S/N Optimized, Programmable 1–10 MHz Bandwidth and 0–20 dB Gain, Precision I-Q Communication Channel for Digital Video Applications

An analog part of a digital-video quadrature demodulation scheme is built using a 7 GHz, 0.8 m biCMOS process. The scheme provides for 1–10 MHz cutoff frequency and 0–20 dB gain controls and dissipates 250 mW from a power supply of 5 V. The channel filtering is realized by two identical 4th Order Butterworth lowpass filters built with the g _m -C technique. They are equipped with cutoff programming and in-package trim tuning for cutoff adjustment. A programmable gain amplifier is placed in front of each filter for better joint noise and intermodulation performance. Such an arrangement allows to operate the filter at a maximum signal level improving the worst-case channel S/N by 6.5 dB. For the in-band components the worst case S/N is better than 41 dB, whereas THD and IMD are less than –48 dB. This single-ended channel achieves PSRR of 42 dB.     

A fast adaptive resonance suppression scheme for high-damping system using R-SDFT detection

Adaptive notch filter resonance suppression scheme is widely used in high-performance servo drivers. For high-damping system, the deviation between resonant and oscillation frequency will cause a long sustained vibration in traditional suppression schemes, which may damage the precision machine irreparably. To reduce the harm of sustained vibration, a fast adaptive notch filter scheme based on range-shifted discrete Fourier transform (R-SDFT) is proposed. Different from the traditional scheme, the new one eliminates the deviation between resonant and oscillation frequency by notch filter other than the low-pass filter, which massively simplifies the suppression process and reduces the number of oscillation frequency detection required. Meanwhile, an oscillation detection method based on R-SDFT is presented to shorten the time of the detective process through interval detection and prediction strategy. Compared with the traditional strategy, the experimental results demonstrate that the proposed adaptive suppression scheme can reduce the oscillation time by more than half.     

消除采样累加过程中的周期性噪声对DTS精度的影响

分布式光纤测温系统中不仅有白噪声干扰,还有周期性噪声干扰,而传统的采样累加平均方法仅能消除白噪声干扰。提出一种在采样累加过程中对采样周期内各点累加的方法,判断和滤除采样周期内的周期性信号。测温实验结果表明,通过在累加过程中设置判据消除周期性噪声,分布式光纤测温系统的精度得到了大幅提高。     

Na+和K+对水泥基材料早期收缩性能的影响

利用压汞、纳米压痕以及27Al固体核磁共振方法,系统研究了不同碱金属离子(Na~+和K~+)与含量对水泥基材料早期自收缩和干燥收缩性能的影响规律。结果表明,超量的Na~+或K~+均促进了水泥基材料早期自收缩和干燥收缩,但K~+的促进作用明显大于Na~+,其机制在于:(1)K~+比Na~+更易促进水泥基材料中小于50纳米孔数量的增加,这使得超量K~+水泥基材料在干燥时具有更大的收缩驱动力;(2)虽然K~+比Na~+更易促进水泥基材料生成高密度水化硅酸钙(HD C-S-H),但同时超量K~+水泥基材料中C-S-H总量也较高,大量的C-S-H是导致较高早期收缩的根源;(3)与Na~+相比,K~+更明显地阻碍了钙矾石(AFt)晶体的形成,削弱了AFt的骨架作用,且K~+可促使AFt向单硫型水化硫铝酸钙(AFm)转变,因而导致超量K~+水泥基材料更易发生收缩变形。     

基于FDMA的超声波室内定位信标识别方法

在超声波室内定位的信标识别问题上,针对无线射频控制分配的信道策略复杂性高、定位滞后和基于码分多址(CDMA,code division multiple access)方法的自相关运算量巨大问题,提出基于频分多址(FDMA,frequence division multiple access)的超声波室内定位信标识别方法,令超声波具备信息携带能力.通过对信号调制技术的分析,在超声波频率响应范围内,利用不同频率的载波调制信源身份识别码,接收节点通过解调、匹配区分信号源进行定位.采用Simulink对多路信号传输过程以及调制与解调进行仿真,并用电路仿真发射、识别了编码.结果表明,FDMA方法能有效区分多路信号源互相干扰,准确恢复发射节点身份识别码,大大减少计算量,有利于定位效率的提高.     

基于神经元阈上非周期随机共振机制的语音复原技术研究

应用随机共振机制.通过噪声能量来加强语音信号,改善低信噪比语音的输出质量.对FitzHugh-Nagumo(FHN)神经元模型中存在的阈上非周期随机共振现象进行了分析,根据其阈值特性,此二维神经元模型可被等价为两状态的阈值跨越非线性动力学系统.因此对含噪语音信号添加噪声,产生阈值化后的二值输出,经迭代收敛进入阈上非周期随机共振状态.在一个非零添加噪声强度上,含噪语音输出的互相关系数将达到最大值.通过语音复原的结果表明,本文方法对噪声的变化有更好的鲁棒性,尤其在强背景噪声下,随机共振方法较其他传统方法有更佳的复原效果.     

基于自适应神经网络的高速数字电路测试的研究

介绍了神经网络的模型建立。针对高速数字电路故障诊断的特点,提出了基于自适应神经网络诊断方法;与传统的神经网络相比,基于自适应神经网络具有学习速度快、网络能够收敛到最优权值、收敛精度很高、网络的分类能力强等特点,从而很好地提高故障诊断的效率;通过一个测试用例验证自适应神经网络在高速数字电路测试诊断中的应用,可以大大提高故障诊断的效率。     

Analysis of dynamic sensing of force between a probe and a vibrating sample for purposes of atomic force microscope

Using a perturbation method, we study the influence of the vibration of the sample on the resonance curve of a probe. The obtained resonance curve indicates that both the resonance frequency shift and the vibration amplitude of the probe are proportional to the gradient of the interaction force between the probe and the sample, even if the probe is not forced to vibrate by an external force. For several surface forces such as the Casimir force, which are described by power functions, we show that the frequency shifts obtained by the perturbation method agree well with those obtained by numerical simulations.     

Performance of thin film silicon MEMS on flexible plastic substrates

The fabrication and characterization of thin film silicon MEMS microbridges on flexible polyethylene terephthalate substrates are described. Surface micromachining using an aluminum sacrificial layer and a maximum processing temperature of 110 °C was used for device fabrication. These microbridges are electrostatically actuated and their deflection at resonance and at low frequencies is measured optically. Quasi-DC deflection with a quadratic dependence of the actuation voltage is observed, and resonance frequencies up to 2 MHz and quality factors of around 500 are measured in vacuum. Bending measurements are performed by subjecting these devices to tensile and compressive strain. The low frequency response (bridge deflection as a function of the applied voltage) was measured in air before bending and after every bending step. Under tensile strain, 16.6% of the devices survive the maximum bending with a radius of curvature of 1 cm, equivalent to a tensile strain 1.25%. In contrast, for compressive strain, 50% of the devices survive the bending corresponding to a radius of curvature of −0.5 cm, equivalent to a compressive strain of −2.5%. Thin film silicon microresonators on flexible plastic substrates can withstand more compressive strain than tensile.     

基于C/A码辅助的GPS M码信号盲解调

针对GPS M码信号受到C/A码和Y码信号的干扰难以直接进行解调的问题,提出了一种基于C/A码辅助的M码盲解调方法。利用解调后的C/A码信号校正信号频偏,通过I/Q支路分离实现将C/A码信号与Y码、M码信号的剥离,最后利用M码信号的特点进行相参增强进一步提高性能。实采数据的解调实验证明了所提算法的可行性。