Weighted median filters with sigma-delta modulation encoding

Digital decimation filters play a fundamental role in oversampled sigma-delta A/D decoders. In this paper, we first show that weighted median (WM) filtering of a demodulated sequence (at the Nyquist rate) can be implemented concurrently in the A/D decoder. Through a simple modification of the binary time-series outputted by the A/D modulator, the sequence obtained after the sigma-delta modulation (SDM) decoder is shown to be equivalent to WM filtering the multilevel sequence at the Nyquist rate. Second, we show that WM filters can be used for SDM decimation filters and that these filters are readily implemented in the SDM binary domain. A very promising characteristic of SDM converters equipped with WM decimating filters is that sharp discontinuities (edges) can be preserved and acquired. Thus, the bandlimited constraint imposed on the input signals can be relaxed making SDM more attractive to A/D conversion of signals containing sharp transitions. The proposed signal processing algorithms, in essence, combine A/D sigma-delta converters and WM filters into a single programmable system     

On the Realization of MOS-Only Allpass Filters

The objective of this paper is to present a simple filter topology, which can be used to implement first- and second-order MOS-only allpass filters. The resulting filters realize the allpass functions without using any external passive components; hence these occupy very small chip area and are capable of operating at high frequencies. Cadence Spectre simulation and experimental results verifying the main advantages of the filters are provided.     

LMS adaptive filters using distributed arithmetic for high throughput

We present a new hardware adaptive filter architecture for very high throughput LMS adaptive filters using distributed arithmetic (DA). DA uses bit-serial operations and look-up tables (LUTs) to implement high throughput filters that use only about one cycle per bit of resolution regardless of filter length. However, building adaptive DA filters requires recalculating the LUTs for each adaptation which can negate any performance advantages of DA filtering. By using an auxiliary LUT with special addressing, the efficiency and throughput of DA adaptive filters can be of the same order as fixed DA filters. In this paper, we discuss a new hardware adaptive filter structure for very high throughput LMS adaptive filters. We describe the development of DA adaptive filters and show that practical implementations of DA adaptive filters have very high throughput relative to multiply and accumulate architectures. We also show that DA adaptive filters have a potential area and power consumption advantage over digital signal processing microprocessor architectures.     

A CMOS transconductance-C filter technique for very highfrequencies

CMOS circuits for integrated analog filters at very high frequencies, based on transconductance-C integrators, are presented. First a differential transconductance element based on CMOS inverters is described. With this circuit a linear, tunable integrator for very-high-frequency integrated filters can be made. This integrator has good linearity properties and nondominant poles in the gigahertz range owing to the absence of internal nodes. The integrator has a tunable DC gain, resulting in a controllable integrator quality factor. Experimental results of a VHF CMOS transconductance-C low-pass filter realized in a 3-μm CMOS process are given. Both the cutoff frequency and the quality factors can be tuned. The cutoff frequency was tuned from 22 to 98 MHz and the measured filter response is very close to the ideal response of the passive prototype filter. Furthermore, a novel circuit for automatically tuning the quality factors of integrated filters built with these transconductors is described     

Compact lowpass filters with very sharp transition bands based on open complementary split ring resonators

It is shown that open complementary split ring resonators (OCSRRs) are useful particles for the design of lowpass filters with very narrow transition bands in microstrip technology. Owing to the small electrical size of OCSRRs, the filters are also very small. These filters are implemented by cascading several OCSRR stages in a microstrip line. The OCSRR stages can be modelled as parallel resonators in series configuration, thus providing a transmission zero at their resonance frequency. By designing the OCSRRs with small inductance and high capacitance, very sharp cutoffs are achieved. To illustrate the possibilities of the approach, a prototype device example is provided. It consists on a five-stage periodic microstrip lowpass filter with 3 dB insertion losses at 1.33 GHz and 40 dB rejection at 1.45 GHz. To improve out-of-band rejection, four additional OCSRR stages tuned at the spurious frequency band have been cascaded. Filter dimensions are 39 x 7.4 mm (i.e. 0.46l x 0.087l, where l is the guided wavelength at the cutoff frequency). These filters are of interest in applications where small size and severe cutoff requirements are required.     

Optimum masking levels and coefficient sparseness for Hilbert transformers and half-band filters designed using the frequency-response masking technique

Hilbert transformers and half-band filters are two very important special classes of finite-impulse response filters often used in signal processing applications. Furthermore, there exists a very close relationship between these two special classes of filters in such a way that a half-band filter can be derived from a Hilbert transformer in a straightforward manner and vice versa. It has been shown that these two classes of filters may be synthesized using the frequency-response masking (FRM) technique resulting in very efficient implementation when the filters are very sharp. While filters synthesized using the FRM technique has been characterized for the general low-pass case, Hilbert transformers and half-band filters synthesized using the FRM technique have not been characterized. The characterization of the two classes of filter is a focus of this paper. In this paper, we re-develop the FRM structure for the synthesis of Hilbert transformer from a new perspective. This new approach uses a frequency response correction term produced by masking the frequency response of a sparse coefficient filter, whose frequency response is periodic, to sharpen the bandedge of a low-order Hilbert transformer. Optimum masking levels and coefficient sparseness for the Hilbert transformers are derived; corresponding quantities for the half-band filters are obtained via the close relationship between these two classes of filters.     

Unloaded Q of Single Crystal Yttrium-Iron-Garnet Resonator as a Function of Frequency (Correspondence)

The practical feasibility of constructing magnetically tunable broad-tuning range microwave filters using single crystal yttriumiron-garnet resonators was demonstrated in a recent paper. Experimental results were presented on one- and two- resonator filters which can be tuned by varying a dc magnetic field bias over a full waveguide bandwidth and greater, at the same time maintaining an insertion loss performance which is comparable to mechanically-tuned cavity filters. The crucial parameter of the resonant elements in a band-pass filter is the unloaded Q, Q/sub u/. With a spherical single crystal of yttrium-iron-garnet the Q/sub u/ decreases with frequency below X-band frequencies reaching very low values at frequencies around 2000 Mc.     

A channelized digital receiver design for UWB systems in a multi-path indoor environment

Due to the very wide bandwidth of UWB system, it is hard if not impossible to design high speed and high resolution ADCs with today’s technology. This problem can be solved if the received UWB signal is split into a number of subbands by power splitters, analog low-pass filters, mixers and digital filters. By doing this, each of subbands can be sampled at a fraction of effective sampling frequency. In this paper, we present a simpler channelized receiver architecture for UWB systems than previously published work. Moreover, we present a new, though more complex, channelized receiver design for UWB systems in a multipath propagation environment. We also show through simulation that this new receiver achieves very good BER performance.     

A wavelet transform with point-symmetric extension at tile boundaries

This paper presents a low-complexity wavelet transform that utilizes point-symmetric extension at the image tile boundaries. The proposed approach is considered as an alternative to the well-known symmetric signal extension in dealing with the boundary artifacts that manifest when tiles of images are lossy compressed. The new solution developed for odd-length filters preserves the perfect reconstruction property of the filter banks and deals efficiently with blocking artifacts without requiring any post processing technique or additional information from the neighboring tiles. It is shown that point-symmetric extension at the tile boundaries does not need to be applied explicitly, but instead the equivalent boundary filters can be derived. The lifting-based implementation of the filters provides a very simple way of changing filter parameters at the boundaries that suits both hardware and software platforms.     

Calcul des tolérances des filtres LC en échelle pour de larges variations

This paper presents two complementary methods for tolerance computation with large-change and discrete variations of the elements for LC ladder filters. It shows the interest of a property, called one-dimensional convexity, which allows a very low-cost determination of these tolerances. This property is shown for very often used cells in ladder filters and can easily be extended to other cells.     

On the robustness of the class of stack filters

A widely held view in the nonlinear signal processing community is that the class of stack filters is robust. Although this is supported by extensive experimental evidence, no systematic theoretical justification exists, despite the availability of analytical tools for studying robustness of individual stack filters. We focus on rank selection probabilities (RSPs) as measures of robustness as it is well known that other statistical characterizations of stack filters, such as output distributions, breakdown probabilities and output distributional influence functions can be represented in terms of RSPs. We show, in a very general sense, that the class of stack filters is highly robust. It is also shown that almost all stack filters have very similar output distributions for independent and identically distributed (i.i.d.) input signals and, thus, very similar statistical behavior     

Wideband planar filters with an extended stopband

An approach to the construction of wideband bandpass filters of microstrip and stripline designs, which have an extended stopband and can incorporate lumped capacitors, is proposed. This approach is based on resonators with the enhanced frequency diversity of fundamental and parasitic resonance frequencies and coupling circuits formed according to an assigned rule. The potential of the filters achieved due to the proposed technique is established. In particular, a very wide passband whose ratio of cuttoff frequencies is 5: 1, as well as the stopband greater than an octave at a level of 40 dB, is demostrated to be attainable. When the passband is narrower, the stopband can exceed two octaves. The given approach can be applied to filters operating in a broad frequency range, including to that corresponding to centimeter and meter waves. The experimental data are presented.     

Equivariant holomorphic filters for contour denoising and rapid object detection.

It is well known that linear filters are not powerful enough for many low-level image processing tasks. However, it is also very difficult to design robust nonlinear filters that respond exclusively to features of interest and that are, at the same time, equivariant with respect to translation and rotation. This paper proposes a new class of rotation-equivariant nonlinear filters that is based on the principle of group integration. These filters become efficiently computable by an iterative scheme based on repeated differentiation of products and summations of intermediate results. The relations of the proposed approach to Volterra filters and steerable filters are shown. In the context of detection problems, the filter may be interpreted as some kind of generalized Hough transform. The experiments show that the new filter can be used for enhancing noisy contours and rapid object detection in microscopical images. In the detection context, our experiments show that the proposed filter is definitely superior to alternative approaches, when high localization accuracy is required.     

Permutation filters: a class of nonlinear filters based on setpermutations

Introduces and analyzes a new class of nonlinear filters that have their roots in permutation theory. The authors show that a large body of nonlinear filters proposed to date constitute a proper subset of permutation filters (𝒫 filters). In particular, rank-order filters, weighted rank-order filters, and stack filters embody limited permutation transformations of a set. Indeed, by using the full potential of a permutation group transformation, one can design very efficient estimation algorithms. Permutation groups inherently utilize both rank-order and temporal-order information; thus, the estimation of nonstationary processes in Gaussian/nonGaussian environments with frequency selection can be effectively addressed. An adaptive design algorithm that minimizes the mean absolute error criterion is described as well as a more flexible adaptive algorithm that attains the optimal permutation filter under a deterministic least normed error criterion. Simulation results are presented to illustrate the performance of permutation filters in comparison with other widely used filters     

MOCCII电流模式二阶滤波器的系统设计

本文提出一种MOCCⅡ电流模式二阶滤波器的一般电路模型和设计理论。根据该电路模型和理论可以产生多种滤波器结构。每一种结构可以实现低通、带通、高通、带阻及全通滤波器或其中的多种滤波器。所有滤波器的无源元件均接地，且具有很低的灵敏度。最后对所产生的滤波器进行了PSPICE模拟。     

A new low-loss mode in semiconductor magnetoplasmas

A new semiconductor plasma wave mode that can propagate with very little attenuation at frequencies smaller than the plasma collision frequency is described. The wave propagates at right angles to a dc magnetic field and may be used for modulation of lasers or for tunable filters in the microwave /millimeter wave region.     

最少元件的多输入多输出MOCCII电流模式滤波器

本文提出了两种基于MOCCⅡ（多端输出的第二代电流传输器）的多输入多输出的电流模式滤波器。两种电路均由2个MOCCⅡ及4个接地RC元件构成。每一种电路除了实现出单输出的低通、带通、高通、带组、全通电流模式滤波器外，还能实现三种不同类型的具有同时多输出的电流模式滤波器，提出的电路具有很低的无源灵敏度；同时应用基本电流镜技术实现出结构简单的高精度CMOS MOCCⅡ，并对MOCCⅡ及提出的滤流器电路进行了PSICE仿真。     

Narrow-Bandpass Waveguide Filters

A procedure is described whereby narrow-bandpass waveguide filters having ripple in both the passbands and stopbands can be synthesized in the form of coupled waveguide cavities. Orthogonal modes in square or circular waveguides are employed to enable negative coupling elements to be realized. As a consequence, very compact filters can be constructed. Experimental results on an 8-cavity orthogonal-mode narrow-bandpass filter are shown to agree well with theory.     

Mahalanobis Distance Based Approach for Anomaly Detection of Analog Filters Using Frequency Features and Parzen Window Density Estimation

Analog filters play a very important role in insuring the availability of electronic systems. Early detection of anomalies of analog filters can prevent the impending failures and enhance reliability. The complex architecture and the tolerances of multiple components make it very difficult to detect anomalies in analog filters. To address this concern, A Mahalanobis distance (MD) based anomaly detection method for analog filters is proposed in this paper. The conventional frequency features and the moment of frequency response are selected as the feature vector. Mahalanobis distance is used to transform the frequency feature vector to one dimensional MD data. The anomaly detection threshold is obtained based on probability density of the health MD data sets which is estimated by Parzen window density estimation method. The efficiency of the proposed method has been verified by two case studies. In the case studies, a comprehensive indicator constructed by miss alarm and false alarm is used to obtain an optimal anomaly detection threshold. One class SVM (OCSVM) based anomaly detection method is used as a comparison with our approach. The results illustrate that: (1) the proposed frequency features can effectively clarify the degradation of analog filters; (2) the proposed MD based approach can detect anomalies in analog filters effectively at an early time stage. (3) the proposed MD based approach can detect anomalies in analog filters more accurately than OCSVM based method.     

Three-tone intermodulation distortion generated by superconducting bandpass filters

Microwave bandpass filters constructed from materials exhibiting some nonlinearity, such as superconductors, will generate intermodulation distortion (IMD) when subjected to signals at more than one frequency. In commercial applications of superconductive receive filters, it is possible for IMD to be generated when a weak receive signal mixes with very strong out-of-band signals, such as those coming from the transmitter. A measurement procedure was developed and data were taken on several different types of superconducting bandpass filters, all developed for commercial application. It was found that in certain interference situations, the three-tone mixing can produce a spur that is noticeable by the receiver, but that there are simple preventative design solutions.