Some system design considerations for a high switching frequency PWM inverter

A sinusoidal PWM inverter is required to faithfully reproduce the control waveforms at the output with minimum distortion. This paper presents some design considerations for such an inverter. The choice of switching frequency is the main criterion which affects the output voltage harmonic distortion at high switching frequencies. This paper shows that there exists an optimum switching frequency above which the output harmonic distortion becomes more visible. The dead time generator circuit for a low cost inverter and effect of driver circuits on the output waveform are discussed. Experimental results from laboratory models are presented.     

环绕声前方三声道全指向传声器阵列定位畸变

以环绕声前方三声道全指向阵列系统为对象,研究声源入射角度与重放声像定位之间的关系。在对理想状态下的阵列系统做出分析的基础上,阐述声道间的串音、声源到传声器之间强度差、频率等因素如何使声像发生畸变。进而讨论为避免声像畸变,如何在实际录音过程中对传声器阵列系统进行调整。     

高精度图像尺寸检测镜头畸变校正方法与实现

在高精度轴类零件尺寸图像检测中,提出了一种基于标准件法对镜头径向畸变进行快速校正的方法。该方法通过建立世界坐标转换到摄像机坐标、然后再转换到图像坐标的理想数学模型,并引入径向畸变参数,最终确立物体在世界坐标中与图像坐标中的映射关系,从而建立误差补偿曲线的高次拟合函数。利用得到的误差补偿函数的系数矩阵和径向畸变参数,实现镜头畸变的误差校正,有效改善了镜头畸变造成的检测误差。实验表明,该方法快速有效,提高了检测精度、降低了设备成本、检测精度可达2 μm。     

Large signal analysis of mixers with difference frequency injection

Large signal analysis of mixers excited by three tone signals is presented. The special case of two equal-amplitude sinusoids plus a difference-frequency injection is considered in detail and the results are compared, whenever possible, with previously published results. Contrary to previously published results, it is shown that even under large signal conditions and strong nonlinearity it is possible, at least in theory, to totally eliminate the third-order intermodulation when the amplitudes of the equal-amplitudes input sinusoids and the difference-frequency injection are equal.     

基于渐变方程的鱼眼图像校正方法

由于具有短焦距、大视场等特点,近年来鱼眼镜头被广泛应用于不同领域。但同时也存在鱼眼图像畸变较严重的问题,针对这一问题,提出了一种基于渐变方程和经纬映射模型的图像校正算法。利用经纬映射模型导出鱼眼图像中的相互关系,提取校正前后坐标的关系方程,然后引入渐变方程,实现图像校正。实验结果表明,该算法具有良好的校正效果。     

应用于矢量量化的竞争学习算法研究

本文依据部分失真定理提出了一种应用于矢量量化的竞争学习新算法－－部分失真均衡竞争学习算法，与目前流行的多种竞争学习算法相比，该算法对于不同尺寸码书的设计均取得了最好的结果，特别是对于大尺寸码书的设计，效果更为明显。     

High Performance Piezoelectric Microspeakers and Thin Speaker Array System

This paper reports on an improved piezoelectric microspeaker with a high sound pressure level of 90 dB, a total harmonic distortion of less than 15%, and coherence higher than 0.9. The fabricated Pb(Zr,Ti)O₃ (PZT) microspeakers have a thickness of only 1 mm including the speaker frame and an active area of 18 mm×20 mm. To achieve higher sound pressure and lower distortion, the PZT piezoelectric microspeaker has a well‐designed speaker frame and a piezoelectric diaphragm consisting of a tilted PZT membrane and silicone buffer layer. From the simulation and measurement results, we confirmed that the silicon buffer layer can lower the first resonant frequency, which enhances the microspeaker's sound pressure at a low frequency range and can also reduce useless distortion generated by the harmonics. The fabricated PZT piezoelectric microspeakers are implemented on a multichannel speaker array system for personal acoustical space generation. The output sound pressure at a 30 cm distance away from the center of the speaker line array is 15 dB higher than the sound pressure at the neighboring region 30 degrees from the vertical axis.     

光分组交换系统中载波抑制光标签的研究

为了研究高带宽利用率和大容量的光分组交换系统,对载波抑制调制原理进行理论分析,提出了一种载波抑制调制光标签的方案,并对基于载波抑制调制的光标签系统进行了仿真分析和实验研究。结果表明,载波抑制光标签的中心载波抑制比达到21.3dB;在622Mbit/s和1.25Gbit/s的标签调制速率下,系统传输距离超过40km时,依然能保持低于10-10的误比特率;以误比特率10-10为标准,在传输距离为40km时,两种标签调制速率的功率代价分别为1.7dB和1.9dB。此结果说明载波抑制光标签在光分组交换系统中具有串扰小、功率代价低等特点,信号质量好,适合远距离传输。     

超高压汞灯电源高压大电流触发干扰分析与抑制措施研究

分析了超高压汞灯电源启动时高压大电流电磁干扰的产生机理,针对启动时高压大电流触发干扰,从频域,空域和时域方面,提出了抑制干扰的方法和措施。     

EUV掩模版在曝光过程中的热变形

极紫外光刻(EUVL)技术是实现45 nm特征尺寸的候选技术之一,产业化设备要求300 mm硅片的产率大于每小时80片(80 wafer/h),此时入射到掩模版上的极紫外光功率密度很高,掩模版上的吸收层和Mo/Si多层膜将分别吸收100%和35%的入射光能量,从而导致其热变形,引起光刻性能下降,因此必须分析和控制掩模热变形。利用有限元方法分析掩模版在不同功率密度下的热变形,结果表明,抗蚀剂灵敏度为7 mJ/cm2和5 mJ/cm2时,入射到掩模版上的光功率密度分别为259.24 W/cm2和184.38 W/cm2,掩模版图形区域x-y平面内最大变形分别为1.11 nm和0.71 nm,z方向最大变形分别为0.26 nm和0.19 nm。