第三章：取样与取样积分原理

1Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST锁相放大器与取样积分器的应用区别锁定放大器：适合对正弦或方波周期信号振幅的检测。取样积分器：适合复杂的宽带周期信号振幅和波形的检测。（信号恢复）；脉冲信号检测。取样积分（或称为累加平均）锁相放大器无法应用的场合：快速变化的信号。观点1：2Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST锁相放大器用于：单频和窄带弱信号的检测。不适用于重复信号（信号可重复的含义是指信号随时间变化的波形，可以多次重复获得，而且波形曲线不变样。）允许是非周期的（例如：网络传输）观点2：3Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST锁相放大器用于：单频和窄带弱信号的检测。我们的观点取样积分器：适合复杂的宽带周期信号、脉冲信号等重复信号的检测。4Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USSTinoutmSSinoutNmmNN效mSNIRSNIRinout平均效果的法则m取样积分的基本概念5Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USSTCH12.噪声测量交流电测量i=Imsinωt整流后测平均值：而有效值：I效/I平＝1.11I效＝1.11I平因而修正刻度，即将测得的I平再乘以1.11后，最后得到I效。mTIdtiTI210平mTIdtiTI21102效11.1221mmIIII平效6Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST3－1取样的物理过程取样的核心是取样门，取样门的开关是由P（t）取样脉冲控制。7Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST取样波形及原理框图：8Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST3－2取样定理一.信号等于取样脉冲序列P(t)与连续信号f(t)的乘积fs(t)=f（t）P(t)取样信号fs(t)的傅立叶变换为：（卷积定理）二．时域取样定理一个频谱有限的信号f(t),如果其频谱只占据-ωn~+ωn的范围，则f(t),可用等间隔的取样值来唯一地表示，但取样间隔必须小于1/(2fm),(其中ωm=2πfm)。即最低取样频率为2fm。)()(21)()(PFtfFFss9Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST10Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST三．从取样信号中恢复原连续信号在满足取样定理的条件下，频谱Fs(ω)是F(ω)周期的重复，并不混叠，为了无失真地选出F(ω),只要使：F(ω)=Fs(ω)H(ω)式中，H(ω)＝1/ω/＜ωc＝0/ω/＞ωcH(ω)是理想的低通滤波器的传递函数。取样信号fs(t)通过低通滤波器即可实现Fs(ω)H(ω)，在输出端就可得到频谱为F(ω)的连续信号f(t)。11Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST3－3实时取样和变换取样一．实时取样在被取样信号的一次有效持续时间内，无失真地取出复现原信号所必须的全部样品，用于低频信号的处理。12Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST二.变换取样在每个信号周期或每隔整数隔信号周期取出一个样品，每次取样时间均比前一次延时Δt,最后复现信号形状与原信号相似，但在时间刻度上比原来信号增加了若干倍，适合于高速、高重复频率信号的取样检测。13Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST三．样品提取方式1．绝对值取样取出信号瞬时绝对值。14Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST2．差值取样取出该瞬时信号幅值与上次取出幅值之差。15Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST3－4取样积分器原理和工作方式（信号平均器）锁定放大器：适合对正弦或方波周期信号振幅的检测。取样积分器：适合复杂的宽带周期信号振幅和波形的检测。（信号恢复）；脉冲信号检测。16Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST单点取样积分器（Boxcar）3-4取样积分器原理和工作方式（信号平均器）17Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST(1).定点式取样积分器波形信噪改善比18Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USSTRtudttCdvtiio)()()(线性门积分器线性积分电路toiovdttuRCtv00')'(1)(输入ui(t)是幅度为Vi的阶跃电压，初始电压vo0=0时，RCtVtvtuioo)()(19Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST1.线性门积分器)/()(0TRCtTVtugi信噪改善比（SNIR）:N20Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST2.指数式门积分器)1()1()(0TRCtTiRCtigeVeVtu信噪改善比：gcTTSNIR221Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST(2).扫描式取样积分器波形复现过程22Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST取样积分器的参数选择1.取样脉冲宽度Tg的选择tVtxmsin)(2200ggTttTt0220sin2sin2sin)(00tTVdttVtugmTtTtmogg00sin22)(tTVtugmo低频2/2/sin||0ggooTtuuA高频23Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST2.积分时间常数Tc=RC的选择2/2/sin||0ggooTtuuA42.0gcTfcgfT/42.0指数式门积分器22gcTSNIRT线性门积分器NSNIR24Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST3.慢扫描时间Ts的选择fTTTnsst/fTTnTtsbtb/bgssTfTTnRCTngs5RC积分器需要5RC时间才能充分充电fTSNIRTfTRCTTgbgbs225.2525Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST例：被测信号周期T=10ms，测量范围Tb=2ms，要求信噪改善比SNIR=10，选Tb=3ms以覆盖测量区，Tg=100us，试求指数式取样积分器的参数Tc和Ts。msTSNIRTgc522sfTTTTgcbs755226Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST二、多点信号平均器利用计算机技术，控制多个电子开关，将采样信号一一对应地存储在相应的电容（模拟）或存储器（数字）内进行累积和平均。27Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST数字式平均的取样和运算过程28Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST29Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST霍尔效应测量dIBRVHH/30Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST超声波检测31Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST激光器研究32Prof.Yang,ThecollegeofOpticandElectronicInformationEngineering,USST