眼图及眼图在信号测试中的运用

眼图及眼图在串行信号测试中的运用DM高级应用工程师:黄腾Email:[e-mail]眼图分析的原始驱动通讯技术发展的需要SONET和SDH的在广域传输中的广泛应用以及以太网技术的爆炸式应用和发展电子系统从传统的并行总线转为串行总线HighlyScable,SerialInterface采用当前许多最新的通讯行业成熟应用的技术:PointtoPointInterconect,Switch-basedTechnology,PacketlizedProtocol2020/3/19V1.0Confidential3高速串行总线和传统并行总线对比2020/3/19V1.0Confidential4高速串行总线－新兴标准和数据速率FibreChannel4X4.25Gb/s4.25Gb/s(1X)FBDIMM4.8Gb/s500Gb/s(14lanesx8channels)2020/3/19V1.0Confidential5眼图定义2020/3/19V1.0Confidential6一般信号与眼图的区别2020/3/19V1.0Confidential7眼图特征定义2020/3/19V1.0Confidential8眼图特征定义2020/3/19V1.0Confidential9眼图形成示意2020/3/19V1.0Confidential10眼图在示波器上的形成2020/3/19V1.0Confidential11眼图的CLK采样示波器的CLK通常可能是用户提供的时钟,恢复时钟,或者与数据信号本身同步的码同步信号.实时示波器通过一次触发完成所有数据的采样,不需附加的同步信号和触发信号.通常通过软件PLL方法恢复时钟.TektronixRT-Eye软件即使用此方法.TDS8200ETScope(20GHz80E03)TDS6154CRTw.DSP2020/3/19V1.0Confidential12眼图与CLK－时钟速率提高,眼图质量下降125MCLK250MCLK500MCLK2020/3/19V1.0Confidential13示波器上的眼图提供串行总线数据的丰富信息:通过比较发送端和接收端的眼图质量可以分析出信号传输的问题眼高,眼底,眼宽上升时间下降时间模板测试2020/3/19V1.0Confidential14眼图与系统速率水平时域上关联因素Transition(rise)timeAperturetimeTiminguncertainty,skewandjitter垂直域幅度损耗和噪声Unimparedbitedge2020/3/19V1.0Confidential15眼图和传输质量LargereyeopeningmeansgreatertolerancetoamplitudeandtimingvariationsLargereyeopeningtranslatestosimplersystemdesignandbetterreliabilityWidertransitionregionindicatesgreaterjitterandhigherbiterrorrateBesterrorrateobtainedwhendecisionpointisnearcenteroftheeye2020/3/19V1.0Confidential16PValuesPTopmean,themeanvalueofPTopPTopsigma,thestandarddevofPTopPBasemean,meanvaluewithinaperturePBasesigma,stddevofPBaseinaperturePcrossmean,verticalmeanofcrossingpt.TValuesTcrossmean,horizmeanofcrossingpt.Tcrosssigma,horizstddevofcrossingpt.Tcrosspk-pk,horizpk-pkofcrossingpt.TheEyeAperturedefaultstothecenter20%oftheintervalfromTCross1toTCross2butissettablefrom0to100%眼图测量特征量TCross1TCross2PCross1PCross2EyeAperturePBasePTop2020/3/19V1.0Confidential17JitterRMS=TCross1sigmaJitterPk-Pk=TCross1pk-pkExtinctionRatio=PTopmean/PBasemean(ERalsoindBand%)QualityFactor=(PTopmean-PBasemean)/(PTopsigma+PBasesigma)EyeHeight=(PTopmean-3*PTopsigma)-(PBasemean+3*PBasesigma)EyeWidth=(TCross2mean-3*TCross2sigma)-(TCross1mean+3*TCross1sigma)CrossingPercent,DutyCycleDistortion,Noisepk-pk,NoiseRMS,SNR眼图测量特征量TCross1TCross2PCross1PCross2EyeAperturePBasePTop2020/3/19V1.0Confidential18眼图的测量近端远端采样点串扰随机抖动确定性抖动–码间干扰(ISI)–占空比失真(DCD)–正弦抖动(SJ)–无关联的幅度损耗2020/3/19V1.0Confidential19串行总线:BasicblocksTransmittersInterconnects(paths)ReceiversTx+-path+-+-path+-+-path+-+-+-RcvDifferentialTransmitterDual-coaxdifferentialcableTwisted-pairdifferentialcableCoupled-pairtracesoncircuitboard(backplanes)DifferentialReceiver2020/3/19V1.0Confidential20高速串行总线－信号线上不仅包含数据信息还包含时钟信息pathTx+-+-+-+-RcvDifferentialserialdataissentwithoutanyclocksignalacrosstheinterconnecttothereceiverCDRDATADATACLOCKAclockis“recovered”fromtheincomingdataatthereceiverthroughaclockanddatarecoverycircuit(CDR).2020/3/19V1.0Confidential21高速串行总线－数据传输过程中干扰因素增多path+-+-path+-+-Tx+-path+-+-+-RcvTx+-path+-+-+-Rcvpath+-+-Tx+-path+-+-+-Rcvpath+-+-Transitionpointsofteninvolvecombinationsofsolderjoints,circuitboardvias,andconnectors:theseallcanhavesubstantialeffectonthetotallinkperformance.2020/3/19V1.0Confidential22高速串行总线－损耗速率越高互连距离越长,损耗越大ReferenceMaximNoteHFDN-27.0(Rev.0,09/03)Tx+-+-Rcvpath+-+-Clean,open,logical1&0atlaunchfromtransmitterSmearededgesatendoflonginterconnect.Logical1&0canbehardtodistinguishatendoflonginterconnects;(thisisoftencalleda“closedeye”)Fast,sharp,edgesattransmitterlaunch2020/3/19V1.0Confidential23高速串行总线－串扰path+-+-Rcv+-+-Rcv+-+-Rcv+-+-RcvSerialdatacanbeasingledifferentialsignal…Tx+-Tx+-Tx+-Tx+-Tx+-+-+-+-Rcv…butgenerallytherearemultiple“lanes”ofserialdatarunningsidebyside;thesecanCROSSTALKwitheachother.2020/3/19V1.0Confidential24高速串行总线－精度设计者要更加精确的掌控设计Tx+-path+-+-6.25Gb/satTxlaunchintobackplane6.25Gb/sat17in(43cm)ofbackplane6.25Gb/safter34in(86cm)ofbackplaneSmalldifferencesinlevelsbeingmeasured2020/3/19V1.0Confidential25如何获得张开的眼图走线长度短走线并非始终能够满足.短走线意味低损耗.走线宽度宽走线可以降低趋肤效应.减小板材的介电常数即降低介电损耗(DielectricLoss),但将增加成本.信号预加重和均衡处理通过对跳变位预加重(Pre-Emphasis)处理补偿线路上因信号跳变产生的针对高频分量的损耗.其它接收端均衡处理等.2020/3/19V1.0Confidential26眼图与BER究竟这个眼睛有多开?(…这却与你观察多久有关)?2020/3/19V1.0Confidential27眼图与BERpdf1pdf2cdf20.5UI12ABC0UI1UIEyeopenforBER@1.0E-12-0.5UI1.5UIcdf1110眼睛睁开度vs误码率2020/3/19V1.0Confidential28眼图与BER利用眼图分析抖动得到浴盆曲线(BathTub),从而进行误码率的估算。2020/3/19V1.0Confidential29泰克提供的眼图测量方案从数据恢复时钟(CDR),眼图模板测试–硬件CDR(PLL)–软件CDR(PLL+其它)测量绘图–抖动:趋势,频谱,直方图,浴盆曲线2020/3/19V1.0Confidential30硬件时钟恢复TDS6000B系列,TDS7704B和CSA7404B显示器锗化硅触发系统放大器/衰减器数据采集系统GoldenPLLFbd/166720dB/dec来自被选中的通道恢复时钟Ch2Ch3Ch4从1Mbit/s到3.125Gbit/s的所有电接口和光接口速率独有的锗化硅触发系统2020/3/19V1.0Confidential31硬件时钟恢复产生的眼图TDS6804B/P7380SMADSP增强功能XAUI超过3.125Gb/s眼图测量和统计2020/3/19V1.0Confidential32新型测试方法RT-Eye™方法生成眼图新兴标准要求新型工具TDSRT-Eye(选项RTE)基于泰克在软件领域的专家经验，创建了一个交钥匙式的一致性测试和分析解决方案2020/3/19V1.0Confidential33新型测试方法RT-Eye™方法生成眼图软件时钟恢复眼图全系列标准专用参数测量，包括幅度、定时和抖动多种格线图，进行补充数据分析标准专用模块作为插件提供用户可定制的波形模板、测量极限和报告功能，支持专有标准和新兴标准生成报告2020/3/19V1.0Confidential34