采样时钟抖动、相噪与输出SNR关系研究

射频数字化技术是软件无线电接收机理想实现形式,并随着高速、高分辨ADC技术的飞速发展在雷达、通信、电子战领域得到了广泛的应用。由于采样时钟对射频信号的卷积效应和采样折叠效应,采样时钟的性能将直接决定输出信号的SNR。文章对射频数字化采样时钟抖动、相位噪声与输出SNR关系进行了研究、仿真和试验,给出了不同应用场合和需求下时钟对抖动、相位噪声的要求,可用于指导射频数字化采样时钟的设计。     

射频直接采样系统中等效相位噪声模型分析

为了分析射频直接采样系统中的等效相位噪声模型,文中给出了射频直接采样接收机的简化构架,然后理论推导了射频直接采样接收机采样输出信噪比与采样时钟之间的关系表达式。最后,通过建立仿真实验平台对推导结论进行了实验验证,结果表明:射频直接采样系统对采样时钟的频谱纯度要求高,采样输出的信噪比和无杂散动态范围会在时钟信号频谱的基础上恶化。射频直接采样系统可视为射频本振混频和量化采样的过程,其等效相位噪声模型与常规超外差式接收机是一致的。     

大动态信号处理中的高速数字采样

本文概述了抗干扰天线的基本原理。根据信号频率、带宽选用合适的采样定理计算出采样频率。根据要处理的信号中的有用信号、噪声、干扰幅值之间的关系确定AD器件的采样精度为14位。采样时钟信号采用差分输入,从而降低了时钟信号的相位噪声减少码间干扰。根据数字信号的特点选择合适的存储方式。     

一种低抖动低杂散的亚采样锁相环

设计了一个5.156 25 GHz低抖动、低杂散的亚采样锁相环,使用正交压控振荡器产生4路等相位间隔时钟。分析了电荷泵的杂散理论,使用差分缓冲器和互补开关对实现了低杂散。使用Dummy采样器和隔断缓冲器,进一步减小了压控振荡器对杂散的恶化。该亚采样锁相环在40 nm CMOS工艺下实现,在1.1 V的供电电压下,功耗为7.55 mW;在156.25 MHz频偏处,杂散为-81.66 dBc;亚采样锁相环输出时钟的相位噪声在10 kHz~100 MHz区间内积分,得到均方根抖动为0.26 ps。     

高速宽带锁相环的相位噪声影响研究

介绍了一种高速宽带锁相环的架构设计和基本原理。设计了双压控振荡器结构,使得锁相环输出时钟信号的频率范围达到6.0~12.5 GHz。基于锁相环的线性模型,从理论上分析了各单元电路的相位噪声对总体输出相位噪声的影响。基于65 nm CMOS工艺,根据各单元电路相位噪声的典型数据,对锁相环的输出相位噪声和等效时钟抖动等参数进行了仿真。结果表明,电荷泵、输入参考时钟、分频器、压控振荡器对整体输出噪声的贡献分别为35.8%、30.3%、18.3%、14.6%,环路滤波器对相位噪声贡献很小。锁相环的整体仿真结果显示,在各种工艺角下,锁相环的输出时钟信号频率均可达到12.5 GHz,高频输出相位噪声带来的时钟抖动均小于1 ps。     

光模数转换系统中幅度不均匀性的校正(本期优秀论文)

分析了采样时钟的幅度不均匀性对高速光模数转换系统性能的影响,提出了一种校正补偿采样时钟幅度不均匀性的方法.该方法通过对系统光采样时钟进行测量和数据处理,来获取校正因子序列,再用校正因子序列对采样结果进行补偿.对提出的方法进行了实验验证,结果表明:该方法可有效抑制了幅度不均匀性的影响,提高系统有效比特精度.     

高速ADC的低抖动时钟设计

本文首先分析了采样时钟抖动对ADC信噪比性能的影响,然后指出产生时种抖动的原因,最后给出了两种实用的低抖动采样时钟产生方案:基于低相位噪声VCO(压控振荡器)的可变采样时钟的产生及基于极低相位噪声温度补偿晶振的非可变采样时钟的产生。     

一种基于噪声的真随机数发生器的ASIC设计与实现

提出了一种应用于密码系统的硬件随机数发生器的ASIC实现,即通过振荡采样把相位噪声转变为随机数.为了使输出平稳,在输出级设计了异或链和伪随机网络.理论研究和仿真测试证明,该方案能生成分布均匀、彼此独立的随机信号.经制版流片后,芯片在1 MHz时钟下输出满足随机性测试的串行随机数.     

高速高清CCD自适应相关双采样技术

相关双采样技术被广泛地应用于CCD 视频采集,能够有效地消除复位噪声,白噪声等CCD输出噪声。但是当CCD 工作在高帧频状态下,需要高速的输出数据,由于像素时钟较快会出现采样位置不稳的情况。文中采用自适应相关双采样技术,可以自适应地调整采样脉冲的相位,使相关双采样的两个采样脉位于合理的采样位置,能够正确地采集像素信息。采用自适应调整CCD 相关双采样位置的技术,能使高清高速CCD 在像素频率很高的情况下,也能稳定地工作,输出高质量的图像。     

16位8通道SPIDAC

AD9548内置一个数字PLL,能对lppsGPS信号进行上变频,同时可将与外部参考相关的输入时间抖动或相位噪声降低至300fs。时钟分配部分提供四个输出驱动器。每个驱动器可编程为一个单一的差分LVPECL／LVDS输出或一对单端CMOS输出。     

High-linearity 208-MS/s photonic analog-to-digital converter using1-to-4 optical time-division demultiplexers

This letter describes a demonstration of a photonic analog-to-digital converter operating at 208 MS/s and utilizing phase-encoded optical sampling to achieve an 87-dB two-tone third-order intermodulation-free dynamic range. A pair of LiNbO₃ 1-to-4 optical time-division demultiplexers with >35-dB channel extinction distribute the 30-ps sampling pulses to an array of photonic integrate-and-reset circuits followed by 12-b 52-MS/s electronic quantizers. Interleaving spurs due to temporal crosstalk currently limit the overall spur-free dynamic range to 65 dB     

基于等光频细分重采样的调频干涉测距方法

为了解决调频连续波(FMCW)激光器调制非线性导致的测量信号频谱展宽降低激光干涉测距精度的问题, 采用一种基于等光频细分重采样的调频干涉测距方法, 进行了理论分析和实验验证, 获得了双光路测距系统对不同位置目标信号等光频细分重采样后的波形数据, 并进行了频谱分析。结果表明, 通过等光频细分重采样的方法, 使用细分后的时钟信号点对距离大于辅助干涉光路光程差的目标测量信号进行重采样, 消除了激光器的调制非线性的影响, 并且避免了采样点数不足引起信号失真的问题; 在4.3m测量范围内, 等光频细分重采样测距系统与激光干涉仪相比最大残余误差不超过±18.46μm, 最大测量标准差为23.39μm; 该方法使用的辅助干涉光路光程差很短, 受环境的影响较小, 可以获得稳定的时钟信号, 并且可以减少双光路FMCW测距系统的体积与成本。该研究为长距离、高精度调频连续波测量提供了实用参考。     

采样时钟抖动在弱光信号检测中的影响分析

信号采样是弱光信号检测的关键技术环节,由于采样时钟抖动引起的采样信号的输出误差会影响后续的信号检测和处理。为此,分析了输入光信号为近高斯分布波形时由时钟抖动引起的采样误差,推导出了采样输出的信噪比损失公式,讨论了采样带宽、输入信噪比以及信号脉宽对输出信噪比损失的影响,最后以取样积分检测技术为对象,计算了在不同累积次数的条件下采样抖动对取样积分检测性能的影响,对弱光信号检测中的采样时钟选取具有一定的指导意义。     

ATM-PON系统的突发同步技术

在采用ＴＤＭＡ协议的无源光网络中,突发同步是一项关键技术,一般采用基于多相对钏的关键字检测法。本文提出了一种新颖的基于数据地的突发同步技术,采用了高速ＦＰ－ＧＡ和ＥＣＬ有源延时器的方式实现１５５Ｍｂｉｔ／ｓ突发同步器。由于膝用同一主时钏对数据抽样,不需要进行相位校准,简化了电路的设计;相对于传统的ＡＳＩＣ设计方案,该 开发成本低、开发周期短的优点。     

Performance analysis on phase-encoded OCDMA communication system

The performance of an asynchronous phase-encoded optical code-division multiple-access system is evaluated on the condition that the impact of fiber channel is neglected. Phase-encoded optical signal (pseudorandom optical signal with low intensity) is analyzed in the view of stationary random process. The pseudorandom optical signal with low intensity is seen as a sample function of a certain stationary random process which is ergodic in strict sense. The analysis results reveal that the variance of the corresponding random process is only inversely proportional to the code length while the root-mean-square width of the phase-encoded optical signal is proportional to the width of initial optical pulse and the code length F. The numerical results demonstrate that the better system performance can be achieved in case of larger code length and shorter initial optical pulse.     

Optical down-sampling of wide-band microwave signals

Phase-encoded optical sampling allows radio-frequency and microwave signals to be directly down-converted and digitized with high linearity and greater than 60-dB (10-effective-bit) signal-to-noise ratio. Wide-band electrical signals can be processed using relatively low optical sampling rates provided that the instantaneous signal bandwidth is less than the Nyquist sampling bandwidth. We demonstrate the capabilities of this technique by using a 60-MS/s system to down-sample two different FM chirp signals: 1) a baseband (0-250 MHz) linear-chirp waveform and 2) a nonlinear-chirp waveform having a 10-GHz center frequency and a frequency excursion of 1 GHz. We characterize the frequency response of the technique and quantify the analog bandwidth limitation due to the optical pulse width. The 3-dB bandwidth imposed by a 30-ps sampling pulse is shown to be 10.4 GHz. We also investigate the impact of the pulse width on the linearity of the phase-encoded optical sampling technique when it is used to sample high-frequency signals.     

无载波幅度相位调制无线光通信系统研究

无载波幅度相位（Carrierless Amplitude and Phase,CAP）调制是一种数字化方式的正交幅度调制（Quadrature Amplitude Modulation,QAM）。由于CAP调制具有频谱利用率高、成本低、复杂度小等优点,所以逐渐成为实现短距离高速光通信系统的一种备选方案。首先通过比较CAP调制和QAM的功率谱分析了这两种调制方式的特性,然后在大气信道仿真模型（Gamma-Gamma光强起伏分布模型）条件下,基于Matlab仿真分析了滤波器滚降系数,滤波器长度和采样时钟偏移对CAP调制无线光通信系统性能的影响并给出最优参数值。由仿真可知,采样时钟偏移会引起接收端信号的相位偏移,所以需要在接收端对相位畸变进行一定的补偿,文中也对后期所需的均衡算法进行了一些研究,希望能对以后CAP系统的设计有所帮助。最后对仿真结果进行了实验验证。     

Retiming circuit for n.r.z. signals in 1.12 Gbit/s optical transmission system

A circuit for retiming a 1.12 Gbit/s n.r.z. signal in an optical transmission system is described. Retiming in the repeater is accomplished by sampling the n.r.z. signal with a 1.12 GHz clock signal. The resulting r.z. signals are fed to a Schmitt trigger which acts as an RS flip-flop, where the r.z. signals are converted back to n.r.z. signals.     

All optical signal regularizing/regeneration using a nonlinearfiber Sagnac interferometer switch with signal-clock walk-off

All-optical signal regularizing/regeneration using a nonlinear fiber Sagnac interferometer switch (NSIS) that employs signal-clock walk-off is investigated. The NSIS realizes all-optical signal regeneration, including timing and amplitude regularizing, by switching clock pulses with amplified input signals using a walk-off-induced, wide, square switching window and intensity-dependent transmittance of the device. First, characteristics (in both the temporal and spectral domains) of the all-optical signal regeneration achieved with the NSIS are investigated theoretically and experimentally. They certify that if clock pulses are within the square switching window obtained with signal-clock walk-off, the clock pulses can be modulated according to the data that the input signals carry and retain their temporal and spectral profiles. This means that if clock pulses can be prepared that meet the system requirements, the NSIS can convert input signals that may not satisfy system requirements into high-quality output signals. Limitations on the switching contrast due to the cross-phase modulation of counterpropagating reference pulses is also discussed. Second, two possible applications of NSIS-based all-optical signal regularizing/regeneration, 1) an all-optical multiplexer with an optical clock and 2) an all-optical regenerative repeater, are discussed. Preliminary experiments with ~10-ps pulses at bit rates of ~5 Gb/s that use locally prepared optical clock pulses, show that the NSIS provides an error-free regeneration function with a certain tolerance for pulse-period irregularity if a proper optical clock is obtained     

基于随路时钟恢复的多源数据光纤传输系统

针对数据互联网络中多源高速并行数据实时传输的问题,提出了一种基于随路时钟恢复的多源数据光纤传输系统,详细介绍了其工作原理和设计思想.系统将现场可编程逻辑门阵列(FPGA)内部高速收发器与专用数字锁相环相结合,给出了随路时钟恢复与数据流量控制的具体实现过程.相比于现有的各类高速并行数据传输解决方案,该系统具备可软件定义的数据接入能力,也能支持更加灵活的随路时钟动态范围.同时,通过设计精简合理的帧结构,推导数据位宽与随路时钟之间的约束关系,有效提高了系统传输带宽.测试结果表明,该系统工作稳定可靠,实时传输效果好,时钟恢复精度可达100 fs,扩展了串并转换与并串转换技术的应用领域.