Study and analysis of coefficient mismatch in a MASH21 sigma-delta modulator

The quantization noise leakage of the first stage in a MASH21 sigma-delta modulator is analyzed.The results show that the finite DC gain of the opamp is the main reason for noise leakage,and finite GBW and SR only generate harmonic distortion.The relationship between DC gain and leakage is modeled and conclusions on design criteria are reached.As an example,a MASH21 modulator for a digital audio application is realized.This modulator, fabricated in an 0.18μm mixed signal process,achieves an SNDR of 91 dB...     

Heat transfer and thermal storage behaviour of gypsum boards incorporating micro-encapsulated PCM

In the application of energy storage and thermal environmental control, PCM (Phase Change Material) is a very promising material choice. This study incorporated mPCM (micro-encapsulated PCM) into gypsum to make mPCM gypsum board and then investigated the physical properties, heat transfer and thermal storage behaviour. The major control parameters are wall temperatures and the weight percentages of mPCM added to the gypsum boards. A melting fraction correlation, reduced from our test data and based on Stefan number (Ste), subcooling (Sb) and Fourier number, is proposed. It shows that case with a higher Ste or Sb can have a higher heat transfer through the hot wall. Thermal storage behaviour of mPCM gypsum boards is then analyzed.     

莫来石结合碳化硅高温吸热陶瓷抗氧化性能的研究

以碳化硅及合成莫来石微粉为主要原料,制备了用于非真空太阳能吸热管的莫来石结合碳化硅高温陶瓷涂层。针对碳化硅基材料高温氧化问题,测定了样品的烧成增重率及亮度并结合XRD、SEM研究了莫来石结合碳化硅陶瓷的抗氧化性能。结果表明,莫来石添加量为20%,经1 380℃烧成样品的抗氧化性最好,其增重率为7.49%,亮度值为46.61。XRD分析烧结体主晶相为碳化硅(α-SiC)和莫来石(3Al2O3.2SiO2),并含有少量的方石英(SiO2),莫来石作为结合相在碳化硅晶粒周围形成"骨架",与SiO2玻璃相形成三围的网状保护层包裹在碳化硅表面,阻止碳化硅氧化。     

低功耗低误码率的传感器网络节点芯片数字基带设计

本文针对无线传感器网络节点片上系统特点和需求,研究一种低功耗、高性能、低误码率的数字基带(Easibaseband),提出了一种复用加法器和乘法器的设计方法,实现了匹配滤波器,可节省硬件资源并提高系统性能;提出了一种自适应门限的自动增益控制方法,可配合软硬件协同的工作方式,节省接收机的功耗;提出了采用自适应门限的施密特触发器方式进行信号相位判决的方法,降低了解调误码率.本设计在Xilinx的Spartan-3E FPGA上验证并实现,测试结果表明,本收发机的数据传输率可达到111kb/s并支持ISM2.4GHz频段的射频芯片,比传统的并行滤波器节省了5/6的硬件资源,比不采用自动增益控制节省了10.8%的接收机功耗,在信噪比13dB时,误码率在10-4以下,远低于WiseNET的接收误码率.     

优质宽带直流功率放大器的研究

对宽带直流放大器进行分析和研究。提出基于差分型双渥尔曼组合电路的解决方案,方案电路简单实用,巧妙地解决了直流放大器中的零点漂移问题,并有效抑制共模信号的影响,确保直流工作状态稳定。同时,在交流状态情况下,能有效地扩展通频带宽。     

化学镀银织物电磁屏蔽效能及透湿透气性能研究

为研究化学镀银对织物性能的影响,采用葡萄糖作还原剂对涤纶织物进行镀银,借助扫描电镜、网络分析仪、织物透湿仪、织物透气量仪等,对镀银织物的表面镀层形貌、织物的电磁屏蔽效能,以及织物的透湿、透气性能进行测试分析。结果表明:随着增重率的变大,织物的屏蔽效能增加,当增重率达到37%时,电磁屏蔽效能增加不明显,故应根据需要合理选择面料的镀层厚度;研究还发现镀层厚度对织物的透湿、透气性有影响。     

环锭细纱机电锭驱动管理技术应用探析与展望(下)

对环锭细纱机电锭驱动管理技术的应用效应和功能进行了分析,并对其促进行业专业与管理技术进步的发展趋势作出了展望,提出了电锭驱动管理技术不仅是生产高品质纱线理想的加捻卷绕驱动技术,而且将会给纺纱过程特别是细纱生产过程的管理和控制带来前所未有的革新.     

Derivation of power gain for three types of three dimensional photovoltaics cells

In order to quantify the higher power output seen from solar cells with a three‐dimensional (3D) topology due to the increased interactions between photons and the cell surface, we have derived a formula for the average number of interactions, Γ, between a photon and the cell surface for 3D cells with vertical sidewalls and flat tops. We have derived Γ for three different cell morphologies, an infinite trench in the x‐ or y‐direction, an enclosed box, and an infinite two‐dimensional (2D) array of towers. Monte Carlo simulations were carried out in order to compare computational results for Γ with those derived. For varying distance between features, d, and photon azimuthal angle, the data fits the derived expressions quite well for a large range of values. For varying tower height, the data fits theory well for both the trench and box morphologies, however, theory overestimates the value of Γ for the 2D array of towers. This is due to simplifications made when deriving Γ. However, the error associated with Γ is small enough that it propagates to a measured power output error of less than 1% for cells with an absorbance efficiency of at least 25%. Even with simplifications, the derived expression for Γ should be usable for predicting the increased power output for 3D cells with vertical sidewalls and flat tops. Copyright © 2011 John Wiley & Sons, Ltd.     

S波段电阻型上变频器的设计

利用双极性三极管的输出特性,设计了一个主要应用于2.4GHz无线局域网中的S波段电阻型上变频器,并在Agilent公司的射频电路设计软件ADS2003进行了S参数和谐波平衡仿真,取得变频增益是8.17dB,射频一本振端口隔离为14dB,射频-中频端口隔离为36dB较好的结果。而电路经过最后的调试,得到的变频增益是6.28dB,射频-本振端口隔离为18dB,射频-中频端口隔离为16dB,结果表明仿真结果跟测试结果十分相近。     

影响STAR微电阻率成像测井效果的因素分析

文章将STAR微电阻率成像电路原理及操作方法结合起来,针对STAR微电阻率成像测井四大影响因素（外界环境影响、极板压力、增益选择、时钟信号及同步信号）进行分析,提供有效地方法以便获得理想的成像效果图。