时变级联滤波器的两种设计方法

本文针对雷达杂波抑制中常用的时变级联滤波器,提出了两种实用的设计方法。第一种方法通过时变级联滤波器与时变非级联滤波器的等效来设计时变级联滤波器。该方法可以使时变级联滤波器具有最佳杂波滤波器的效果。第二种方法通过对总的等效滤波器的设计来得到级联滤波器第二级的权系数。分析表明,时变级联滤波器第二级的频率响应很难写出,但可以通过总的等效频率响应来体现。     

TWO APPROACHES TO THE DESIGN OF TIME-VARYING CASCADED FILTERS

Two approaches to the design of time-varying cascaded filters used in radar clutter rejection are presented. In the first approach, by fitting the cascaded filter to the noncascaded filter, the time-varying cascaded filter can be designed, which makes it possible that the time-varying cascaded filter behaves just like an optimum clutter filter. The second approach can be used to design the second-stage filter in a time-varying cascaded one by setting zeros in its equivalent overall frequency response. It has been shown that it is difficult to express the frequency response of the second-stage filter in the time-varying cascaded one, however, it is convenient to be involved in the overall response.     

A dynamic frequency grid allocation scheme for the efficient designof equiripple FIR filters

In the design of a digital filter, the frequency response is often optimized to meet a given set of specifications on a dense grid of frequency points. The density of the frequency grid points must be sufficiently high so that the frequency response of the filter does not violate the specifications at frequencies in between the grid points. However, the computational complexity of the design process and the storage requirements of the computer increase with the number of frequency grid points. We propose a novel dynamic: grid point allocation technique for the design of minimax optimum FIR filter. It uses a sparse frequency grid but will produce a design that is the same as one designed on very dense frequency grid points. It requires significantly less computer time and memory resources compared with fixed grid point algorithms     

A weighted least squares algorithm for quasi-equiripple FIR and IIRdigital filter design

It has been demonstrated by several authors that if a suitable frequency response weighting function is used in the design of a finite impulse response (FIR) filter, the weighted least squares solution is equiripple. The crux of the problem lies in the determination of the necessary least squares frequency response weighting function. A novel iterative algorithm for deriving the least squares frequency response weighting function which will produce a quasi-equiripple design is presented. The algorithm converges very rapidly. It typically produces a design which is only about 1 dB away from the minimax optimum solution in two iterations and converges to within 0.1 dB in six iterations. Convergence speed is independent of the order of the filter. It can be used to design filters with arbitrarily prescribed phase and amplitude response     

Recirculating fiber-optic notch filter employing fiber gratings

We present here a new recirculating fiber-optic notch filter employing fiber Bragg gratings, in which both the filter notch depth and free-spectral range can be configured so to give an optimum frequency response     

An elliptic continuous-time CMOS filter with on-chip automatic tuning

A voice-band continuous-time filter is described which was designed based on the technique of fully balanced networks and was fabrication in a 3.5-/spl mu/ CMOS technology. The filter implements a fifth-order elliptic low-pass transfer function with 0.05-dB passband ripple and 3.4 kHz cutoff frequency. A phase-locked loop control system fabricated on the same chip automatically references the frequency response of the filter to an external fixed clock frequency. The cutoff frequency was found to vary by less than 0.1% for an operating temperature range of 0-85/spl deg/C. The absolute value accuracy of the cutoff frequency was 0.5% (standard deviation). With /spl plusmn/5-V power supplies the measured dynamic range of the filter was approximately 100 dB.     

Optimization of the frequency response of a semiconductor opticalamplifier wavelength converter using a fiber Bragg grating

Cross-gain modulation in a semiconductor optical amplifier (SOA) is one of the simplest techniques for all-optical wavelength conversion. However, the finite gain recovery time of the semiconductor optical amplifier causes distortion and pattern dependence at high bit rates. Here we show that filtering the output of a semiconductor optical amplifier wavelength converter with the transmission edge of a fiber grating filter improves its frequency response. The grating sharpens the transition between the bits by converting the phase modulation at the edge to useful amplitude modulation. We determine the filtering condition that produces the optimum frequency response and reduces bit-pattern dependence for nonreturn-to-zero (NRZ) data. For small modulation, the apparent frequency response increases by the linewidth enhancement factor α_H of the SOA. In this case, pattern dependence is eliminated completely by the fiber grating filter. For large modulation, pattern dependence can be substantially reduced, but not completely eliminated. We show that after spectral filtering, the residual pattern dependence of an SOA depends only on modulation depth. For a given SOA, we find the optimum grating for minimum conversion penalty at 12 Gb/s for a wide range of operating parameters. Using a fiber grating filter reduces the required optical power for conversion in a semiconductor optical amplifier     

An iterative algorithm for optimal design of non-frequency-selective FIR digital filters

This paper proposes a novel iterative algorithm for optimal design of non-frequency-selective Finite Impulse Response （FIR） digital filters based on the windowing method. Different from the traditional optimization concept of adjusting the window or the filter order in the windowing design of an FIR digital filter, the key idea of the algorithm is minimizing the approximation error by successively modifying the design result through an iterative procedure under the condition of a fixed window length. In the iterative procedure, the known deviation of the designed frequency response in each iteration from the ideal frequency response is used as a reference for the next iteration. Because the approximation error can be specified variably, the algorithm is applicable for the design of FIR digital filters with different technical requirements in the frequency domain. A design example is employed to illustrate the efficiency of the algorithm.     

Optimization of RC active filters for extended bandwidth operation

An optimization procedure is suggested that maximizes the highest usable frequency of operation of active RC filters for a given permissible value of deviation of the actual response from the expected one. The procedure is applied to a recently reported filter, and both the theoretical as well as the practical results are given that confirm the effectiveness of the approach.     

Digital Laguerre filter design with maximum passband-to-stopband energy ratio subject to peak and Group delay constraints

In this paper, we formulate a general design of transversal filter structures with maximum relative passband-to-stopband energy ratio subject to complex frequency response constraints in the passband and the stopband as well as additional constraints such as constraints. These constraints are important for applications where the suppression of noise at certain frequencies are important. Additional constraints are introduced allowing approximately linear phase and constant group delay in the passband. For a given set of basis functions, the design problem can be formulated as a semi-infinite quadratic optimization problem in the filter coefficients, which are the decision variables to be optimized. In this paper, we focus on the design of digital Laguerre filter and digital finite impulse response (FIR) filter structures. A modified bridging algorithm is developed for searching for the optimum pole of the Laguerre filters. Design examples are given to demonstrate the effectiveness of the proposed algorithm.     

Optimal FIR filter for suppression of power line frequency component

In this paper a design technique for multiband FIR filter for DC and power line frequency component suppression is described. The digital filter has a linear phase characteristic and equiripple amplitude characteristic in the passband. The amplitude characteristic of this filter satisfies the alternation theorem and consequently has the lowest complexity in obtaining a prescribed maximum deviation in the passband and the fastest possible rate of attenuation near the cutoff frequency. In this sense this filter is optimal. Closed-form expressions for direct calculation of filter coefficients, cutoff frequency and maximal passband attenuation are derived.     

基于直扩的伪码频偏估计

提出了一种基于直接序列扩频信号的伪码频偏估计方法。介绍了解扩原理,包括中频采样、数字下变频、相关累积、伪码频率估计、环路滤波和伪码跟踪等。分析了伪码频偏估计的具体方法:伪码搜索的方法实现伪码大频偏的粗略估计;用锁相环实现伪码的同步;对锁相环的相位误差的提取,环路滤波器的结构和参数给出了具体的实现方法和表达式,并对环路等效噪声带宽的选取及其影响进行了讨论。     

Using a Genetic Algorithm to Optimize Capacitance Ratio Approximations in SC Filters

Accurate capacitance matching is one of the main design issues in switched-capacitor (SC) filters. Using identical unit capacitors in parallel to implement each filter capacitor, combined with a careful layout design, can provide an accuracy of 0.1% in the filter coefficients. The disadvantage of this technique is the fact that it can be directly applied only if the coefficients can be expressed as ratios of integer numbers. As a result, coefficient approximations are required, leading to frequency response errors. In this paper, a genetic algorithm (GA) is used to find the optimum capacitance ratio approximations by rational numbers that minimize the total number of unit capacitors for a given error tolerance in the frequency response. Design examples in 0.35 μm CMOS are presented and simulated to illustrate the proposed approach and verify its effectiveness.     

Analysis and optimization of DS-CDMA systems with time-limited partial response chip waveforms

Conventional direct sequence code division multiple access systems (DS-CDMA) using offset quadrature phase shift key (OQPSK) usually employ a strictly bandlimited partial response square-root raised cosine pulse as the chip waveform. They have the disadvantage of large envelope fluctuation that will incur performance degradation due to the intermodulation and bandwidth enlargement caused by post nonlinear processing. To improve the performance of DS-CDMA systems, the chip waveform and receiver should be properly selected. This paper presents a systematic performance analysis of a matched filter receiver and zero-forcing filter (ZF) receiver for DS-CDMA using a time-limited partial response chip waveform. Nevertheless the systematic performance analysis is applicable to bandlimited chip pulse as well. For the zero-forcing filters, we propose to select the frequency responses that satisfy the first Nyquist criterion. With this class of filters, we can choose the roll-off factor to minimize the total power of multiple access interference and noise power. The zero-forcing filter with proper choice of roll-off factor, referred to as optimum ZF, yields a performance better than the matched filter counterpart. The bit error rate (BER) performance of the optimum ZF with superposed quadrature amplitude modulation signal as the time pulse waveform is evaluated. It is shown that the optimum ZF provides better BER performance than conventional OQPSK and minimum shift keying, and its envelope uniformity is much better than that of OQPSK.     

软件接收机中DSB-SC信号载波同步的一种算法

本文提出了软件妆收机中抑制载波双边带调幅（DSB-SC）信号载波同步的一种算法，根据下变频后的基带信号估计出收发载波的频差，并经卡尔曼滤波后结合数字锁相环以达到载波捕获范围宽、跟踪速度快、环路噪声小的特点。文章最后给出了一个具体实例的仿真结果。     

Structure of optimum receiving filters in data transmission systems (Corresp.)

It has been observed by several authors that a number of different optimum receiving filters (corresponding to different criteria of goodness) for sampled-data transmission systems can be factored as a product of a matched filter and a periodic filter with the period equal to the sampling frequency. By a simple argument it is shown in this correspondence that any reasonable criterion of goodness will lead to an optimum filter that has this form.     

Modulation frequency characteristics of directly optical frequency modulated AlGaAs semiconductor laser

Optical frequency spectra of directly frequency modulated AlGaAs semiconductor laser in the 0?5.2 GHz range were measured by using a Fabry-Perot interferometer and a birefringent optical filter. The frequency deviation is linearly proportional to the RF modulation current. The measured modulation frequency characteristics for the frequency deviation show that the thermal effect is predominant in the frequency below 10 MHz. It has a resonance peak which behaves just like the peak observed in the modulation. Experimental results agreed well with theoretical values calculated by considering thermal effect and carrier-dependent refractive index variation.     

基于遗传算法的递归式MTI滤波器的设计

递归式MTI滤波器从理论上讲几乎可以合成任意形状的频率响应函数,因而具有很广的应用范围。为了能够灵活设计出满足系统要求的递归式MTI滤波器,提出了一种设计方法。该方法以遗传算法(GA)的基本思想为基础,利用滤波器的改善因子、通带宽度和通带波纹来构成适应函数,并用GA来加快参量搜索速度和获取全局近似最优解。实验仿真设计了两种典型的递归式MTI滤波器,结果证明该方法是一种有效的设计方法,它可以灵活而快速地设计出所需要的滤波器。     

An Optimal Control Method for Buck ConvertersUsing a Practical Capacitor ChargeBalance Technique

A novel control method is presented in this paper which utilizes the concept of capacitor charge balance to achieve optimal dynamic response for Buck converters undergoing a rapid load change. The proposed charge balance method is implemented with analog components and is cheaper and more effective than its digital counterparts since complex arithmetic and sampling delay is eliminated. The proposed controller will consistently cause the Buck converter to recover from an arbitrary load transient with the smallest possible voltage deviation in the shortest possible settling time. Since the controller is nonlinear during transient conditions, it is not limited by bandwidth/switching frequency. Unlike conventional linear controllers, the dynamic response (voltage deviation, settling time) of the proposed controller can be estimated using a set of equations. This greatly simplifies the design process of the output filter. Simulation and experimental results show the functionality of the controller and demonstrate the superior dynamic response over that of a conventional linear controller.      

A fast adaptive resonance suppression scheme for high-damping system using R-SDFT detection

Adaptive notch filter resonance suppression scheme is widely used in high-performance servo drivers. For high-damping system, the deviation between resonant and oscillation frequency will cause a long sustained vibration in traditional suppression schemes, which may damage the precision machine irreparably. To reduce the harm of sustained vibration, a fast adaptive notch filter scheme based on range-shifted discrete Fourier transform (R-SDFT) is proposed. Different from the traditional scheme, the new one eliminates the deviation between resonant and oscillation frequency by notch filter other than the low-pass filter, which massively simplifies the suppression process and reduces the number of oscillation frequency detection required. Meanwhile, an oscillation detection method based on R-SDFT is presented to shorten the time of the detective process through interval detection and prediction strategy. Compared with the traditional strategy, the experimental results demonstrate that the proposed adaptive suppression scheme can reduce the oscillation time by more than half.