JTA2 Jitter & Timing Analysis Operator’s Guide December 2003
LeCroy Corporation 700 Chestnut Ridge Road Chestnut Ridge, NY 10977–6499 Tel: (845) 578 6020, Fax: (845) 578 5985 Internet: www.lecroy.com © 2003 by LeCroy Corporation. All rights reserved. LeCroy, ActiveDSO, ProBus, SMART Trigger, JitterTrack, WavePro, WaveMaster, and Waverunner are registered trademarks of LeCroy Corporation. Information in this publication supersedes all earlier versions. Specifications subject to change without notice.
ACCESSING JTA2 ...............................................................................................3 TIMING FUNCTIONS............................................................................................3 TIMING PARAMETERS........................................................................................4 Statistical Tools................................................................................................................................. 4 HOW JITTERTRACK WORKS ...........
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ACCESSING JTA2 To access JTA2's special features, you must first purchase and install the option. Once installed, JTA2's math and parameter selections will appear in the Math and Measure menus. TIMING FUNCTIONS JitterTrack, PersistenceHistogram and PersistenceTrace are timing functions in LeCroy’s JitterPro and JTA jitter and timing analysis packages. The JitterTrack feature is key to identifying the source of excessive jitter or non-normal jitter characteristics.
JTA2 Option TIMING PARAMETERS Timing parameters can also be used to measure cycle-to-cycle jitter, the width of positive and negative pulses, the duty cycle of either polarity, and an infinite number of cycles on long records. Pulses or cycles can be counted using one of these parameters. As interpolation filtering is applied to signal edges in the vicinity of measurement points, timing parameters operate on acquired waveform levels that may be selected in either volts or percentage of signal amplitude.
HOW JITTERTRACK WORKS Using “Clock” or “Data” Use this function to plot as a bar chart the evolution over time of this and five other waveform attributes in simple steps.
JTA2 Option When “Data” Mode is selected. 1. Set the desired reference clock frequency for an ideal position against which the signal is to be compared, or use “Find Frequency.” 2. Specify the level at which the jitter measurement is to be made, as well as the rising or falling edge on which the measurement is to start. 3. Timing errors are graphically revealed.
WHEN TO USE JITTERTRACK The JitterTrack Function charts the evolution in time of these waveform attributes: • Cycle-to-Cycle deviation • Duty Cycle • Interval Error • Period • Pulse Width • Frequency Each is time-correlated to its source trace and contains the same number of points as the waveform. JitterTrack or Trend? Whether it is more appropriate to use JitterTrack or the statistical tool, Trend will largely depend on the application, as well as the other factors set out in the tables below.
JTA2 Option When you need to Use… monitor the evolution of a waveform parameter Trend - Jitter works only on one acquisition at a or attribute over several acquisitions... time time-correlate an event and a parameter value... JitterTrack monitor an evolution in the frequency domain... JitterTrack - Trend points are not evenly spaced in time and therefore cannot be used for FFT (Fast Fourier Transform). monitor JTA parameters...
CLOCK OR DATA? For most waveform attributes, JitterTrack offers the choice of Clock or Data modes for measuring clock signals or data streams. "Data" should be used (where available) when the pulse widths, intervals, periods or other significant instants being measured are randomly distributed and contain multiples of the clock period. On the one hand, apart from jitter, clock signals ought to be regular. On the other hand, data streams by their very nature have irregular pulse widths.
JTA2 Option Comparing a Random Data Stream Analyzed Using Clock and Data Modes.
SETTING UP JITTER MEASUREMENTS Jitter Math Setup 1. Touch Math in the menu bar, then Math Setup... in the drop-down menu. 2. In the "Math" dialog, touch an unused Fx button to simply make a selection from the Select Math Operator menu. Or, touch an Fx tab options. for more setup Note: By default, unused Fx positions are designated as zooms of C1. However, the traces are disabled, as indicated by an unchecked On box alongside the Fx button: 3.
JTA2 Option 4. Touch a persistence function. The Select Math Operator menu closes, and the trace is automatically enabled. JitterTrack If you want to enable JitterTrack in addition to (or instead of) a persistence function trace, touch the Jitter button in the Select Math Operator menu, then the Track button. The Select Math Operator menu closes, and the JitterTrack is automatically enabled. Jitter Parameters Setup 1. Touch Measure in the menu bar, then Measure Setup... in the drop-down menu. 2.
appears. 5. Touch a parameter. The setup dialog for the Px position you selected opens automatically. A mini-dialog also opens to the right of the main dialog, giving you more setup options for the selected parameter.
JTA2 Option WHEN TO USE PERSISTENCE HISTOGRAMS The Persistence Histogram function builds a histogram from a persistence map to reveal the features that are only visible when several acquisitions have been superimposed on one another. In contrast to this, the histogram as statistical tool simply graphs waveform parameters such as amplitude, frequency, or pulse width on an acquisition or series of acquisitions. Both Histogram and Persistence Histogram bar charts are divided into intervals, or bins.
SETTING UP PERSISTENCE HISTOGRAMS Selecting the Math Function 1. Touch Math in the menu bar, then Math Setup... in the drop-down menu. 2. In the "Math" dialog, touch an unused Fx button to simply make a selection from the Select Math Operator menu. Or, touch an Fx tab options. for more setup Note: By default, unused Fx positions are designated as zooms of C1. However, the traces are disabled, as indicated by an unchecked On box alongside the Fx button: 3.
JTA2 Option Setting Up the Histogram The mini-dialog contains setup fields for your histogram. Selecting the Cut Touch inside the Cut Direction field and select either Vertical or Horizontal. If you choose to cut a vertical slice, the units of the center and width of the slice are given in nanoseconds. If you choose a horizontal cut, the units of the center and width of the slice are given in millivolts.
HOW TO TRACE PERSISTENCE A persistence waveform created by turning on persistence is show here. From this waveform, you can create three types of shapes on which waveform processing can be performed. From left to right are shown Average, Range, and Sigma An Innovative Visual and Processing Tool With this timing function, not only can waveform noise and jitter be displayed but further processing can also be done.
JTA2 Option Displaying data acquired from multiple sweeps of the waveform, Persistence Trace computes a vector trace based on the bit map of the underlying signal acquisitions. Detail is then shown in a choice of three shapes: average, range, and sigma. These are created without destroying the underlying data, allowing the display of analytical results from raw data.
A setup mini-dialog opens to the right of the main dialog, offering the following additional setup options: Function Options How It Works Ptrace Mean Clear Sweeps For each vertical time slice on the persistence map, Ptrace Mean calculates and plots a trace corresponding to the map’s mean value. Single-shot signals sampled at or above 2 GS/s and accumulated in the persistence map can be traced at a resolution of 10 ps (100 GS/s equivalent sampling).
JTA2 Option CHOOSING A TIMING PARAMETER This table lists the Jitter and Timing Analysis (JTA) parameters and the tasks that they can perform. Additional analysis and processing of the waveform can be carried out by activating Statistics and using histogram parameters. For some parameters, one of the variants of JitterTrack can perform the same task.
HOW TO USE THE TREND TOOL The Basic Idea The Trend statistical tool displays the evolution of a timing parameter over time, in the form of a line graph. The graph’s vertical axis is the value of the parameter; its horizontal axis is the order in which values are acquired. • Display the waveform to be analyzed. • Apply a timing parameter: period at level (p@lv), for example. • Plot the trend of the parameter.
JTA2 Option To Set Up and Configure Trend Parameter Setup Before a Trend can be plotted, the timing parameter must be selected, as follows: 1. Touch Measure in the menu bar, then Measure Setup... in the drop-down menu. 2. In the "Measure" dialog, touch the My Measure button . . The Select Measurement menu 3. Touch an unused "Px" button: opens. on the Select Measurement menu and select a 4. Touch the Jitter button Jitter parameter. The setup dialogs for the Px position open.
8. A second setup dialog opens to the right of the main with more setup options. The options offered depend on the parameter you chose, but all include Level is, Percent Level, Slope, and Hysteresis. A Find Level button is also provided in this mini-dialog.
JTA2 Option Math Setup Now that the parameter setups are done, you have to set up the Trend math function. 1. Touch Math in the menu bar, then Math Setup... in the drop-down menu. 2. In the "Math" dialog, touch the Fx tab the trend. for the math trace you chose to display 3. Touch the "Trend" tab in the setup dialog to the right of the main setup dialog. Touch inside the Values to Trend data entry field and enter a value from 20 to 20,000, using the pop-up numeric keypad. 4.
HISTOGRAM AND TREND CALCULATION With the instrument configured for Histograms or Trends, the timing parameter values are calculated and the chosen function performed on each following acquisition. The Histogram or Trend values themselves are calculated immediately after each acquisition. The result is a waveform of data points that can be used the same way as any other waveform.
JTA2 Option Parameter Events Capture The number of events captured per waveform acquisition or display sweep depends on the type of parameter. Acquisitions are initiated by the occurrence of a trigger event. Sweeps are equivalent to the waveform captured and displayed on an input channel. For non-segmented waveforms, an acquisition is identical to a sweep, but for segmented waveforms an acquisition occurs for each segment and a sweep is equivalent to acquisitions for all segments.
Example A histogram of the voltage value of a five-volt amplitude square wave is centered on two peak value bins: 0 V and 5 V (see figure). The adjacent bins signify variation due to noise. The graph of the centered bins shows both as peaks. Determining such peaks is very useful because they indicate dominant values of a signal.
JTA2 Option The instrument’s parameter buffer is very effective for determining the optimal number of bins to be used. An optimal bin number is one where the change in parameter values is insignificant, and the histogram distribution does not have a jagged appearance. With this buffer, a histogram can be dynamically redisplayed as the number of bins is modified by the user. In addition, depending on the number of bins selected, the change in waveform parameter values can be seen.
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