Jitter Measurement V0.5

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饼贺米
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1 时钟抖动测量

2 简介抖动的峰峰值和有效值 Pk-pk jitter, RMS jitter JTA2 抖动分析软件包的功能 Jitter Track Jitter Histogram Jitter FFT Page 2

抖动定义抖动的定义为信号的定时事件与其理想位置之间的偏差 SONET SPEC: Jitter is defined as the short-term variations of a digital signal s significant instants from their ideal positions in time.

3 抖动定义抖动的定义为信号的定时事件与其理想位置之间的偏差 SONET SPEC: Jitter is defined as the short-term variations of a digital signal s significant instants from their ideal positions in time. 按待测试信号的种类来划分时钟抖动数据抖动按计算方法来划分 TIE 抖动 : 信号周期相对于一个已知或恢复时钟的误差 Period 抖动 : 是在多个周期内对信号周期的变化进行的测量 Cycle to Cycle 抖动 : 是对信号相邻周期的变化进行测量的结果 Half Period 抖动 : 半个周期的抖动变化 ( 与 Period jitter 的计算类似 ) Page 3

4 抖动定义 ( 续 ) Pk-pk jitter: 峰峰值抖动随着测量时间的增加, 测量值变大, 测试结果不具备重复性, 不能将 jitter 值与误码率 (BER) 直接联系起来 RMS jitter: 抖动测量值的有效值 Total jitter: 在某 BER 下总的抖动值测量 Tj(BER) 的目的是在某 BER 下确保互操作性通常 TJ 是针对串行数据的一般测量 Tj(BER=10e-12) 一般是数据信号测试 Tj 和 Dj Tj(BER<10e-8) 只能用 BERT 测量到, 但是示波器可以精确的估算出该值 Tj 可以分解为 Rj, Dj, DCD, ISI, Pj Page 4

5 三种抖动计算举例某 100MHz 时钟, 第一个到第四个周期分别为 9.9ns, 10.1ns, 9.9ns, 10.0ns, 假设其理想时钟固定在 10ns TIE Jitter: T1 = = 0.1, T2 = = -0.1, T3 = = 0.1 T4 = = 0 TIE pk-pk jitter = 0.1 (-0.1) = 0.2 ns TIE RMS jitter = 参数 T1..T4 的标准偏差 Period Jitter P1 = 9.9 P2 = 10.1 P3 = 9.9 P4 = 10 Period Jitter pk-pk value = = 0.2 ns Period Jitter RMS value = 参数 P1..P4 的标准偏差 Cycle to Cycle jitter C1 = P2-P1 = = 0.2 C2 = P3-P2 = = -0.2 C3 = P4-P3 = = 0.1 Cycle to cycle jitter PK-PK value = 0.4 ns Cycle to cycle jitter RMS value = 参数 C1..C4 的标准偏差标准偏差的计算公式 ( Xi n Xmean 1 ) 2 Page 5

6 传统的抖动测试方法 : 余辉显示设置非常简单, 使用 cursor 测量波形边沿的宽度像素或屏幕分辨率 ( 量化误差 ) 会降低精度只有单个波形, 引入了触发抖动 Page 6

7 时钟常见的三种抖动测量 Cycle to cycle jitter period jitter TIE jitter 必须配备 JTA2 软件包才可以测量三种抖动 Page 7

8 Jitter Histograms Page 8

9 快速设置 TIE 直方图 Step1:TIE 直方图的快速设置方法 Step4: 设置相关参数 Step2: 测量参数选择 TIE Step3: 图形选择 Histogram Page 9

10 设置 TIE 参数查找 TIE 的参考时钟 Page 10

11 设置 TIE 直方图的参数设置 TIE 直方图的参数 Page 11

12 测量直方图直方图的 range 为抖动峰峰值直方图的 sdev 为抖动 RMS 值 Step1: 选择 P2=hsdev(F8) Page 12

13 TIE 的测量 TIE jitter 的峰峰值与 RMS 值 Page 13

14 Sinusoidal Jitter 周期性抖动 Page 14

15 Random Jitter Page 15

16 几种抖动理论上的关系 Waveform With Jitter Reference Frequency Distributions Of Edge Locations TIE Measurement Width Measurement Single Edge, Jitter = Jn Two Edges, Jitter = SQRT(J n 2 +J n+1 2 ) = 1.41 J n Period Measurement Two Edges, Jitter = SQRT(J n 2 +J n+2 2 ) = 1.41 J n Cycle to Cycle Measurement Three Edges, Jitter = SQRT(J n 2 + 4J n J n+2 2 )= SQRT(6) J n Page 16

17 Rule of Thumb TIE=J n Width= 2 J n Period= 2 J n Cycle-Cycle = 6 J n Period/TIE = 2 Cyc-Cyc/Period = 3 All the above can vary depending on specific measurement setup These relationships don t always show up! The relationship between Cycle to cycle and period is the most repeatable. Page 17

18 Jitter Track Page 18

19 Jitter Track 抖动追踪 Jitter Track 波形 :X 轴为时间,Y 轴为某时间的抖动测量值反映了抖动测量值随时间变化的趋势测量 jitter track 波形的峰峰值即可得到该抖动的峰峰值测量 jitter track 波形的标准偏差即可得到抖动的有效值通过 jitter track 功能可以找到调制 ( 或干扰 ) 到时钟的信号 Page 19

20 The JitterTrack Function Source Trace P 1 P 2 P 3 P N-1 P N... Period Jitter Function... P 1 P 2 P 3 P N-1 P N Period Jitter Page 20

21 The JitterTrack Function Source Trace I 1 I 2 I 3... I N-1 I N Reference Clock Edge Interval Error Jitter Function... I 1 I 2 I 3 I N-1 I N Time Interval Error (TIE) Page 21

22 The JitterTrack Function Source Trace P 1 P 2 P 3 P N-1 P N... Frequency Jitter Function... 1/P 1 1/P 2 1/P 3 1/P N-1 1/P N Frequency Jitter Page 22

23 时钟的抖动追踪 Page 23

24 抖动追踪案例 2 通过对 track(freq(c1)) 的波形做 FFT, 可以在频谱中观察到该时钟受到 2.275MHz 的干扰 Page 24

25 抖动追踪案例 3 -SATA 的扩频时钟测试 Serial ATA Waveform Unfiltered Track Filtered Track Conventional Track Display Unique LeCroy Filtered Track Page 25

26 抖动追踪案例 4: : 电源不稳定造成的抖动 Clock signal Track(period(c2)) Track(TIE(c2)) Power Ripple Page 26

27 JTA2 软件包括哪些功能? TIE cycle to cycle period 等的抖动测试抖动的直方图分析 Jitter track 抖动追踪其他水平测量参数 Page 27

28 JTA2 软件包中包括了以下测量参数 Symbol Parameter Name Parameter Definition delta period at level Difference of adjacent periods at specified slope and level frequency at level Cycle frequency at specified slope and level duty at level Percent of period for which data is above or below a specified level edge@lv edge at level The number of transitions or edges with a specified slope and level p@lv period at level Cycle duration at a specified slope and level tie@lv time interval error at level Fractional interval time error for a specified slope and level wid@lv width at level Duration of signal excursion above or below a specified level Page 28

29 抖动测量精度 AMPLITUDE v AMPL Δv VERTICAL UNCERTAINTY DUE TO: NOISE QUANTIZATION NON-LINEARITY VERTICAL UNCERTAINTY, Δv MAPS INTO TIME UNCERTAINTY, Δt Δt = (Δv * t R(20-80) ) / 0.6 v AMPL 通道的噪声频响的非线性 ADC 的量化误差导致了垂直方向测量的不确定性垂直方向的不确定性投影到水平方向导致时间的不确定性信号的上升时间越快, 抖动的测量精度越高 Δt Δt HORIZONTAL UNCERTAINTY DUE TO: SIGNAL JITTER APERTURE UNCERTAINTY TRIGGER JITTER TIMEBASE INSTABILITY 使用高精度的 ADC 可以提高抖动测量精度通道噪声越小, 抖动测量精度越高 TIME UNCERTAINTIES ARE UNCORRELATED AND ADD IN QUADRATURE 对于频率较低抖动很小的时钟测试, 可以适当使用 ERES 降噪后测量抖动 Page 29

30 Gaussian Distribution Random jitter is distributed as gaussian % of population is in +/-1σ range 95.45% in +/-2σ range 99.73% in +/-3σ range % in +/-4σ range % in +/-5σ range % in +/-6σ range % in in +/-7σ range 68.27% Page 30

31 Gaussian Distribution 68.28% of population is in +/-1σ range means 31.73% of population is out of +/-1σ. Recognize the events out of the specified range as Error, then +/-1σ range could be related with 31.73% Error rate. 4.55% out of +/-2σ 0.27% out of +/-3σ 0.006% out of +/-4σ % out of +/-5σ % out of +/-6σ % out of +/-7σ 31.73% Page 31

32 Gaussian Distribution Range as multiple of σ refer to Error rate Error Rate Peak Pk-Pk /-3.09σ 6.180σ /-3.719σ 7.438σ /-4.265σ 8.530σ /-4.754σ 9.507σ /-5.199σ σ /-5.612σ σ /-5.998σ σ /-6.361σ σ /-6.706σ σ /-7.034σ σ /-7.349σ σ /-7.650σ σ /-7.941σ σ /-8.222σ σ Page 32

33 抖动分解绝大多数情况下, 时钟的固有抖动只有 Pj, 不包括 DDJ 总体抖动 (Tj) 随机抖动 (Rj) 固有抖动 (Dj) Tj = N(BER)*Rj + Dj Page 33

34 FAQ 三种时钟抖动通常用在什么场合? 怎样测量某 PLL 或晶振的相噪? 某时钟芯片的手册要求 80k-20MHz 的 RMS 抖动小于 1ps, 怎样测试这类时钟? 怎样测量时钟的 Tj? Page 34

35 Any Question?

36 The end!

國家圖書館典藏電子全文

國家圖書館典藏電子全文 I Abstract II III ... I Abstract...II...III... IV... VI 1...1 2...3 2-1...3 2-2...4 2-3...6 2-4...6 3...8 3-1...8 3-2...10 4...12 5...15 5-1...15 5-2...17 IV 5-3...18 6...21 6-1...21 6-2...22 6-3...22