基于MCU+FPGA双系统架构下的直接数字频率合成技术设计

介绍了DDS技术在MCU FPGA双系统的一种实现方法,重点介绍了MCU的控制系统设计与现场可编程逻辑门阵列FPGA实现直接数字频率合成的原理及其电路结构,并给出了利用ALTERA公司的Flex10K系列EPF10K10LC84-4设计实现方案.     

基于FPGA直接数字频率合成两种控制电路设计

本文介绍了利用FPGA器件实现直接数字频率合成的两种控制电路方案,即采用相位累加器和比例乘法器实现控制。介绍了它们工作原理和设计实现。控制电路设计采用VHDL语言和原理图相结合的形式,在FPGA芯片EPF10K片内实现。由此控制电路组成的直接数字频率合成与单片机相结合,可以方便、灵活和准确地实现信号发生器。     

直接数字频率合成器的FPGA设计与实现

在节约成本的前提下,为了提高主频频率,实现复杂的调制功能并具有良好的实用性,由相位概念出发,利用高性能的现场可编程门阵列(FPGA)器件(ACEXEP1K50)设计符合自己性能指标的要求的直接数字频率合成(DDS)电路,实现直接数字频率合成器的设计。对设计工作原理、电路结构进行了详细介绍,对设计的性能指标进行严格测试,同时提出了优化方法更好的提高了性能指标。设计结果达到预期效果,性能指标优良。     

基于FPGA的直接数字频率合成器的设计和实现

介绍了利用Altera的FPGA器件(ACEXEP1K50)实现直接数字频率合成器的工作原理、设计思路、电路结构和改进优化方法。     

FPGA在超声气体温度测量中的应用

现场可编程门阵列FPGA(Field Programmable Gate Array)是新一代可编程ASIC器件,它综合了分立器件和大规模集成芯片的优点,在数字电路设计中应用极其广泛.在超声温度测量系统中,应用数字移相技术,结合现场可编程门阵列器件(FPGA)设计了一个高速计数器,实现燃烧气体温度的快速、准确测量.     

基于FPGA的函数信号发生器

提出了一种通过直接数字合成(DDS)技术,利用FPGA(现场可编程门阵列)设计并实现函数信号发生器的方法,通过仿真与实验验证该方案可以产生各种常用的基本电信号.     

基于FPGA的DDS设计与实现

随着数字信号处理和集成电路技术的发展,直接数字频率合成(DDS)的应用越来越广泛。DDS具有相位和频率分辨率高、稳定度好、频率转换时间短、输出相位连续、可以实现多种数字与模拟调制的优点,而可编程门阵列(FPGA)具有集成度高、通用性好、设计灵活、编程方便、可以实现芯片的动态重构等特点,因此可以快速地完成复杂的数字系统。由于模拟调相方法有生产性差、调试不方便、调制度控制不精确等缺点,因此采用数字方法实现各种模拟调制也越来越普遍。现在许多DDS芯片都直接提供了实现多种数字调制的功能,实现起来比较简单。     

基于现场可编程门阵列的分频器的设计

现场可编程门阵列FPGA是近年来迅速发展的可编程ASIC器件,介绍了FPGA的特点和应用范围,并用FPGA设计不同频率和同频率不同相位的分频器,其中FPGA采用VHDL语言编写。现场可编程门阵列(FPGA)是近年来迅速发展起来的,一种可编程ASIC器件,本文介绍了特征和FPGA和FPGA设计了一种使用不同频率的分频器,采用VHDL语言进行编写。     

基于FPGA的高精度信号发生器的实现与优化

针对科里奥利质量流量计在线测试系统的需要,设计了一种基于现场可编程门阵列(FPGA,field programmable gate array),以直接数字频率合成技术(DDS,direct digital synthesis)为基础的高精度信号发生器.通过对其进行改进,在保证原有分辨率的情况下使研制方案节省了硬件资源...     

基于FPGA的并行DDS

介绍一种提高直接数字合成器(DDS)系统时钟频率的并行处理方法。给出了一个基于现场可编程门阵列(FPGA)的具有400MHz系统时钟频率DDS电路的实现方法和实验测试结果。采用直接中频输出方式,输出频率范围250MHz～350MHz,频率分辨率6Hz,寄生信号抑制50dB。该DDS电路具有接口简单、使用灵活等优点,可用于雷达、电子战领域的宽带信号产生。     

Thermal expansion of Chromium (Cr) to melting temperature

In situ x-ray data on molar volumes of chromium have been collected over the temperature range from 300 K to melting. The sample was heated to melting by passing an electrical current through the sample (the technique of electrical resistance wire heating). The sample consists of a tungsten wire as a heater and a mixture of Cr and W powder, which is placed in a hole of 250 μm diameter. Tungsten was used as an internal standard for temperature determination. In order to prevent the specimen from oxidation, the experiments were carried out in an argon flow. Unit cell parameters of Cr at different temperatures were calculated using (110), (200), (211), and (220) reflections. Precision of determination of lattice parameter is 10⁻⁴ A at 300 K and 5 10⁻⁴ A at 2000 K. Thermal expansion of Cr increases rapidly at temperatures higher than 1200 K. The linear thermal expansion () of chromium between 300 and 2130 K is given by: = 1.220(5) 10⁻⁵ − 1.150(6) 10⁻⁸ T + 1.132(8) 10⁻⁶ T² − 0.507(7)/T² (T, K). In our experiments, Cr melted between 2120 and 2150 K.     

用于低温环境的铂电阻温度微传感器

目前,铂电阻温度传感器主要应用于73 K(-200℃)以上环境的温度检测。设计了可用于10 K(-263℃)～200 K(-73℃)低温区的铂电阻温度微传感器。铂电阻温度微传感器采用对称的折回型结构,这种结构有效地降低了交流感抗的影响。传感器的敏感薄膜是一层采用磁控直流溅射沉积厚度为200 nm的铂薄膜。采用QD PPMS仪器测试传感器的电阻与温度的变化关系,得出传感器的电阻温度系数(TCR):研制的温度传感器的电阻温度系数在温度高于30K(-243℃)时可达到9980×10-6/K,同时在低于30K(-243℃)的深低温区域TCR也可达到3730×10-6/K。     

Fabrication and measured performance of a first-generation microthermoelectric cooler

The measured performance of a column-type microthermoelectric cooler, fabricated using vapor-deposited thermoelectric films and patterned using photolithography processes, is reported. The columns, made of p-type Sb/sub 2/Te/sub 3/ and n-type Bi/sub 2/Te/sub 3/ with an average thickness of 4.5 /spl mu/m, are connected using Cr/Au/Ti/Pt layers at the hot junctions, and Cr/Au layers at the cold junctions. The measured Seebeck coefficient and electrical resistivity of the thermoelectric films, which were deposited with a substrate temperature of 130/spl deg/C, are -74 /spl mu/V/K and 3.6/spl times/10/sup -5/ /spl Omega/-m (n-type, power factor of 0.15 mW/K/sup 2/-m), and 97 /spl mu/V/K and 3.1/spl times/10/sup -5/ /spl Omega/-m (p-type, power factor of 0.30 mW/K/sup 2/-m). The cooling performance of devices with 60 thermoelectric pairs and a column width of 40 /spl mu/m is evaluated under a minimal cooling load (thermobuoyant surface convection and surface radiation). The average cooling achieved is about 1 K. Fabrication challenges include the reduction of the column width, implementation of higher substrate temperatures for optimum thermoelectric properties, and improvements of the top connector patterning and deposition.     

高灵敏光波导传感器检测H2S气体

将甲基绿-聚乙烯醇薄膜固定在钾离子(K )交换玻璃光波导表面,研制出一种光学硫化氢气体传感器.实验结果表明,本传感器对浓度在20×10-9 ～1.3×10-6范围内的硫化氢气体有良好的线性响应(R= 0.989 7)和快速响应(t0.9小于3 s).本传感器具有灵敏度高、可逆性好、重现性高、成本低,结构简单和易制作等特点.     

Experimental investigation of phase relations in Bi-Te-RE (Yb,La, Ce) ternary systems

Rare earth (RE) elements especially Yb, La and Ce have been frequently doped to Bi-Te alloys to improve thermoelectric performance. Three isothermal sections: Bi-Te-Yb at 573 K, Bi-Te-La and Bi-Te-Ce at 673 K were partly established by means of electron probe micro-analysis (EPMA) and powder X-ray diffractometry (XRD). The determined maximum solubilities of RE elements in Bi-Te alloys are very small and that of Yb reached the maximum about 0.3 at% at 573 K. Both LaTe₂ and CeTe₂ can dissolve a large amount of Bi, about 10 and 13 at% at 673 K, respectively. No ternary compound has been confirmed.     

A micromachined system for the separation of molecules using thermal field-flow fractionation method

All silicon-glass micromachined thermal field-flow fractionation (TFFF) microsystem has been developed and presented for the first time. The device consists of seven layers of double side, deep, selectively etched silicon and glass substrates, bonded anodically. The built-in fluidic heater and cooler allows producing the high thermal gradient. In the 30 μm deep, 2 mm wide and 50 mm long separation channel, the temperature gradient 1.5×10⁶ K/m has been obtained for relatively low heating agent temperature (343 K). The TFFF microsystem has been equipped with two integrated, three-electrodes conductivity detectors. Some basic separation properties have been evaluated for low concentrated KCl test samples in water. It has been found that retention time of 0.6 μl sample of 0.01 M KCl in water, for 293/321 K (cooling/heating agents) compared to 0.9×10⁶ K/m, is almost two times longer than it has been obtained in the device during the absence of the temperature gradient.     

用Alter CPLD实现的虚拟相位差计设计

以 Alter CPL D FL EX10 K器件为虚似仪器核 ,在 Windows 95 /98下借助 Delphi 5 .0实现操作界面 ,对二个 5 0 m V～ 10 V、0 .2 Hz～ 13.8k Hz的正弦波、短形波等周期信号实现 4 7πf /10 7(f为待测信号频率 )分辨率相位差自动测量和分辨率显示的设计原理与实现方案     

O(N) parallel tight binding molecular dynamics simulation of carbon nanotubes

We report an O(N) parallel tight binding molecular dynamics simulation study of (10×10) structured carbon nanotubes (CNT) at 300 K. We converted a sequential O(N³) TBMD simulation program into an O(N) parallel code, utilizing the concept of parallel virtual machines (PVM). The code is tested in a distributed memory system consisting of a cluster with 8 PC's that run under Linux (Slackware 2.2.13 kernel). Our results on the speed up, efficiency and system size are given.     

Microfabrication of thin film temperature sensor for cryogenic measurement

In this paper, thin film Pt temperature microsensor in the temperature range of 10–100 K for cryogenic engineering applications is proposed and researched. The sensor is designed with two structures, and they are obtained by micro fabrication technology. The sensors are annealed in different conditions. The degree crystallization and grain size are analyzed by X-ray diffraction and SEM for both as-deposited and annealed sensors. The resistance dependency on temperature test result shows that when temperature is larger and smaller than 50 K, the average temperature coefficient resistance (TCR) of rectangular shape sensor could achieve 3,118 ppm/K and above 257 ppm/K, respectively. Meanwhile, TCR of circular shape sensor is 2,778 ppm/K and above 249 ppm/K, respectively. The good thermal cycle stability is observed. After three cycles between 10 and 100 K, the maximum resistance variation values are 0.0034 and 0.0137 %, which correspond to 0.0082 and 0.061 K temperature shift for the rectangular and circular sensors, respectively. The ΔT/T (%) of rectangular and circular sensors is performed with the magnetic field up to 6T in the temperature range of 10–100 K, and they are within the range of ?19.84 to 0.137 and ?2.18 to 11.33 for rectangular and circular sensors,respectively. The impedance test shows that the sensors have the same electric properties under direct current and alternating current condition.     

AVR单片机Atmega128在FPGA配置中的运用

在嵌入式系统设计中，掌握MCU对FPGA的配置，对系统的设计是十分必要的。根据EPF10K10的配置时序和AVR单片机Atmega128的接口特点，详细介绍了Atmega128对EPFl0K10配置的软硬件设计原理。