基于重叠与正交信号的超宽带系统性能研究

文章首先介绍了跳时超宽带(TH-UWB)信号,推导了在加性高斯白噪声(AWGN)信道条件和多径条件(MP)下,基于重叠和正交脉冲信号的系统误码率公式,并给出了仿真结果.仿真结果表明,在AWGN信道条件下,基于重叠脉冲信号的跳时二进制脉位调制(TH-BPPM)系统的性能优于基于正交脉冲信号的系统.多径条件下的正交TH-BPPM系统的性能优于AWGN信道条件下的系统性能.     

SrCoO_(3–δ)陶瓷材料的导电机理和低温热敏特性

用固相反应法合成了可在液氦(4.2K)温度下使用的、非化学计量结构氧化物SrCoO3–δ热敏电阻材料,用XRD、SEM对其进行了表征,同时还测试了低温条件下的电阻值,分析了材料的导电机理和磁阻特性。测试结果表明:材料的B值为35K左右,与在液氢(20K)温度下使用的热敏电阻元件参数(B=300K)比较,SrCoO3–δ热敏材料可在液氦(4.2K)温度下使用。     

光纤位移传感器在77和4.2 K下的输出特性研究

介绍了一种可用于低温装置内的补偿式光纤位移传感器(CFODS),讨论了该传感器在低温下的输出特性并在液氮温度(77 K)和液氦温度(4.2 K)下进行了实验研究.结果表明,该传感器在液氮温度下的灵敏度0.311 mm-1,高于液氦温度下的灵敏度0.278 mm-1.     

双势垒量子阱薄膜力电耦合特性实验

用分子束外延方法在(001)GaAs衬底上生长了AlAs/InGaAs双势垒量子阱薄膜结构.介绍了量子阱薄膜在(110)与(110)方向单轴压应力作用下的力电耦合实验,测试出量子阱薄膜在室温下随着外加压力变化的I-V曲线.测试结果表明:量子阱薄膜I-V曲线的共振峰在(110)方向单轴应力作用下向正偏压方向漂移,在(110)方向应力作用下向负偏压方向偏移,并分析了量子阱薄膜力电耦合效应的物理成因.该结果与基于量子阱力电耦合特性的介观压阻理论的研究结果相吻合.     

氧气压强对Si基片上沉积YIG薄膜微观结构和磁性的影响

本文研究了氧气压强对用脉冲激光沉积技术(PLD)在Si(100)基片上制备的YIG薄膜性能的影响。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、震动样品磁强计(VSM)、铁磁共振仪(FMR)等检测了薄膜微观性能及磁性。研究发现:(1)在0.3Pa和1Pa下制备的YIG薄膜中没有杂相,而在4Pa和16Pa的薄膜中出现了YIP相;(2)薄膜的晶粒尺寸随氧压增大而减小;(3)在1Pa下制备得到的薄膜共振线宽最小,为91Oe;(4)薄膜饱和磁化强度(Ms)随氧压的增加而降低,1Pa下得到的薄膜的Ms为138Oe,最接近理论值。     

弱湍流信道MIMO-FSO系统误时隙率分析

分析了在弱湍流信道模型下基于开关键控(OOK)、脉冲位置调制(PPM)、差分脉冲位置调制(DPPM)和数字脉冲间隔调制(DPIM)方式的多输入多输出自由空间光(MIMO-FSO)通信系统模型。首先推导了各调制方式下单输入单输出(SISO)系统的误时隙率(SER)计算公式,以此作为参考,在独立同分布的条件下,推导出MIMO-FSO系统的平均SER计算公式,并用数值仿真的方法,分析了它们的平均SER性能。仿真结果表明,在弱湍流信道模型下,PPM可获得最好的SER性能,采用MIMO方法能有效提高FSO系统的平均SER性能。     

基于部分码字消息传递的SCMA多用户检测算法

基于消息传递算法(MPA)进行多用户检测的稀疏码多址接入(SCMA)技术是一种面向5G的非正交多址技术(NOMA)。针对MPA复杂度较高的问题,该文首先分析接收信号概率密度函数值在不同信噪比(SNR)下的统计结果,并根据SCMA的非正交特性,综合考虑资源节点和用户节点之间的数据映射关系,提出基于概率密度函数值门限判决的部分码字搜索(PCS)MPA多用户检测算法(PCS-MPA)。仿真结果表明,在门限值合理的条件下,PCS-MPA在几乎不改变系统误比特率(BER)的条件下,降低了MPA的复杂度,尤其在高SNR条件下效果更好。     

在不同衬底上生长ZnO薄膜及其特性研究

在不同衬底温度下用脉冲激光沉积法(PLD)分别在n-Si(111)、蓝宝石(001)和非晶石英衬底上生长了ZnO薄膜。首先对薄膜进行了X射线衍射(XRD)分析,找出在三种不同衬底上制得的结晶质量最好的ZnO薄膜所对应的最佳衬底温度。然后对最佳衬底温度下得到的ZnO薄膜分别进行了X射线衍射(XRD)、光致发光谱(PL)和原子力显微镜(AFM)分析。结果表明,在硅衬底上生长的ZnO薄膜XRD谱半高宽最小,PL谱特征发光峰强度最强,AFM下的平均粒径最大,说明硅衬底上生长的ZnO薄膜结晶质量最好,而在石英衬底上生长的ZnO薄膜结晶质量最差。     

基于OpenCV在Android平台下实现人脸识别

本文提出了使用OpenCV(Open Source Computer Vision Library)在Android平台下实现人脸识别的方法。首先,本文介绍了OpenCV2.4的人脸识别算法类FaceRecognizer的使用以及在Windows平台下的实现,接着详细的阐述了利用Android下的JNI(Java Native Interface),并结合Android NDK(Native Development Kit)调用和编译OpenCV下的相关函数,生成共享函数库。经过实验的在Android下人脸识别效果良好。     

浅析静电纺丝技术制备多种结构的纳米线

文章采用静电纺丝法制备La_(0.325)Pr_(0.3)Ca_(0.375)MnO_3和TiO_2的纳米线,先配置La_(0.325)Pr_(0.3)Ca_(0.375)MnO_3和TiO_2的前驱体溶液,并把它们放在静电纺丝机下纺丝后退火,得到了La_(0.325)Pr_(0.3)Ca_(0.375)MnO_3和TiO_2的单根纳米线。在此基础上,利用同轴针头,在外层加入La_(0.325)Pr_(0.3)Ca_(0.375)MnO_3溶液,芯层加入TiO_2溶液,观察得到纳米线的结构形貌,确定得到了La_(0.325)Pr_(0.3)Ca_(0.375)MnO_3_TiO_2的同轴纳米线。在静电纺丝技术下,笔者成功实现了对纳米线结构的控制。     

A novel one-stage forward-type power-factor-correction circuit

A novel power-factor-correction (PFC) circuit is proposed which is constructed with one stage by using a single forward converter. This PFC circuit has functions of high power factor and suppression of the output voltage ripple. The high power factor is accomplished by making the PFC circuit operate in the discontinuous conduction mode and the suppression of the output voltage ripple by using the exciting energy of the transformer in the forward converter     

DC voltage sensorless single-phase PFC converter

We propose a simple DC voltage sensorless single phase PFC converter by detecting an AC line voltage waveform. Both DC voltage and AC current sensors used in the conventional PFC converter are not required to construct the control system. The conventional converter circuit with a boost chopper circuit in the DC side from a rectifier circuit is used as the main PFC converter circuit. In the control system, the circuit parameters such as a series inductance L and equivalent load resistance value R/sub d/ are used to generate the sinusoidal current waveform. The DC voltage is directly controlled by the command input signal k/sub d/(=E/sub d//E/sub a/) for the boost chopper circuit. The DC voltage regulation is small because of the feed forward control for the AC line voltage E/sub a/ and no dependence of the circuit parameters. The sinusoidal current waveform in phase with the AC line voltage can be obtained. The feasibility of the proposed control system is verified by some simulation and experimental results.     

无直流电压传感器的单相APFC变换器

文章对一种只检测交流输入电压而不需要检测输出直流电压的简化单相PFC变换器进行了理论分析和研究。在构建控制电路时,不需要常规PFC变换器中的输出电压传感器和输入电流传感器。PFC变换器的主电路为整流电路的直流侧接一级Boost电路。在控制电路中,使用电感L、等效负载电阻Rd等电路参数产生正弦电流波形基准,输出电压直接由控制量Kd(=Ed/Ea)来调节。通过控制,可以得到恒定的直流输出电压和与交流输入电压同相位的正弦电流波形。仿真结果证明了该变换器的可行性。     

A family of PFC voltage regulator configurations with reducedredundant power processing

This paper discusses a systematic method for deriving basic converter configurations that achieve power factor correction (PFC) and voltage regulation. The discussion begins with a general three-port representation of power supplies that provide PFC and voltage regulation. Based on this representation and a power flow consideration, a systematic procedure is derived to generate all possible minimal configurations. Among these configurations, only a few have been known previously and used in practice. It is found that the efficiency of PFC voltage regulators can be improved by reducing the amount of redundant power to be processed by the constituent converters. A systematic circuit synthesis procedure is proposed for creating PFC voltage regulators with reduced redundant power processing. Experimental measurements verify the improved efficiency     

Low-power variable frequency PFC converters

Based on the SinoMOS 1 μm 40 V CMOS process, a novel power factor corrention (PFC) converter with a low-power variable frequency function is presented. The circuit introduces a multi-vector error amplifier and a pro-grammable oscillator to achieve frequency modulation, which provides a rapid dynamic response and precise output voltage clamping with low power in the entire load. According to the external load variation, the system can modulate the circuit operating frequency linearly, thereby ensuring that the PFC converter can work in frequency conversion-mode. Measured results show that the normal operating frequency of the PFC converter is 5-6 kHz, the start-up current is 36 μA, the stable operating current is only 2.43 mA, the efficiency is 97.3%, the power factor (PF) is 0.988, THD is 3.8%, the load adjust rate is 3%, and the linear adjust rate is less than 1%. Both theoretical and practical results reveal that the power consumption of the whole supply system is reduced efficiently, especially when the load varies. The active die area of the PFC converter chip is 1.61×1.52 mm~2.     

A soft-switching mode rectifier with power factor correction andhigh frequency transformer link

This paper presents a soft-switching mode rectifier (SSMR) consisting of a power factor correction zero-voltage-transition-pulse-width-modulated (PFC ZVT-PWM) converter and a high-frequency transformer-coupled DC/DC zero voltage switching clamped voltage (ZVS-CV) converter. An easily implemented ZVT soft-switching mechanism is developed to reduce the switching losses and stresses of the power switches in the PFC ZVT-PWM converter. The operations of the proposed SSMR in various modes are analyzed in detail and the associated governed equations are derived. Then accordingly, a quantitative design procedure is developed to find the values of soft-switching circuit components. In the control aspect, the dynamic model of the SSMR is derived and a current waveform controller is designed, such that sinusoidal line current with low harmonics and near unity power factor is obtained. Under this condition, a voltage controller is also designed for yielding good DC output voltage control characteristics. Validity of the designed SSMR is verified experimentally     

一种改进的ZCT无桥功率因数校正电路设计

为了降低开关损耗,提高变换器的效率,提出了一种改进的零电流转化软开关无桥功率因数校正电路,实现了变换器主开关管和辅助开关管的零电流导通和零电流关断,有效地减小了导通损耗,提高了电路的效率。详细分析了电路的工作模态、工作条件和主开关管的导通损耗。仿真和实验结果表明,该功率因数校正电路实现了输入电流对输入电压的良好跟踪,功率因数高,谐波含量少,效率较传统的全桥功率因数校正电路有明显的提高。 关键词：全桥;零电流转换;无桥;功率因数校正     

单相两级有源功率因数校正变换器的研究

文中对两级有源功率因数校正变换器进行研究,设计了一台510W两级式开关电源。该电源前级采用平均电流控制的Boost型PFC电路,实现功率因数校正;后级采用不对称半桥型DC／DC变换器,实现开关管的零电压开关。控制电路采用PFC／PWM复合控制芯片ML4824,缩小电源体积。通过实验证实该开关电源具有高功率因数与高效率的特点。     

Novel zero-voltage-transition current-fed full-bridge PWM converterfor single-stage power factor correction

A novel zero-voltage-transition (ZVT) current-fed full-bridge pulsewidth modulation (PWM) power converter for single-stage power factor correction (PFC) is presented to improve the performance of the previously presented ZVT converter. A simple auxiliary circuit which includes only one active switch provides a zero-voltage-switching (ZVS) condition to all semiconductor devices (two active switches are required for the previous ZVT converter). This leads to reduced cost and a simplified control circuit compared to the previous ZVT converter. The ZVS is achieved for wide line and load ranges with minimum device voltage and current stresses. Operation principle, control strategy and features of the proposed power converter are presented and verified by the experimental results from a 1.5 kW 100 kHz laboratory prototype     

基于开环的临界续断模式交错并联Boost PFC

文中主要研究的对象是开环控制的交错并联BOOST PFC,且工作于临界续断模式,它的从变换器与主变换器在开通时同步,且主从变换器都工作在电流模式。文章指出只有这种主从方式能提供一个稳定的开环工作点。仿真实验设计了一台输入功率为400W,宽范围输入电压,400V输出电压的实验样机,实验结果验证了理论分析的正确性。