Magnitude Of Jitter Research Articles

Jitter-Robust Phase Retrieval Wavefront Sensing Algorithms.

Phase retrieval wavefront sensing methods are now of importance for imaging quality maintenance of space telescopes. However, their accuracy is susceptible to line-of-sight jitter due to the micro-vibration of the platform, which changes the intensity distribution of the image. The effect of the jitter shows some stochastic properties and it is hard to present an analytic solution to this problem. This paper establishes a framework for jitter-robust image-based wavefront sensing algorithm, which utilizes two-dimensional Gaussian convolution to describe the effect of jitter on an image. On this basis, two classes of jitter-robust phase retrieval algorithms are proposed, which can be categorized into iterative-transform algorithms and parametric algorithms, respectively. Further discussions are presented for the cases where the magnitude of jitter is unknown to us. Detailed simulations and a real experiment are performed to demonstrate the effectiveness and practicality of the proposed approaches. This work improves the accuracy and practicality of the phase retrieval wavefront sensing methods in the space condition with non-ignorable micro-vibration.

Microphonic detuning induced coupler kick variation at LCLS-II

The LCLS-II free-electron laser will be an upgrade of the existing Linac Coherent Light Source (LCLS), including a 4GeV CW superconducting linac based on the TESLA technology. The high quality factor of the cavity makes it very sensitive to vibrations. The shift of its eigenfrequency (i.e., detuning) will be compensated by the power source in order to assure a constant accelerating voltage. Significant variations of the forward power are expected which result in coupler kick variations induced by the fundamental power coupler. In this work we estimate the magnitude of trajectory jitter caused by these variations. High precision 3D field maps including standing and traveling-wave components for a cavity with the LCLS-II coupler design are presented.

Optimization and Validation of a Visual Integration Test for Schizophrenia Research

The Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia initiative highlighted a contour integration test as a promising index of visual integration impairment because of its well-established psychometric properties; its prior validation in healthy adults, patients, and nonhuman primates; and its potential sensitivity to treatment effects. In this multisite study, our goals were to validate the task on the largest subject sample to date, clarify the task conditions and number of trials that best discriminate patients from controls, and determine whether this discrimination can occur in standard clinical trial settings. For our task, subjects briefly observed a field of disconnected, oriented elements and attempted to decide whether a subset of those elements formed a leftward- or rightward-pointing shape. Difficulty depended on the amount of orientational jitter that was added to the shape's elements. Two versions of this Jittered Orientation Visual Integration task (JOVI) were examined. Study 1 did not reveal between-group differences in threshold (ie, the jitter magnitude needed to reach a performance level of ∼80%), but this likely owed to the wide sampling distribution of jitter levels and resulting floor/ceiling effects in many conditions. Study 2 incorporated a narrower range of difficulty levels and revealed lower thresholds (worse performance) among patients (p < .001). This group difference remained even when only the first half of the trials was analyzed (p = .001). Thus, the JOVI-2 provides a brief, sensitive measure of visual integration deficits in schizophrenia. Neural implications and potential future applications of the JOVI are discussed.

A DLL With Jitter Reduction Techniques and Quadrature Phase Generation for DRAM Interfaces

A DLL featuring jitter reduction techniques for a noisy environment is described. It controls a loop response mode by monitoring the magnitude of input jitter caused by supply noise. This technique varies the probability of phase error tracking. It reduces the output jitter of the DLL due to a low effective variance of input phase error and a narrow effective loop bandwidth. The DLL is implemented in a 0.13 mum CMOS process. Under noisy environments, the output clock of 1 GHz has 4.58 ps RMS and 29 ps peak-to-peak jitter.

Jitter models for the design and test of Gbps-speed serial interconnects

We present a comprehensive analysis of jitter causes and types, and develops accurate jitter models for design and test of high-speed interconnects. The recent deployment of gigabit-per-second (Gbps) serial I/O interconnects aims at overcoming data transfer bottlenecks resulting from the limited ability to increase chip pin counts in parallel bus architectures. The traditional measure of a communication link's performance has been its associated bit error rate (BER), which is the ratio of the number of bits received in error to the total number of bits transmitted. When data rates increase, jitter magnitude and signal amplitude noise must decrease to maintain the same BER. As data rates exceed 1 Gbps, a slight increase in jitter or amplitude noise has a far greater effect on the BER.

Analyzing jitter at high data rates

Jitter is timing noise that causes bit errors in high-speed data transmission lines. If the data rate of a system is increased, the magnitude of jitter measured in seconds is roughly unchanged, but measured as a fraction of a bit period, it increases proportionally with the data rate and causes errors. Emerging technologies require the ratio of the number of errors to the total number of transmitted bits (the bit error rate, BER) to be less than one in a trillion (10/sup -12/). As datacom, bus, and backplane data rates have increased, many different techniques for characterizing jitter have been introduced, each using a variety of different types of laboratory equipment. To fix difficult jitter problems at high data rates, engineers need to understand the diverse jitter analysis techniques used in both synchronous and asynchronous networking. The article focuses on data rates of emerging technologies above 3 Gb/s. Below 3 Gb/s, real-time oscilloscopes can capture a contiguous data stream that can be analyzed simultaneously in both the time and frequency domains; at higher data rates jitter analysis is more challenging. This discussion is from the perspective of a digital engineer, drawing on the experience of synchronous optical network/synchronous digital hierarchy (SONET/SDH) where many challenges have already been addressed.

Reduced BOLD response to periodic visual stimulation

The blood oxygenation level-dependent (BOLD) response to entrained neuronal firing in the human visual cortex and lateral geniculate nuclei was investigated. Periodic checkerboard flashes at a range of frequencies (4–20 Hz) were used to drive the visual cortex neurons into entrained oscillatory firing. This is compared to a checkerboard flashing aperiodically, with the same average number of flashes per unit time. A magnetoencephalography (MEG) measurement was made to confirm that the periodic paradigm elicited entrainment. We found that for frequencies of 10 and 15 Hz, the periodic stimulus gave a smaller BOLD response than for the aperiodic stimulus. Detailed investigation at 15 Hz showed that the aperiodic stimulus gave a similar BOLD increase regardless of the magnitude of jitter (±17 ms compared to ±33 ms), indicating that flashes need to be precise to at least 17 ms to maintain entrainment. This is also evidence that for aperiodic stimuli, the amplitude of the BOLD response ordinarily reflects the total number of flashes per unit time, irrespective of the precise spacing between them, suggesting that entrainment is the main cause of the BOLD reduction in the periodic condition. The results indicate that, during entrainment, there is a reduction in the neuronal metabolic demand. We suggest that because of the selective frequency band of this effect, it could be connected to synchronised reverberations around an internal feedback loop.

A 5-Gb/s 0.25-μm CMOS jitter-tolerant variable-interval oversampling clock/data recovery circuit

This paper describes a clock/data recovery circuit (CDR) incorporating a variable-interval 3/spl times/-oversampling method for enhanced high-frequency jitter tolerance. The CDR traces the eye-opening region to place the data-sampling clock exactly at the center of the data eye, responding to the shape and magnitude of jitter. A sampler with a pair of input-holding switches enables high-speed data sampling with reduced dynamic offset voltage. From the linearized model of the phase detector, the loop dynamics of the CDR are analyzed. Integrated in a single-chip transceiver with 0.25-/spl mu/m CMOS technology, the CDR operates at a data rate of 5 Gb/s. The CDR shows a bit error rate of less than 10/sup -13/ when the magnitude of data jitter reaches 60.5% of bit time.

Fundamentally excited flow past a surface-mounted rib. Part I: Turbulent structure characterisation

Different data analysis techniques for characterisation of the turbulent flow past a surface-mounted rib are reviewed. Deficiencies of the existing techniques are explained and modified techniques for determination of coherent structure magnitude and phase jitter are suggested. The effect of fundamental excitation on the flow is studied by using these turbulent signal analysis techniques. The appropriate length scale for characterizing the large-scale structures present in the reattaching shear layer of the surface-mounted rib is found to be the momentum thickness at the downstream edge of the rib, and the corresponding Strouhal number is 0.013. This is in contrast to a rib in the free stream, where the rib height is the correct scaling parameter. The post reattachment region is observed to be dominated by large-scale structures contrary to the traditional belief that large eddies break into small scales at the reattachment location. Low magnitude of phase jitter in the near field region is observed, indicating coherence of the flow structures. Phase decorrelation begins to occur beyond three rib heights from the downstream edge of the rib. From the quadrant analysis results, the outer edge of the shear layer is observed to be dominated by large-scale ejection motions.

Jitter and stability analysis of an actively mode-locked dispersion-managed fiber laser

The jitter and stability of an actively mode-locked (ML) dispersion-managed (DM) fiber ring laser are theoretically studied. A linearized analysis based on the variational approach is used to investigate the timing and energy jitter. We show that the timing jitter becomes smaller for stronger dispersion management. Too large dispersion management, however, may cause instability of the pulse energy. We further show that the magnitude of timing and energy jitter is significantly dependent on the location of the filter, amplifier, and modulator in the cavity. In the system operated with a narrow-band filter, low-amplitude pulses with long duration might coexist with the DM soliton pulse. We also examine the stability of DM soliton against the linear-mode growth in the ML DM fiber ring laser.

Magnetic field effects on CRT computer monitors

Summary form only as given. This paper discusses the effect of external low frequency magnetic field interference on cathode ray tube (CRT) computer monitors. The paper describes a new test facility and presents a quantitative measuring method which has been developed to characterize the field effects. A total of monitors from major manufacturers were tested. It was found that larger monitors are more sensitive and that the relationship between the magnitude of jitter and the magnetic flux density is linear and independent of the refresh rate and the frequency of the interfering magnetic field. The monitors are most sensitive to magnetic fields parallel to the screen. Monitor sensitivity is specified and presented for the tested monitors. A statistical survey was carried out to determine the human perceptibility level of jitter. It was found that 12 mG may cause detectable jitter for the common 14 monitor. This value drops to around 7 mG for a 21 monitor.

A fundamental limit on delay estimation using partially correlated speckle signals

Delay estimation is used in ultrasonic imaging to estimate blood or soft tissue motion, to measure echo arrival time differences for phase aberration correction, and to estimate displacement for tissue elasticity measurements. In each of these applications delay estimation is performed using speckle signals which are at least partially decorrelated relative to one another. Delay estimates which utilize such data are subject to large errors known as false peaks and smaller magnitude errors known as jitter. While false peaks can sometimes be removed through nonlinear processing, jitter errors place a fundamental limit on the performance of delay estimation techniques. The authors apply the Cramer-Rao Lower Bound to derive an analytical expression which predicts the magnitude of jitter errors incurred when estimating delays using radio frequency (RF) data from speckle targets. The analytical expression presented includes the effects of signal decorrelation due to physical processes, corruption by electronic noise, and a number of other factors. Simulation results are presented which show that the performance of the normalized cross correlation algorithm closely matches theoretical predictions. These results indicate that for poor signal to noise ratios (0 dB) a small improvement in signal to noise ratio can dramatically reduce jitter magnitude. At high signal to noise ratios (30 dB) small amounts of signal decorrelation can significantly increase the magnitude of jitter errors. >

A fundamental limit on the performance of correlation based phase correction and flow estimation techniques

Cross correlation and similar operations are used in ultrasonic imaging to estimate blood or soft tissue motion in one or more dimensions and to measure echo arrival time differences for phase aberration correction. These estimates are subject to large errors known as false peaks and smaller magnitude errors known as jitter. While false peaks can sometimes be removed through nonlinear processing, jitter errors place a fundamental limit on the performance of delay estimation techniques. This paper applies the Cramer-Rao Lower Bound to derive analytical expressions which predict the magnitude of jitter for 1-D and 2-D problems using both radio frequency (RF) and envelope detected data. One-dimensional simulation results are presented which closely match theoretical predictions. These results indicate that for typical clinical conditions axial jitter for detected data is approximately five times greater than that for RF data. Lateral jitter is approximately ten times greater than axial jitter for RF data. Examples are presented which utilize these results to predict the performance of phase aberration correction and flow estimation systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Acoustic image representation of a point target in the bat E p t e s i c u s f u s c u s: Evidence for sensitivity to echo phase in bat sonar

Echolocating bats, Eptesicus fuscus, were trained in two distinct behavioral tasks to investigate the images they perceive of a sonar point target. In the first task, bats were trained in a two-alternative forced-choice procedure to detect electronically simulated target echoes at a range of approximately 57 cm. Half of the trials in the detection task contained echoes from a stationary target (simulated by a fixed echo delay) and half contained echoes from a jittering target (simulated by an echo delay alternating between two time values over successive sonar emissions). In the second task, bats were trained in a two-alternative forced-choice procedure to discriminate between electronically simulated stationary and jittering targets, centered about a range of 57 cm. Both target detection and target jitter discrimination performance were assessed as a function of jitter magnitude, with jitter values ranging from 0-60 microseconds (corresponding to a change in distance of 0 to 10.3 mm). In both detection and discrimination tasks, the bat's performance changed cyclically with the magnitude of echo jitter. Specifically, when the phase of the playback echoes was unchanged, performance levels were poorest at 0 and 30 microseconds, and when the phase of the echoes alternated by 180 deg from one to the next, performance levels were poorest at 15 and 40-50 microseconds. The results suggest that Eptesicus is sensitive to the phase reversal of echoes and thus have implications for assessing receiver models of echolocation.

On the relationship between vocal sound-pressure level and the magnitude of jitter and shimmer in the normal voice

The relationship between vocal sound-pressure level (SPL) and the magnitude of cycle-to-cycle fundamental frequency (jitter) and amplitude (shimmer) perturbation measured in the voice was examined. Ten normal adult men prolonged the vowel /ɑ/ in a modal register phonation maintained within three SPL ranges: 60–68 dB (“soft”), 70–78 dB (“moderate”), and 80–88 dB (“loud”). Statistically significant differences were found between measured mean and percent jitter and shimmer and the sound-pressure level of the subjects' voices, such that the degree of perturbation was inversely related to the acoustic amplitude of the vowel. These results indicate that mean phonatory frequency and intensity must be controlled or accounted for to maintain the validity and reliability of voice perturbation measurement, especially when such measures are intended as aids to the detection and discrimination of vocal pathology.

Vocal jitter at different fundamental frequencies: A cardiovascular-neuromuscular explanation

<h2>Summary</h2> As a widely used descriptor of phonatory behavior, vocal fundamental frequency perturbation (jitter) has received much attention in the recent voice literature. Despite this, the exact causes of this cycle-to-cycle frequency variability are only poorly understood. Associated with attempts to characterize this vocal parameter and to standardize its measurement, many investigators have alluded to a relationship between jitter magnitude and the fundamental frequency of phonation without mention of the underlying physiology. This article reviews two jitter-inducing mechanisms (one based on normal cardiovascular function and the other on normal neuromuscular function) and describes how they help to explain the observed nonlinear dependence of short-term frequency variability on the frequency of phonation in the normal voice.

Timing Recovery in Digital Subscriber Loops Using Baud-Rate Sampling

Sampled-data techniques are the most practical means of obtaining the necessary signal processing functions for timing recovery in the VLSI implementation of a digital subscriber loop transceiver. The sampled-data timing recovery techniques described in this paper are applicable to both echo cancellation and time-compression multiplexing systems. Timing recovery using baud-rate sampling in conjunction with a special pulse-shaping and timing function fulfills all the objectives for timing recovery in this application. It recovers a timing phase that has minimum precursor intersymbol interference, and makes possible the combination of decision feedback equalizer and echo canceler, reducing the convergence time and increasing the step size. The pulse-shaping function can be performed either in the transmitter by means of digital coding, or in the receiver by means of analog filtering. In the latter case, the transmitted pulse is compatible with more conventional approaches. The proposed partial-response line coding, a special form of AMI coding, is less susceptible to line impairments if detected as a two-level signal. Performance by analysis, simulation, and experimental measurements is reported on a variety of cable configurations, some including bridged taps. Analysis of jitter performance leads to design techniques for reducing the jitter magnitude.

Place 2.0-An Interactive Program for PLL Analysis and Design

Phase Locked Loop Analysis and Circuit Emulation (PLACE) is an interactive program to assist in the design of Phase Locked Loop (PLL) systems. Written in C language, PLACE computes the loop filter components (up to active third-order filters); performs a stability analysis (finding the phase margin and damping ratio); and calculates the lockup time, hold range, and capture range. PLACE computes the PLL output jitter response due to incoming reference signal jitter, output jitter due to reference leakage through the phase detector, and output jitter response due to phase noise of the PLL components. The open and closed loop gain and phase, as well as jitter response, is plotted. Additional features found in PLACE 2.0 are frequency and magnitude of jitter peaking; a sensitivity analysis, which computes changes in loop performance as a function of component variation; and an interactive routine to help the designer optimize PLL performance. Currently residing on Digital Equipment Corporation's VAX-11/780, AT&T 3B20, and IBM System/370 processors, PLACE is presently available at most AT&T Bell Laboratories locations. This paper illustrates the capabilities of PLACE, shows several examples, and discusses the required calculations.

Discrimination of temporal jitter in patterned sequences of tones.

The perception of pure tone sequences in highly dependent on the serial pattern of tone frequencies. We propose that this phenomenon is mediated by a frequency-selective mechanism. Three models of the selective mechanism were evaluated in a temporal discrimination task. The observer was required to discriminate between two sequences of tone bursts. In one sequence the time interval between each tone burst was constant; in the other sequence the time interval was a random variable. A set of fixed and random pattern rules determined the frequency of each tone in the sequence. Discrimination performance was studied as a function of the magnitude of the time interval jitter and the serial pattern of tone frequency. Performance in the fixed pattern conditions was well described by a multiple-channel model in which timing information is available between tones within the same frequency region. The influence of higher order attentional factors was randomly determined. The frequency-selective mechanism appears to be sensitive to uncertainty about the frequency pattern of the input. Repeating the random pattern within each trial effectively eliminated this uncertainty. This result is consistent with experiments on the discrimination of word-length auditory patterns and temporal cues in speech.

Fundamental frequency perturbation observed in sustained phonation.

The middle segments of sustained phonations of /i/, produced by six male adults at fo's ranging from 98 to 298 Hz, were examined for cycle-to-cycle frequency perturbation. The voice samples were analyzed by a peak-picking fo analysis program (Horii, 1975). The results showed that, between 98 Hz and 210 Hz, mean jitter size decreased as the fo increased, whereas the corresponding jitter ratios remained relatively constant. Above about 210 Hz, mean jitter remained relatively constant and, consequently, the jitter ratio increased as fo increased. The problems of temporal resolution for vocal jitter studies, vowel-dependent jitter magnitude characteristics and various perturbation measures are discussed.