Direct design of transitional Butterworth-Chebyshev recursive digital filters

A simple method for the approximation of an all-pole transfer function directly in the digital domain for the design of recursive digital filters is described. The transfer function of these filters, referred to as transitional Butterworth-Chebyshev filters, has properties that lie between Butterworth and Chebyshev functions.<>     

Transitional Murromaf?Murroer filters

A new class of lowpass filters with all transmission zeros at infinity, having equal-ripple behaviour in the passband, is described. The transfer function of these filters, referred to as transitional Murromaf-Murroer filters, is obtained by adding the multiple real poles and reducing the number of complex pole pairs to realise a lowpass RC active filter with a reduced number of amplifiers with respect to the classical transitional Butterworth-Cheby?shev filters.     

Transitional Halpern-Thomson filters

A new class of lowpass filter, with all transmission zeros at infinity, having a monotonic passband response is described. The transfer function of these filters, referred to as transitional Halpern-Thomson (t.h.t.) filters, depends on a variable parameter that enables a tradeoff between, the overshoot and the risetime in response to a unit-step input.     

Transitional MURROMAF-MURROER filters with additional members

Recently, a method [4] has been described for the design of transitional MURROMAF-MURROER filters whose members exhibit odd numbers of passband ripple peaks. An additional technique is proposed here to find also those with even numbers of the ripple peaks. Hence, transitional MURROMAF-MURROER filters with complete transitional members.     

B-spline design of maximally flat and prolate spheroidal-type FIRfilters

A digital FIR filter is described that offers excellent passband and stopband characteristics for general applications. Design formulae include parameters that adjust the magnitude response from one having characteristics like the maximally flat designs of Hermann (1971) and Kaiser (1975, 1979) to one having characteristics like the minimum-sidelobe energy approximations of Kaiser and Saramaki (1989). The impulse response coefficients are more straightforward to obtain than these filter designs while offering preferable response characteristics in many instances. Unlike FIR filters designed by window- or frequency-sampling methods, the filter coefficients are determined from the inverse Fourier transform in closed form once B-splines have been used to replace sharp transition edges of the magnitude response. Although the filters are developed in the frequency domain, a convergence window is identified in the convolution series and compared with windows of popular FIR filters. By means of example, adjustment of the transitional parameter is shown to produce a filter response that rivals the stopband attenuation and transition width of prolate spheroidal designs. The design technique is extended to create additional transitional filters from prototype window functions, such as the transitional Hann window filter. The filters are particularly suitable for precision filtering and reconstruction of sampled physiologic and acoustic signals common to the health sciences but will also be useful in other applications requiring low passband and stopband errors     

Tables for Butterworth-digital-filter design

A method for constructing tables for digital-filter design is described. Filters whose transfer functions are similar to those of Butterworth analogue filters are considered.     

On the theory of chained-function filters

For the first time, the new class of filter transfer functions, called chained-function filters, is described in theoretical detail. The chained-function concept can give a variety of transfer functions, having the same order, but different frequency domain, time domain, and implementation characteristics. As a result, a filter can be selected to have the required reduction in sensitivity to manufacturing errors, resonator unloaded-Q, and filter losses. This can be achieved while maintaining a given return-loss level and a predetermined out-of-band rejection performance that is comparable with conventional Chebyshev filters. The transfer-function formulations are given in detail, as well as the analysis of frequency- and time-domain responses, resonator unloaded-Q requirements, and filter loss responses. Theoretical comparison with conventional Chebyshev filter characteristics confirm the already demonstrated advantages of this new family of filter transfer functions.     

Least-squares magnitude filters with self-equalised delay characteristic

A new class of nonminimum-phase transfer functions with one pair of real-axis transmission zeros is described. These functions are suitable for determining the lowpass prototype networks in the design of narrow bandpass filters at microwave frequencies with small passband loss and very flat delay response over the central part of the passband.     

Dual-Mode Canonical Waveguide Filters

This paper introduces a new form of dual-mode narrow-bandpass waveguide cavity filter. The filters, which can be constructed from either dual mode circular or square waveguide cavities, can realize the optimum transfer functions (including the exact elliptic function response). One of the unique features of these filters is that all the intercavity coupling irises may take the form of circular holes rather than long narrow slots. Several alternative input-output configurations are described. Experimental results on several filters indicate excellent agreement with theory.     

Chebyshev过渡型滤波器设计和分析

传统的Chebyshev滤波器具有较差的相位特性,其阶跃响应具有较大的过冲和较长的调节时间。本文从传递函数的极点角度,对Chebyshev滤波器进行了改进,改进后的滤波器表现出典型的过渡特性,在对幅度特性影响较小的情况下,改善了传统Chebyshev滤波器的相位特性和阶跃响应。通过对滤波器极点的调整,消除了传统Chebyshev滤波器过冲和传统偶数阶Chebyshev滤波器的稳态误差。     

Cascade Directional Filter

A directional filter is a completely matched four-port which exhibits a directional and a filter-like frequency characteristic. This paper explores the properties of N-directional filters connected in cascade through sections of transmission lines. Analysis shows that if a directional filter admits the equivalent circuit representation offered here, its transfer functions are functions of only one parameter, a susceptance function. When the directional filters are cascaded in a certain way, the overall transfer functions have the same form as before except that the susceptance function is now the sum of the susceptance functions of the component filters. The last property is an important one. Given a transfer function expressed in terms of a susceptance function, the network designer can expand the susceptance in partial fraction and realize the transfer function using directional filters in cascade, each being characterized by a much simpler susceptance.     

聚合物微环谐振滤波器特性的研究

利用耦合模理论,计算了聚合物微环谐振滤波器的通路和下话路的传输函数,分析了耦合系数和损耗对传输函数的影响,并推导出了谐振滤波器的谐振波长、自由光谱范围、腔的品质因子、半峰全宽和精细度等特性参数,分析了不同的滤波器结构参数(如环形半径和有效折射率)对滤波特性的影响.     

Synthèse et réalisation de filtres hyperfréquences à cavités bimodes ayant une réponse en fréquence dissymétrique

This article presents the study and the realization of microwave filters with asymmetric frequency characteristics using dual-mode cylindrical cavities. The synthesis method of such characteristics using generalized Chebyshev transfer functions is described. These functions allow the realization of symmetrically or asymmetrically prescribed transmission zeros. The method consists in synthetizing a generalized low-pass filter, in order to calculate the coupling matrix, the dual-mode structure has to realize. Concerning the practical design of the filter, a method is described for the realization of asymmetric characteristics with dual-mode cavities. Several measured characteristics of different laboratory models are presented.     

OTA-C realisation of general high-order transfer functions

OTA-C technology has become a very important topic in continuous-time integrated circuits owing to its advantages over other realisation techniques. In the research of OTA-C filters, the synthesis of second-order filters has been widely investigated but the realisation of high-order transfer functions has not received similar attention. The authors propose a novel higher-order OTA-ground capacitor network and explicitly formulate realisation techniques for general transfer functions.<>     

Lightwave lattice filters for optically multiplexed communicationsystems

It has proven desirable to use multistage etalons and resonators in lightwave communication systems. The design of these linear structures, however, is made difficult by the manner in which their transfer functions are nonlinear with respect to their composite reflection coefficients. If we interpret the etalons as discrete-time lattice filters, then z-transform techniques may be used to recursively synthesize filters with desirable properties. An algorithm is developed which can be used to design the arbitrary all-pole transfer functions in transmission, and the restricted class of pole-zero transfer functions in reflection, which are possible to implement with this architecture. We present some design examples such as notch, or channel-blocking, filters and flat-top bandpass, or channel-passing, filters which are appropriate for frequency-division multiple access and wavelength-division multiplexed communications systems. The theory predicts, and we show experimentally, how these structures may be used to discriminate, or route, signals based on their modulated or coded characteristics     

Novel realization of monotonic Butterworth-type lowpass, highpass,and bandpass optical filters using phase-modulated fiber-opticinterferometers and ring resonators

A novel realization of monotonic Butterworth-type lowpass, highpass, and bandpass optical filters (from their electrical digital filter characteristics) by cascading the all-pole and all-zero resonators is presented. A graphical method for fast derivation of the transfer functions, quick inspection of the resonance effects, and important characteristics of any photonic circuits is described. It is shown that incorporation of the optical amplifiers and optical phase modulators into the delay lines of two basic optical resonators, whose pole and zero can be adjusted independently of each other, provides great design flexibility which would otherwise not possible using conventional passive optical resonators. Possible applications of these optical filters as optical pulse equalizers and receiver shaping filters in long-haul coherent lightwave transmission systems are discussed. Possible application of basic resonators comprising of optical phase modulators as tunable optical filters for spectrum analyzers is also considered     

An optimum generalized cross-spectrum symbol-rate detector

The optimal design of a precorrelation filtering system for use in cross-spectrum symbol-rate detectors in the presence of additive Gaussian noise is described. This approach generalizes practical cross-spectrum symbol-rate detectors, and derives a necessary condition which achieves the maximum processed signal-to-noise ratio at an integer multiple of the symbol rate. The resultant optimum condition depends on the transfer functions of precorrelation filters and fixed signal model parameters. As a by-product, a performance measure applicable to any quadrature amplitude modulation format and including the effects of self-noise and intersymbol interference is derived. An algorithm for constructing physically realizable precorrelation filters that satisfy the optimum condition is given to complete the design process     

Implementation of 2-D denominator-separable digital filters using first-order all-pass sections

It is established that denominator-separable transfer functions which characterize an important subclass of 2-D filters can be expressed as a linear combination of first-order (1-D or 2-D separable) all-pass transfer functions with real or complex coefficients. This type of expansion is referred to as all-pass expansion of the corresponding transfer function. Based on this all-pass expansion, we derive some efficient structures for the realization of 2-D denominator-separable filters using all-pass sections.On leave from S.V. University College of Engineering. Tirupati-517502, India.     

Transfer functions of wave-digital filters

The letter presents a numerical algorithm for computing the polynomial coefficients of the transfer functions of a class of wave-digital filters derived from all-pole reference filters, given the multiplier coefficients.     

Synthesis of Elliptic Optical Filters Using Mutually Coupled Microring Resonators

Integrated optical filters having elliptic transfer functions are proposed using two-dimensional arrays of synchronously tuned mutually coupled microring resonators. Analysis of microring filter topologies of the most general form is facilitated by the formulation of an energy-coupling matrix for the microring array. A method for synthesizing elliptic microring filter transfer functions having the prescribed transmission poles and zeros is also presented. The approach involves representing the microring filter by an equivalent electrical network of coupled LC oscillators and applying the coupling matrix technique developed for micro-wave filters to determine the coupling parameters. An example of a sixth-order elliptic function filter is presented to demonstrate the feasibility of using mutually coupled microring resonators to realize optical filters having finite transmission zeros in the transfer function