An estimate of the jitter of test generators using time-measuring apparatus

A method of estimating the jitter of test pulse generators using time-measuring apparatus (event timers) is considered. It is shown that the covariance of results of simultaneous measurements of the period by two measuring instruments gives an estimate of the jitter of the period of the test sequence. An experimental estimate of a jitter of 0.66 psec with an error of 8 fsec is obtained. The method enables generators of test pulse trains with small jitter to be checked and enables the results to be used further to test precision time measuring instruments.     

Generation and Measurement of Phase Jitter Using Phase-Lock Techniques

The phase-locked loop (PLL) is applied to generating and measuring large phase jitter that can be encountered in digital transmission systems. It is shown that jitter can be generated and measured by a PLL operated as a phase modulator and phase demodulator, respectively. Equations and examples are given for practical PLL designs to generate and measure jitter of a certain amplitude range and bandwidth. Practical considerations such as 1) phase detector range, 2) limited voltage-controlled oscillator sensitivity, 3) frequency tolerances, 4) pull-in time, and 5) calibration are included. PLL's designed in this way can be useful in evaluating digital transmission systems. Jitter measuring sets have been designed to measure jitter on the 1.5, 6.3, 45, and 274 Mbit/s signals used in the LD-4 digital cable system [1]. A jitter set for measuring jitter on 45 Mbit/s signals is described in this paper.     

IEEE 1057 Jitter Test of Waveform Recorders

The jitter test of waveform recorders and analog-to-digital converters (ADCs) is traditionally carried out using one of the methods recommended in the IEEE standard for digitizing waveform recorders, i.e., IEEE Standard 1057. Here, we study the uncertainty of one of those methods, point out the bias inherent to the estimator recommended for measuring the ADC jitter, and suggest an alternate estimator. Expressions are also presented for the determination of the precision of a given estimate from the number of samples used, the standard deviation of the additive noise present in the test setup, the jitter standard deviation, and the stimulus signal parameters. In addition, an expression for the computation of the minimum number of samples required to guarantee a given bound on the estimation uncertainty is presented, which is useful in optimizing the duration of the test.      

Time interval analysis errors in measuring recording mediatransition jitter

Media transition position jitter noise can be a dominant signal-to-noise ratio (SNR) issue in magnetic recording systems with magnetoresistive (MR) heads and (0,k) PRML channels, since the high MR head “gain” emphasizes media jitter noise over electronic noise, and (0,k) codes are sensitive to dibit jitter. Time interval analyzer (TIA) instruments are useful for measuring transition jitter (write jitter), since they can separate write jitter from electronic noise (read jitter) with minimal synchronization and speed variation difficulties. This paper analyzes TIA errors due to read channel intersymbol interference (ISI), which occurs even though TIA measurements are made with periodic LF or HF bit patterns at equal bit intervals “T”, which should be unchanged by ISI. Theory and data show that TIA measurements underestimate jitter by as much as 40% at low channel bit density D_c≡P₅₀/T≈1.5-1.8, and overstate jitter at high density. Even though typical TIA jitter measurements are made between nonadjacent pattern pulses, these errors still occur due to ISI by unmeasured neighbor pulses. It is shown that similar errors occur with TIA electronic read jitter noise measurements. At channel densities above D_c≈2.6, channel amplification of transition jitter occurs, which may be a factor in PRML channel bit density limits     

Analysis and measurement of timing jitter induced by radiated EMI noise in automatic test equipment

This paper deals with the generation, measurement and modeling of the jitter encountered in the signals of a testhead board for automatic test equipment (ATE). A novel model is proposed for the jitter; this model takes into account the radiated electromagnetic interference (EMI) noise in the head of an ATE. The RMS value of the jitter is measured at the output signal of the testhead board to validate the proposed model. For measuring the RMS value, a novel circuitry has been designed on a daughter board to circumvent ground noise and connectivity problems arising from the head environment. An H-field is applied externally at the loop filter of a phase-locked loop (PLL), thus permitting the measurement of the RMS jitter to verify the transfer function between radiated EMI and jitter variation. The error between measured and predicted jitters is within a 15% level at both 200 kHz and 500 kHz.     

Jitter Measurement Technique for Image-Converter Streak Cameras

Measurement Techniques - The phenomenon of jitter is examined in image-converter (electro-optical) streak cameras used for studies of high-speed processes. A method for measuring jitter in streak...     

Effect of sampling jitter on some sine wave measurements

The effect of sampling jitter on some periodic signal measurements, namely, the amplitude and phase of a pure sinusoid, is investigated. The parameters are determined by the fast Fourier transform (FFT) algorithm, which is used for manipulating samples in a data-acquisition system. Results are expressed in terms of mean values and variances of the measured parameters. Computer simulation results, based on Gaussian jitter, show the changes of amplitude and phase standard deviations versus the changes of standard deviation of jitter and signal amplitude for different numbers of FFT points     

Optimization of a laser satellite communication system with an optical preamplifier

We derive a model that optimizes the performance of a laser satellite communication link with an optical preamplifier in the presence of random jitter in the transmitter-receiver line of sight. The system utilizes a transceiver containing a single telescope with a circulator. The telescope is used for both transmitting and receiving and thus reduces communication terminal dimensions and weight. The optimization model was derived under the assumption that the dominant noise source was amplifier spontaneous-emission noise. It is shown that, given the required bit-error rate (BER) and the rms random pointing jitter, an optimal transceiver gain exists that minimizes transmitted power. We investigate the effect of the amplifier spontaneous-emission noise on the optimal transmitted power and gain by performing an optimization procedure for various combinations of amplifier gain and noise figure. We demonstrate that the amplifier noise figure determines the optimal transmitted power needed to achieve the desired BER but does not affect the optimal transceiver telescope gain. Our numerical example shows that for a BER of 10(-9), doubling the amplifier noise figure results in an 80% increase in minimal transmitted power for a rms pointing jitter of 0.44 microrad.     

Fabrication, characterization and mode locking application of single-walled carbon nanotube/polymer composite saturable absorbers

We present the fabrication of a high optical quality single-walled carbon nanotubes (SWNTs) polyvinyl alcohol (PVA) composite film. The composites demonstrate strong saturable absorption at ～1.5 μm, the spectral range for optical communications. By measuring the nonlinear transmission of a sub-picosecond pump pulse through the film, we were able to deduce a saturation fluence of ～13.9 μJ/cm² and a modulation depth ～16.9% (in absorption) at a high pulse fluence ～200 μJ/cm². Transient saturable absorption is investigated by measuring the transmitted autocorrelation traces at various incident power levels. Observed side-peak suppression indicates a fast recovery time on the scale of ～1 ps for our saturable absorber devices. Furthermore, we use these SWNT-PVA composite saturable absorbers as mode-lockers in an Er³⁺ fiber ring laser and achieve ～560 fs pulse generation with good jitter performance and long term stability. The laser performance is also associated with the parameters of our SWNT based saturable absorber.     

The effects of accumulated timing jitter on some sine wavemeasurements

This paper investigates the effects of accumulated timing jitter on the signal-to-noise ratio (SNR) and on the phase angle measurement of real sine waves. These measurements are done via the Fast Fourier Transform (FFT) method. Accumulated timing jitter occurs when the sine wave is sampled by an unstable clock where the clock periods are randomly changing. Also, accumulated jitter is a problem in ramp-type bases that were often used in sampling oscilloscopes. Expressions for an estimate of the signal-to-noise ratio [SNR_(est.)] and phase variance in terms of the jitter distribution parameters and the number of FFT points (N) are derived. The derived expressions are verified through computer simulations. Finally, a comparison between independent and accumulated jitter is presented     

Uncertainty of oscilloscope timebase distortion estimate

We study several problems related to the characterization of the timebase in high-speed sampling oscilloscopes. First, we examine the bias of using the method of the first-order approximation to estimate the additive and time jitter noises, and present a procedure to adjust for the bias in the estimates. We then study the bias and variance of a least-squares timebase distortion estimate that uses multiple sets of waveforms. Based on simulations, a method for calculating the uncertainty of the timebase distortion estimate is proposed. We also study the effects of amplitude and phase drifts, as well as jitter error on the estimation of timebase distortion. Results are shown using simulations with parameters that are closely related to those we observe in our laboratory     

Radio-frequency spectrum analysis of a jittery train after a second-order dispersive Talbot line

The power spectral density of the intensity of coherent Gaussian pulse trains suffering timing jitter after a dispersive line with arbitrary first- (beta(2)) and second-order (beta(3)) dispersion is computed in the small-signal approximation. Due to timing jitter noise, the initial radio-frequency spectrum shows noise bands whose bandwidth and position depend, respectively, on the jitter's standard deviation and on the jitter's pulse-to-pulse correlation. After setting the accumulated first-order dispersion to Talbot conditions, it is shown that the influence on the noise spectrum is a multiplicative factor with a multiple-bandpass structure. This factor depends on both the dispersive characteristics of the line and the pulse parameters, but not on the timing jitter's correlation properties, and represents the filtering mechanism responsible for Talbot repetition-rate multiplication. It is shown that the integer or fractional temporal Talbot effect does not worsen the timing properties of the initial train. In addition, and depending on the type of jitter correlation, the pulse width, and the total dispersion, it is shown that the temporal Talbot effect may lead to significant jitter reduction. The theory is exemplified by use of simulations. The applicability of the model to practical situations is also analyzed.     

双工位清洗机智能检测DCS系统的实现

针对国内清洗机检测完全人工化、效率低下的状况,开发了基于高性能、高集成度ATmega16单片机的智能清洗机检测DCS系统,实现了双工位清洗机检测工艺流程自动化、性能参数的实时采集及数据集中管理,并利用电能计量专用芯片CS5460A实现了电压、电流及功率因数等电参数测量高度集成化,提高了清洗机检测系统的可靠性、生产效率和质量管理水平。     

Combined methodology for measurement of available bandwidth and link capacity in wired packet networks

Accurate measurement of network parameters such as available bandwidth (ABW), link capacity, delay, packet loss and jitter are used to support and monitor several network functions, for example traffic engineering, quality-of-service (QoS) routing, end-to-end transport performance optimisation and link capacity planning. However, proactive network measurement schemes can impact both the data traffic and the measurement process itself, affecting the accuracy of the estimation if a significant amount of probe traffic is injected into the network. In this work, the authors propose two measurement schemes, one for measuring ABW and the other for measuring link capacity, both of them use a combination of data probe packets and Internet control messaging protocol (ICMP) packets. Our schemes perform ABW and link-capacity measurements in a short time and with a small amount of probe traffic. The authors show a performance study of our measurement schemes and compare their accuracy to those of other existing measurement schemes and also show that the proposed schemes achieve shorter convergence time than other existing schemes and high accuracy.     

Standard Reference Specimens in Quality Control of Engineering Surfaces

In the quality control of engineering surfaces, we aim to understand and maintain a good relationship between the manufacturing process and surface function. This is achieved by controlling the surface texture. The control process involves: 1) learning the functional parameters and their control values through controlled experiments or through a long history of production and use; 2) maintaining high accuracy and reproducibility with measurements not only of roughness calibration specimens but also of real engineering parts. In this paper, the characteristics, utilizations, and limitations of different classes of precision roughness calibration specimens are described. A measuring procedure of engineering surfaces, based on the calibration procedure of roughness specimens at NIST, is proposed. This procedure involves utilization of check specimens with waveform, wavelength, and other roughness parameters similar to functioning engineering surfaces. These check specimens would be certified under standardized reference measuring conditions, or by a reference instrument, and could be used for overall checking of the measuring procedure and for maintaining accuracy and agreement in engineering surface measurement. The concept of “surface texture design” is also suggested, which involves designing the engineering surface texture, the manufacturing process, and the quality control procedure to meet the optimal functional needs.     

Features of the procedure for measuring the amplitude backscattering diagrams of very large objects using ground radar measuring systems

A procedure for measuring the backscattering diagrams of large objects is considered, which reduces the components of the error due to the long-term instability of the parameters of radar measuring stations, when using a calibration without removing the object being investigated from the operating region of the measuring system. The results of an experimental check of the procedure are presented. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 48–50, June, 2008.     

Digital filtration of the signal from a moisture content sensor for flowing granular materials

We consider the design of a digital low-frequency FIR (finite impulse response) filter for a capacitive sensor measuring the moisture content of flowing granular materials. We have developed a technique for calculating the filter parameters, taking into account the requirements for ensuring that the amplitude—frequency characteristic is wideband and based on an approximation in the frequency domain. We propose a procedure for choosing the order of the filter. We have analyzed the filtration error and we present an example. Translated from Izmeritel'naya Tekhnika, No. 9, pp. 55–58, September, 1998.     

Optimum divergence angle of a Gaussian beam wave in the presence of random jitter in free-space laser communication systems

The average bit error rate (BER) of optical communication systems is considered in the presence of random angular jitter. First, the received power and the BER in the absence of jitter are reviewed. Then the average BER is obtained in the presence of circularly symmetric, normally distributed jitter by using the probability density function of the optical signal. By minimizing the power penalty for average BER, the optimum ratio of the divergence angle of the laser beam to the random angular jitter at the desired BER is obtained. An analytic approximation of the optimum ratio is derived as a function of the desired average BER. The results can be used for designing the link budget of optical communication and tracking channels in the presence of jitter.     

超短孤子脉冲在色散缓变光纤中的时间抖动

通过微扰理论分析了超短孤子在色散缓变光纤(DDF)中传输的时间抖动。结果发现三阶色散和拉曼散射分别影响了孤子的位置和频率,是决定时间抖动大小的重要因素。在光纤的拉曼系数一定的情况下,选择不同的三阶色散参数,系统的时间抖动存在一个最小值。当DDF的三阶色散参数为接近零的一个负值的时候,系统时间抖动最小,这个负值与拉曼系数和传输距离有关,其绝对值随传输距离的增大而增大。在采用色散缓变光纤进行超短孤子传输的系统设计中应该重点考虑三阶色散的影响,当DDF的三阶色散参数较大的时候,必须对系统的三阶色散进行补偿,使时间抖动达到最小,能够极大地增加了孤子的传输距离。     

Damage assessment on plate-like structures using a global-local optimization approach

A new method for finite element model updating using simulated data is presented. A global-local optimization (GLO) approach was adopted to adjust the uncertain properties of the FE model by minimizing iteratively the differences between the measured dynamic modal parameters and the corresponding analytical predictions. In contrast with most of the existing updating techniques, which minimize modal force errors, objective functions based on Coordinate Modal Assurance Criterion (COMAC) and Frequency Response Assurance Criterion (FRAC) were employed. The GLO procedure was employed to minimize the norm of these vectors by updating the physical model variables (thickness, Young modulus, etc.). The proposed model updating procedure was applied to damage localization and quantification of structures, whose damage characteristics can be represented by a reduction of the element bending and axial stiffness. Results showed that a significant reduction in terms of computer run-time and improved damage assessment can be achieved. The procedure is illustrated on a plate-like structure by measuring dynamic properties before and after structural changes for four different damage cases.