Dynamic Cancellation Research Articles

A 10-bit 100-MS/s Dual-Channel Pipelined ADC Using Dynamic Memory Effect Cancellation Technique

This brief presents a 10-bit 100-MS/s 1.2-V dual-channel pipelined CMOS analog-to-digital converter (ADC). The nine dual-channel pipelined stages share the operational amplifiers (op-amps) to optimize power and area. The proposed dynamic memory effect cancellation technique reduces the cross coupling caused by the residual charge in the op-amp sharing topology. The op-amp gain requirement of the dual-channel sample-and-hold circuit is also relaxed by the proposed memory effect cancellation technique. The prototype ADC achieves a peak signal-to-noise and distortion ratio of 56 dB for a 1-MHz input signal and a peak cross-coupling ratio of 67.4 dB at 100 MS/s while consuming 16.2 mW/channel from a 1.2-V supply. The prototype ADC occupies 1.96 mm2 using a 0.13-μm CMOS technology.

Dynamic Inter-cell Interference Cancellation for Uplink in Multi-cell OFDMA Systems

Dynamic Inter-cell Interference Cancellation for Uplink in Multi-cell OFDMA Systems

Bifurcation analysis and synchronisation issues in a three-echelon supply chain

In today's global marketplace, supply chains are dynamic and volatile. This dynamic and volatile nature produces various types of uncertainties along the supply chain, for example, demand uncertainty, supply uncertainty, delivery uncertainty and forecasting uncertainty. These uncertainties make supply chains complex and nonlinear systems as they propagate both upstream and downstream. This work investigates the dynamic behaviour of a three-echelon supply chain. Modelling of this structure is carried out to display its nonlinear dynamic behaviour. It is shown that the dynamics (stability) of the supply chain are very sensitive to external uncertainties. Specifically, a supply chain subjected to these uncertainties can exhibit strange and undesired states such as saturation and chaos. An adaptive algorithm for the automatic cancellation of these strange dynamics due to uncertainties is developed by re-adjusting the internal parameters of the supply chain to achieve its synchronisation. A bifurcation analysis is carried out. This analysis is essential and useful for strategic decision-makers as it allows both the visualisation and control of the states/dynamics of the entire supply chain. The internal parameters of the supply chain are used as control parameters, and various remarkable states are discovered towards the achievement of synchronisation.

On game-theoretic power control under successive interference cancellation

Game-theoretic analytical techniques have been applied, of late, to uplink power control in DS-CDMA networks. We extend our previous analysis [1] of game-theoretic power control under successive interference cancellation performed under a dynamic cancellation ordering. Both continuous and discrete power control are investigated. Under continuous power control, we prove the nonexistence of a symmetric power control equilibrium, illustrating that no easily applicable equilibrium existence result applies to this power control problem. Under discrete power control, we demonstrate empirically a high probability of equilibrium if the action set is not too precise, an encouraging result in the absence of a pure-strategy equilibrium guarantee.

Binaural technology for virtual reality

The use of nonintrusive virtual environments is gaining more and more importance but was focused mainly on addressing the visual sense. However, the human perception consists not only of visual input and thus it would be worthwhile to create multimodal and interactive virtual environments. This thesis describes the techniques required to include the acoustic component into virtual environments and the implementation of a software system, which creates complex artificial acoustical scenes in real time. The system is based on the binaural technology. It features spatially distributed sound sources, which are utilized to create an environment that is as authentic as possible. This comprises a description of the source, including its relevant angle-, distance-, and time-dependent radiation, the sound distribution in the virtual scene, the perception-related consideration of all sound field components, and the exact reproduction at the ears of the user. In this context, an approach for dynamic crosstalk cancellation is presented, which enables a loudspeaker-based reproduction. The required filters are processed in real time on the basis of the position data and measured transfer functions of the outer ear. Furthermore the integration of this spatial audio system into a five-sided Virtual Reality display system is described and evaluated.

Dynamic low-frequency noise cancellation in quantum well Hall sensors (QWHS)

We show that the low-frequency noise of AlGaAs/InGaAs/GaAs quantum well Hall sensors (QWHS) can be cancelled using a method similar to the spinning current method. A two-phase permutation of the current biasing electrodes and the voltage sensing electrodes of the Hall cross is performed by a switching circuit made of field effect transistors (FET). A Hall cross and eight switching FETs are integrated on the same chip. This system yields to a noise reduction of 30 dB around 1 Hz. However, the noise floor, typically 140 nT/ Hz in 8 μm devices, remains larger than the expected thermal noise, and is shown to be correlated with leakage current in the FET gates. For comparison, hybrid microsystems using a discrete QWHS and leakage-free CMOS switches were fabricated. They are shown to have a record noise level of 30 nT/ Hz at 1 Hz at room temperature.

Wave-function analysis of dynamic cancellation of ac Stark shifts in optical lattice clocks by use of pulsed Raman and electromagnetically-induced-transparency techniques

We study analytically the dynamic cancellation of ac Stark shift in the recently proposed pulsed electromagnetically-induced-transparency (EIT-)Raman optical lattice clock based on the wave-function formalism. An explicit expression for the time evolution operator corresponding to the effective two-level interaction Hamiltonian has been obtained in order to explain the atomic phase shift cancellation due to the ac Stark shift induced by the time-separated laser pulses. We present how to determine an optimum value of the common detuning of the driving fields at which the atomic phase shift cancels completely with the parameters for the practical realization of the EIT-Raman optical lattice clock with alkaline-earth-metal atoms.

Virtual Reality System with Integrated Sound Field Simulation and Reproduction

A real-time audio rendering system is introduced which combines a full room-specific simulation, dynamic crosstalk cancellation, and multitrack binaural synthesis for virtual acoustical imaging. The system is applicable for any room shape (normal, long, flat, coupled), independent of the a priori assumption of a diffuse sound field. This provides the possibility of simulating indoor or outdoor spatially distributed, freely movable sources and a moving listener in virtual environments. In addition to that, near-to-head sources can be simulated by using measured near-field HRTFs. The reproduction component consists of a headphone-free reproduction by dynamic crosstalk cancellation. The focus of the project is mainly on the integration and interaction of all involved subsystems. It is demonstrated that the system is capable of real-time room simulation and reproduction and, thus, can be used as a reliable platform for further research on VR applications.

Real-time audio rendering system for virtual reality

Systems of virtual acoustics are more and more coming into the focus of research and application. Creating a virtual sound scene with spatially distributed sources requires a technique for adding spatial cues to audio signals and an appropriate reproduction. A real-time audio rendering system is introduced that combines room acoustics, dynamic crosstalk cancellation, and multitrack binaural synthesis for virtual acoustical imaging. The room acoustics component takes into account the full up-to-date algorithmic approach of specular reflections and scattering, but with real-time processing. The real-time performance of the software was reached by introduction of a flexible framework for the interactive auralisation of virtual environments. The concept of scene graphs for the efficient and flexible linkage of autonomous-operating subscenes by means of so-called portals has been incorporated into the existing framework, combined with an underlying BSP-tree structure for processing geometry issues very fast. Using this framework enables a significant reduction of computation time for both applied algorithms (deterministic image sources and a stochastic ray tracer). This enables the simulation of indoor or outdoor spatial distributed sources and, in addition to that, near-to-head sources for a freely moving listener in room-mounted virtual environments without the use of headphones.

Design and implementation of a sliding-mode controller and a high-gain observer for output tracking of a three-axis pickup

A novel decoupling actuation scheme applied to a new three-axis four-wire optical pickup is synthesized in this study based on theories of sliding-mode control and high-gain observer. The three-axis pickup owns the capability to move the lens holder in three directions of focusing, tracking and tilting. This capability is required particularly for higher data-density optical disks to annihilate the non-zero lens tilting. To achieve control design, Lagrange's equations are first employed to derive equations of motion for the lens holder. A sliding-mode controller is then designed to perform dynamic decoupling and nonlinearity cancellation with the aims of precision tracking, focusing and no tilting. A full-order high-gain observer is next forged to estimate the velocities of the moving lens holder in order to provide low-noised feedback velocity signals for the designed sliding-mode controller. Simulations are carried out to choose appropriate parameter values of the designed controller and observer. Finally, experiments are conducted to validate the effectiveness of the controller for annihilating lens tilting and the capability of the observer for reducing the effects of digital noises on pickup positionings.

Cosmological model with dynamical cancellation of vacuum energy and dark energy

We propose a model with a compensating scalar field whose back reaction to the cosmological curvature cancels possible vacuum energy density down to the terms of the order of the time-dependent critical energy density. Thus, the model simultaneously solves the mystery of the compensation of vacuum energy with an accuracy of 120 orders of magnitude and explains the existence of the observed dark energy. At an early stage, the suggested cosmological model might experience exponential expansion without an additional inflaton field. However, the solution found is unstable with respect to small perturbations. The stability can be ensured by introducing nonanalytical terms depending upon the absolute value of the curvature scalar R. Unfortunately, stable solutions do not describe realistic cosmology at the matter-dominated stage.

Dynamic Cancellation: Selecting Time WarpCancellation Strategies at Runtime

The performance of Time Warp parallel discrete event simulators can be affected by the cancellation strategy used to send anti‐messages. Under aggressive cancellation, antimessage generation occurs immediately after a straggler message is detected. In contrast, lazy cancellation delays the sending of anti‐messages until forward processing from a straggler message confirms that the premature computation did indeed generate an incorrect message. Previous studies have shown that neither approach is clearly superior to the other in all cases (even within the same application domain). Furthermore, no strategy exists to make a priori determination of the more favorable cancellation strategy. Most existing Time Warp systems merely provide a switch for the user to select the cancellation strategy employed. This paper explores the use of simulation time decision procedures to select cancellation strategies. The approach is termed Dynamic Cancellation and it assigns the capability for selecting cancellation strategies to the Logical Processes (LPs) in a Time Warp simulation. Thus, within a single parallel simulation both strategies may be employed by distinct LPs and even across the simulation lifetime of an LP. Empirical analysis using several control strategies show that dynamic cancellation always performs with the best static strategy and, in some cases, dynamic cancellation provides some nominal (5–10%) performance gain over the best static strategy.

An Experimental Study of a Prototype Active Anti-Roll Suspension System

SUMMARY Active roll control is known to offer substantial improvements in ride and handling performance over the most sophisticated passive suspension systems. However although many different active suspension systems have been discussed and analysed through simulation little information regarding experimental performance data from a prototype active roll control system has been published. This study focuses on the design, development, commissioning and experimental evaluation of a roll control suspension based on active anti-roll bar actuation. In tests, the prototype vehicle demonstrated excellent steady state and dynamic roll cancellation within the lateral acceleration range of 0.5g. Subjective assessments of the system confirmed the benefits of a level ride together with the added benefit accrued from the elimination of roll dynamics.

Monolithic magnetic Hall sensor using dynamic quadrature offset cancellation

The offset voltage and its temperature drift and production spread, which generally degrades the zero-level stability and reproducibility of magnetic Hall sensors, can be reduced using a single Hall plate and switching means for periodic permutation of the supply and output contact pairs. The present work describes a chopper-based 5-V monolithic linear Hall sensor with a /spl plusmn/0.1 T full scale where this dynamic plate offset cancellation technique has been employed together with a cost-effective signal conditioner. The device was integrated using a 2-/spl mu/m conventional BiCMOS process and the final chip, measuring 15/spl times/1.5 mm/sup 2/, shows, after packaging in a 3-pin plastic package, a residual offset with a production spread and a temperature-induced drift five to ten times smaller than in currently used multiplate dc quadrature cancellation approaches. The device does not require external components and provides an output free of HF residues.

Dynamical cancellation of the environmental magnetic disturbing fields

A cubic Helmholtz-coil triaxial system, with a mean side of 2 m and a volume of uniform field of 0.2 m3, allows the compensation of both the main ambient magnetic field and the urban magnetic noise, in the frequency band of 0–10 Hz. The main ambient magnetic field can be cancelled, or controlled, by a stabilised power supply. The alternating disturbing fields are compensated by a triaxial magnetometric system. The triaxial sensor unit is placed near the homogenous volume of the Helmholtz system. The feed-back loops of the magnetometer channels are closed using special windings of the triaxial Helmholtz system. This configuration enables one to cancel out the simulated disturbances at a ratio of 1 × 102 − 5 × 102 and the industrial noise at a ratio of 1 × 102. Functional studies of the magnetometric sensors and magnetometric devices can be performed in the homogenous volume created by the triaxial Helmholtz system. A system of cylindrical multilayer shielding can be placed in the volume of the dynamically compensated field: thus the ratio of magnetid field cancellation becomes 104.

High power laser diode driver based on power converter technology

This paper describes the design of a high speed semiconductor laser diode driver designed for driving 500 mW to 1.5 W diodes at full optical power modulation up to frequencies of 10 MHz. The duty cycle of the modulation may be varied. A switching power-converter based current source allows a higher power delivery efficiency to the diode than in previous designs, allowing for a more modest power supply and dissipation requirements. A dynamic ripple cancellation circuit reduces the power converter output current ripple to less than 1% of full-scale current. The circuit is capable of delivering up to 2.5 A to a laser load, with a 10-90% switching risetime from laser threshold to full on of less than 20 ns.

IMMERSIONS AND FOLDS IN STRING THEORIES OF GAUGE FIELDS

A two-dimensional string model with dynamical cancellation of folds is considered. The action of the model contains the self-intersection number which is defined for surfaces immersed in 4D targets. The two additional variables are not dynamical and live on a compact manifold. In this sense the model is a compactification of a 4D theory. The cancellation forces the string θ angle to be equal π Candidates for string states are constructed. Some mathematical background is given.

An active line conditioner to balance voltages in a three-phase system

In this paper a new configuration for an active line conditioner is proposed to correct dynamically voltage unbalances in a three-phase AC system. In the proposed system it is shown that the injection of a correction voltage V/sub inj/ in one phase is sufficient to nullify the negative sequence voltage component in the incoming three phase supply. The resulting three phase voltages at the load terminals are essentially positive sequence voltages and hence are balanced. It is further shown that the kVA requirement of the proposed active line conditioner is small, typically 3% for a ten percentage unbalance in the input supply. The dynamic cancellation of the negative sequence voltage component by the proposed scheme drastically improves the performance of induction motor loads connected to a weak AC system. A thorough analysis of the scheme along with the suitable design guides are presented. Finally selected experimental results on a laboratory prototype active line conditioner are detailed.

Increased CDMA system capacity through adaptive cochannel interference regeneration and cancellation

Asynchronous code division multiple access (CDMA) systems using digital matched filtering (DMF) reception techniques suffer from poor multiple access spectral efficiency. This is due entirely to the lower bound on the mean square crosscorrelation levels which exist between the orthogonal codes allocated to each system subscriber. This interference can be estimated through channel measurement, and it is then possible to regenerate and subsequently cancel crosscorrelation components from individual interfering channels, thereafter increasing the effective signal-to-interference ratio on the desired channel for a given subscriber activity level. This paper suggests a technique to exploit this ability in order to gain an increase in the number of multiple access channels available within a particular bandwidth. Theoretical analysis of the proposed cancellation scheme shows an upper bound on the spectral efficiency approaching 130% or 1.3 normalised channels per hertz for successive cascaded cancellation stages. Simulation results for CDMA systems show that, for the traditional DMF receiver without dynamic cancellation, the CDMA efficiency is approximately 10% for a bit error rate of 10−4. Analysis is presented for single and two stage cancellation receivers showing 40% and 50% capacity, respectively, for the same error rates derived from a receiver whose complexity is linear in the number of supported active subscribers.

Dynamical adjustment of the cosmological constant

We examine a recent proposal by Peccei, Sola and Wetterich for the dynamical cancellation of the cosmological constant and explicitly demonstrate that their mechanism is plagued by a fine-tuning problem, order-by-order in perturbation theory. Our analysis, however, suggests a modification of their scheme which seems to have a good chance of solving the cosmological constant problem. It involves the existence of more than one dilaton. We also discuss the relevance to “fifth” forces.