欠采样条件下金属构件近表面缺陷深度高精度测量方法

针对欠采样条件下金属构件近表面缺陷深度测量时,缺陷回波与表面回波重叠,导致缺陷深度测量不准确的问题,提出一种基于超声回波信号重采样和时频变换的金属构件近表面缺陷深度高精度测量方法。采用变分模态分解将超声回波信号分解为一系列窄带模态分量,根据相关系数实现有用模态分量聚类,得到预处理信号;对预处理信号进行三次样条插值处理,实现欠采样回波信号数据扩充,得到重构信号;基于同步提取变换得到重构信号的时频谱及其幅值分布曲线,并根据超声单收发原理,实现金属构件近表面缺陷深度高精度测量。实验结果表明,本文方法可实现欠采样条件下金属构件近表面缺陷深度的准确测量,测量相对误差为2.161%,明显优于包络法和时频变换法,其测量相对误差分别为3.570%和13.182%。此外,分析了欠采样率、信号噪声和缺陷位置对近表面缺陷深度测量精度的影响,结果一致表明本文方法在不同采样率、不同噪声和不同缺陷深度情况下对近表面缺陷深度测量,比传统方法均具有更好的准确性和鲁棒性。

A 6-bit 4 GS/s pseudo-thermometer segmented CMOS DAC

A 6-bit 4 GS/s, high-speed and power-efficient DAC for ultra-high-speed transceivers in 60 GHz band millimeter wave technology is presented. A novel pseudo-thermometer architecture is proposed to realize a good compromise between the fast conversion speed and the chip area. Symmetrical and compact floor planning and layout techniques including tree-like routing, cross-quading and common-centroid method are adopted to guarantee the chip is fully functional up to near-Nyquist frequency in a standard 0.18 #m CMOS process. Post simulation results corroborate the feasibility of the designed DAC, which can perform good static and dynamic linearity without calibration. DNL errors and INL errors can be controlled within 4-0.28 LSB and 4-0.26 LSB, respectively. SFDR at 4 GHz clock frequency for a 1.9 GHz near-Nyquist sinusoidal output signal is 40.83 dB and the power dissipation is less than 37 roW.