Improved roundoff noise performance in a direct-form IIR filter using a modified delta operator

Among various direct-form delta operator filters, the delta direct-form II transposed (δDFIIt) has been shown to produce the lowest roundoff noise in finite-word-length implementations. Recent analyses focus on the optimization of the free parameter Δ of the delta operator, with scaling of the structure to prevent arithmetic overflow. This paper proposes a modified δDFIIt second-order section in which the Δs at different branches are separately optimized to further suppress roundoff noise gain. Noise variance plots against pole locations are presented. Closed-form expressions for the optimal filter coefficients are derived and reduction of noise gain is confirmed by numerical examples.published_or_final_versio

Roundoff noise minimization in a modified direct-form delta operator IIR structure

Among various direct-form delta operator realized filter structures, the delta transposed direct-form II (δDFIIt) has been shown to produce the lowest roundoff noise gain in finite wordlength implementations. Recent analyses focus on the optimization of the free parameter Δ of the delta operator, with scaling of the structure to prevent arithmetic overflow. This paper proposes a modified δDFIIt second-order section in which the Δs and filter coefficients at different branches are separately scaled to achieve improved roundoff noise gain minimization. Expressions for the filter coefficients are derived, and reduction of roundoff noise gain is verified by numerical examples.published_or_final_versio

NATURAL ALGORITHMS IN DIGITAL FILTER DESIGN

Digital filters are an important part of Digital Signal Processing (DSP), which plays vital roles within the modern world, but their design is a complex task requiring a great deal of specialised knowledge. An analysis of this design process is presented, which identifies opportunities for the application of optimisation. The Genetic Algorithm (GA) and Simulated Annealing are problem-independent and increasingly popular optimisation techniques. They do not require detailed prior knowledge of the nature of a problem, and are unaffected by a discontinuous search space, unlike traditional methods such as calculus and hill-climbing. Potential applications of these techniques to the filter design process are discussed, and presented with practical results. Investigations into the design of Frequency Sampling (FS) Finite Impulse Response (FIR) filters using a hybrid GA/hill-climber proved especially successful, improving on published results. An analysis of the search space for FS filters provided useful information on the performance of the optimisation technique. The ability of the GA to trade off a filter's performance with respect to several design criteria simultaneously, without intervention by the designer, is also investigated. Methods of simplifying the design process by using this technique are presented, together with an analysis of the difficulty of the non-linear FIR filter design problem from a GA perspective. This gave an insight into the fundamental nature of the optimisation problem, and also suggested future improvements. The results gained from these investigations allowed the framework for a potential 'intelligent' filter design system to be proposed, in which embedded expert knowledge, Artificial Intelligence techniques and traditional design methods work together. This could deliver a single tool capable of designing a wide range of filters with minimal human intervention, and of proposing solutions to incomplete problems. It could also provide the basis for the development of tools for other areas of DSP system design

Aktiivinen magneettinen suoja optisiin neuromagneettisiin mittauksiin

Optically-pumped magnetometers, based on optical measurement of the magnetization of an alkali vapor, are emerging as a promising alternative sensor for recording magnetic fields generated by the human brain. These sensors can only operate at very low absolute magnetic fields and therefore efficient shielding against the ambient magnetic field is required. The standard in biomagnetism is to use a passive magnetically shielded room to obtain sufficient shielding; however, the remanent magnetic field in a typical shielded room often exceeds the limits of these new magnetometers. In this thesis, a suitable ultra-low-field environment for the use of these sensors in Aalto University was set up. First, the magnetic fields inside the two- and three-layer magnetically shielded rooms of Aalto University were surveyed and then a portable active compensation system for further reducing the fields was built. Without compensation, the measured remanent magnetic fields were on the order of 100 nT and 5 nT in the two- and three-layer rooms while the gradients were about 40 nT/m and 5 nT/m, respectively. Both rooms had low-frequency field drifts of approximately 1 nT in a measurement period of 200 s. With the constructed compensation coil set, the static field could be reduced by a factor of about 10 in a head-sized volume. The feedback loop of the compensation system was also capable of locking the field to zero at the sensor site and could also remove the low-frequency fluctuations in the field. This study showed that neuromagnetic measurements with optically-pumped magnetometers should be feasible in standard shielded rooms by utilizing the constructed compensation system.Optisesti pumpatut magnetometrit, jotka perustuvat alkalimetallikaasun magnetisaation optiseen mittaukseen, ovat lupaavia vaihtoehtoisia antureita ihmisaivojen synnyttämien magneettikenttien rekisteröimiseen. Nämä sensorit toimivat vain hyvin alhaisissa magneettikentissä, joten tehokkaita menetelmiä tarvitaan ympäröivältä magneettikentältä suojautumiseen. Tyypillisesti biomagneettisia kenttiä mitattaessa vaadittava suojaus on saatu käyttämällä passiivista magneettisesti suojattua huonetta; jäännöskenttä tyypillisen suojahuoneen sisällä kuitenkin ylittää optisten magnetometrien vaatimukset. Tämän työn tarkoituksena oli luoda suotuisa magneettinen ympäristö Aalto-yliopistoon näiden anturien käyttöä varten. Ensiksi remanenssimagneettikentät Aallon kaksi- ja kolmikerrossuojahuoneissa mitattiin ja mallinnettiin, jonka perusteella suunniteltiin ja rakennettiin liikuteltava aktiivinen kompensointijärjestelmä näiden kenttien pienentämistä varten. Mitatut remanenssikentät olivat suuruusluokaltaan 100 nT kaksikerroshuoneessa ja 5 nT kolmikerroshuoneessa; gradientit olivat vastaavasti noin 40 nT/m ja 5 nT/m. Kentän matalataajuiset fluktuaatiot olivat noin 1 nT:n luokkaa molemmissa huoneissa mittausajan ollessa 200 s. Rakennetulla kompensointijärjestelmällä suojahuoneiden staattinen kenttä pystyttiin pienentämään kymmenesosaan pään kokoisessa tilavuudessa. Järjestelmän takaisinkytkentäsilmukka pystyi nollaamaan kentän anturin kohdassa ja poistamaan matalataajuiset häiriöt kentästä. Tämä työ osoitti, että rakennettua kompensointijärjestelmää käyttämällä optisesti pumpatuilla magnetometreillä voidaan tehdä herkkiä neuromagneettisia mittauksia tyypillisissä magneettisesti suojatuissa huoneissa

Digital signal processing algorithms and structures for adaptive line enhancing

Imperial Users onl

Digital Filters and Signal Processing

Digital filters, together with signal processing, are being employed in the new technologies and information systems, and are implemented in different areas and applications. Digital filters and signal processing are used with no costs and they can be adapted to different cases with great flexibility and reliability. This book presents advanced developments in digital filters and signal process methods covering different cases studies. They present the main essence of the subject, with the principal approaches to the most recent mathematical models that are being employed worldwide

Finite worldlength effects in fixed-point implementations of linear systems

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (p. 173-194).by Vinay Mohta.M.Eng

Digital Filters

The new technology advances provide that a great number of system signals can be easily measured with a low cost. The main problem is that usually only a fraction of the signal is useful for different purposes, for example maintenance, DVD-recorders, computers, electric/electronic circuits, econometric, optimization, etc. Digital filters are the most versatile, practical and effective methods for extracting the information necessary from the signal. They can be dynamic, so they can be automatically or manually adjusted to the external and internal conditions. Presented in this book are the most advanced digital filters including different case studies and the most relevant literature

Real-time flutter identification

The techniques and a FORTRAN 77 MOdal Parameter IDentification (MOPID) computer program developed for identification of the frequencies and damping ratios of multiple flutter modes in real time are documented. Physically meaningful model parameterization was combined with state of the art recursive identification techniques and applied to the problem of real time flutter mode monitoring. The performance of the algorithm in terms of convergence speed and parameter estimation error is demonstrated for several simulated data cases, and the results of actual flight data analysis from two different vehicles are presented. It is indicated that the algorithm is capable of real time monitoring of aircraft flutter characteristics with a high degree of reliability