数字下变频中的FPGA高效滤波器设计

介绍了一种在FPGA上实现高效窄带有限冲击响应滤波器(FIR)的设计方法.该方法利用数字下变频抗混叠滤波器的多速率和窄带的特点,采用插值FIR滤波器(IFIR)和多相滤波器相结合的设计思路,实现了该滤波器的高效设计.     

高频信号直接采样系统中的抗混叠滤波器设计

针对实时控制系统中,高频信号直接采样时易出现带内混叠的现象,而影响系统的采样结果和动态性能,采用三阶巴特沃斯滤波器和低噪声超宽带宽差分放大器ADL5562设计出用于高频信号直接采样系统中的抗混叠滤波器。经测试,该电路可有效消除信号混叠现象,系统运行稳定、可靠。     

余弦调制子带滤波器组迭代设计的改进算法

余弦调制子带滤波器组的设计可以转化成一个高维非线性优化问题,传统迭代设计方法虽然避免了复杂的直接求解过程,但是其混叠误差的抑制依赖于滤波器阻带衰减的大小,设计出的滤波器往往阶数过高。本文提出了一种改进的子带余弦调制滤波器组迭代设计算法,其代价函数除了包括子带系统响应和子带滤波器阻带能量之外,还添加了系统一次混叠项因子,因此更好地抑制了混叠误差。本文将新的代价函数表示成滤波器系数的二次函数形式,并推导出其极值点的闭合解表达式。算法保留了传统迭代方法逐渐逼近极值点的思想,简单易于实现。仿真结果表明与传统迭代设计方法相比,本文算法获得的子带滤波器组具有更小的混叠误差和更低的滤波器阶数。     

数据采集中滤波问题的探讨

在数据采集系统中,低通滤波器常被用作抗混叠滤波器,以滤除或衰减高频噪声的影响。由于无源滤波器频率特性较差,在精度要求高的应用中多采用有源滤波器。文章详细讨论了两种常用的有源低通滤波器的频率特性,给出了它们各自的应用实例及详细的对比分析。     

一种八阶开关电容带通滤波器的设计

采用数模混合CMOS工艺,设计了一种八阶开关电容带通滤波器以及辅助的低通抗混叠滤波器和平滑滤波器。仿真结果表明设计的开关电容滤波器实现了中心频率57KHz,通带增益20dB,3dB带宽3KHz,阻带衰减35dB。设计的开关电容滤波器在一款RDS解调芯片中成功实现了RDS信号的中频选择功能。     

近似完全重构DFT调制滤波器组的设计

提出了一种新的近似完全重构（NPR）离散傅立叶变换（DFT）调制滤波器组的原型滤波器设计方法。其优化的目标函数由滤波器组的输出混叠、输出失真及原型滤波器的阻带能量所导出。在此设计方法中,利用DFT调制滤波器组的特殊结构合理简化了滤波器组的输出混叠,输出失真。原型滤波器的设计最终被转化为一个简单的非线性优化问题。与目前的DFT调制滤波器组的设计方法相比,该方法提供了相当大的灵活性同时具有简单的优化描述。仿真结果证实了所提出的设计方法的有效性。     

抗混叠轮廓波HMT模型的医学图像融合

为了更好地对医学图像进行融合,提出了一种利用抗混叠轮廓波HMT模型的图像融合新算法。该算法首先对原始轮廓波变换的频谱混叠问题展开研究,明确LP分解中的两个低通滤波器不满足Nyquist抽样定律是造成混叠的主要原因。接着,在对低通滤波器考虑带限约束条件下,设计了一种能抑制混叠的利用双通道滤波器组结构的多尺度分解方案,用于代替原始轮廓波变换的LP分解,结合方向滤波器组,实现了一种抗混叠的轮廓波变换。在此基础上,提出一种采用隐马尔可夫树（HMT）来刻划变换系数尺度间相关性的医学图像成像模型,并以期望最大化算法估计模型参数,得到融合图像。CT与MR图像以及MR-T1与MR-T2图像的融合实验表明,该算法的融合结果无论在视觉质量及定量指标上都明显优于基于小波变换和原始轮廓波变换的方法。     

线性相位NPR DFT滤波器组设计

提出了一种具有不同分析和综合原型滤波器的线性相位过采样NPR DFT调制滤波器组的设计方法。根据滤波器组在子带混叠、系统输出混叠、系统失真三方面的要求,推导并给出了相应的设计算法。不同的分析、综合原型滤波器的使用增加了设计自由度,可以有效改善滤波器组的整体性能。另外,由于考虑了线性相位约束,滤波器组的通带平坦性约束变得更为简单,简化了设计算法。     

Contourlet-1.3纹理图像检索系统

针对轮廓波变换纹理图像检索系统检索率较低的问题,提出了一种基于较强抗混叠能力的Contourlet-1.3纹理图像检索系统。该系统采用的Contourlet-1.3变换由抗混叠临界下采样拉普拉斯金字塔级联临界下采样方向滤波器构成,特征向量采用变换域子带系数的能量和标准偏差连接而成,以Canberra距离为相似度度量标准。实验结果表明：在特征向量长度、检索时间、所需存储空间基本相同的情况下,基于抗混叠Contourlet-1.3的检索系统比相同架构的轮廓波变换、无下采样轮廓波变换以及Contourlet-2.3检索系统具有更高的检索率;该检索系统中抗混叠Contourlet变换分解结构参数的选择对于检索率也有较大影响。     

利用单片集成有源滤波芯片设计抗混滤波器

利用MAx280低通滤波芯片设计了一种抗混滤波器,介绍了滤波器电路参数计算方法,并对滤波器进行了测试,取得了满意的滤波效果。     

时滞滤波器抑制残留振荡:理论、 方法及应用

回顾了时滞滤波器的发展背景和近年来的研究状况,介绍了对滞滤波器的各种设计方法和主要研究领域。时滞滤波器可从根本上避免激发对象的振动模态而消除残留振荡,在柔性结构系统中得到了广泛应用。最后 对时滞滤波器技术中存在的问题及未来的研究方向进行了探讨。     

Time–frequency localized three-band biorthogonal wavelet filter bank using semidefinite relaxation and nonlinear least squares with epileptic seizure EEG signal classification

In this paper, we design time–frequency localized three-band biorthogonal linear phase wavelet filter bank for epileptic seizure electroencephalograph (EEG) signal classification. Time–frequency localized analysis and synthesis low-pass filters (LPF) are designed using convex semidefinite programming (SDP) by transforming a nonconvex problem into a convex SDP using semidefinite relaxation technique. Three-band parameterized lattice biorthogonal linear phase perfect reconstruction filter bank (BOLPPRFB) is chosen and nonlinear least squares algorithm is used to determine its parameters values that generate the designed analysis and synthesis LPF such that the band-pass and high-pass filters are also well localized in time and frequency domain. The designed analysis and synthesis three-band wavelet filter banks are compared with the standard two-band filter banks like Daubechies maximally regular filter banks, Cohen–Daubechies–Feauveau (CDF) biorthogonal filter banks and orthogonal time–frequency localized filter banks. Kruskal–Wallis statistical test is employed to measure the statistical significance of the subband features obtained from the various two and three-band filter banks for epileptic seizure EEG signal classification. The results show that the designed three-band analysis and synthesis filter banks both outperform two-band filter banks in the classification of seizure and seizure-free EEG signals. The designed three-band filter banks and multi-layer perceptron neural network (MLPNN) are further used together to implement a signal classifier that provides classification accuracy better than the recently reported results for epileptic seizure EEG signal classification.     

High‐rejection wide‐stopband lowpass filters using signal interference technique

A design of compact, sharp rejection microstrip lowpass filters (LPF) with wide‐stopband is presented by using signal interference technique. The filter parameters can be easily controlled by the characteristic impedances of the configuration. Explicit design equations with graphs are presented. To validate the theoretical prediction, two prototype LPFs are fabricated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

宽带滤波器的优化设计及其MATLAB仿真

该文介绍了一种宽带滤波器的优化设计方法,即结合采用影像参数法的定K式和m导出式,分别设计相应的低通、高通滤波器,将其级联后得到初步的宽带带通滤波器;然后利用MATLAB进行仿真调试,对比设计要求和滤波器响应特性,反复调整滤波器LC参数,以获得最好的滤波性能。这种方法设计的带通滤波器带宽大、噪声低、频率响应特性较理想,并且设计简单、计算容易,也易于实现。这种设计方法特别适用于本身计算、比较复杂的宽带滤波器的设计。本文设计的宽带LC滤波器在实际应用中获得了良好的效果。     

Design and fabrication of a compact microstrip lowpass‐bandpass diplexer with high isolation for telecommunication applications

This study aimed to design and fabricate a lowpass‐bandpass (LP‐BP) diplexer with high isolation for telecommunication applications including wireless communications. The results revealed that the ?3 dB cutoff frequency of the lowpass filter (LPF) was equal to 0.82 GHz. The advantages of the LPF section include a very high suppression factor (SF) parameter (about 4.4), very sharp roll‐off‐rate (ROF or ζ) parameter (687), and a very high figure of merit (FOM) (about 233491). The bandpass filter (BPF) section was designed applying dual‐mode resonators with triband. The central frequencies of these tribands were equal to 2.38, 3.93, and 5.65 GHz. In the following, an SMV‐1247‐079LF SMD varactor diode is used to adjust the proposed LPF. The tuning range for the proposed LPF is 0.3‐0.72 GHz. In the proposed diplexer, the isolation between the output ports was higher than 45 dB. The results of measurements were in good agreement with those of the simulation.     

A New Design Approach for Nearly Linear Phase Stable IIR Filter using Fractional Derivative

In this paper,a new design method for digital infinite impulse response(IIR)filters with nearly linear-phase response is presented using fractional derivative constraints(FDCs).In the proposed method,design problem of an IIR frlter is constructed as the minimization of phase error between the desired and designed phase response of an allpass filter(APF)such that the designed lowpass filter(LPF)or highpass frlter(HPF)yields less passband(ep),and stopband errors(es)with optimal stopband attenuation(As).In order to have accurate passband(pb)response,FDCs are imposed on appropriate reference frequency,where the optimality of these FDCs are ensured by using a new greedy based sorting mechanism.The simulated results reflect the efficiency of the proposed method in term of improved passband response along with better transition width.However,small reduction in^is observed within the allowable limit,when compared to noin-fractional design approach,but the designed filter remains immune to wordlength(WL)effect.     

Design and fabrication of microstrip lowpass filter using asymmetric hairpin resonator

In this letter, a compact microstrip lowpass filter (LPF) is designed using serial connecting of two modified asymmetric hairpin resonators. The proposed design is consists of four open‐circuited stubs that are used to suppress spurious harmonics in the stopband. The proposed filter has wide‐stop band with attenuation level better than ?28 dB from 2.16 up to 26.1 GHz and sharp roll‐off. The proposed LPF has ?3 dB cutoff frequency equal to 2.11 GHz, wide stopband width around 12th harmonic suppression and insertion loss less than 0.1 dB at about 85% of the passband. The excellent agreement is observed between the simulated results and measured values of the fabricated LPF.     

Improved method for development of parsimonious orthonormal basis filter models

One of the major advantages of orthonormal basis filter (OBF) models is that they are parsimonious in parameters. However, this is true only if appropriate type of filter and reasonably accurate dominant poles of the system are used in developing the model. An arbitrary choice of filter type and poles may lead to non-parsimonious model. While the selection of the type of filter may be simple if the damping characteristics of the system are known, finding good estimates of the dominant pole(s) of the system is not a trivial task. Another important advantage of OBF model is the fact that time delays can be easily estimated and incorporated into the model. Currently, time delay of the system is estimated from the step response of the OBF model using the tangent method. While this method is effective in estimating the time delay of systems that can be accurately modeled by first order plus time delay (FOPTD) models, the accuracy is low for systems with second- and higher-order dynamics. In this paper, a scheme is proposed that will result in parsimonious OBF model and a better estimate of time delay starting from an arbitrary set of poles.     

Taylor series expansion based repetitive controllers for power converters,subject to fractional delays

Digital repetitive controllers are widely employed to track/reject the periodic signals with zero steady-state error. Their implementation involves the use of single or multiple digital delay elements. Practically, the delay element is implemented by the use of memory locations, where samples are held and released after a specific number of sampling periods, equivalent to the desired time delay. A problem arises when the desired time delay becomes a non-integer multiple of the sampling time. Such time delays can be accurately realized by employing a fractional delay filterThis paper presents a Taylor Series expansion based digital repetitive controller designed to implement any (integer, non-integer) delay in the control of power converters, occurring due to uncontrollable variations in the reference frequency. The T3644aylor Series expansion transforms the fractional delay filter design problem to a differentiator/sub-filter design. Finite impulse response (FIR) and infinite impulse response (IIR) fractional delay (FD) filter concepts can be applied to realize the required fractional delay. This structure provides efficient on-line tuning capabilities i.e. FD can easily generate any required fractional delay without redesigning the filter when the delay parameter varies. An example is demonstrated to show the effectiveness of this approach, for a single-phase power inverter feeding a passive load.     

数字锁定放大器中窄带低通滤波器的设计

根据锁定放大器的原理,讨论了应用于锁定放大器之中的低通滤波器的性能要求.从多采样率信号处理原理出发,提出了可满足锁定放大器要求的窄带低通滤波器的实现结构以及软件实现方法.最后通过DSP硬件仿真,验证了该窄带低通数字滤波器在锁定放大器中的性能.