Growth of SiGe by D-UHV/CVD at Low Temperature

The temperature is a key factor for the quality of the SiGe alloy grown by D-UHV/CVD. In conventional conditions,the lowest temperature for SiGe growth is about 550℃. Generally, the pressure of the growth chamber is about 10~(-5) Pa when liquid nitrogen is introduced into the wall of the growth chamber with the flux of 6sccm of the disilane gas. We have succeeded in depositing SiGe films at much lower temperature using a novel method. It is about 10.2 Pa without liquid nitrogen, about 3 magnitudes higher than the traditional method,leading to much faster deposition rate. Without liquid nitrogen,the SiGe film and SiGe/Si superlattice are grown at 485℃. The DCXRD curves and TEM image show that the quality of the film is good. The experiments show that this method is efficient to deposit SiGe at low temperature.

A 12bit 300MHz Current-Steering CMOS D/A Converter

The proposed DAC consists of a unit current-cell matrix for 8MSBs and a binary-weighted array for 4LSBs, trading-off between the precision, speed, and size of the chip. In order to ensure the linearity of the DAC, a double Centro symmetric current matrix is designed by the Q2 random walk strategy. To achieve better dynamic performance, a latch is added in front of the current switch to change the input signal, such as its optimal cross-point and voltage level. For a 12bit resolution,the converter reaches an update rate of 300MHz.

一个10位、50MS/s CMOS折叠流水结构A/D���换器

在0.6μm DPDM标准数字CMOS工艺条件下,实现10位折叠流水结构A/D���换器,使用动态匹配技术,消除折叠预放电路的失调效应;提出基于单向隔离模拟开关的分步预处理,有效压缩了电路规模,降低了系统功耗.在5V电源电压下,仿真结果为:当采样频率为50MSPS时,功耗为120mW,输入模拟信号和二进制输出码之间延迟为2.5个时钟周期,芯片面积1.44mm2.

一种用于高速A/D���换器的高精度参考电压电阻网络

于2010-11-23批量导入

D���数字功率放大器电路失真分析及其负反馈方案讨论

于2010-11-23批量导入

Influences of initial nitridation process on the optical and structural characterization of GaN layer grown on sapphire (0001) by metalorganic chemical vapor deposition

In this paper. we investigate the influences of the initial nitridation of sapphire substrates on the optical and structural characterizations in GaN films. Two GaN samples with and without 3 min nitridation process were investigated by photoluminescence (PL) spectroscopy in the temperature range of 12-300 K and double-crystal X-ray diffraction (XRD). In the 12 K PL spectra of the GaN sample without nitridation, four dominant peaks at 3.476, 3.409 3.362 and 3.308 eV were observed, which were assigned to donor bound exciton, excitons bound to stacking faults and extended structural defects. In the sample with nitridation, three peaks at 3.453, 3.365. and 3.308 eV were observed at 12 K, no peak related to stacking faults. XRD results at different reflections showed that there are more stacking faults in the samples without nitridation.

D-木糖异构酶基因亚克隆及其序列分析

我们大肠杆菌K12的D-木糖操纵子中克隆了D-木糖异构酶基因，并以Bal31缩短DNA方法，获得了彼此相差约200bp的亚克隆。而后，用质粒系统直接测定了这些亚克隆片段的基因序列，并进一步得出含有D-木糖异构酶基因的1620bp全序列。序列结果表明，其结构基因长为1320bp，编码着由440个氨基酸组成的蛋白，与Lawlis和Schellerberg发表的D-木糖异构酶基因序列相比，同源性达99.8%。

加速器高频D���路Q值的计算与测量

介绍了回旋加速器高频单D���盒D���路Q值的计算与测量方法。重点对Q值的理论计算进行推导,并对计算原理进行说明。然后对计算结果和测量结果进行比较。得出的计算和测量结果基本吻合。误差产生的主要原因是计算过程中的近似和短路片接触电阻的取值,其中短路片接触电阻是一个重要因素,在设计腔体时应引起足够的重视。

关于量化和A/D-D/A的讨论

数字、量化、量化效应、模拟、模拟量、A/D���换、D/A转换是计算机控制工程和控制理论上的常见概念。静心推敲,发现有不少流行性的误解。例如:不是“量化”而是截尾或四舍五入,不是“数字量”而是bit量,不是“模拟量”而是物理量等。

Tree-ring-derived precipitation records from inner Mongolia；China；since a.d. 1627

IEECAS SKLLQG

Tree-ringbased drought reconstruction (a.d. 1855-2001) for the Qilian mountains；northwestern China

IEECAS SKLLQG