A dynamic neuromuscular model for describing the pendulum test ofspasticity

Both dynamic and static thresholds, as well as the gain in the stretch reflex loop, affect the sensitivity of motoneurons to muscle stretch. How the variation in each parameter will influence the mechanical behavior of patients with spasticity is not well understood because of the difficulty in experimentally isolating individual parameters. A neuromuscular dynamic model, based on the pendulum test of spasticity, has been developed to study the specific contribution of individual parameter abnormalities in stretch reflex loops to the observed mechanical abnormalities. The model contains detailed nonlinear dynamics of muscle force generation and stretch reflexes. A computer simulation of the model indicates that the stretch reflex thresholds and the gain have different influences on the leg swing in the pendulum test of spasticity. Individual changes in the static stretch reflex threshold, in the dynamic threshold, or in the gain can not stimulate the whole spectrum of spasticity severity. When simultaneous changes in all three parameters of the stretch reflex loop occur, a small variation of the gain coupled with changes in both static and dynamic thresholds can produce increasing severity of spasticity as the thresholds further decrease. The model is also successful in simulating the effect of posture changes on spasticity     

Effects of bulk trapping on the memory characteristics of thick-oxide MNOS variable-threshold capacitors

Charge-storage measurements have been performed at room temperature on thick-oxide MNOS structures using on automatic measuring system which allows a detailed and quite accurate investigation of the hysteresis loops (flat-band voltage versus stress voltage characteristics) of such devices. The experimental data have revealed several anomalous features, previously unreported in the literature, which are very general properties of double-layer devices. It is found that the initial hysteresis loop of a virgin device is very similar to the ‘conventional’ hysteresis loop, with flat bottoms and tops and steeply-rising sides. However, the second and subsequent hysteresis loops show dramatic changes in the flat-band voltage in the formerly flat regions. The results are interpreted in a selfconsistent manner, in terms of trapping phenomena throughout the bulk of both insulator regions. The trapped charge is found to produce strong internal fields that cause redistribution of the trapped charge in both the nitride and the oxide; it is these trapping effects which lead to the dramatic changes in the hysteresis loops after the initial pulse sequence. The existence of trapping levels in the bulk of the nitride is a necessary extension of the idealized model in which trapping levels are assumed to exist only at the oxide-nitride interface.     

高动态GPS接收机环路跟踪技术研究

为了解决加速度45g、加加速度10g/s的高动态环境下GPS信号的载波跟踪、码跟踪及其精度问题,提出了一种综合考虑动态和精度性能的载波环和码环优化设计方案,探讨了高动态情况下载波环和码环的结构设计及捕获转跟踪技术,分析了FLL/PLL/DLL环路的动态应力、暂态响应和鉴别器特性,总结了实用的控制策略和环路带宽。该方案经自主开发的软件接收机测试验证,可以在达到很高动态特性的同时满足一定的测距精度和定位精度要求。     

Phase Noise and Transient Times for a Binary Quantized Digital Phase-Locked Loop in White Gaussian Noise

Digital phase-locked loops of the type employing discrete phase adjustments form an interesting class for which both steady-state and transient performance may be determined in the presence of additive white Gaussian noise. A general technique for obtaining this analysis is presented. A class of "sequential filters" is described that appears to be well suited to this type of loop. Their performance is characterized by a variable number of inputs per output (depending upon the input sequence) and the use of coarse quantization. Two specific examples are discussed. The closed-loop transient analysis shows these loops to have effectively a slew-rate limited phase adjustment, indicating that they are decidedly nonlinear. A digital loop "quasi-bandwidth" measure is defined in terms of this transient response. This definition allows the comparison of digital loops on a basis of equal signal-to-noise ratios within the loop bandwidth and, to a limited extent, makes possible a similar comparison of the digital loops with linear loops. Performance of the digital loops is found to be similar to that of the first-order linear phase-locked loop model for low loop bandwidth signal-to-noise ratio but reaches a limiting minimum phase error due to quantization of the phase adjustments for high signal-to-noise ratio. This limit, however, can be set as low as desired by choosing a small enough phase-correction quantum. The digitalloop bandwidth is found to vary with the signal energy per noise spectral density ratio rather than with the signal amplitude as in the case of the linear analog model.     

Self- and mutual admittances of two identical circular loop antennas in a conducting medium and in air

The normalized self- and mutual admittances of two identical bare circular loop antennas have been evaluated when the loops are immersed in either air or an infinite homogeneous conducting medium. By decomposing the voltage and current into symmetric and antisymmetric components, the simultaneous integral equations for the distribution of current along the loop have been converted into a single integral equation similar to that for the isolated circular loop antenna which has already been studied. The computed results are presented graphically. The measured results are in good agreement with theory.     

xDSL loop qualification and testing

Due to increased pressure from alternatives, the pace of xDSL deployment must accelerate. This acceleration places increased emphasis on copper loop prequalification, which determines the suitability of a given loop for some class of xDSL service, and turn-up verification, which verifies that the customer is receiving the service tariffed or contracted. Although the physical characteristics and electrical impairments on copper loops are well understood, the variety of possible xDSL service types, both symmetrical and asymmetrical, current and anticipated, has complicated the deployment process. In the past, xDSL loop qualification and testing have been mostly ad hoc and labor-intensive activities. But a whole array of tools and test equipment have come along to make xDSL prequalification and turn-up verification less of an adventure and more of a key aspect of a for-profit business venture. Initial techniques can still be time-consuming and the new equipment expensive, but the new methods hold a lot of promise for the future of xDSL loop qualification and testing     

Entire-domain MoM analysis of an array of arbitrarily oriented circular loop antennas: a general formulation

This paper presents a general formulation for the entire-domain method of moments analysis of an N-element array of arbitrarily oriented coupled circular loop antennas. The orientations of the loops with respect to each other are defined through the use of Eulerian angles. The positions of the loops in space are defined by translation vectors from the center of a loop to another. By making use of coordinate transformations and vector algebra, a concise set of linear equations for solving the currents on the loops is obtained. The formulation is sufficiently general to be used for all the previously reported coupled loop orientations. It is also ideal for the study of skewed circular loops which may be oriented in innumerable ways and in turn demand a general formulation for their analysis. The use of the general formulation is illustrated by analyzing the coupling currents between collocated skewed loops. The formulation is also applied to study the effects on the transfer impedance between a pair of noncollocated skewed loops as one of the loops is rotated about various axes.     

Statistical Model for a Failure Mode and Effects Analysis and its Application to Computer Fault-Tracing

This paper presents a mathematical model of a general statistical approach to a system Failure Mode and Effects Analysis (FMEA). It describes, in particular, the FMEA theory itself, and its application to computer fault-tracing, using a Markov model. The theory yields both a reliability table showing system failure-state probabilities, and a criticality table identifying probable causes of system failure. Computer fault-tracing is implemented by using Markov chains to generate system output-state conditional probabilities. Feedback loop effects are eliminated by using Markov recursive relations for absorption probabilities. This statistical FMEA technique examines individual outputs on every individual component to determine statistically its critical impact on every system output. The fault tracing required is done by computer processing and is exhaustive. The reliability analyst is not required to make any intultive assumptions or simplifications on the complexity of the system block diagram or the effects of feedback loops, and the analyst does not have to decide which components should be examined for criticality. Instead, the analyst's work is shifted to understanding how each component works and relating this understanding to the FMEA technique.     

Subsystem backstepping design for controlling a class of nonlinear SISO systems with cascade structure

This paper presents a controller design, referred to as the subsystem backstepping design (SSBD), for a class of nonlinear SISO mechatronic systems that comprise several cascaded subsystems. Compared with the conventional integrator backstepping design (CIBD) that deals with a first-order equation at each design step, the SSBD manages at each design step a subsystem that can be of high order. This both simplifies the design procedure and also makes controller parameters conveniently determined according to dynamic characteristics of each subsystem as in the conventional cascade control design with multiple feedback loops. However, in contrast to the conventional cascade control design, the SSBD does not require the inner feedback loop to respond much faster than the outer feedback loop, while guaranteeing system stability for a class of nonlinear systems. In addition, a variant of the SSBD, called internal model principle-based SSBD (IMP-SSBD), is presented to both further demonstrate the advantages of the SSBD procedure over the CIBD and also achieve robust tracking performance. The effectiveness of the proposed scheme is demonstrated through experimental studies of a harmonic drive system suffering from transmission compliance and periodic disturbances.     

The multiturn half-loop antenna

The multiturn half-loop antenna consists of a coaxial array of N circular, half loops mounted perpendicular to a conducting image plane and interconnected beneath the image plane by a set of N-1 coaxial transmission lines. This antenna is analyzed using a Fourier series expansion for the current in the loops and a new, accurate model for the excitation of the loops by the TEM field in the coaxial apertures at their ends. When this structure is electrically small, the currents in all of the loops are approximately equal; hence, it has the well-know characteristics of an electrically small multiturn loop antenna. For a structure of general electrical size, both the radius of the loops and the lengths of the transmission lines can be adjusted to optimize the performance of the antenna for a particular application. Surprisingly, proper phasing of the excitations can make a multiturn half-loop antenna of moderate electrical size have a simple toroidal pattern, a pattern that can be obtained for a single-turn, half-loop antenna only when it is electrically small. This result is verified experimentally for a two-turn loop. Examples are shown where electrically large loops are phased with the interconnecting transmission lines to produce nearly optimum end-fire and broadside patterns     

GPS接收机PLL与卡尔曼跟踪环路性能分析

本文重点研究传统 PLL 环路和卡尔曼跟踪环路理论性能分析方法，理论上分析比较两种跟踪环路的跟踪灵敏度和动态应力性能，并通过 GPS 软件接收机仿真验证得出结论，相对于 PLL 环路，卡尔曼跟踪环路灵敏度最大可提高 3dB 左右，动态性能最大可提高 27g/s 左右。     

Non-ideal behavior of a driving resonator loop in a vibratory capacitive microgyroscope

Many researches have been carried out on the dynamic characteristics of vibratory microgyroscope, but only a few have been carried out on the non-ideal behaviors observed in the driving loop of the vibratory microgyroscope. In this paper, characterization and evaluation of the non-ideal behavior of the vibratory microgyroscope, “peak-and-valley” magnitude phenomenon and phase lag distortion, are discussed. To characterize the non-ideal behavior of a microgyroscope driving loop, a new electro-mechanical simulation model based on the HSPICE of microgyroscope driving loop is proposed. The parasitic capacitive components of the driving loop are found to be the major sources of non-ideal behavior in microgyroscope and it is verified with the simulation results. The validity of the proposed simulation model and the parasitic effects on microgyroscope driving loop is evaluated with the actual fabricated gyroscope.     

Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.     

An adaptive phase alignment algorithm for cartesian feedback loops [Applications corner]

An adaptive algorithm to correct phase misalignments in Cartesian feedback linearization loops for power amplifiers has been presented. It yields an error smaller than 0.035 rad between forward and feedback loop signals once convergence is reached. Because this algorithm enables a feedback system to process forward and feedback samples belonging to almost the same algorithm iteration, it is suitable to improve the performance not only of power amplifiers but also any other digital feedback system for communications systems and circuits such as all digital phase locked loops. Synchronizing forward and feedback paths of Cartesian feedback loops takes a small period of time after the system starts up. The phase alignment algorithm needs to converge before the feedback Cartesian loop can start its ideal behavior. However, once the steady state is reached, both paths can be considered synchronized, and the Cartesian feedback loop will only depend on the loop parameters (open-loop gain, loop bandwidth, etc.). It means that the linearization process will also depend only on these parameters since the misalignment effect disappears. Therefore, this algorithm relieves the power amplifier linearizer circuit design of any task required for solving phase misalignment effects inherent to Cartesian feedback systems. Furthermore, when a feedback Cartesian loop has to be designed, the designer can consider that forward and feedback paths are synchronized, since the phase alignment algorithm will do this task. This will reduce the simulation complexity. Then, all efforts are applied to determining the suitable loop parameters that will make the linearization process more efficient.     

Performance Analysis of Small Tuned Transmitting Loop Antennas Evaluated by Experiment and Simulation [Antenna Designer's Notebook]

Frequency-swept input-impedance measurements to determine Q factors and field strengths for an electrically small tuned transmitting loop antenna in its operating environment have recently been made. These observational results are compared with numerical modeling by the computational electromagnetic code NEC-4D, since the validity of this code to simulate the performance of electrically small loops - and, in fact, even the fundamental characteristics of small loop antennas - has been questioned.     

Note on two integrator loop OTA-C configurations

A two integrator loop structure with six operational transconductance amplifiers (OTAs) and two capacitors has been proposed by Sanchez-Sinencio, et al. (1988). However, the filter functions which can be provided by this general architecture have not been available to date, although its special four OTA and two OTA derivatives have been studied. It is demonstrated that this circuit, with voltages applied to the input terminals of the OTAs inside the loops and output voltages from the circuit nodes inside the loops, offers many very useful and interesting functions such as LP, BP, HP, BS, LPN, HPN and AP without using floating capacitors, coefficient difference nulling and additional OTAs. Other existing two integrator loop structures cannot offer all the functions under similar conditions     

An enhanced adaptive Q-tuning scheme for a 100-MHz fully symmetric OTA-based bandpass filter

A tuning scheme for continuous-time high-Q biquad filters is presented. An improvement over the existing implementation of the modified-LMS Q-tuning scheme is proposed and efficiently combined with the frequency tuning based on phase-locked loops. The proposed scheme takes much less area without compromising the accuracy achieved previously. The proposed unified Q- and f/sub 0/-tuning scheme does not require the Q-tuning loop to be slower than the f/sub 0/-tuning loop. The optimal case is to have equal speeds for both loops. Also, a low-voltage pseudo-differential operational transconductance amplifier with inherent common-mode feedforward is introduced. The structure is fully symmetric and suitable for high-frequency applications. An experimental test chip is fabricated in standard CMOS 0.5-/spl mu/m technology, with a bandpass filter of center frequency 100 MHz and Q of 20, along with the proposed tuning scheme. The measured Q-tuning error is around 1%. Expected and experimental results are in good agreement.     

Loop Evolution--Its Dynamics and Driving Forces

The basic concept of the present loop was initiated with the invention of the telephone. The loop plant has persistently been responsible for a major share of the total capital expenditures in the telephone network. It has also been the most reluctant part of the network to benefit from new technologies. Its evolution has been mostly confined to areas of distribution topologies, administration, and improvement in hardware. The main driving forces shaping the evolution of the loop plant in the past have been the cost effectiveness in loop subsystems and the interactive forces resulting from the evolution of the switching machines and the subscriber terminals. The emergence of new services, demanded by the subscribers as a result of socioeconomic evolution, and solicited by the common carriers with the promise of additional revenues and better utilization of "network resources," can be considered as a new dimension to the driving forces. Related new technologies are the vehicles enabling the actualization of the above driving forces. The main aim of this paper is to identify the interrelationships that exist between various elements of the loop system as well as assessing the nature of the impact which various evolutionary forces exert upon it. Logical arguments are offered to demonstrate that the loop evolution is pointing towards loop systems that provide more throughput at less cost and greater service flexibility. Terms and concepts are defined and introduced to support the above arguments. It is concluded that the short-term evolution of the loop plant will be dominated by the marriage of copper loops and electronics prior to the introduction of integrated fiber optics distribution systems.     

Acquisition performance of various QPSK carrier tracking loops

The frequency and phase acquisition performance of three quadrature phase shift keying (QPSK) carrier tracking loops, the MAP estimation loop, the Costas crossover loop, and the generalized Costas loop, is described. Acquisition time and probability of acquisition as a function of both loop signal-to-noise ratio and frequency offset to loop bandwidth ratio are obtained via computer simulations for type II and III loops. It is shown that the MAP loop, which results in the smallest squaring loss for all signal-to-noise ratios, is sometimes outperformed by the other two loops in terms of acquisition time and acquisition probability