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1、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: *1V1.0 Confidential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Highly Scable,Serial Interface采用当前许多最新的通讯行业成熟应用的技术:Point to Point Interconect,Switch-based Technology,Packetlized ProtocolDate2V1.0 Confidential高速串行总线和传统并行总线对比Date3V1.0 Co
2、nfidential高速串行总线新兴标准和数据速率FibreChannel 4X 4.25 Gb/s 4.25Gb/s (1X)FBDIMM 4.8 Gb/s 500 Gb/s (14 lanes x 8 channels)Date4V1.0 Confidential眼图定义Date5V1.0 Confidential一般信号与眼图的区别Date6V1.0 Confidential眼图特征定义Date7V1.0 Confidential眼图特征定义Date8V1.0 Confidential眼图形成示意Date9V1.0 Confidential眼图在示波器上的形成Date10V1.0 Con
3、fidential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.Tektronix RT- Eye软件即使用此方法.TDS8200 ET Scope (20GHz 80E03)TDS6154C RT w. DSPDate11V1.0 Confidential眼图与CLK时钟速率提高,眼图质量下降125M CLK250M CLK500M CLKDate12V1.0 Confidential示波器上的眼图图提供串行总线数据的丰富信息:通
4、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Date13V1.0 Confidential眼图与系统速率水平时域上关联因素Transition (rise) timeAperture timeTiming uncertainty, skew and jitter垂直域幅度损耗和噪声Unimpared bit edgeDate14V1.0 Confidential眼图和传输质量Larger eye opening means greater tolerance to amplitude and timing variationsLarger
5、eye opening translates to simpler system design and better reliabilityWider transition region indicates greater jitter and higher bit error rateBest error rate obtained when decision point is near center of the eyeDate15V1.0 ConfidentialP ValuesPTopmean , the mean value of PTopPTopsigma , the standa
6、rd dev of PTopPBasemean , mean value within aperturePBasesigma , std dev of PBase in aperturePcrossmean , vertical mean of crossing pt.T ValuesTcrossmean , horiz mean of crossing pt.Tcrosssigma , horiz std dev of crossing pt.Tcrosspk-pk , horiz pk-pk of crossing pt.The Eye Aperture defaults to the c
7、enter 20% of the interval from TCross1 to TCross2 but is settable from 0 to 100%眼图测量特征量TCross1TCross2PCross1PCross2Eye AperturePBasePTopDate16V1.0 Confidential4 Jitter RMS = TCross1sigma4 Jitter Pk-Pk = TCross1pk-pk4 Extinction Ratio = PTopmean /PBasemean(ER also in dB and %)4 Quality Factor = (PTop
8、mean-PBasemean)/(PTopsigma+PBasesigma)4 Eye Height = (PTopmean-3*PTopsigma)-(PBasemean+3*PBasesigma)4 Eye Width = (TCross2mean-3*TCross2sigma)-(TCross1mean+3*TCross1sigma)4 Crossing Percent, Duty Cycle Distortion, Noisepk-pk, NoiseRMS, SNR眼图测量特征量TCross1TCross2PCross1PCross2Eye AperturePBasePTopDate1
9、7V1.0 Confidential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Date18V1.0 Confidential串行总线总线: Basic blocksTransmittersInterconnects (paths)ReceiversTx+-path+-+- path+-+-path+-+-+-RcvDifferential TransmitterDual-coax differential cableTwisted-pair differential cableCoupled-pai
10、r traces on circuit board (backplanes)Differential ReceiverDate19V1.0 Confidential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+-+-+-+-RcvDifferential serial data is sent without any clock signal across the interconnect to the receiverCDRDATADATACLOCKA clock is “recovered” from the incoming data at the receiver
11、through a clock and data recovery circuit (CDR).Date20V1.0 Confidential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+-+-Transition points often involve combinations of solder joints, circuit board vias, and connectors: these all can have substanti
12、al effect on the total link performance.Date21V1.0 Confidential高速串行总线损耗 速率越高互连距离越长,损耗 越大Reference Maxim Note HFDN-27.0 (Rev. 0, 09/03)Tx+-+-Rcvpath+-+-Clean, open, logical 1 (this is often called a “closed eye”)Fast, sharp, edges at transmitter launchDate22V1.0 Confidential高速串行总线串扰 path+-+-Rcv +-+-R
13、cv +-+-Rcv +-+-RcvSerial data can be a single differential signalTx+-Tx+-Tx+-Tx+-Tx+-+-+-+-Rcvbut generally there are multiple “lanes” of serial data running side by side; these can CROSSTALK with each other.Date23V1.0 Confidential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/s at Tx launch into backpla
14、ne6.25Gb/s at 17in (43cm) of backplane6.25Gb/s after 34in (86cm) of backplaneSmall differences in levels being measuredDate24V1.0 Confidential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(Dielectric Loss),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
15、理等.Date25V1.0 Confidential眼图与BER8究竟这个眼睛有多开?(这却与你观察多久有关)?2018/7/2826V1.0 Confidential眼图与BERpdf 1pdf 2cdf 20.5UI12ABC0UI1UIEye open for BER 1.0E-12- 0.5UI1.5UIcdf 1 110眼睛睁开度 vs 误码率Date27V1.0 Confidential眼图与BER利用眼图分析抖动得到浴盆曲线 (Bath Tub),从而进行误码率的估 算。Date28V1.0 Confidential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
16、 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Date29V1.0 Confidential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Golden PLLFbd/166720 dB/dec来自被 选中的 通道恢复 时钟Ch2 Ch3Ch4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Date30V1.0 Confidential硬件时钟恢复产生的眼图TDS6804B/P7380SMA DSP增强功能 XAUI 超过 3.125Gb/s眼图测量和统计Date31V1.0 Confidential新型测试测试方法 RT-Eye方法生成眼图新兴标准要求新型工具TDS RT-Eye (选项RTE)
