I/Q方法用于高频信号鉴相

在加速器高频相位控制环路中, 相位检测是影响控制精度的关键环节. 讨论了两种将I/Q技术用于高频信号鉴相的方法. 具体内容包括数学算法的研究和硬件系统的搭建. 两种方法分别是: 1) 利用I/Q解调模块、AD采集卡和数字处理技术进行鉴相; 2) 直接数字I/Q方法. 在第一种方法中, 提出了一种可行的、针对I/Q模块固有误差的修正算法. 第二种方法, 通过对参考相位进行(2π/N)步进调制, 获得I, Q分量. 两种鉴相方法都达到了误差<0.5°.     

BEPCⅡ直线加速器相控系统PAD的研制

相位和幅度测量是BEPCⅡ直线加速器相控系统中最重要的部分之一. 基于模拟和 数字I/Q解调器, 构建了两种PAD, 并分别在实验室和速调管长廊进行了测试. 基于LMS方法的校准算法用于补偿模拟I/Q解调器的各种不匹配误差. 实验 证明, 两种PAD都能正常稳定地运行, 可以满足相控系统对相位和幅度测量的要求.     

基于I/Q解调原理的数字PAD研制

 I/Q解调器可以同时测量微波信号的相位和幅度。为了消除传统I/Q解调器的不平衡误差，根据I/Q解调原理，应用数字滤波器及Hilbert变换等数字信号处理方法实现了对微波信号的正交解调，可以精确测量任意包络形状微波信号的相位和幅度。测试表明，数字相位和幅度探测器的精度可达±0.5°，重复性误差小于0.2°，温度系数约为-0.1°/℃，相位测量的动态范围为-18~5 dBm，幅度测量的动态范围为-20~0 dBm，其各项指标都达到了BEPCⅡ直线加速器相控系统的要求。     

利用实验I(L)/I(K)比值改进薄膜无标样定量分析

利用透射扫描电子显微镜和X射线能谱仪,在入射电压V₀为40,80,100,120,160和200kV下,测定了从Ge到Sn八种元素薄膜的标识X射线强度比值I(L)/I(K),并结合Cliff-Lorimerk_XSi因子和它的内插值,扩充了目前仅有的少数几个L系的Cliff-Lorimer因子。为了确定哪个电离截面Q公式最好,比较了利用九种不同Q公式计算出的I(L)/I(K)和我们的实验值I(L)/I(K)。发现两者之间存在着很大的差别。进一步考虑计算强度公式中各物理参量引起的误差后,我们认为上述差别主要来源于不准确的Q公式,而且和实验值符合最好的Fabredela Ripelle的电离截面也需要进行修正。利用我们修正后的Q公式,在V₀为100和200kV下,分析了几种已知成分的样品并和EDAX的分析结果进行了比较。结果表明:在不同电压下,利用不同线系K—K,K—L,我们分析结果的误差有显著的降低。 关键词：     

相位敏感光时域反射系统的时钟同源I/Q解调方法

提出一种基于时钟同源I/Q解调的相位敏感光时域反射系统解调方法.分析了调制信号与混频信号非同源不一致对解调结果的影响,采用声光调制器调制信号、斩波信号与I/Q混频信号时钟同源的方法以消除残余频率的影响.实验采用双压电陶瓷作为扰动源,通过I/Q解调实时获得后向瑞利散射光幅值和相位,进而实现扰动的定位和还原.实验结果表明,该系统能有效地探测到5km和9km处的正弦扰动,定位信号信噪比分别达17.8dB和16dB,相位解调结果准确还原正弦扰动,与正弦曲线的拟合系数分别为0.994和0.991,均方根误差分别为0.116和0.141.实验进一步验证了该方法能够测得不同扰动幅度下的相位正弦变化曲线,并能准确得到不同扰动频率,且扰动位置处相位变化幅度与扰动强度具有良好的线性关系,线性拟合系数达0.992,均方根误差为0.499,均优于非同源解调结果.     

超声波电源中数字鉴相器设计

超声波电源系统中电压电流相位差测量精度影响着换能器振幅稳定性以及系统工作效率。目前基于异或门原理,采用分立数字芯片实现鉴相的方案,存在信号调理电路复杂、线性范围小、精度低等问题。为提高电压电流鉴相精度,该文提出了一种数字鉴相器设计。该数字鉴相器采用正交解调原理鉴相,并使用坐标旋转数字算法在FPGA上实现了鉴相器的设计,简化了电路,减少了杂散信号的干扰。经过Modelsim仿真测试表明在30 dB信噪比条件下鉴相误差为0.21°,最后经过实验测试,数字鉴相器鉴相最大误差绝对值为0.256°,提高了测量精度。     

水-气界面参数和二向性影响因素交互作用研究

基于光学辐射传输软件HYDROLIGHT,模拟不同外界和水质条件下水气界面透射率T,Gordon模型参数f和二向性因子Q,研究风速、太阳天顶角、单次反照率和拉曼散射对T、f和Q及其组合f/Q的影响和交互作用,确定T、f、Q和f/Q的主导影响因子,以期为确定水色反演算法误差来源以及减小反演误差提供定量的依据。研究结果表明,T、f和Q的主导影响因素为太阳天顶角,单次反照率和风速对T、f和Q的影响相对较小,而对f/Q影响最大是单次反照率,其次是太阳天顶角,风速最小,且各影响因素之间具有较强的交互作用。高散射特性水体中,拉曼散射对f、f/Q和T的影响可忽略不计;黄质(CDOM)和叶绿素的荧光特性对f和f/Q的影响随着叶绿素和CDOM浓度的增加不断减小,但在高CDOM和叶绿素浓度的富营养化水体中该影响仍难以忽略。     

An Experiment for Generating the 14-Tone Stable Carriers Using Recirculating Frequency Shifter

In experiment, the generation of 14-tone stable carriers with recirculating frequency shifter is realized. Some factors that impact the performance of the carrier generation are discussed. It is experimentally found that the balance and the insertion loss of the inphase/quadrature （I/Q,） modulator, the accurate π/2 phase difference and equal power level of two rf signals which are applied to the two ports of the I/Q, modulator, the gain of the optical amplifier, the bandwidth and sharp window spectrum of the tunable filter and the stability of the optical signals＇ states of polarization fed into I/Q, modulator, play important roles in the generation of a stable multi-tone carrier source. By employing appropriate techniques we obtain 14-tone stable carriers in the experiment.     

最小均方误差解调算法在彩色超声血流成像中的研究

研究了最小均方误差正交解调算法在超声血流成像中的应用。首先由设计的期望信号与接收信号在最小均方误差原则下得到其迭代解调形式,获得回波信号同相分量和正交分量,然后由得到的正交解调信号通过自相关的方法对血流流速进行估计。解调算法的仿真结果表明,对高斯噪声信噪比为0.5¹0 dB的正弦波调制信号,解调输出平均信噪比与Hilbert变换法和I/Q解调法相比分别提高了15 dB和4 dB;血流成像的仿真结果表明,在流速估计性能相当的情况下,解调的乘法运算量仅分别为上述对比方法的18%和9%。因此在超声血流成像中应用最小均方误差正交解调算法,对于提高估计性能和降低运算量都有一定意义。     

如何使高三學生正確地理解“焦耳-楞次定律”和“电能輸送”

据我所知,高三学生中有相當一部分對焦耳-楞次定律和远距離電能輸送的理解是十分不够的,具體表現在下述兩個方面: (1)我們知道,焦耳-楞次定律的數學表現形式是: Q=0.24I~2Rt, 或Q=0.24IUt, 或Q=0.24U~2/Rt。在一個不是完全由電阻構成的電路中,学生們不会使用Q=0.24IUt或Q=0.24U~2/Rt。 (2)對遠距離輸電的提高電压、減小電流强度能够減少熱耗損表示懷疑。所持的理由是:電流强度(I)雖然减小,但電压(U)却昇高了,电流强度(I)与电压(U)的乘积(IU),仍然不变,因之熱量耗損Q=0.24IUt,並不     

序加实验理论模型误差修正的研究

针对序进应力加速实验理论模型中数学算法的误差,提出一种新的计算模型,新模型利用计算机编程辅助计算,显著地减小了模型误差.利用新、旧模型算法对理论数据进行计算,表明原模型算法存在13%以上的激活能计算误差以及150%以上的寿命计算误差（Q≤10　eV）,而新模型算法可以将激活能误差控制在1%以内,寿命计算误差控制在-41%以内. 关键词： 加速实验 序进应力 理论模型 误差修正     

Frequency offset and I/Q imbalance estimation for orthogonal frequency division multiplexing based wireless local area networks

The paper proposes a novel joint estimation of the frequency offset, frequency-independent I/Q imbalance, and frequency-dependent I/Q imbalance, using periodic pilots in orthogonal frequency division multiplexing (OFDM) based wireless local area networks (LANs). Although a low-complexity frequency offset estimation in the presence of I/Q imbalance can be obtained via a periodic pilot, the corresponding closed-form solution encounters a sign ambiguity. A method based on a power comparison between the signal and image interference is then proposed to detect the sign. Meanwhile, since one periodic pilot only is unable to estimate I/Q imbalance in the absence of a frequency offset, we also propose an estimation method based on two different periodic pilots available in the preamble. The validity and superiority of the proposed method are demonstrated by computer simulations.     

Error-compensating algorithms in phase-shifting interferometry: a comparison by error analysis

In this paper, two families of phase-shifting algorithms with π/2 phase steps are studied. In family I, three new algorithms are derived by using the averaging technique based on the Surrel six-sample algorithm with phase shifts of π/2. Family II includes four well-known algorithms derived by the averaging technique based on the conventional four-sample algorithm with π/2 phase steps. A polynomial model of phase-shift errors used to describe general expressions for calculation of the correct object phase via the Fourier spectra analysing method as a function of the harmonic order in the fringe signal is presented. The error-compensating properties of the algorithms in families I and II are investigated by the Fourier spectra analysing method. It is found that the averaging technique, when used in any of the algorithm with π/2 phase steps, can improve the phase-shifting algorithm property: it is insensitive to phase-shift error when the fringe signal contains the first harmonic, but it can't be used to enhance the phase-shifting algorithm properties when the fringe signal contains higher order harmonics (n2). P–V (peak–valley) phase errors are calculated by the computer simulation and tables and plots are presented, from which the algorithms in families I and II are compared. It is shown that the algorithms in family I are more insensitive to phase-shift errors when the fringe signal contains the second harmonic and the algorithms in family II are more insensitive to phase-shift errors when the fringe signal is a sinusoidal waveform.     

PAD Design for the Phasing System of BEPCⅡ Linac

Phase and amplitude measurement is one of the most important issues for the phasing system of BEPCⅡ linac. Two kinds of PAD, based on analog and digital I/Q demodulator respectively, have been constructed and tested in both laboratory and the klystron gallery of BEPCⅡ linac. A calibration algorithm based on LMS method is used to compensate the mismatches of the analog I/Q demodulator. Experiments show that both kinds of PAD run stably and can meet the requirements of the phasing system.     

A quadrature demodulation method based on tracking the ultrasound echo frequency

The ultrasound echo attenuation depends on frequency, propagating depth and tissue characteristics. Thus, the attenuation dependent on frequency results in a larger attenuation of high frequencies than lower when the wave propagates through the tissue. As a result, the central frequency of the echo generates the increasing downshift with the increasing of depth. In the traditional I/Q demodulation method, it is assumed that the central frequency of the echo is the same as the transmitting frequency and unchanged all time. The assumption directly causes that the acquired I/Q signals are not perfect baseband ones but biased due to the echo attenuation. In addition, the unreasonable assumption will keep the echo from getting better signal-to-noise ratio. A quadrature demodulation method based on tracking the ultrasound echo frequency is proposed in this paper. The method consists of the traditional I/Q demodulator, the frequency tracking module, the phase compensation module and the dynamic filtering module. The outputs of I/Q demodulator are biased. Autocorrelation technique is utilized in the frequency tracking unit to estimate the frequency bias according to the outputs of I/Q demodulator. The estimated bias feeds to the phase compensation unit which can eliminate the frequency bias by simple trigonometric function transform. The compensated signals feed to the dynamic filter and are further processed. The bandwidth of the dynamic filter decreases with the increasing of the depth, which makes the echo acquire better SNR in different depth. The efficiency of the proposed method is testified by both simulations and experiments.     

Small-x behavior of parton distributions from the observed Froissart energy dependence of the deep-inelastic-scattering cross sections

We fit the reduced cross section for deep-inelastic electron scattering data to a three parameter ln2s fit, A + beta ln2(s/s0), where s = (Q2/x)(1-x) + m2, and Q2 is the virtuality of the exchanged photon. Over a wide range in Q2 (0.11 < or = Q2 < or = 1200 GeV2) all of the fits satisfy the logarithmic energy dependence of the Froissart bound. We can use these results to extrapolate to very large energies and hence to very small values of Bjorken x-well beyond the range accessible experimentally. As Q2-->infinity, the structure function F2(p)(x,Q2) exhibits Bjorken scaling, within experimental errors. We obtain new constraints on the behavior of quark and antiquark distribution functions at small x.     

基于期望最大化框架的医学超声图像去斑

针对医学超声图像斑点噪声,提出一种基于期望最大化(EM)框架的去斑算法.先从超声I/Q图像中提取实部;然后从该实部图像中"盲估计"出系统的点扩散函数;最后利用EM算法,在维纳滤波和各向异性扩散间进行迭代,从而获得去斑后的超声图像.对不同信噪比的仿真图像和实际图像采用本文方法和现有方法进行比较实验,结果表明,采用本文方法...     

Full-band direct-conversion receiver with enhanced port isolation and I/Q phase balance using microwave photonic I/Q mixer

A full-band direct-conversion receiver using a microwave photonic in-phase and quadrature(I/Q) mixer is proposed and experimentally evaluated in terms of radio frequency(RF) range, port isolation, phase imbalance,conversion gain, noise figure, spurious-free dynamic range, and error vector magnitude. The proposed microwave photonic I/Q mixer shows significant advantages in local oscillator leakage and I/Q phase imbalance over entire RF bands, which are recognized as major drawbacks of conventional direct-conversion receivers.