AM noise impact on low level phase noise measurements

The influence of the source AM noise in microwave residual phase noise experiments is investigated. The noise floor degradation problem, caused by the parasitic detection of this type of noise by an imperfectly balanced mixer, is solved thanks to a refinement of the quadrature condition. The parasitic noise contribution attributable to the AM to PM (phase modulation) conversion occurring in the device under test is minimized through the development of a dedicated microwave source featuring an AM noise level as low as -170 dBc/Hz at 10 kHz offset from a 3.5 GHz carrier     

Vibration-induced PM and AM noise in microwave components

The performance of microwave components is sensitive to vibrations to some extent. Aside from the resonator, microwave cables, and connectors, bandpass filters, mechanical phase shifters, and some nonlinear components are the most sensitive. The local oscillator is one of the prime performance-limiting components in microwave systems ranging from simple RF receivers to advanced radars. The increasing present and future demand for low acceleration sensitive oscillators, approaching 10?13/g, requires a reexamination of sensitivities of basic nonoscillatory building-block components under vibration. The purpose of this paper is to study the phase-modulation (PM) noise performance of an assortment of oscillatory and nonoscillatory microwave components under vibration at 10 GHz. We point out some challenges and provide suggestions for the accurate measurement of vibration sensitivity of these components. We also study the effect of vibration on the amplitude-modulation (AM) noise.     

Shot noise measurements on a single molecule

We report measurements of shot noise in the current through a single D2 molecule. The molecular junctions were formed by means of the mechanically controllable break junction technique. The configuration of the D2 molecule bridging the gap between two Pt tips is verified by use of point contact spectroscopy. Maintaining the same junction shot noise measurements were performed and the observed quantum suppression shows that conductance is carried dominantly by a single, almost fully transparent conductance channel. This observation allows us to decide between conflicting model calculations for this system, and this may serve as a benchmark for further computations on molecular junctions.     

Relationship of AM to PM noise in selected RF oscillators

We have studied the amplitude modulation (AM) and phase modulation (PM) noise in a number of 5 MHz and 100 MHz oscillators to provide a basis for developing models of the origin of AM noise. To adequately characterize the AM noise in high performance quartz oscillators, we found it necessary to use two-channel cross-correlation AM detection. In the quartz oscillators studied, the power spectral density (PSD) of the f(-1) and f(0) regions of AM noise is closely related to that of the PM noise. The major difference between different oscillators of the same design depends on the flicker noise performance of the resonator. We therefore propose that the f(-1) and f(0) regions of AM and PM noise arise from the same physical processes, probably originating in the sustaining amplifier.     

Accuracy of nonoscillating one-port noise measurements

This paper presents a detailed analysis of the accuracy of nonoscillating one-port device noise measurements. A new expression is given for the calculation of the noise temperature from parameters that can be measured directly by using either a power sensor or a noise meter with the capability of making power measurements. A general expression for the DUT noise temperature error function is also obtained, which enables the authors to study how the noise measurement accuracy is affected by a number of different factors. This expression has been found very useful in order to study how the accuracy can be improved in a given noise measurement system. The error function has been applied to evaluate the uncertainty of Schottky barrier device noise measurements     

The effect of cluster size on thin film media noise

A dynamic micromagnetic model of thin film magnetic recording media with generalised structure has been used to study the effect of cluster size on thin film media noise. Clusters formed by common crystallography and by intergranular exchange coupling have been simulated, and the effects of clustering on hysteresis and noise are presented. For small clusters of a few grains, crystallographic correlations are shown to have the same effect on noise as intergranular exchange coupling, giving an increase in magnetic feature size and noise     

The effect of location on closure measurements after overloads

Crack opening displacements were measured before and after single overloads on 2024-T351 aluminum specimens. A computer-controlled in-plane optical interferometric system was used to measure the displacements at various positions behind the crack tip. Opening load ratios were determined from those records and found to be higher closer to the tip and higher after an overload.     

The effect of work-hardening and pile-up on nanoindentation measurements

Nanoindentation is performed on the cross-section of copper samples subjected to surface mechanical attrition treatment (SMAT). The cross-section of the SMAT samples provides a unique microstructure with varying amounts of work-hardening depending on the distance from the SMAT surface. Results show that for a given indentation load the pile-up height decreases and the indentation depth increases as the distance from the SMAT surface increases, both following a power law relationship. Based on image analysis of the indented surface this increase in the pile-up height and decrease in indentation depth is attributed to the localization of plastic strain due to the increased resistance to dislocation motion in the work-hardened region. For a given amount of work-hardening (in terms of distance from SMAT surface), the indentation depth increased with the indentation load obeying a power law relationship with the exponent ranging from 0.58 to 0.68. However, the pile-up height increased linearly with the load, with the rate (slope) increasing with the amount of work-hardening. The observed linear increase in pile-up height with indentation load would naturally introduce an indentation size effect (ISE) if the hardness is corrected for the pile-up. Interestingly, this ISE associated with pile-up increased with an increase in indentation depth, in contradiction to the ISE associated with strain gradient. Deviation of the hardness values corrected for pile-up from the bulk behavior due to surface effect is highlighted and a method to obtain a bulk-equivalent hardness quantity representing the bulk behavior is proposed.     

交通噪声对儿童影响的研究综述

作为城市最普遍存在的环境噪声,交通噪声对儿童的健康成长会产生负面影响。通过对13个国家67项实证研究的文献分析,发现交通噪声对儿童影响主要表现在以下三个方面:在身体健康方面,交通噪声影响儿童的听觉、睡眠和心率血压等;在认知能力方面,影响儿童的阅读表现、记忆力、数学能力、注意力等,但目前对各种认知能力的研究深入程度不一;在心理健康方面,交通噪声引发儿童烦恼、心理压力和行为问题。通过对文献的梳理与总结,发现目前的研究存在如下问题:评价指标各异,难以形成统一结论;相关因素众多,混淆变量干扰研究结论;研究范式不同,研究结论存在差异。基于问题提出相关对策:构建标准化指标体系与规范化研究范式;深入运用社会学方法,明确社会环境因素对儿童的影响;开展交通噪声与交通空气污染综合影响的研究,厘清后者对结论的混淆。     

Low-frequency noise measurements on semiconductor devices using aprobe station

We report a measurement technique that would allow the mapping of the low-frequency noise characteristics of devices across a wafer. We show that we can reliably measure the noise by using a probe station. We also show that the sensitivity of the setup is not limited by the probes     

A new method for high-sensitivity noise measurements

A new method for high-sensitivity noise measurement, based on the elaboration in the time domain of the signals coming from two identical amplifiers, is presented in this paper. The most important advantage of this method, which in most cases allows obtaining an equivalent background noise 30 dB below that of the amplifiers which are used in the measurement chain, lies in its simplicity and in the fact that it does not depend on the method used for the estimation of the noise spectra.     

Transition shape analysis from medium noise measurements

We present a technique to determine the transition shape in digital magnetic recording. The method involves analyzing both temporal and spectral transition noise measurements. This combined method simultaneously determines the transition parameter and the cross-track correlation width along with the transition shape.     

基于掺铒光纤放大器的AM—VSBCATV系统载噪比的优化

研究了掺铒光纤放大器在ＡＭ－ＶＳＢＣＡＴＶ系统中产生的噪声效应,分析了为获得最大接收端载噪比应如何优化掺铒光纤放大器长度,同时还分析了何时可用简单算法进行系统设计以及何时必须进行数值求解。     

A study on phase-noise reduction method in phase-locked loop systems

Experimental studies are carried out on phase noise and the correlation coefficient between the phase and average current noises of the voltage-controlled oscillator in phased-locked loop (PLL) systems. The precise phase stabilization technique is discussed, and new methods to reduce the phase noise are described in PLL systems, using the correlation.     

Methods for direct-reading noise measurements of low-gain two-ports

This paper describes direct-reading measurement methods of noise figure F_m displayed by an automatic noise figure indicator. The F_m readings should be equal to F_x, which are the true noise figure values of the two-port under test, regardless of its available power gain G_Ax, and the noise figure of the measurement receiver F_t. Technical problems of these F_x direct readings are shown. They particularly occur while using the conventional measurement methods. Methods that allow elimination of the influence of the F_r value on F_m readings as well as the influence of both F_r and G_ax on F_m are discussed. An important advantage of using the method with elimination of the F_r value is presented. Formulas are given which allow the estimation of the technical requirements for additional blocks of measurement systems or to count measurement error components, specific for the chosen measurement method     

Up-converted 1/f PM and AM noise in linear HBT amplifiers

In this paper we describe a technique to predict the 1/f phase modulation (PM) and 1/f amplitude modulation (AM) noise due to up-conversion of 1/f baseband current noise in microwave heterojunction bipolar transistor (HBT) amplifiers. We obtain an accurate model for the amplifier and find the expression for voltage gain in terms of DC bias, transistor parameters, and circuit components. Theoretical 1/f PM and AM noise sensitivities to 1/f baseband current noise are then found by applying the definitions of PM and AM noise to the gain expression of the amplifier. Measurements of PM and AM sensitivities at 500 MHz and 1 GHz were in good agreement with the values predicted by theory, verifying the validity of this technique. This method can be used to optimize amplifier design for low PM and AM noise. We show that the amplifier PM noise can be reduced by 9 dB by adjusting the value of the input coupling capacitor.     

深海海洋环境噪声垂直相关性研究

海洋环境噪声场是海洋中的固有声场,其空间结构特性是影响水声系统的重要因素之一。在风成海洋环境噪声波数积分模型的基础上,对深海噪声场的垂直相关性进行了研究。通过数值仿真讨论了深海环境下,海底声速、衰减系数、海面噪声源深度及接收器深度对均匀分布于海面附近的噪声源的垂直相关性的影响。仿真结果表明:噪声场的垂直相关随海底声速、衰减系数和接收器的绝对深度的变化较小;高频噪声的垂直相关性对噪声源的深度较敏感,低频噪声的垂直相关性受噪声源深度的影响几乎可以忽略。在此基础上,分析了某次海试噪声数据,并结合数值计算结果对实验测得噪声数据的垂直相关性进行了合理的解释。