Statistical analysis using histograms is a powerful technique for looking at and processing large amounts of data. It is sometimes useful to view the source waveforms corresponding to an individual measurement appearing in the histogram for more detailed analysis. Of course the scope has always "captured" the source waveforms -- that is how the measurements get into the histogram. But sometimes you want to be able to view and measure the waveforms that produce interesting measurements.
LeCroy oscilloscopes make such recovery possible due to the high level of functional integration designed into them. Among the available tools is the powerful WaveScan Scan and Search analysis tool.
Consider the histogram of delta time at level (dt@lV) measurements shown in the bottom trace of Figure 1. This histogram shows the uniform distribution of the delay between the two source waveforms shown in the traces marked C1 and C2. These waveforms are from a trigger circuit which synchronizes an external event (trace 1) with an internal 400 MHz clock to produce a synchronous pulse output (trace C2).
This histogram shows the uniform distribution of the delay between the two source waveforms shown in the traces marked C1 and C2. These waveforms are from a trigger circuit which synchronizes an external event (trace C1) with an internal 400 MHz clock to produce a synchronous pulse output (trace C2).
The expected delay between the input and output is uniformly distributed over a range of 2.5 ns. Note that a small number of output pulses are delayed by an additional 2.5 ns clock period. This behavior was not expected.
It would be useful to be able to capture these delayed input/output pairs. This can be easily accomplished using LeCroy’s WaveScan Analysis tool which permits scanning for events that meet set measurement limits. In this case we would like to examine waveforms with unusual values of delta time at level parameter. The histogram can be used to determine the search criteria.
In Figure 2 a cursor is used to determine the upper limit of the expected range of delay values. That cursor indicates the upper limit is 55.18 ns as indicated by the cursor horizontal readout under the timebase annotation box.
WaveScan is setup in measurement mode to scan the incoming acquisitions and stop if the delay between C1 and C2 exceeds 55.18 ns. It has captured a waveform with a delay of 57.568 ns. This is reported in both the value of the parameter P1 which show the last measurement in the acquisition and well as the WaveScan table in the upper left corner of the figure.
This is a great example of how LeCroy oscilloscopes allow users to combine functions easily and seamlessly to solve tough measurement problems. In this example, statistical analysis, automatic parameter measurements, and WaveScan were combined to acquire, store, analyze, and document the desired waveforms.