多采样率控制器设计在光电跟踪系统中的应用

采用保持器、采样器和提升技术对输入、反馈和输出多采样率多环路系统进行分析,并将多采样率的周期离散时变系统化为时不变系统,且在输入和反馈端依据信号特性引入高频低通滤波器进行信号频谱延拓周期的扩展.在三环结构光电跟踪控制系统中的应用表明:离散控制器有和连续控制器一致的阶跃响应,在引入高频低通滤波器扩展频域延拓周期后,由低频位置输入引入的系统速度震荡基本上完全被抑制.     

基于异采样率的频率解算技术

采样保持器可有效扩展模拟带宽,后级模数转换器(ADC)以较低的采样率即可完成对超宽带射频信号的采集处理。由采样定理可知,当信号带宽超过采样率的1/2时,会产生频率模糊。提出了一种基于异采样率解频率模糊的算法,可适应输入射频信号带宽数倍于采样率时的频率解模糊,分析该算法原理以及关键参数设置,采用实例对该算法的可行性进行验证。     

一种25 MS/s高精度采样保持器的设计

介绍了一种高精度采样保持器。密勒电容反馈的引入,使等效保持电容大大增加,从而有效地抑制了模拟开关的电荷注入效应带来的采样误差;设计大共模输入范围的高增益带宽积的放大器,以提高信号差模输入范围和精度;采用由分频器组成的准采样电路,避免了保持输出信号的抖动对后级电路(如ADC的比较器)的影响。设计采用TSMC 0.25μm 3.3 V CMOS工艺,仿真结果表明,该采样比较器在全范围输入1.1 MHz,采样率25 MS/s时,单音主杂比高于56 dB;全范围输入110 kHz,采样率10 MS/s时则高达近80 dB。     

基于锁模脉冲源和高速光开关的时分抽样模数转换

提出了一种基于锁模脉冲源和高速光开关的时分抽样模数(A/D)转换系统。使用高重复频率、窄脉宽的锁模脉冲串对射频信号进行抽样,利用高速光开关进行时分复用,将高采样率的信号转换为并行的多路低采样率信号,以适应现有的电模数转换器进行量化和编码,并且通过改变光开关的频率,可以灵活地改变解复用后每路信号的频率。系统的优点在于可扩展性高,只需一个锁模脉冲源。使用10 GHz重复频率的锁模脉冲和1.25 GHz的高速光开关验证了系统方案的可行性。利用实验中得到的采样点可以较好地恢复出时域信号,并且得到了各个频率的频谱图。其信噪比可达32.02 dB,等效于5.03 bit的有效比特数。     

导航信号的射频直接采样与数字下变频方法

研究导航信号的射频直接采样与数字下变频方法,并对1.2GHz和1.5GHz2个频点附近的导航信号进行了仿真验证。首先运用带通采样原理,选择合适的采样频率完成对导航信号的射频直接采样,然后结合积分梳状滤波器、半带滤波器,对采样后的信号进行抽取滤波,实现了降采样率的目的。最后,通过Matlab对5个频点的导航信号进行了仿真验证,完成了导航信号的射频直接采样并降低了采样率,恢复且分离了原始导航信号,从而验证了射频直接采样与数字下变频方法是可行的。     

基于无载频脉冲雷达信号的高速数字采样方法与实现

该文针对无载频脉冲雷达信号周期重复性的特点,提出了一种全新的高速数字采样方法和原理。该方法利用FPGA 的差分比较器端口构成高速1 bit 量化器,采用FPGA 内部多相位时钟,对1 bit 数据流进行并行交替数字采样,并缓冲编码,从而获得上吉赫兹的等效数字采样率。通过将多个比较电平下的1 bit 采样数据进行累积,从而完成高速数字采样过程。在Xilinx 的XC2V3000 的FPGA 中实现了该方法,获得了采样率达1.6 GHz 的8 bit等效高速模数转换器功能。该设计方法不仅能够提高等效采样方式的效率,而且与高速实时采样相比,具有低功耗、低成本的优势,在实际中获得了良好的应用。      

一种二极管桥结构7位60 MSPS采样保持器

提出了一种二极管桥结构的采样保持器。理论分析和实验仿真结果表明，该采样保持器采样率达60MSPS，在0．6～5．0MHz输入信号频率范围内，其有效位数达到7．43～6．68位。利用这种二极管桥结构的电压差异，可以降低保持电容上的电压跌落率，提高精度和采样率。     

基于Xampling的MWC系统信号盲恢复

Modtlated Wideband Corwerter(MWC)调制宽带转换器系统是一个将原始的模拟信号送入多通道,进行同时调制滤波之后,以一个较低的采样率进行采样,为稀疏多频带信号采样率高的问题提供了一种欠采样解决方案。同时基于Xampling算法对稀疏多带信号进行未知载波频率的信号盲恢复。恢复出的信号与原始信号相比,虽然在频域上引入了能量很低的新的频谱分量,但是信号主要的参数没有改变。     

基于等效和实时采样的数字示波器设计

基于数字示波器的基本原理,以单片机和FPGA组成的最小系统为控制核心,实现了普通示波器对被测信号的采样、存储与回放,并且增加了等效采样和采样保持功能,极大地提高了系统的测量范围。该系统具有实时采样和等效采样两种方式,以不大于1Ms／s的A／D转换实现200MS／s的等效采样率对输入1Hz-10MHz,yp-p为2mV-8V的信号进行采样处理,并能进行单次触发,自动和存储／输出波形。     

基于等效和实时采样的数字示波器设计

基于数字示波器的基本原理,以单片机和FPGA组成的最小系统为控制核心,实现了普通示波器对被测信号的采样、存储与回放,并且增加了等效采样和采样保持功能,极大地提高了系统的测量范围.该系统具有实时采样和等效采样两种方式,以不大于1 Ms/s的A/D转换实现200 MS/s的等效采样率对输入1 Hz～10 MHz,Vp-P为2 mV～8 V的信号进行采样处理,并能进行单次触发,自动和存储,榆出波形.     

微波电路的MEMS天关进展

开关是微波信号变换的关键元件,和传统的半导体开关相比,射频微机电系统（RF MEMS）开关具有优良的高频特性和固有的重量轻、尺寸小、低功耗等优点,而且其制作工艺和传统的CMOS工艺相兼容。本文较为详细地了串联悬臂梁开关、并联悬臂梁开关和膜开关的工作原理及典型的性能参数。由于其优越的微小特性,MEMS开关已在许多电路和系统中,包括微波前端电路、数字电容器组和移相网络中得到应用。     

融合压缩采样与深度神经网络的直接序列扩频参数估计

直接序列扩频(Direct Sequence Spread Spectrum,DSSS）信号的宽频带特性所带来的高采样率增加了参数估计的实现难度。针对现有技术所面临的问题与挑战,融合压缩采样与深度神经网络(Deep Neural Network,DNN),提出了用于估计DSSS信号参数的方法。一方面,压缩采样能够利用信号的冗余性,以较低的采样率获取信号中的有效参数信息;另一方面,DNN在提取数据特征方面具有高效准确的特点。通过对压缩采样与参数估计网络的整体训练,实现两者的有效配合,进而实现以较低采样率对DSSS信号参数的准确估计。仿真实验证明了该参数估计方法在低信噪比下的估计能力相对于传统方法具有一定的提升。     

基于时域特性的并行系统的采样误差估计算法

为了降低并行时间交替采样系统中通道失配误差的 硬性,利用两个标准斜波 信号的时域特性,对斜波信号多次采样,采样点减去偏置误差得到的无偏置采样值,从而求 解采样点的时间误差和增益误差联立方程,计算时间和增益误差。本文算法的采样点数和推导计算量较少,是一种快速而 精确的工程实用算法;并使用Matlab对本文算法进行模拟仿真证明其可行性,并通过Farrow 结构的滤波器对估计所得的通道失配误差进行校正验证,校正后的无杂散动态范围(SFDR,spurious free dynamic range)至少达到50dB。     

Photonic A/D conversion using low-temperature-grown GaAs MSM switches integrated with Si-CMOS

By linking the unique capabilities of photonic devices with the signal processing power of electronics, photonically sampled analog-to-digital (A/D) conversion systems have demonstrated the potential for superior performance over all-electrical A/D conversion systems. We adopt a photonic A/D conversion scheme using low-temperature (LT)-grown GaAs metal-semiconductor-metal (MSM) photoconductive switches integrated with Si-CMOS A/D converters. The large bandwidth of the LT GaAs switches and the low timing jitter and short width of mode-locked laser pulses are combined to accurately sample input frequencies up to several tens of gigahertz. CMOS A/D converters perform back-end digitization, and time-interleaving is used to increase the total sampling rate of the system. In this paper, we outline the development of this system, from optimization of the LT GaAs material, speed and responsivity measurements of the switches, bandwidth and linearity characterization of the first-stage optoelectronic sample-and-hold, to integration of the switches with CMOS chips. As a final proof-of-principle demonstration, a two-channel system was fabricated with LT GaAs MSM switches flip-chip bonded to CMOS A/D converters. When operated at an aggregate sampling rate of 160 megasamples/s, the prototype system exhibits /spl sim/3.5 effective number of bits (ENOB) of resolution for input signals up to 40 GHz.     

基于FPGA的空间电场信号采集系统设计

提出一种基于FPGA的空间电场信号数据采集与处理系统的设计方案,FPGA为主控制器控制A/D采样和同步422发送。X,Y,Z三个方向的空间电场信号经过信号处理和A/D采样,在FPGA片内滤波划分为不同的频段,通过同步422接口发送到后续设备。该系统性能可靠稳定,致力于应用在探空火箭有效载荷——箭载电场仪上,对其他电场信号采集与处理系统也有一定的应用价值。     

Accurate error-rate performance analysis of OFDM on frequency-selective Nakagami-m fading channels

Error rates of orthogonal frequency-division multiplexing (OFDM) signals in multipath slow fading Nakagami-m fading channels are considered. The exact probability density function of a sum of Nakagami-m random phase vectors is used to derive a closed-form expression for the error rates of OFDM signals. The precise error-rate analysis is extended to a system using multichannel reception with maximal ratio combining. An asymptotic error-rate analysis is also provided. For a two-tap channel with finite values of Nakagami-m fading parameters, our analysis and numerical results show that the asymptotic error-rate performance of an OFDM signal is similar to that of a single carrier signal transmitted over a Rayleigh fading channel. On the other hand, our analysis further shows that a frequency-selective channel that can be represented by two constant taps has similar asymptotic error-rate performance to that of a one-sided Gaussian fading channel. It is observed that, depending on the number of channel taps, the error-rate performance does not necessarily improve with increasing Nakagami-m fading parameters.     

Accurate Error-Rate Performance Analysis of OFDM on Frequency-Selective Nakagami-$m$Fading Channels

Accurate Error-Rate Performance Analysis of OFDM on Frequency-Selective Nakagami-$m$Fading Channels Error rates of orthogonal frequency-division multiplexing (OFDM) signals in multipath slow fading Nakagami-$m$fading channels are considered. The exact density function of a sum of Nakagami-$m$random phase vectors is used to derive a closed-form expression for the error rates of OFDM signals. The precise error-rate analysis is extended to a system using multichannel reception with maximum ratio combining. An asymptotic error-rate analysis is also provided. For a two-tap channel with finite values of Nakagami-$m$fading parameters, our analysis and numerical results show that the asymptotic error-rate performance of an OFDM signal is similar to that of a single-carrier signal transmitted over a Rayleigh fading channel. On the other hand, our analysis further shows that a frequency-selective channel that can be represented by two constant taps has similar asymptotic error-rate performance to that of a one-sided Gaussian fading channel. It is observed that depending on the number of channel taps, the error-rate performance does not necessarily improve with increasing Nakagami-$m$fading parameters.     

一种相干环境下的稳健自适应波束形成算法

针对均匀线阵提出了一种相干环境下的稳健自适应波束形成算法.该算法首先对接收数据采样协方差矩阵进行迭代Toeplitz处理,一方面可实现对相干信号的去相关,另一方面避免了由噪声子空间扰动引起的性能下降;然后利用处理后的矩阵进行基于特征空间的自适应波束形成,从而很好地解决了存在波束指向误差时的相干干扰抑制问题,并且在小快拍情况下也具有良好的阵列输出性能.计算机仿真实验结果证明了该方法的有效性.     

Reconstruction of two-dimensional signals from level crossings

Recent results indicate that reconstruction of two-dimensional signals from crossings of one level requires, in theory and practice, extreme accuracy in positions of the samples. The representation of signals with one-level crossings can be viewed as a tradeoff between bandwidth and dynamic range, in the sense that if the available bandwidth is sufficient to preserve the level crossings accurately, then the dynamic range requirements are significantly reduced. On the other hand, representation of signals by their samples at the Nyquist rate can be considered as requiring relatively small bandwidth and large dynamic range, because, at least in theory, amplitude information at prespecified points is needed, to infinite precision. An overview of existing results in zero crossing representation is presented, and a number of new results on sampling schemes for reconstruction from multiple-level threshold crossing are developed. The quantization characteristics of these sampling schemes appear to lie between those of Nyquist sampling and one-level crossing representations, thus bridging the gap between explicit Nyquist sampling and implicit one-level crossing sampling strategies     

基于FABA-SISO的时变频率选择性衰落信道CPM信号盲均衡

该文针对时变频率选择性衰落信道下高阶连续相位调制(CPM)信号盲均衡中存在的均衡性能较差、复杂度较高以及收敛速度慢等问题,从双向自适应信道均衡的角度出发,将线性调制信号均衡中使用的前后向自适应软输入软输出(FABA-SISO)算法推广,建立一种新的基于FABA-SISO的信道盲均衡方法,并结合逐幸存处理(PSP)思想和Kalman滤波,提出一种适用于高阶CPM信号的自适应盲均衡算法。该算法通过使用FABA-SISO算法,同时利用过去、现在和将来的观察数据进行Kalman滤波信道估计,有效改善了信道估计的精度,同时使用PSP算法来降低系统的复杂度,使得算法具有较好的工程应用性。仿真结果表明所提算法具有良好的盲均衡性能以及收敛性。