RC文氏电桥振荡条件的分析

RC文氏电桥振荡器广泛用于需要信号源的仪器设备中.简介了文氏电桥振荡器的工作原理,说明了"复数阻抗法"分析振荡器特性的优缺点.建立了文氏电桥的闭环传递电路模型,运用拉氏变换对电桥电路的传递函数进行了理论推导,讨论及仿真了RC文氏电桥振荡电路的工作及应用条件.     

单运放甚低频正弦波振荡器

本文讨论了几种以集成运放为基础，由单个元件控制的甚低频正弦波振荡器．电路简单．它们克服了以往甚低频正弦波振荡器的一些不足．实验结果表明本文所讨论的甚低频振荡器具有频率灵敏度低，调节方便的优点．     

一种新的有源电阻正弦波振荡器

本文提出并论述了一种新的有源电阻正弦波振荡器。这种振荡器仅由两个集成运放和电阻组成。理论分析和实验结果表明:只需调节一个接地的电阻,振荡频率可调范围相当宽;两个运放输出的正弦波是正交的。这种振荡器在数字通信和测量仪器中很有用。它可用作为波形、频谱分析仪的本机振荡器,也可用作为数字调制的移频键控(FSK)、移相键控(PSK)信号发生器。     

有源R型矩形波振荡器

本文给出一种有源Ｒ型矩形波振荡器电路，该电路由集成运放和电阻所构成，因此十分有利于振荡电路的集成化。     

有源R型矩形波振荡器

本文给出一种有源R型矩形波振荡器电路。该电路由集成运放和电阻所构成，因此十分有利于振荡电路的集成化．     

一种可调频率多相正弦波振荡器

文章论述一种采用跨导型集成运算放大器的多相正弦波振荡器，其振荡频率与运放的跨导（或偏置电流）成线性关系，可做成电压（或电流）控制振荡器，电调频率范围大，电路结构简单，有利于集成化，在测量、通信、信号处理、电力电子技术领域有着重要应用的前景。     

一种高稳定度的石英晶体微量天平

介绍一种频率稳定度优于０．３ＨＺ的石英晶微量天平，在微量天平的电路中采用了高稳定度的时期振荡器，探头采用丝或半导体致冷器件恒温结构，频率稳定度优于０．３ＨＺ。     

氦光泵磁力仪中压控振荡器设计

压控振荡器是跟踪式氮光泵磁力仪的核心部件。为了满足磁力仪的测量要求,需要一个频率范围宽,且振荡稳定度高,线性度好的压控振荡器。本文用多个变容二极管并联的方法,设计实现了一个西勒振荡电路,并在氦光泵磁力仪中得到应用。     

改进型高稳定度LC振荡电路的研究

在通信、检测电路中,作为调制和解调载波信号发生器的振荡电路,其频率稳定度是振荡器的一个很重要的指标.在阐明了频率稳定度的基础上,分析了三点式振荡电路中影响频率稳定性的各种因素,最后给出了一种改进型高稳定度的振荡电路.     

BD031 MEMS信号处理电路的研制及测试

本文报道了一个为电容式微加速度计传感器信号处理而设计的全集成化的BD031 CMOS MEM信号处理电路.电路设计采用了对信号的差分电容采样方式和过采样技术、前置采样放大器高增益和低噪声设计措施、可调节选通带宽的的低通滤波器及为提高电容噪声性能的带有虚开关结构的开关电容滤波器设计技术、可微调节增益(常规情况下恒定增益为2)的输出缓冲放大器、可调节振荡频率(正常情况下为800KHz)的本地CMOS时钟产生振荡器及为上述模拟电路提供基准电压和基准电流的基准电压源等设计技术、以及可以进行输入失调调节和对差分电容变化量△C的自测试电路.电路使用单一5伏电源,采用1.2微米、双多晶硅、双铝、N-阱CMOS工艺加工,芯片面积为2.82×3.61平方毫米.芯片性能测试表明其差分小电容变化量△C传感范围达到0.06pF-5pF、带宽为300Hz-5KHz.     

超高纯氯气的大规模产业化生产

超纯氯是半导体、光纤生产的重要原材料。近年来我国的半导体、光纤工业已从研究向产业化发展,作为重要电子气体的超纯氯将发挥重要的作用。为确保产品质量稳定、降低成本,对该产品进行产业化生产十分必要。     

麻武高速大别山隧道出口洞顶危石稳定性评价及开挖方案探讨

介绍了危石稳定性评价方法.采用危石爆破垂直振动最大速度作为评判标准,对隧道爆破掘进危石的稳定性进行了分析探讨,提出了确保危石安全稳定下的隧道爆破掘进参数.实践表明,爆破参数合理,危石在施工中安全稳定,说明这种方法可行.     

Extending the frequency range of a Wien-bridge oscillator usingcomposite operational amplifiers

The author describes the use of composite operational amplifiers to extend the useful operating frequency range of an operational amplifier-based Wien-bridge oscillator. The effect of the finite gain-bandwidth product (GB) of the operational amplifier (OA) is analyzed. This analysis shows that for a certain GB the frequency of oscillation is less than the theoretical value and that the error increases with frequency. A composite OA is then used to decrease the errors due to GB. This is verified theoretically and experimentally. Although the composite OA improves the frequency performance of the oscillator, the amplitude of the output decreases with frequency. An automatic-gain control circuit is incorporated to keep an output amplitude constant over the useful frequency range. Distortion measurements are presented     

基于动态特性的印制板结构改进

印制板的动态特性对电子设备的可靠性有较大的影响。本文结合计算方法和实验方法对印制板的动态特性进行研究 ,对二种方法所得结果进行比较 ,证实了本文所采用的印制板有限元模型成型技术的有效性。一般地 ,船舶运行时外界环境所引起的激励频率范围为几Hz至几百Hz ,为了避免印制板共振引起的产品失效 ,希望印刷板的基频越高越好。通过计算 ,证明了本文提出的二种结构改进设计方法不同程度地提高了印制板基频     

High-frequency overtone TCXO based on mixing of dual crystal oscillators

To implement a high-stability and high-frequency overtone temperature-compensated crystal oscillator (TCXO) conveniently, an improved design of the novel overtone TCXO is described in this paper. A 120-MHz TCXO based on mixing of dual crystal oscillators is implemented. It utilizes a 100-MHz AT-cut 5th-overtone crystal oscillator mixed with a 20-MHz AT-cut voltage-controlled crystal oscillator (VCXO). The 120-MHz mixed product is filtered to produce the output signal. The total frequency deviation of 20-MHz and 100-MHz crystal oscillators is compensated by adjusting the output frequency of the 20-MHz oscillator to produce the stable 120-MHz output frequency. In this work, verifying experimental results of the compensation are presented. The stability of the experimental 120-MHz overtone TCXO with microprocessor temperature compensation achieves +/-2 X 10(-7) over the temperature range from -30 degrees C to +70 degrees C. A phase noise level of -133 dBc/Hz at 1 kHz offset has been initially measured for the prototype TCXO. The experimental result demonstrates this approach can conveniently implement the high-frequency overtone temperature compensation with a relatively high stability, and it is available for a wider frequency range as well.     

Primary investigation on sound absorption performance of highly porous titanium foams

A novel sort of cellular titanium foam, whose total porosity was achieved as high as 86%–90% and main pores were spherically millimeter-scaled, was recently prepared successfully by an improved foaming method of melting the metallic powder. This titanium foam showed a good performance of sound absorption, and its sound absorption coefficient could be more than 0.6 in the sound-wave frequency range of 3150–6300 Hz and even exceed 0.9 at the resonance frequency. The main mechanism of sound absorption for this foam should be of interference silencing due to the surface reflection when the sound wave frequency is lower than about 4250 Hz, and the viscous dissipation when the frequency is higher than about 4250 Hz. A reticular product with millimeter-scaled pore size and about 90% porosity was also made by means of slurry-immersed sintering, and the resultant titanium foam might display an effect for sound absorption, but on the whole, its absorption was evidently inferior to that of the cellular product. The corresponding sound absorption coefficient could not be above 0.2 until sound-wave frequency is higher than 3150 Hz, keeping a relatively low value except for resonance occasion only, on which it could reach up to around 0.9 at about 4000 Hz.     

溶剂溶胀对聚丙烯熔喷非织造布过滤性能的影响

通过跟踪测试表面电位和过滤效率,研究了聚丙烯熔喷非织造布驻极体空气过滤材料经不同溶剂浸泡后过滤性能的变化及其与驻极体电场的相关性.结果表明:聚丙烯熔喷非织造布的高过滤效率主要源于驻极体电场产生的静电效应,而过滤阻力的大小则由其本身的结构所决定;驻极体电场的稳定性依赖于溶剂的溶胀作用.根据Flory-Huggins的溶剂溶胀理论探讨了溶剂浸泡对材料电荷存储能力和过滤效率的影响规律.     

A Meihod of Preparing Gelatin Microcapsules

In the pharmaceutical industry, microencapsulation has been applied to a variety of drug dosage forms. Usually a mechanical method produces a narrowly defined final product with a specific coating material and size of the core particles. Microcapsules were prepared by passing molten drug-gelatin mixture through a vibrating needle at a known frequency and amplitude. The microcapsules obtained were spherical, rigid, discrete, and had a narrow size range.     

三聚氰胺-甲醛成型品甲醛迁移量与生产工艺关系的研究

阐述了三聚氰胺-甲醛制品的生产加工工艺。 分析并试验研究了成型时间、排气次数、表面罩光和产品器型对甲醛迁移量的影响。 结果表明:相同原料加工的仿陶瓷餐具,在允许的成型时间和温度范围内,甲醛迁移量随时间的延长和温度的升高而降低;纯三聚氰胺-甲醛树脂罩光后甲醛迁移量降低;不同器型的甲醛迁移量不同。     

地基土上水工建筑物的抗滑动稳定研究

研究地基土上水工建筑物滑动设计和计算中存在的问题。利用基坑内压板抗滑动试验成果,确定地基土包括回弹影响后的抗滑动承载能力。采用地基土承受偏心荷载的最大压应力σmax控制地基土与压板的位移和抗滑动形式,可以发生不同的3种最大位移面,形成6种抗滑动形式。根据地基土承受的最大压应力,提出设计抗滑动的计算方法:定量确定地基土与压板抗滑动的摩擦系数计算值,地基土的抗滑动安全系数由指标安全系数控制,修正在地基土上建筑物整体滑动的计算公式,计算预测可能发生的多种最大位移面和抗滑动形式及绘制地基土滑动区轮廓,限定地基土发生平面抗滑动形式时承受的最大压应力值。按拟定方法,回顾分析3座已建水工建筑物,分析计算成果符合实物工况。