Introduction

Often, validation testing requires that a signal meet certain specific criteria in terms of various parameters, such as amplitude, pulse width, rise time, and so forth. Teledyne LeCroy’s WaveJet Touch oscilloscope provides pass/fail mask or measurement testing to check signals for these specific criteria.

Using Pass/Fail Mask Testing

Initiate pass/fail testing by pressing the front-panel Measure button, then touching the onscreen Pass/Fail button. From there, one may touch the Actions button to determine what the oscilloscope will do when a pass/fail limit is exceeded. Options include:

  • Stopping the acquisition
  • Creating a screen capture
  • Saving the waveform
  • Outputting a pulse to another instrument using the WaveJet Touch’s AUX Out connector
  • Beeping

For this demonstration, Channel 1 of a WaveJet Touch is fed with a simple square wave plagued by an intermittent runt pulse. Such pulses can be difficult to capture. The initial oscilloscope setup is shown in Figure 1.

Figure 1:

This is the initial setup with a square wave with a runt pulse on Channel 1 of the WaveJet Touch oscilloscope. Note the basic Measure menu at the right of the screen capture

A mask may be loaded from memory or created using the waveform displayed onscreen. To create a mask, open the Pass/Fail menu and touch the Condition button. The Mask Condition menu allows users to determine the signal source (Channels 1-4 or a Math function) and to set the Pass If criteria for whether the signal is all within the mask’s boundaries or all outside of the boundaries. Touching the Edit Mask button provides controls with which to widen or narrow the mask’s vertical and horizontal dimensions (Figure 2).

Figure 2:

Using the Edit Mask menu, a mask is created with dimensions of about half a division in height and width

With the mask created and in effect, the oscilloscope runs until it encounters a failing condition. In this example, the Pass If condition is set to All In and the Action is set to Stop Sweep when a failing condition is encountered. As shown in Figure 3, the signal went out of the mask boundaries in the 58th capture from start, causing the trigger to stop.

Figure 3:

With the Pass/Fail mask set to stop the instrument upon encountering a failing condition, a glitch is discovered in the 58th capture (shown in the Replay Mode counter at the upper right). Note also that the Pass counter at bottom center shows that 57 of 58 instances have passed

Using Pass/Fail Measurement Testing

One also may apply measurement criteria to pass/fail testing for as many as four different measurements simultaneously. Continuing with the example of the glitch square wave, it might be interesting to measure the signal’s rise time (20-80%). Ordinarily, the signal has a rise time ranging from about 18 to 20 ns. With the Pass/Fail function set to stop the trigger when rise time exceeds 30 ns, an anomaly turns up in short order (Figure 4).

Figure 4:

Using the Pass/Fail function to find a signal anomaly has turned up an edge with a rise time exceeding 30 ns

Conclusion

The Pass/Fail testing function built into the WaveJet Touch oscilloscope uses either a user-defined mask or measurement criteria to perform validation testing.