Jitter Basics Lab Using SDAIII & Jitter Sim

Transcription

1 Jitter Basics Lab Using SDAIII & Jitter Sim TUTORIAL August 1, 2012 Summary JitterSim is a math function, enabled by the Serial Data Analysis option, which allows various aspects of jitter to be simulated either singly or in groups. It is ideal for experimenting with how various jitter components are manifested in the jitter measurement displays available in SDAIII. Powerful SDAIII Serial Data Analysis Unleash the power of serial data analysis to understand and characterize your design, prove compliance, and determine why a device or host fails compliance. The SDAIII analysis package is the only solution that fully integrates jitter measurements into the oscilloscope software leading to greater confidence in jitter measurements. Key Features Integrated jitter and timing analysis for clock and data signals Many plot types for jitter and eye diagram analysis including: Eye Diagram, IsoBER, DDj Plot, Digital Pattern, DDj Histogram, Jitter Track, PLL Track, Jitter Spectrum (with peak annotation), Spectrum Threshold, Pj Inverse FFT, Jitter Histogram, CDF, Bathtub, and NQ-Scale IsoBER displays the lines of constant Bit Error Ratio Configurable software PLL uses up to two poles for non-standard clock requirements Three jitter breakdown methods (Spectral Rj Direct, Spectral Rj+Dj CDF Fit and NQ-Scale) indicate pathological jitter measurement conditions Teledyne LeCroy s quick view displays the eye diagram, TIE track, bathtub curve, jitter histogram, NQ-scale, and jitter spectrum all on the screen at the same time Eye diagram display and jitter measurements/analysis on up to four lanes of serial data Complete Data Dependent Jitter (DDj) decomposition with histograms, plots, and InterSymbol Interference (ISI) parameters and plots Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 1 of 13

2 Complete Random Jitter (Rj) + Bounded Uncorrelated Jitter (BUj) views include Histogram, Spectrum and Track Complete Period Jitter (Pj) analysis with a time domain view of Pj (Pj Inverse FFT) A new Vertical Noise and Crosstalk package that determines total noise due to interference caused by crosstalk, and decomposes it into random and deterministic noise The LaneScape Comparison mode and Reference Lane for aggressor on/off and other multi-scenario comparisons The ability to determine what the signal will look like where you cannot place the probe, while also deembedding or emulating up to 6 circuit elements Equipment Required Teledyne LeCroy WavePro/SDA/DDA 7 Zi/Zi-A, WaveMaster/SDA/DDA 8 Zi/Zi-A, LabMaster 9 Zi-A and 10 Zi series oscilloscopes with the SDAIII Serial Data Analysis option enabled. Screen images in this tutorial were taken from a WaveMaster 820Zi-A Tutorial 1. Recall the default setup on the scope (File>Recall Setup>Recall Default). 2. Turn off channels 1 and 2 using the front panel 1 and 2 buttons in the vertical control group or by accessing the C1 and C2 dialog boxes via the vertical pull down. 3. Using the Timebase Horizontal setup (Timebase > Horizontal Setup, set the WM8Zi for operation with a sampling rate of 40 GS/s and 800kS acquisition memory (2 s Time/division). 4. Setup Math trace F1 to use the Jitter Sim function (Math> Math Setup>F1>Source C2>Operator Jitter Sim). Turn the F1 trace on. 5. Using the Sim Signal right hand tab of the F1 dialog box setup Sim Signal to use a frequency of 2.48 GHz, a risetime of 200 ps, and NRZ data type. The screen should appear similar to Figure 1. Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 2 of 13

3 Figure 1: The JitterSim setup 6. Open the SDAIII setup dialog and display (Analysis pull down > Serial Data). 7. On the Serial Data Analysis III dialog box press the Quick View button. A pop up will appear as shown in Figure 2. Figure 2: The Quick View Input selection pop up box 8. In the QuickView pop press the 1 Input button and select F1 as the data source. Press OK. 9. The oscilloscope will bring up the Quick View display consisting of the Eye diagram, PLL Track, Jitter Spectrum, Bathtub curve, RjBUj histogram, Q scale, and RjBUj Track. This is shown in Figure 3. Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 3 of 13

4 Figure 3: The SDAII Quick View Display setup 10. JitterSim allows the users to independently simulate various aspects of jitter. This includes jitter associated with vertical noise, random horizontal jitter, sinusoidal periodic jitter, duty cycle distortion (DCD), and Inter-Symbol Interference (ISI). Our initial measurements are made with the default jitter separation model, Spectral Rj+Dj CDF Fit. Record the values of the parameters Tj, Rj, and Dj from the scope display 11. As a first step let s see what happens if we increase the vertical (Rn) noise on the Vertical tab in Jitter Sim. Open the F1 dialog box (Math > Math Setup > F1 tab > Vertical right hand tab. Change the Gaussian vertical noise level to 5 mv and record Tj, Rj, and Dj: Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 4 of 13

5 Describe what happened to the Normalized Q-Scale, Bathtub Curve, Eye Diagram, RjBUj track, and histograms Figure 4: Effect of Increasing Vertical Noise 12. You know that vertical noise maps into horizontal jitter proportional to the risetime of the data. Increase the Risetime setting on the Sim Signal tab to 400 ps (F1 > Sim Signal right hand tab). 13. Record Tj, Rj, and Dj Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 5 of 13

6 14. Describe what happened to the Normalized Q-Scale, Bathtub Curve, Eye Diagram, RjBUj track, and histograms Figure 5: Increased vertical noise along with increased risetime 15. Restore both the Gaussian vertical noise level to 1 mv and risetime to 200 ps. Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 6 of 13

7 16. Let s add periodic jitter. Go to the Jitter right hand tab of the F1 dialog box and set the Jitter Freq setting on the first line of the sinusoidal jitter field to 1 MHz with a Peak to Peak level of 5 ps. Record Tj, Rj, and Dj here and on the following page. Describe what happened to the Normalized Q-Scale, Bathtub Curve, Eye Diagram, RjBUj track, and histograms _ Figure 6: The effect of adding periodic jitter Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 7 of 13

8 17. Repeat this test for Peak to Peak levels of 10 ps and 20 ps. 5 ps 10 ps 20 ps 18. Save and compare the Bathtub curves for each level of sinusoidal periodic jitter into memories M1-M3. File > Save Waveform> Save To Memory> Source> Category>SDA> Source Bathtub> Destination > M1 (then M2 and M3)> What effect does increasing Deterministic (periodic) jitter have on the bathtub curve Figure 7: The saved Bathtub curve for 5 ps (M1), 10 ps (M2), and 20 ps (M3) periodic jitter amplitudes 19. Turn off the memory traces. Restore the QuickView Display (Analysis > Serial Data >QuickView Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 8 of 13

9 20. Touch or click the RjBUj Spect trace annotation box. Use the Zoom of RjBUj Spect right hand tab to setup the zoom on the RjBUj Spectrum to show the periodic jitter component at 1 MHz as shown in Figure 8. Turn on Show Peaks in the Jitter Spectrum tight hand tab. Figure 8: The periodic component shown on the RjBUj spectrum display 21. Restore the Peak to Peak level of the sinusoidal component in JitterSim to 0 ps 22. We will now see the effect of Duty Cycle Distortion (DCD) on jitter levels. Set the DCD under the Vertical tab to 40 ps. Record Tj, Rj, and Dj _Tj Rj Dj DCD Describe what happened to the Normalized Q-Scale, Bathtub Curve, Eye Diagram, RjBUj track, and histograms 23. Restore the DCD to 0 ps. Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 9 of 13

10 Figure 9: Investigating the effects of DCD 24. We will now see the effect of Intersymbol Interference (ISI) on jitter levels. We will use a low pass filter to create ISI. On the Sim Signal tab set the Cutoff Frequency to 1.8 GHz and Order to 3. Check the box labeled BWL (Band width limit ) On. Record Tj, Rj, and Dj ISI Describe what happened to the Normalized Q-Scale, Bathtub Curve, Eye Diagram, RjBUj track, and histograms Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 10 of 13

11 Figure 10: How ISI affects jitter levels 25. Open the Math trace F1 dialog box. Set the jitter simulation parameters as follows: F1 Tab Function Values Jitter Sinusoidal Jitter Jitter frequency 1 MHz, Pk-Pk 5 ps Vertical Rn (Gaussian) 5 mv Sim Signal Riwetime 200 ps BWL On CutOff 1.8 GHz Order 2 Vertical DCD 40 ps 26. Record Tj, Rj, and Dj The display should appear similar to Figure 11. Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 11 of 13

12 Figure 11: The Spectral Rj+Dj CDF Fit measurement 27. Open the SDA dialog box (Analysis>Serial Data). Click on the Jitter tab. Change the Dual-Dirac Model from Spectral Rj+Dj CDF Fit to NQ-Scale. The display should be similar to Figure Record Tj, Rj, and Dj Figure 12: The NQ-Scale measurement Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 12 of 13

13 29. Change the Dual-Dirac Model from NQ-Scale to Spectral Rj Direct. The display should be similar to Figure Record Tj, Rj, and Dj Figure 11: Spectral Rj Direct model Note that the jitter measurements using the three models are similar, but they can be quite different depending on the type of jitter present. For example, when there is crosstalk, the two Spectral methods will report high values of Rj due to the rise in the noise floor of the jitter spectrum. Variations of this magnitude among the model responses, in the absence of crosstalk, can be expected and are explained in the Teledyne LeCroy White Paper: Understanding SDAlIl Jitter Calculation Methods This completes the tutorial. Teledyne LeCroy Jitter Basics Lab Using Jitter Sim page 13 of 13