Showing papers on "Transfer function published in 2004"

Complex signal processing is not complex

Abstract: Wireless systems often make use of the quadrature relationship between pairs of signals to effectively cancel out-of-band and interfering in-band signal components. The understanding of these systems is often simplified by considering both the signals and system transfer functions as "complex" quantities. The complex approach is especially useful in highly integrated multistandard receivers where the use of narrow-band fixed-coefficient filters at the RF and high IF must be minimized. This paper first presents a tutorial review of complex signal processing for wireless applications. The review emphasizes a graphical and pictorial description rather than an equation-based approach. Next, a number of classical modulation architectures are described using this formulation. Finally, more recent developments such as complex filters, image-reject mixers, low-IF receivers, and oversampling analog-digital converters are discussed.

Procedures for detecting winding displacements in power transformers by the transfer function method

Abstract: The paper investigates three different ways of using the transfer function method for detecting mechanical winding displacements in power transformers. The most reliable approach is time-based comparison , which requires finger print data from a previous measurement. Such information is, however, usually not available. For multilegged transformers without zigzag-connected windings the results of separately tested legs can be used as mutual references (construction-based comparison ). A third approach is to compare the transfer functions with those obtained from an identically constructed transformer ( type-based comparison). However, for a transformer with given nominal specification data, the winding design may over time undergo changes which causes changes to the transfer function. It is proposed to solve this problem by calculating tolerance bands using transfer functions from a big group of the same-type transformers. A novel statistical algorithm for this purpose is presented. The approach is demonstrated for a set of 28 specified identically 200-MVA power transformers.

Analysis of charge-pump phase-locked loops

Abstract: In this paper, we present an exact analysis for third-order charge-pump phase-locked loops using state equations. Both the large-signal lock acquisition process and the small-signal linear tracking behavior are described using this analysis. The nonlinear state equations are linearized for the small-signal condition and the z-domain noise transfer functions are derived. A comparison to some of the existing analysis methods such as the impulse-invariant transformation and s-domain analysis is provided. The effect of the loop parameters and the reference frequency on the loop phase margin and stability is analyzed. The analysis is verified using behavioral simulations in MATLAB and SPECTRE.

Optimal filters for extended optical flow

Abstract: Estimation of optical flow and physically motivated brightness changes can be formulated as parameter estimation in linear models. Accuracy of this estimation heavily depends on the filter families used to implement the models. In this paper we focus on models whose terms are all data dependent and therefore are best estimated via total-least-squares (TLS) or similar estimators. Using three different linear models we derive model dependent optimality criteria based on transfer functions of filter families with given fixed size. Using a simple optimization procedure, we demonstrate typical properties of optimal filter sets for optical flow, simultaneous estimation of optical flow and diffusion, as well as optical flow and exponential decay. Exemplarily we show their performance and state some useful choices.

Equalization strategy for dual-polarization optical transport system

Abstract: A method is provided for an equalization strategy for compensating channel distortions in a dual-polarization optical transport system wherein the received signal includes a complex signal of a first transmitted polarization component and a complex signal of a second transmitted polarization component. In a first step, a blind self-recovery mode used a blind adaptation algorithm in calculating and modifying multiple complex equalizer transfer function coefficients to enable recovery of only the complex signal of the first transmitted polarization component. By recovering only a single polarization component in the first step the degenerate case of recovering only a single transmitted signal at both polarization component outputs of an equalizer is prevented. In a second step, equalization is performed in a training mode for calculating and modifying the multiple complex equalizer transfer function coefficients to enable recovery of the complex signals of the first and second transmitted polarization components. In a third step, equalization is performed in a data directed mode for continuing to calculate and modify the multiple complex equalizer transfer function coefficients to ensure continued recovery of the complex signals of the first and second transmitted polarization components. The method is suited for a digital signal processing implementation in a coherent receiver when a modulation scheme used on a transmitted signal is quadriphase-shift keying (QPSK). In other embodiments, the method can be used with modulation schemes such as binary PSK, M-ary PSK where M>4, or Quadrature Amplitude Modulation (QAM).

Defocused transfer function for a partially coherent microscope and application to phase retrieval.

Abstract: The defocused weak-object transfer function of a partially coherent bright-field microscope is calculated. For weak defocus, this can be expressed analytically. Use of this transfer function for phase restoration (quantitative phase retrieval) from images of weak mixed phase-amplitude objects is discussed.

Using magnetic coupling to eliminate right half-plane zeros in boost converters

Abstract: A dynamic analysis of the boost converter with an output filter reveals that magnetic coupling between inductors allows transfer of the zeros to the left half-plane of the control-to-output transfer function. Similar results requiring smaller magnetic components are obtained by combining magnetic coupling with damping of the output filter. The analysis is based on the application of the Routh-Hurtwitz's criterion to the numerator of the transfer function in order to derive the design conditions for the converter parameters. A design example illustrates the procedure, and experimental results verify the theoretical predictions. The application of these techniques will allow the design of high efficiency voltage boost-based regulators with dynamic behavior similar to buck-derived structures.

World function and time transfer: general post-Minkowskian expansions

Abstract: In suitably chosen domains of spacetime, the world function may be a powerful tool for modelling the deflection of light and the time/frequency transfer. In this paper, we work out a recursive procedure for expanding the world function into a perturbative series of ascending powers of the Newtonian gravitational constant G. We show rigorously that each perturbation term is given by a line integral taken along the unperturbed geodesic between two points. Once the world function is known, it becomes possible to determine the time transfer functions giving the propagation time of a photon between its emission and its reception. We establish that the direction of a light ray as measured in the 3-space relative to an observer can be derived from these time transfer functions, even if the metric is not stationary. We show how to derive these functions up to any given order in G from the perturbative expansion of the world function. To illustrate the method, we carry out the calculation of the world function and of the time transfer function outside a static, spherically symmetric body up to the order G2, the metric containing three arbitrary parameters β, γ, δ.

Linear systems with slowly varying transfer functions and their application to x-ray phase-contrast imaging

Abstract: A novel theoretical treatment of linear shift-invariant imaging systems is developed, which allows explicit solution of forward and inverse problems in the case of large values of the generalized Fresnel number. The method will be useful in a variety of domains including optical instrumentation, biomedical imaging and materials science. Our approach is used to integrate two particularly topical x-ray imaging methods, namely propagation-based and analyser-crystal-based x-ray phase-contrast imaging.

Transfer functions for infinite-dimensional systems

Abstract: In this paper, we study three definitions of the transfer function for an infinite-dimensional system. The first one defines the transfer function as the expression $C(sI-A)^{-1}B+D$. In the second definition, the transfer function is defined as the quotient of the Laplace transform of the output and input, with initial condition zero. In the third definition, we introduce the transfer function as the quotient of the input and output, when the input and output are exponentials. We show that these definitions always agree on the right-half plane bounded to the left by the growth bound of the underlying semigroup, but that they may differ elsewhere.

Digital implementation of a line current shaping algorithm for three phase high power factor boost rectifier without input voltage sensing

Abstract: In this paper the implementation of a simple yet high performance digital current mode controller that achieves high power factor operation for three phase boost rectifier is described. The indicated objective is achieved without input voltage sensing and without transformation of the control variables into rotating reference frame. The controller uses the concept of resistance emulation for shaping of input current like input voltage in digital implementation. Two decoupled fixed frequency current mode controllers calculate the switching instants for equivalent single phase boost rectifiers. A combined switching strategy is developed in the form of space vectors to simultaneously satisfy the timing requirements of both the current mode controllers in a switching period. Conventional phase locked loop (PLL) is not required as converter switching is self-synchronized with the input voltage. Analytical formula is derived to obtain the steady state stability condition of the converter. A linear, low frequency, small signal model of the three phase boost rectifier is developed and verified by measurement of the voltage control transfer function. In implementation Texas Instruments's DSP TMS320F240F is used as the digital controller. The algorithm is tested on a 10-kW, 700-V dc, three phase boost rectifier.

Optimal Length and Signal Amplification in Weakly Activated Signal Transduction Cascades

Abstract: Weakly activated signaling cascades can be modeled as linear systems. The input-to-output transfer function and the internal gain of a linear system provide natural measures for the propagation of the input signal down the cascade and for the characterization of the final outcome. The most efficient design of a cascade for generating sharp signals is obtained by choosing all the off rates equal and a “universal” finite optimal length.

A novel 5GHz RF power detector

Abstract: The principles of a RF power detector using bipolar transistors are analyzed and a new RF power detector for embedded RF IC test is proposed. The new detector uses a voltage divider to provide unequal ac signals for its differential input. It has a more linear transfer function for large-signal detection than previously reported detectors. Also, the detector retains its square-law transfer characteristics for low-level-signal detection. The errors in linear or square-law region operation are within 2%. The crossover region between detector linear and square-law operation is minimized to 30/spl sim/50mV and its detection error is within 8% using either linear or square-law estimation. The detector has 65dB dynamic range and it can work with 5GHz or higher signals as compared to roughly 30dB dynamic range in R.G. Meyer (1995).

Instrumentation and control systems

Abstract: Preface. Measurement systems. Instrumentation systems elements. Instrumentation case studies. Control Systems. Process controllers. Correction elements. PLC systems. Systems. Transfer function. Systems response. Frequency response. Nyquist diagrams. Controllers. Appendices: Errors. Differential equations. Laplace transform. Answers. Index.

Adaptive Calibration of Dynamic Speed-Density Relations for Online Network Traffic Estimation and Prediction Applications

Abstract: A dynamic speed-density relation is identified by using a transfer function model. The model recognizes the time-lagged response of speed to density as well as autocorrelated system noise. A framework for the adaptive calibration of dynamic speed-density relations in the context of real-time dynamic traffic assignment-simulation operation is presented. The model and the approach are evaluated on the basis of actual sensor data from the Irvine, California, network. The results indicate that use of the transfer function approach in the context of real-time simulation is preferable to the use of conventional static traffic flow models.

Saturation effects in active noise control systems

Abstract: The reference and error sensors of active noise control (ANC) systems will be saturated in real-world applications if the noise level exceeds the dynamic range of the sensors. However, there is a lack of analysis of saturation effects on the performance of ANC systems. This paper proposes an indirect method for analyzing the saturation effects in steady state using Fourier analysis. This indirect method uses clipping to approximate saturation and decomposes the saturated narrowband signal as the summation of a set of rectangular waves and a pulse-amplitude modulated signal. The theoretical analysis shows that the clipping of a sinusoidal signal produces extra odd harmonics, thus affecting the convergence speed and steady-state solution of adaptive filter in ANC systems. This analysis can be extended to narrowband noises that consist of multiple sinusoidal components such as engine noise in many ANC applications. A low-pass filter is effective in reducing saturation effects for harmonic-related noises. Analysis results are verified by computer simulations using recorded engine noise and transfer functions measured from an experimental setup.

Binaural sound localization using a formant-type cascade of resonators and anti-resonators

Abstract: This invention is a method for binaural localization using a cascade of resonators and anti-resonators to implement an HRTF (head-related transfer function) The spectrum of the cascade reproduces the magnitude spectrum of a desired HRTF The proposed method provides a considerably more computationally efficient implementation of HRTF filters with no detectable deterioration of output quality while saving memory when storing a large quantity of HRTFs due to the parameterization of its resonators and anti-resonators Finally, the method offers additional flexibility since the resonators and anti-resonators can be manipulated individually during the design process, making it possible to interpolate smoothly between HRTFs, reduce spectral coloring or achieve higher accuracy at perceptually relevant frequency regions These HRTF are useful in stereo enhancement and multi-channel virtual surround simulation

Tunable optical transversal filters based on a Gires-Tournois interferometer with MEMS phase shifters

Abstract: We present tunable optical filters based on a modified Gires-Tournois interferometer. The back reflection plane of the interferometer is replaced with a one-dimensional micromirror array for phase modulation. Using Gaussian beam optics, we show that the transfer function of the device has the form of the transversal filter in digital signal processing. The design and analysis techniques of conventional digital filters can, therefore, be adapted to tunable optical filters. Both the amplitude and phase of the transfer function can be controlled by reconfiguring the micromirrors. Application examples in dispersion compensation and variable bandwidth bandpass filtering are discussed and experimentally demonstrated.

Wide-band measurements and characterization at 2.1 GHz while entering in a small tunnel

Abstract: The wide-band complex transfer function and propagation characteristics in a small passageway tunnel for nonline-of-sight are studied in this paper. A two-dimensional wide-band model based on the uniform theory of diffraction (UTD) and geometric optics (GO) is implemented and a network analyzer is used to perform measurements. In order to obtain the power delay profile, a correction factor is used, which adjusts the deviation caused by the windowing and zero padding performed in frequency domain. The UTD model predicts quite well the averaged path loss, power delay profile, root-mean-square (rms) delay spread and coherence bandwidth, even when the curved tunnel is approximated to two straight lines. Furthermore, it is shown that the position of the transmitter is crucial in the performance of the system: the path loss slope and rms delay spread are increased when the inclination of the transmitter is increased. In all cases, the rms delay spread is lower than 40 ns, where the coherence bandwidth decreases to 20 MHz. This parameter is proposed to estimate the excitation zone inside a tunnel.

Binder MIMO channels

Abstract: This paper introduces a multiple-input multiple-output channel model for the characterization of a binder of telephone lines. This model is based on multiconductor transmission line theory, and uses parameters that can be obtained from electromagnetic theory or measured data. The model generates frequency-dependent channel/binder transfer function matrices as a function of cable type, geometric line-spacing and twist-length parameters, and source--load configurations. The model allows the extraction of the magnitude and the phase of individual near end crosstalk, far end crosstalk, split-pair, and phantom transfer functions from the transfer function matrix of the binder. These individual crosstalk transfer functions are often found to be very sensitive to small imperfections in the binder. Examples of category 3 twisted pair American telephone lines and ldquoquadrdquo telephone cables are also presented.