WaveScan provides powerful isolation capabilities that hardware triggers can’t provide. WaveScan provides the ability to locate unusual events in a single capture (i.e., capture and search), or “scan” for an event in many acquisitions over a long period of time. Select from more than 20 search modes to find events on any analog or digital channel or search for a pattern across multiple digital channels. Since the scanning “modes” are not simply copies of the hardware triggers, the utility and capability is much higher. For instance, there is no “frequency” trigger in any oscilloscope, yet WaveScan allows for “frequency” to be quickly “scanned.” This allows the user to accumulate a data set of unusual events that are separated by hours or days, enabling faster debugging. When used in multiple acquisitions, WaveScan builds on the traditional LeCroy strength of fast processing of data. Displays shown in the tutorial are based on the following initial setup on a WaveRunner 6 Zi scope:
- Connect a passive probe from channel 1 to the Cal test point on the front panel, ground the probe to the adjacent ground terminal.
- Recall the default setup: File pulldown > Recall Setup> Recall Default.
- Turn off channel 2.
- . Change the frequency of the oscilloscope Cal signal from 1 kHz to 1 MHz. Utilities pulldown > Utilities Setup >Aux Output Tab>double click on Frequency>Set to Max button on Frequency pop up, then OK.
- Auto Setup the scope: Press Scope Setup then select Auto Setup from the fly-out menu.
This completes the initial setup. The scope display should be similar to Figure 1.
At this point we can evoke WaveScan. In the WaveRunner 6 Zi series scopes you do this by pressing the WaveScan button in the WavePilot area on the front panel. For other scopes WaveScan is accessed using the Analysis pull down menu. Analysis > select WaveScan from the pulldown.
Click on the Enable checkbox in the WaveScan dialog box to turn WaveScan on.
Figure 3 shows WaveScan’s default setup. It is using Edge Mode and this finds each edge in the source trace. Study the WaveScan dialog box, you will note it is set to find positive edges where the edge threshold is 50% of the signal amplitude. Each event (edge) meeting the criterion is highlighted with a red line. The locations of each edge are shown in a table in the upper left hand corner of the display. Note also that trace Z1, the zoom of trace C1 has also been turned on. This zoom trace is showing the source trace expanded horizontally by a factor of ten to one (10:1). The highlighted area on the source trace shows the specific edge being expanded.
Stop the acquisition update by pressing the Stop button in the Trigger area of the front panel. Click or touch any entry in the WaveScan table. Note that the zoom trace source jumps to that pulse. The table entries are hyperlinked to the zoom setup so you can bring any WaveScan event into the zoom trace for closer study. Zoom controls on the front panel can be used to control the Zoom trace settings.
Click or touch the Mode field in the WaveScan dialog box. The mode selection popup will be displayed. Search modes are used to locate anomalies during acquisitions.
Edge Mode – for detecting the occurrence of edges; Selectable slope and level.
Non-monotonic Mode - for detecting threshold re-crosses; selectable slope, hysteresis, and level.
Runt - for detecting pulses that fail to cross a threshold; selectable polarity and thresholds
Measurement Mode - for filtering and performing parameter measurements
Serial Pattern – Searches from 2 to 64 bits; ideal for bursted patterns where a PLL cannot lock.
Bus Pattern – Searches from 2 to 64 bits; enhances
In this tutorial we will use the edge and measurement modes as the primary examples.
Use the WaveScan Mode field and set WaveScan to the measurement mode. Touch or click the measurement field. Investigate the measurements which are available in the scroll list. Select Risetime.
Let’s start by examining our waveform. Use the Measure pulldown menu and select Standard Horizontal (STD Horizontal). Use the Measure pulldown again and select Statistics on. At this point you should see The measurements displayed under the grid area as shown in Figure 5. The first parameter, P1, is reading the risetime of trace C1. We have nine pulses on the screen and the statistics include all nine risetime values. The number (Num) readout for P1 should reflect this value. Additionally, we can read the mean, minimum (min), maximum (max), and standard deviation (sdev) of the 9 instances. The value field reads the last measured value and corresponds to the last value in the WaveScan table. Use the hyperlinks of the WaveScan table to find and display the min and max pulse ristimes. Note that the values you see on your scope for risetime will vary and will be scope bandwidth dependent. Do not expect to get the same values shown here, they will be similar but not identical.
Touch or click on the Filter Method field in the WaveScan dialog box. The Filter Method pop up will appear. This shows the available search criteria for evaluating measured values. Select Rarest events. Let’s use this filter to find the smallest risetime. Touch or click on the Rarest Mode field and select smallest. Touch or click on # Rare Events and set the value to 1.
The WaveScan table should now consist of a single entry. Touch or click that table entry. The zoom trace Z1 will now contain the pulse with the smallest risetime.
WaveScan includes a Filter Wizard to aid in setting up the values in the measurement filter.
The filter wizard uses the statistics from the actual measurement. You can select to use the average or mean value of the measurements. The Find Rare, Rarer, and Rarer Events buttons set the filter limits to the mean ±1 standard deviation, mean ± 3 standard deviations, and mean ± 5 standard deviations. The select Rarest events duplicates what we have just done manually by setting the filter to find the largest or smallest measured value.
So far we have been using WaveScan to search in a single acquisition. This is called search mode. If we allow the scope to acquire waveforms continuously in normal of auto trigger modes we can use WaveScan it the scan mode. We can then evoke a variety of actions to see any WaveScan event.
Clicking on or touching the Trigger Action the field in the WaveScan dialog will bring up a pop up menu with seven choices as shown in Figure 10. Each of these allows the user to call attention to the event or store it for later study. Set up WaveScan Trigger Action to Stop Acquisition on a filter method that is outside a limit + delta. Use the Filter Wizard and select the center Find Rarer Events. This will set the limits to the mean ± 3 standard deviations. Press the Auto Trigger button in the trigger control group on the front panel. After a few seconds the acquisition will stop and the WaveScan table will have the single value, the pulse with the smallest risetime will be highlighted and shown in the zoom trace in Figure 11.
In this example the filter limits are 28.74810 ± 1.0818435 ns. In the example in Figure 11 the lower limit is 27.666 ns and the scope stopped after finding a risetime of 27.388 ns. This can be tried with other filter settings and actions in order to learn the capabilities of this feature. When you are finished reset the Filter Method to No Filter.
When in either single shot search mode or continuous update scan mode it is possible to analyze the measurement data statistically by using WaveScan’s Scan Histogram. Checking the Histogram box on the WaveScan dialog box will bring up the Scan Histo trace. This is a histogram of all the measurement values meeting the filter requirements. Click or touch the Histogram box in the WaveScan dialog box as shown in Figure 12.
Click or touch the ScanHisto trace annotation box or click or touch the Scan Histo tab on the WaveScan dialog box. The Scan Histo tab shows the controls for controlling the histogram display.
Change the # Values in the ScanHisto dialog from 1000 to its maximum 2,000,000,000. Similarly, change the # Bins from 100 to 2,000. Change the Vertical Scale to Linear Constant Max. This keeps the histogram at a constant height as data is being gathered. The histogram display is showing a histogram of all the risetime values because we have turned the Filter Method to No Filter. Note that it approximates a Gaussian shape. Go back to the WaveScan dialog, use the Filter Wizard to Find Rare Events. This will change the Filter Method to Outside Limit ± Delta. The limit will be set to the mean value and the delta values will be the standard deviation of the distribution of measured values.
Note that the histogram, which only shows the measured risetime values that meet the filter criterion, now has a ‘hole’, shown in Figure 14, where it has excluded all the measured values inside of the Filter limits.
Scan Histogram allows the user to see the range and distribution of measured values. You can determine worst case values over a large number of measurements.
Spend some time trying other filter methods and see what effect they have on the Scan Histogram display. When you are finished turn off the Scan Histo trace by unchecking the Trace On box in the Scan Histo dialog box.
The final WaveScan feature we will investigate is ScanOverlay. This is a persistence display of all the measured edges that meet the Filter Limit criteria. ScanOverlay is turned on by checking the Overlay check box in the WaveScan dialog box as shown in Figure 15.
ScanOverlay shows all the pulses that meet the filter criteria. If you look closely at the ScanOverlay trace in Figure 16 you will note that there is a gap between traces from about 10% to 40% of the pulse height. Remembering that we excluded all risetimes within a standard deviation from the mean, we eliminated traces with those risetimes from the overlay and we can see the resulting gap. ScanOverlay allows you to see differences in traces, even those as subtle as this one.
This completes this ten minute tutorial.