A step-by-step active-filter design

This article presents, in a simplified manner, a design method for active filters intended for those who are not filter specialists. By following the described five-step approach, a circuit designer who has some knowledge of passive filters will (without having to learn a whole new technology) be able to design active filters just as easily as he now handles conventional passive filters. Starting with the filter specification, it is shown sequentially how to realize a network that meets the prescribed requirements. Configurations and element values are given for the low-pass (LP), bandpass (BP), high-pass (HP), all-pass (AP), and band-elimination (BE), second-order active filter building blocks.     

Compensation strategies for shunt active-filter control

Compensation strategies for control of shunt active filters are compared in the paper. It is shown that the strategy based on unity-power factor control is appropriate when the supply voltage waveform of the plant where the active filter is connected shows significant distortion. As voltage distortion increases, this strategy provides compensated line current having lower harmonic distortion and RMS value with respect to the strategy generally used. This contributes to diminish the current and voltage distortion in networks. The unity-power factor compensation strategy conditions the current flowing in the plant where compensation is realized to fit the voltage waveform, thus reaching a unity power factor. Hence, the line current RMS value is minimum. The comparison of the strategies is performed by both Monte Carlo and ATP simulation     

Approximate transfer functions for multivariable systems

An approximation, valid over a limited region of the s plane, is given to a single path in a multivariable system. The inference of system instability from instability of this approximate transfer function is discussed, and it is shown that it is not sufficient for the approximation to be valid over a region of the real-frequency axis alone. This point is demonstrated by an example.     

Rotator and reflector for transfer functions

A practical solution of the problem of the transformation of a nonlinear 2-port voltage transfer function T=Uy/Ux is presented. The proposed structure consists of summers and its features are analogous to the features of the Chua's rotator or reflector for driving-point functions.     

Novel g.i.c. suitable for RC active-filter applications

A novel generalised immitance convertor (g.i.c.) is described that uses a high-quality nullor-type analogue gain block. The usefulness of this g.i.c. is experimentally confirmed by means of a simulated-inductance high-order 20?24 kHz bandpass-filter implementation.     

Stray-insensitive switched-capacitor-network realisation for voltage transfer functions

A signal-flow-graph synthesis procedure for the realisation of z-domain voltage transfer functions using an operational amplifier and switched capacitors is presented.     

Low-order realizations for 2-D transfer functions

In this note, a realization result for casual 2-D transfer functions with separable numerator or separable denominator is generalized. A possible dimension of the local state space will be determined and system matrices will be given.     

Modelling of acoustic transfer functions for echo cancellers

ARMA modelling (infinite impulse response filters having both poles and zeros), rather than MA modelling, of acoustic transfer functions is potentially capable of reducing the number of coefficients required to achieve a given level of echo cancellation. The amount of reduction obtainable, however, has received little attention in the literature. To arrive at quantitative figures for the complexity reduction possible, equation error and output error ARMA and MA modelling of acoustic impulse responses are compared experimentally. It is shown, for both fullband and subband implementations, that the potential for reducing the number of coefficients required is small     

Robust algorithm for estimation of time-varying transfer functions

We introduce a new method to estimate reliable time-varying (TV) transfer functions (TFs) and TV impulse response functions. The method is based on TV autoregressive moving average models in which the TV parameters are accurately obtained using the optimal parameter search method which we have previously developed. The new method is more accurate than the recursive least-squares (RLS), and remains robust even in the case of significant noise contamination. Furthermore, the new method is able to track dynamics that change abruptly, which is certainly a deficiency of the RLS. Application of the new method to renal blood pressure and flow revealed that hypertensive rats undergo more complex and TV autoregulation in maintaining stable blood flow than do normotensive rats. This observation has not been previously revealed using time-invariant TF analyses. The newly developed approach may promote the broader use of TV system identification in studies of physiological systems and makes linear and nonlinear TV modeling possible in certain cases previously thought intractable.     

Evaluation of transfer functions for punctured turbo codes

A modified algorithm for evaluating transfer functions of turbo codes with punctured systematic bits is presented. The obtained transfer function leads to a more accurate estimation of the weight distribution of the code. Consequently, a tighter upper bound on the bit error rate performance of the code is obtained     

Quasi-Linear allocation functions for efficient array design

We propose a class of functions called quasi-linear functions to be used as allocation functions in systolic array synthesis. We describe the special properties of such functions that make them suitable as allocation functions, and give necessary and sufficient conditions that they must satisfy. The main advantage of quasi-linear allocation functions is that they provide a unified framework for dealing with a technique called clustering which is often used as apost-processing technique to improve the efficiency of systolic arrays. We show that it is always possible to choose quasi-linear allocation functions so that the derived arrays have 100% efficiency. Our method is constructive and the allocation function can be obtained automatically. We also generalize our result to deal witharbitrary systolic arrays (outside the context of synthesis). The technique can also be extended to any (piece-wise) systolic array to derive arrays with 100% efficiency.Supported by NSF grant MIP-8802454.     

Realization of two-variable transfer functions

The state-space realization from the given two-variable transfer function has been described using newly defined Markov parameters and a moments of impulse response matrix.     

New conversion methods for realizing nonminimum phase transfer functions

New methods are described for converting second-order active-RC low-pass, high-pass, and bandpass filters to obtain nonminimum phase-transfer characteristics. Some of the realizations obtained are superior to other realizations arrived at using well-known conversion methods. Design equations for each realization are summarized in a table. Experimental results are included.     

Simplified procedure for indirect tests of optical-fibre transfer functions

Differential mode delays and attenuations are measured by scanning the fibre output field, at one source modulation frequency. The results allow a simple evaluation of the baseband transfer function. A cylindrical lens can be used to simplify the data collection.     

Minimal positive realizations for a class of transfer functions

It is a standard result in linear-system theory that an nth-order rational transfer function of a single-input single-output system always admits a realization of order n. In some applications, however, one is restricted to realizations with nonnegative entries (i.e. a positive system), and it is known that this restriction may force the order N of realizations to be strictly larger than n. In this brief we present a class of transfer functions where positive realizations of order n do exist. With the help of our result we give improvements on some earlier results in positive-system theory.     

Strays-insensitive switched-capacitor network realisation for nth-order voltage transfer functions

A general synthesis method is given for the realisation of nth-order voltage transfer functions in the z-domain by active SC (switched-capacitor) networks using only biphased switches, capacitors and ideal operational amplifiers. The method presented is based on signal-flow graphs and the resulting networks are completely insensitive to stray capacitances.     

Using nullors for realisation of inverse transfer functions andcharacteristics

A general method is proposed for obtaining the inverse transfer function (for linear dynamic systems) and the inverse transfer characteristic (for nonlinear resistive circuits). The presented method makes use of nullors, known to be the most important active circuit elements. The procedure, initially introduced to obtain the system inversion for circuits already containing nullors, can easily be extended to any general circuit     

Verifications of the Kalman conjecture for irrational transfer functions

The sufficient conditions for the Kalman conjecture to be satisfied given by Fannin and Rushing [1] are relaxed in such a way as to allow their approach to be applied to irrational transfer functions. Specific results for a class of systems containing transportation lag are presented.