Adaptive 1-D and 2-D Filtering with Internally Passive Structures

Internally passive filters such as wave digital filters (WDF) and orthogonal filters, which have desirable properties, are developed as filter structures for adaptive filters. The equations for updating the multiplier coefficients as well as for computing the gradients are derived for these filters. The stability monitoring during the adaptation process for these filters is simple to implement. Simulation results are included to demonstrate the capability of these filters in system identification and noise cancellation. Moreover, motivated by applications of multidimensional adaptive filters in video compression and image enhancement, the proposed adaptive wave digital filters have been extended to two dimensions and applied as adaptive fan filters. Computer simulations are also conducted to show their potential applications to two-dimensional system identification and image enhancement.     

On the Elimination of Reactive Element Loops and the Use of Special Approximations in the Design of OTA-C Filters

Loops of reactive elements in passive filters cause a series of problems in OTA-C simulations of these structures. These loops can be eliminated in a systematic way by the procedures described in the paper. The use of special approximations in the design of the passive prototype filters allows the elimination of multiple loops of reactive elements that appear in usual LC ladder filters with finite transmission zeros. This leads to more efficient active simulations, where problems with floating capacitors, DC or high-frequency instability, or limited operating frequency are avoided.     

Novel single-stage second-order structure for low-pass wide-band low-power continuous-time filters

A novel single-stage second-order structure for Gm-C filters is presented. It allows ample reduction in hardware and thus power consumption. Moreover, due to exploiting otherwise parasitic poles, the structure allows much higher bandwidth than in conventional designs, be achieved. To verify effectiveness of new concept, and based on the new approach to implement second-order stages, a third-order and a fifth-order continuous-time low-pass filters were implemented. The filters fabricated in a CMOS process, achieved more than 430 MHz, bandwidth and less than THD for a 400 mV_p–p 100 MHz input signal. All these accomplished with a factor of about four reduction in hardware and power. The bandwidth, output voltage swing, and dynamic range are far larger than those of any other CMOS low-pass filters thus far reported, which have bandwidth higher than 100 MHz.     

Flexible frequency selective passive circuits based on memristor and capacitor

In analog electronic communication and signal processing applications, programmable analog filters are desirable to reduce the hardware requirement. Memristor is two states configurable nonvolatile resistor, which is small size, low power, and fast switching device. To achieve tunable cut-off frequency and bandwidth, flexible memristor-capacitor (MC) circuits are proposed, which can be applied as low pass, high pass, and band pass filters. They can be fabricated on a flexible polyethylene terephthalate (PET) substrate through electrohydrodynamic (EHD) technique. In the proposed filters, two cut-off frequencies are selected through switching two resistive states of the memristor either in high resistance state (HRS) or low resistance state (LRS), whereas the capacitor has a fixed value. The memristor is composed of graphene quantum dots (GQDs)/poly 4-vinlyphenol (PVP) composite to achieve highly stable and linear behavior and the dielectric layer of capacitor is consisted of graphene/PVP composite. The fabricated MC filters are electrically and mechanically characterized, which are matched quite well with theoretical results. From these results, it can be a good basis for tunable analog filters in wearable electronics.     

双模曲折悬置带线环四极微波滤波器

该文研制了双模曲折悬置带线环四极微波滤波器。采用全波技术对该种滤波器特性进行的计算表明,它具有优良的窄通带、高选择性和小体积,与同类型二极滤波器相比,过渡带更陡峭。采用优化设计方法设计出了滤波器电路尺寸,制造了以r=2.8的Teflon为介质基片的滤波器,测试得到的双模曲折悬置带线四极滤波器的中心频率为f0=1.194 GHz,△f=19.4 MHz,通带插入损耗LP4.3 dB,阻带衰减Ls50 dB,实验结果和CAD预测作了比较,两者基本一致。这种滤波器可望在多种微波系统和移动通信系统中应用。     

Current-Mode Universal Filters Using Current Conveyors: Classification and Review

Several current-mode universal filters are reviewed. The filters are classified in two classes. The class I filters have floating passive elements, whereas class II filters have all resistors and capacitors grounded. Each class of filters includes two subclasses based on the filter’s capability to have independent control of the filter quality factor or not. The effects of nonideal second generation current conveyors are briefly discussed. Spice simulations using BSIM3 version 3.1 parameters, feature size 0.5 μm from MOSIS, are given, and a detailed comparison table is included.     

Nonlinear order statistic filters for image filtering and edge detection

A novel class of nonlinear filters for image processing is proposed. This class is a combination of nonlinear mean and order statistic filters. Median, homomorphic, α-trimmed mean, nonlinear mean, order statistic, and linear filters can be considered as special cases of this class. The properties of these filters in the presence of different kinds of noise are investigated. It is shown that these filters can be used for the reduction of additive white noise, signal-dependent noise, and impulse noise. It is also shown that they preserve edges better than linear filters. Such filters can successfully be used as edge detectors, by appropriate adjustment of some of their parameters. Edge information can be used as an input to these filters to perform in an adaptive manner, changing their behaviour near the edges of an image. It is finally shown that many of the filters proposed have a reasonable (and in certain cases small) computational complexity.     

908厂早期高效空气过滤器

介绍中国早期高效空气过滤器制造过程。原苏联提供了全套图纸和工艺文件,908厂利用国产材料研制出高效过滤器。1961年研制成功并批量制造第一批高效空气过滤器。1981年停止了老型号产品的生产。     

A Practical Parallel Architecture for Stacks Filters

Stack filters belong to the class of non-linear filters and include the well-known median filter, weighted median filters, order statistic filters and weighted order statistic filters. Any stack filter can be implemented by using the parallel threshold decomposition architecture which allows implementing their non-linear processing by means of a collection of identical binary filters (Boolean logic circuits). Although it is conceptually simple and useful to study the filter properties, this architecture is not practical for direct hardware implementation because as many as (M – 1) binary filters are required for a M-valued input signal and M is large in many applications.In this paper we introduce a new parallel architecture for stack filter implementations. The complexity is now proportional to the window width L of the filter, instead of to M. In most applications L is much smaller than M which translates into efficient hardware implementations. The attractive characteristic of ease of design exhibited by the threshold decomposition architecture is kept. In fact, for a given stack filter both in the conventional implementation and in the proposed one, the same binary filter is required. The key concept supporting the new architecture is a modified decomposition scheme which generates L binary signals for a multi-valued input. As an application example, a complex WOS filter is designed and prototyped in an FPGA.     

应用于掺铒超荧光光纤光源的滤波器研究

介绍了应用于掺铒光纤光源的几种滤波器的研究状况，阐述了它们的优缺点，简述了长周期光纤光栅滤波器的设计过程。指出现阶段使用均匀长周期光纤光栅作为掺铒光纤光源滤波器是比较理想的选择。     

Switched-Current Filters by Component Simulation

This paper discusses the synthesis of switched-current filters from continuous-time prototypes by the simulation of components, particularly capacitors and transconductors in Transconductance-C filters. The obtained structures implement discrete-time versions of the prototype circuit using bilinear or Euler formulas. All the proposed structures work with doubled effective sampling rate (sampling the input and updating the output at each phase), make strict use of voltage-sampling switches and naturally admit two-phases nonoverlapping clocks.     

On the practical realization of higher-order filters with fractional stepping

We propose the use of a compact integer-order transfer function approximation of the fractional-order Laplacian operator s^α to realize fractional-step filters. Lowpass and bandpass filters of orders (n+α) and 2(n+α), where n is an integer and 0<α<1, can, respectively, be designed. A 5th-order lowpass filter with fractional steps from 0.1 to 0.9 (i.e. 5.1→5.9) is given as an example with its characteristics compared to 5th- and 6th-order Butterworth filters. Spice simulations and experimental results are shown.     

Analysis of two-dimensional center weighted median filters

Center weighted median (CWM) filters, which have been recognized as detail preserving filters, are an important and the simplest subclass of weighted median (WM) filters. In this paper, we analyze the root signals of two-dimensional (2-D) CWM filters. In particular, we derive the required form for a signal to be a root of a 2-D CWM filter. The required form of signals to be roots is then used to evaluate the detail preserving properties of 2-D CWM filters. As examples, the detail preserving properties of some 2-D CWM filters are compared with other detail preserving filters, i.e. multilevel median filters. The generation of binary root signals of some 2-D CWM filters is treated in the term of the smallest surviving object (SSO). It is illustrated by some examples that CWM filters with different orientation of windows can be useful in image segmentation.     

HIGH SELECTIVITY SC BANDPASS FILTERS WITH LESS CAPACITOR SPREAD

Two novel switched-capacitor(SC)bandpass filters using a single operational am-plifier(op amp)are presented.Optimal designs for minimizing capacitor spread are also given.Gain-bandwidth product(GB)effects of op amps on the proposed SC circuits are taken intoconsideration.Comparisons with the proposed circuits and the circuits given by the literatureshow that the new circuits require less chip area in monolithic integration and are less sensitiveto the GB effects.     

频域反卷积滤波器的因果性的研究

本文首先介绍了成功应用于现代时域测量中的几种频域反卷积滤波器.并说明了这些反卷积滤波器元旦是非因果的.显然,滤波器非因果化要影响反卷积的估值,因此,对反卷积滤波器进行因果化是很必要的.进而,介绍了将这些反卷积滤波器因果化原理和方法,并给出了因果化的流程图.最后,对常用的反卷积滤波器的因果化进行了仿真研究,分别给出了这些反卷积滤波器困晨化前后的滤波效果.仿真结果表明,因果化的滤波器可改善反卷积的估值.     

A new approach for the realization of voltage-mode second-order universal filters using current conveyors

In this work two different types of topologies are derived for realization any second-order filter characteristic by choosing properly, the admittances of passive elements. These topologies use two second-generation current conveyors (CCIIs). One of the topologies involves different types of CCIIs whereas the other uses the same type of CCIIs together with a unity gain voltage buffer. The buffer used provides not only low output impedance but also facilitates cascading of the filter circuits thus obtained. It is possible to derive many different filters realizing any second-order transfer function by the use of the proposed topologies. Moreover, the produced filters have low-sensitivity performance and permit orthogonal controlling of both the quality factor and the natural angular frequency.     

L,S波段高性能窄带有源滤波器的研制

本文研究了一种直接利用晶体管或场效应管来模拟高Ｑ值电感，并利用此电感来制作Ｌ波段和Ｓ波段窄带有源滤波器的方法。利用此方法制作了两个高性能的窄带有源带通滤波器：一个中心频率为２．３ＧＨｚ，其带宽为９０ＭＨｚ左右，带内插入损耗为０ｄＢ；一个中心频率在１．５ＧＨｚ左右，并且中心频率可调，其带宽为８０ＭＨｚ左右，带内有１０ｄＢ的增益     

Generalized polyphase structure-based Mth-band filter design and application to image interpolation

A generalized polyphase (GP) structure-based method for the design of linear-phase Mth-band FIR filters satisfying the time-domain interpolation condition is presented. Some new transform matrices that allow for the use of an arbitrary number of branches in the GP structure are developed. Closed-form frequency specifications for constituent filters of the GP realization are obtained, making an independent and fast design of the short-length constituent filters possible. The proposed GP-based method is then extended for the design of a class of interpolation filters with certain regularities. Some of the interpolation filters designed based on the proposed GP structure are also applied to image resizing. Simulation results show that our interpolation filter gives a superior resized image than the common cubic spline interpolation does.     

一种多模微带方形贴片带通滤波器的设计

提出了一种多模方式工作的微带方形贴片带通滤波器。通常设计微带方形贴片滤波器主要是利用TM1,0,0和TM0,1,0这一对简并主模实现单模或双模的工作方式。但是这些滤波器尚存一些有待完善的地方,诸如带内插损偏大,带宽受限等等。本文设计的带通滤波器不使用主模,而是利用三个高次模分量,通过一种简单的微扰方式和馈电方式激励起除简并主模以外的三个高次模分量,并使之相互耦合实现通带。仿真和测量结果充分说明,这种滤波器能够实现宽频段的通带响应,并且在通带内具有很低的插损和良好的阻抗匹配特性,能够广泛地适用于微波平面电路。     

Realization of current-mode high-order filters employing multiple output OTAs

Current-mode linear transformation (CMLT) high-order filters with minimum number of multiple output operational transconductance amplifiers (MOOTAs) are presented. Based on proposed design methods, we can synthesize current-mode high-order all-pole filters with minimum number of MOOTAs and all grounded capacitors efficiently. Moreover, high-frequency canonical CMLT elliptic filters with minimum number of MOOTAs and floating capacitors are also presented. Our proposed filters have the following merits: simplified design procedures, minimum number of active elements and simple design equations. Two design examples are demonstrated in this paper. Experimental results that confirm the theoretical analysis are provided.