Wavecrest SIA-3000 Manuale utente
WAVECREST Corporation
Examining Clock Signals And Measuring Jitter
with the
WAVECREST
SIA-3000™
Application Note No. 142
200142-00 REV A
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WAVECREST
Corporation continually engages in research related to
product improvement. New material, production methods, and design
refinements are introduced into existing products without notice as a
routine expression of that philosophy. For this reason, any current
WAVECREST
product may differ in some respect from its published
description but will always equal or exceed the original design
specifications unless otherwise stated.
Copyright 2002
WAVECREST
Corporation
A Technologies Company
7626 Golden Triangle Drive
Eden Prairie, Minnesota 55344
(952) 831-0030
(800) 733-7128
www.wavecrest.com
All Rights Reserved
U.S. Patent Nos. 4,908,784 and 6,185,509, 6,194,925, 6,298,315 B1,
6,356,850, 6,393,088 and R.O.C. Invention Patent No. 146548; other United
States and foreign patents pending.
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Contents
Introduction................................................................................................1
Amplitude Measurements..........................................................................2
Measuring Jitter with Histogram Tool.........................................................3
Use Tail-Fit to Separate RJ and DJ ...........................................................4
Find the Causes of DJ; Identify PJ, Crosstalk and Modulation ..................5
Identify the Spectral Content of the Jitter...................................................6
Identify Possible Low Frequency Jitter Content.........................................7
Analyze Long-term Drift/Wander................................................................8
Measure Duty Cycle and Frequency........................................................10
Measure Cycle-to-Cycle........................................................................... 11
Measure Skew or Propagation Delay.......................................................12
Conclusion............................................................................................... 13
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EXAMINING CLOCK SIGNALS AND MEASURING JITTER
WITH THE
WAVECREST
SIA-3000™
Application note #142
IntroductionThe purpose of this application note is to highlight the various clock measurement tools
available in the VISITM software. The basic steps for specific tool setup and
interpretation of the resulting plots are covered. More details for each tool are provided
in the following
WAVECREST
Quick Reference Guides: Understanding Jitter, SIA-
3000 Measurement Technique, Oscilloscope, Histogram, and High Frequency
Modulation. These guides provide details of tool settings, measurement setup and
theory of measurement.
This application note will discuss how to use the various VISITM tools to fully
characterize your signal. These tools allow many different parameters of a clock signal
to be measured including:
• Random Jitter (RJ)
• Deterministic Jitter (DJ)
• Total Jitter (TJ)
• Periodic Jitter (PJ)
• Cycle-to-Cycle Jitter
• Duty Cycle
• Frequency
• Low Frequency Periodic Jitter
• Spectral View of PJ and RJ
• Timing Characteristics:
Positive Pulse width
Negative Pulse width
Period (rising edge to rising edge)
Negative Period (falling edge to falling edge)
• Long term changes (varying Vcc or Temperature)
• Skew or Propagation delay between any combination of rising and falling
edges on 2 channels
Clock Tools Overview Page 1 of 13
Oscilloscope
To Measure:
Risetime
Falltime
Voltage Parameters
Eye Mask
For more information
on this tool, refer
to:
Oscilloscope Quick
Reference Guide
available at
www.wavecrest.com
Amplitude Measurements
Assuming the engineer has an idea of the device’s pins or test setup probe points, it is
helpful to view the signal in the Oscilloscope Tool. Eye masks can be created using
the integrated sampling oscilloscope on the channel cards. The information in this tool
is for qualitative analysis as well as measuring voltage parameters including rise or fall
times. A different measurement engine is used for jitter analysis (those tools follow this
page).
• Connect the clock signal under test to IN1 on the front panel.
• Press the Oscilloscope button. This will open the Oscilloscope tool. The channel and
trigger settings default to IN1.
• Press the Auto Scale button to configure the display and perform an initial
measurement. Signal should be <= 1Vpk-pk single ended or <=2Vpk-pk differential.
• Press the SINGLE/STOP button to acquire the signal. The signal will be displayed.
Figure 1 - Oscilloscope example
Clock Tools Overview Page 2 of 13
HISTOGRAM
To Measure:
For more information
on this tool, refer
to:
Histogram Quick
Reference Guide
available at
www.wavecrest.com
Measuring Jitter with Histogram tool: 1-sigma, peak-to-peak
• Press “Tool” to open the main menu
• Press Clock then Histogram to open the histogram tool.
• Press the SINGLE/STOP button on the front panel or the top menu. The tool
defaults to make a period measurement (rising edge to the next rising edge). The tool
defaults to a sample size of 10,000 measurements.
Basic statistics displayed on the Histogram Summary View are: Mean, Min, Max, 1-
sigma, peak-to-peak, and number of hits (Figure 2).
Results from the most recent pass are displayed as “Latest” text. Results from
accumulated statistics are display as “ACCUM” text. The Maximum Histogram view
(below) shows all accumulated measurements.
Figure 2 - Histogram Period Measurement
A histogram can be made of PERIOD (+), PERIOD (-), PULSE WIDTH (+) and PULSE
WIDTH (-) measurements.
These Histogram statistics may be sufficient for jitter analysis when no deterministic
jitter is present, but with the addition of DJ, it is helpful to perform a more
comprehensive analysis. When the histogram is Gaussian, the 1-sigma equals the
Random Jitter (RJ). The addition of Deterministic Jitter (DJ) will increase the 1-sigma.
WAVECREST’s
Tail-FitTM algorithm can be enabled to better estimate the true RJ.
Clock Tools Overview Page 3 of 13
HISTOGRAM with
TAIL-FITTM enabled
To Measure:
For more
information on this
tool, refer to:
Histogram Quick
Reference Guide
available at
www.wavecrest.com
Use Tail-FitTM to separate RJ and DJ. Predict Total Jitter (TJ) at a
specific Bit Error Rate (BER) or amount of time
• Press the Tail-Fit button. This will open the Tail-Fit menu
• Under the Tail-Fit selection, change “off” to “Enabled”.
• Press Clear to clear your measurements.
• Press RUN. The measurement will stop when the tail regions can be fit. Additional
information can now be displayed.
Figure 3 - Results of Histogram with Tail-Fit™ enabled. Measurement is on
a 2GHz clock
• Add a view by pressing ADD VIEW on the front panel or press on the top menu bar.
Change this view to “bathtub” to display the bathtub curve.
We can now see additional values in Figure 3 summary view at the top (which were not
available in Figure 2). The first value is Total Jitter (TJ), which includes contributions
from all deterministic and random components, and is a pk-pk value specified for a Bit
Error Rate (BER), or amount of time. The Bathtub curve shows the TJ as a function of
BER or time. To predict TJ, we must measure DJ and RJ accurately. Random jitter (RJ)
is characterized by a Gaussian distribution and assumed to be unbounded. As a result, it
generally affects long-term device stability. Because RJ is Gaussian in nature, the
distribution is quantified by the standard deviation (1σ) and mean (µ). Because RJ can
be modeled as a Gaussian distribution, it can be used to predict pk-pk jitter as a function
of BER or time. The Tail-FitTM algorithm curve fits a Gaussian model independently to the
right and left sides of the distribution. The Values of DJ, LtRMS (left-tail RJ), and RtRMS
(right-tail RJ) are displayed below the TJ. Chi-squared values are also displayed as an
indication of the goodness of fit from model to acquired measurements. Once DJ has
been found, we can determine the causes.
Clock Tools Overview Page 4 of 13
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