-end resonators. Then, discontinuity effect of the filter open-end lines is considered and completely confirmed. The frequency response of filter in the absence of discontinuity effect shows the cutoff frequency of 4.55THz while by applying it, cutoff frequency is shifted to 5THz.

Chebyshev approximation problem of multidimensional IIR digital filters in the frequency domain

This paper investigates the problem of simultaneous approximation of a prescribed multidimensional frequency response. The frequency responses of multidimensional IIR digital filters are used as nonlinear approximating functions. Chebyshev approximation theory and the notion of line homotopy are used to reveal the approximation properties of this set of IIR functions. A sign condition is derived to characterize a convex stable domain in this set. This sign condition can be incorporated into the optimization of the Chebyshev simultaneous approximation. The generally sufficient global Kolmogorov criterion is shown to be a necessary condition, for the characterization of best approximation, in the considered set of approximating functions. Thus, it can be incorporated, as a stopping constraint, in the design of the optimal filter. Moreover, the local Kolmogorov criterion is shown to be also necessary for the set of approximating functions. Finally, it is proved that the best approximation is a global minimum.

Graph Sampling for Covariance Estimation

In this paper, the focus is on subsampling as well as reconstructing the second-order statistics of signals residing on nodes of arbitrary undirected graphs. Second-order stationary graph signals may be obtained by graph filtering zero-mean white noise and they admit a well-defined power spectrum whose shape is determined by the frequency response of the graph filter. Estimating the graph power spectrum forms an important component of stationary graph signal processing and related inference tasks such as Wiener prediction or inpainting on graphs. The central result of this paper is that by sampling a significantly smaller subset of vertices and using simple least squares, we can reconstruct the second-order statistics of the graph signal from the subsampled observations, and more importantly, without any spectral priors. To this end, both a nonparametric approach as well as parametric approaches including moving average and autoregressive models for the graph power spectrum are considered. The results specialize for undirected circulant graphs in that the graph nodes leading to the best compression rates are given by the so-called minimal sparse rulers. A near-optimal greedy algorithm is developed to design the subsampling scheme for the nonparametric and the moving average models, whereas a particular subsampling scheme that allows linear estimation for the autoregressive model is proposed. Numerical experiments on synthetic as well as real datasets related to climatology and processing handwritten digits are provided to demonstrate the developed theory.

Polarization- and wavelength-independent SBS-based filters for high resolution optical spectrum measurement.

A polarization-independent narrow passband optical filter with a FWHM bandwidth of ~10 MHz based on stimulated Brillouin scattering (SBS) effect is proposed and experimentally demonstrated. By optimizing the parameters of a depolarizer consisting of a power-splitting Mach-Zehnder interferometer (MZI) structure, degree of polarization (DOP) of the pump source can be reduced to less than 5%. Consequently frequency response of the SBS-based filter remains almost unchanged when the state of polarization (SOP) of the input signal varies and the corresponding polarization-dependent gain (PDG) is less than 1 dB. And the experimental results also indicate that the proposed filter can realize the wavelength-independent operation over a range of ~30 nm. Furthermore, high resolution optical spectrum measurement utilizing this novel filter is investigated. For an input signal with a frequency interval of 30 MHz in arbitrary SOP, spectral details can be clearly observed and the power stability of the measured spectra can be improved from 3~5 dB to less than 0.5 dB, which benefitting from the polarization independent operation of the forementioned filter. Moreover, considering the resolution degradation of the measured spectra induced by the frequency shift in the depolarizer, a sweep speed of 5 nm/s for the pump source and a delayed fiber length of 2000 m in the MZI should be used to guarantee the desired high spectral resolution of ~10 MHz.

Four Input Single Output based third order universal filter using Four Terminal Floating Nullor

This paper presents a Four Input Single Output based third order universal filter that offers all five sections of filter frequency responses with some passive components using active block named as Four Terminal Floating Nullor (FTFN). The design schematic uses two number of Four Terminal Floating Nullor (FTFN) with three numbers of resistors and capacitors each. The proposed universal filter is realised with CMOS implementation of FTFN as well as Current Feedback Operational Amplifier (CFOA) namely IC AD844 for FTFN realisation. The viability of the universal filter circuit is justified with PSPICE simulation that includes both CMOS and AD844 based realization of FTFN. Also theoretical verification is well performed for the sustainability of the proposed circuit along with experimental verification by using IC AD844.

Log-domain high-order low-pass and band-pass filters

Continuous time current-mode high-order low-pass and band-pass filters based on the log-domain concept are presented in this paper. The passive RLC ladder networks are used as the prototype to achieve the proposed filter by simulating the RLC network synthesis method. The achieved filters have inherited the good sensitivity performance from the RLC passive prototype. Fifth-order RLC ladder low-pass filter and sixth-order RLC ladder band-pass filter are used as prototypes and the signal flow graph (SFG) technique is used for the synthesis. The SFG can identify group of integrators and several signal paths. Log-domain lossy and lossless integrators based on BJT technology are deployed to achieve the integrators for realization of proposed filters. The simulations were carried out and the results exhibited several features which are in agreement with the RLC prototype. The frequency response of filters along 100kHz to 10MHz can be electronically tuned through 5–500µA of bias currents. The THD lower than 1% of LP and BP filters were measured at 10MHz input. The multi-tone tested was included in the paper for verifying the performance of proposed LP and BP filters. The intermodulation distortions around −50dB and −60dB were also investigated for the proposed LP and BP filters.

Derivative Kernels: Numerics and Applications.

A generalized framework for numerical differentiation (ND) is proposed for constructing a finite impulse response (FIR) filter in closed form. The framework regulates the frequency response of ND filters for arbitrary derivative-order and cutoff frequency selected parameters relying on interpolating power polynomials and maximally flat design techniques. Compared with the state-of-the-art solutions, such as Gaussian kernels, the proposed ND filter is sharply localized in the Fourier domain with ripple-free artifacts. Here, we construct 2D MaxFlat kernels for image directional differentiation to calculate image differentials for arbitrary derivative order, cutoff level and steering angle. The resulted kernel library renders a new solution capable of delivering discrete approximation of gradients, Hessian, and higher-order tensors in numerous applications. We tested the utility of this library on three different imaging applications with main focus on the unsharp masking. The reported results highlight the high efficiency of the 2D MaxFlat kernel and its versatility with respect to robustness and parameter control accuracy.

Combline filters designed on symmetric stripline

Problems arising during the design of stripline combline filters, which until quite recently were considered as all-stop microwave structures, are considered. It has been shown that the electromagnetic coupling coefficient of quarter-wave stripline resonators increases with the value of material permittivity er, the operating frequency, and the thickness of the filter resonators. For er = 92 and a thickness of stripline resonators of 4 mm, it exceeds 12% at frequencies higher than 2.2 GHz. Two alternative versions of combline filters have been designed: a filter with a coupling strip and a filter without a coupling strip. Experimental data for a nine-resonator combline filter with a thickness of 4 mm, er = 9.7, and the center frequency f 0 = 2.4 GHz are presented. A method for increasing the selectivity of combline filters with the same number of resonators is proposed. It has been found that amplitude–frequency responses of stripline combline filters are near-symmetric, unlike the responses of microstrip combline filters.

Optimal Design of Oversampled Modulated Filter Bank

This letter proposes an optimal design of the filter bank with minimum inband aliasing, residual aliasing together with restrictions on the frequency response of the analysis filter and the distortion level for the filter bank. A new procedure that includes the combination of one parameter filled function and an iterative method is developed to solve the optimization problem. The advantage of using the iterative algorithm within the filled function is that a lower basin can be obtained with a low computational complexity. Design examples show that a significant improvement can be obtained using the proposed method over existing methods.

Calibration of Time-Interleaved ADCs via Hermitianity-Preserving Taylor Approximations

A new calibration technique for time-interleaved analog-to-digital converters is proposed, based on Hermitianity-preserving complex Taylor approximations of the frequency response of the correction filters. Calibration is interpreted as approximating these filters with linear combinations of base filters obtained by the proposed Taylor expansion. Known calibration techniques are reinterpreted in this way and compared in terms of accuracy, computational complexity, numerical stability, and convergence time. The new technique is shown to be accurate and to require few hardware resources. The limited number of parameters to estimate enables good performance in fixed-point arithmetic and fast convergence. This is important in background calibration schemes in which parameters need to be estimated in real time.

Novel realization of GIC based wave digital filters using Al-Alaoui transform

By using the concepts of wave characterization, Al-Alaoui transform and generalized immittance converter (GIC), a new digital GIC structure is proposed which is capable of realizing all the standard second-order digital filter sections. The Al-Alaoui transform is utilized for reference circuit discretization, leading to development of second-order digital filter sections which possess better noise properties than the conventional GIC and GIC discretized using the fractional bilinear transform. The proposed second-order digital filter sections are used as building blocks in cascade synthesis of filter. Two design examples are considered to analyze the effectiveness of the proposed filter sections and their comparison with the other filter sections is performed in terms of quantization noise and approximation to analog filter response. The proposed synthesis yields lowpass and highpass filters that have a better signal to noise ratio and better approximation of the analog filter frequency response than the conventional GIC digital filters and fractional GIC digital filters.

Thin stripline bandpass filters for the centimeter band

This article considers the design of thin stripline (1 mm) bandpass filters in the centimeter band, which contain dielectrics with different relative permittivity er. This includes the choice of the resonators, the dielectric material, the preliminary assessment of resonators’ unloaded quality factors and taking into account the features of the frequency response curve of the filter. It was found, that the passband width of the thin comb filters with λ/4 resonators and array-type filters with λ/2 resonators cannot exceed 6% for any values of er and the length of resonators of at least 2 mm. The array-type filters with resonators of half-wave type and with alternating signs of the coupling factors between resonators were proposed. Under certain additional conditions, the attenuation poles appear in such filters, resulting in improved selectivity. The results of computer modelling of the frequency response curve of thin filters of cm band are presented. They are compared to the frequency response of other filters. The data obtained from computer modelling showed good correspondence with the experimental data.

Single Scale CWT Algorithm for ECG Beat Detection for a Portable Monitoring System

This paper introduces an algorithm for ECG beat detection for portable monitoring systems using the continuous wavelet transform technique. It uses the Mexican-Hat wavelet as an analyzing wavelet. The central frequency of the corresponding band-pass filter frequency response is chosen to be 32 Hz after performing scale analysis. It relies on the adaptive threshold technique to minimize the number of false positive beats and therefore guarantee robustness against high motion artifact noise levels, it also relies on search back to avoid missing real heart beats and hence obtain a high sensitivity. The algorithm was implemented using MATLAB and has a sensitivity Se = 99.37% and a positive predictivity P+ = 99.83% with the MIT-BIH arrhythmia database. Furthermore, in order to test the performance of the algorithm against motion artifact noise, a noise stress test was performed by adding motion artifact noise to the ECG records of the same database at various signal to noise ratio values. The results of the noise stress test were benchmarked against some existing algorithms in the literature such as Pan and Tompkins and Romero.

Extending Classical Multirate Signal Processing Theory to Graphs—Part II: M-Channel Filter Banks

This paper builds upon the basic theory of multirate systems for graph signals developed in the companion paper (Part I) and studies $M$ -channel polynomial filter banks on graphs. The behavior of such graph filter banks differs from that of classical filter banks in many ways, the precise details depending on the eigenstructure of the adjacency matrix $\boldsymbol {A}$ . It is shown that graph filter banks represent, (linear and) periodically, shift-variant systems only when $\boldsymbol {A}$ satisfies the noble identity conditions developed in Part I. It is then shown that perfect reconstruction graph filter banks can always be developed when $\boldsymbol {A}$ satisfies the eigenvector structure satisfied by $M$ -block cyclic graphs and has distinct eigenvalues (further restrictions on eigenvalues being unnecessary for this). If $\boldsymbol {A}$ is actually $M$ -block cyclic then these PR filter banks indeed become practical, i.e., arbitrary filter polynomial orders are possible, and there are robustness advantages. In this case, the PR condition is identical to PR in classical filter banks—any classical PR example can be converted to a graph PR filter bank on an $M$ -block cyclic graph. It is shown that for $M$ -block cyclic graphs with all eigenvalues on the unit circle, the frequency responses of filters have meaningful correspondence with classical filter banks. Polyphase representations are then developed for graph filter banks and utilized to develop alternate conditions for alias cancellation and perfect reconstruction, again for graphs with specific eigenstructures. It is then shown that the eigenvector condition on the graph can be relaxed by using similarity transforms.

Влияние режекторного фильтра на эффективность линеаризации фазочастотной характеристики аналогового полосового фильтра

The previously published works of the authors dealt with methods aimed at linearizing the phase frequency responses of analog filters using digital linearizing finite impulse response (FIR) filters. If the operating frequency band contains narrow-band interference, such interference often needs to be suppressed by using a narrow-band analog band-stop filter. However, when a band-stop filter is connected in series, the linearized phase frequency response may become distorted. The article examines the influence of a narrow-band analog band-stop filter on the effectiveness of linearizing the phase frequency responses of a complex analog band-pass filter using a complex band-pass linearizing digital FIR filter. The study was conducted using a circuit simulation program based on a model consisting of the following modules: a complex analog band-pass filter with a sixth-order Butterworth low-pass filter prototype, a narrow-band complex analog band-stop filter with a third-order Butterworth low-pass filter prototype, and a complex digital band-pass linearizing FIR filter. The article presents the results from studying the frequency band in which the phase frequency response linearity is distorted to an acceptable degree. A sharp change in the group delay time level takes place in the stopband vicinity. The frequency band in which the group delay ripple is larger than the pre-linearization group delay ripple is referred to as the linearization effect loss band. If the difference between the band-stop filter’s passband boundary frequencies is much (by dozens of times) smaller than the band of the complex band-pass filter, the linearization effect is retained over most of the passband. With the selected parameters and orders of the complex analog filter and band-stop filter, the frequency band in which the linearization effect vanishes is approximately seven times greater than the difference between the band-stop filter’s passband boundary frequencies. Such an approach is relevant in filtering narrow-band interference within the frequency band of broadband signals.

A Real time Alternative to the Hilbert Huang Transform Based on Internal Model Principle

This article presents a new tuning approach for an adaptive internal-model-principle based signal identification algorithm whose computational costs are low enough to allow a realtime implementation. The algorithm allows an instantaneous Fourier decomposition of non-stationary signals that have a strongly predictable component. The algorithm is implemented as a feedback loop resulting in a closed loop system with a frequency response of a bandpass filter with notches at the frequencies of the Fourier decomposition. This is achieved through real time selection of the coefficients of the transfer functions in the feedback loop. Previously these coefficients were selected by solving a large set of coupled linear equations. Rules for explicitly solving for these parameters are given that only involve evaluating frequency responses at the frequencies of the instantaneous Fourier decomposition. This allows realtime implementation on a low cost lap top with sampling rates up to 10 kHz.

A Numerical Methodology for the Analysis of Switched-Capacitor Filters Taking Into Account Non-Ideal Effects of Switches and Amplifiers

This paper presents an efficient numerical methodology to obtain the frequency response of switched-capacitor filters based on the circuits' differential equations. This methodology uses a non-hierarchical approach in which the non-ideal effects of the transistors (in the switches and in the amplifier) are taken into consideration, allowing the accurate computation of the frequency response, even in the case of incomplete settling in the SC branches. The accuracy is demonstrated by comparing the results obtained using the proposed methodology with those obtained using transient electrical simulation results for three different SC circuits: a first order SC passive filter, a second order SC lowpass filter, and a second order SC bandpass filter, showing that the results are in good agreement with the more time consuming electrical simulation of the circuits.

LTE for Public Safety Networks: Synchronization in the Presence of Jamming

In this paper, an algorithm for timing synchronization, cell identity detection, and carrier frequency offset (CFO) estimation is presented for long-term evolution (LTE) systems. The proposed algorithm is robust against partial-band interference and/or jamming. It utilizes adaptive filtering to suppress the contribution of the jamming signal to the timing detection metric without using any a priori knowledge of the jamming signal characteristics. The timing detection metric is computed by minimizing the output of the adaptive filter corresponding to any received signal that does not match the signature of the LTE primary synchronization signals (PSS). The filter coefficients are updated iteratively using the recursive least squares algorithm. The frequency response of the adaptive filter at the PSS detection instant is used to weight the contribution of different subcarriers to the metrics used in cell identity detection and CFO estimation. Simulation results are presented showing the ability of the proposed algorithm to complete the synchronization process successfully even in the presence of partial-band jamming signals that cover one third of the frequency band of the LTE synchronization signals.

Design of image enhancement filters using a novel parallel particle swarm optimisation algorithm

Designing image enhancement filters with arbitrary frequency response subject to stability constraints is a complex multidimensional optimisation problem. In this paper a novel parallel particle swarm optimisation algorithm (PPSO) is proposed and applied to the design of infinite impulse response image filters. The proposed PPSO consists of two phases: in the first phase, the particle swarm in the classical PSO algorithm is divided into subpopulations that evolve on separate cores of a multi-core machine. Best solutions from each sub population are then interchanged between cores. In the second phase a local search using Nelder-Mead simplex is done to refine the solution. Classical PSO is used for global exploration to explore multiple local minima whereas Nelder-Mead helps refine the solution computed by the PSO. The PPSO outperformed other global optimisation algorithms in terms of the mean square error between the ideal and designed filter frequency responses and CPU usage.

Experimental investigation of frequency characteristics of the multistage slot membranes waveguide filters

In this article, we present results of experimental investigation of amplitude-frequency characteristics (AFC) of the five-stage “filters with the waveguide-slot membranes” (FWSM) in the range of frequencies 5.4…8.5 GHz for six filters. Article shows the following trend change filter frequency response by increasing the width of the slots of the second and fourth membranes: decrease the quality factor, resonant frequency increase, reducing losses in the passband.