In some applications oscilloscope users would like to separate pulses based on waveshape or some parametric value and average only those pulses meeting a desired criteria. Teledyne LeCroy oscilloscopes allow the use of pass/fail testing, using masks and/or parameter readings, to qualify waveforms before they are added into an average or other processing function.
To setup a selective average based on waveshape, a tolerance mask is created using the Pass/Fail set up dialog box for condition Q1. The example in Figure 1 shows the waveform C1 being tested against such a tolerance mask. If all points of the trace are inside the mask the waveform is saved to memory M1. The averager uses M1 as its source and accumulates only those pulses which match the tolerance mask.
The trace F1, shown in the lower grid of Figure 1, is defined using the Math setup, to be the average of M1. Only waveforms that match the shape of the mask are added into the average. Waveforms, such as the one marked Q1 ( the red circles show mask violations), which do not match the match are not saved to M1 and are, therefore, not accumulated in the average. Note that the Pass/Fail action selected is to save the waveform if it passes (defined as having all points inside the mask). The save action has to be setup in advance using the save waveform selection under the file pull down menu.
This principle can be expanded to average only pulses meeting the mask criteria as well as satisfying specific parameter limits. Pass/Fail testing support up to 8 criteria with a variety of logical combinations to initiate actions. Figure 2 shows an example of a similar selective averaging arrangement. Here only pulses with a pulse width less than 4.65 µs are accumulated in the average.
Display persistence has been applied to the Channel 1 trace so that the full range of pulse widths are displayed. Only those with the specified width are accumulated in the average.
These examples illustrate the flexibility and high level of integration built into every Teledyne LeCroy oscilloscope allowing diverse features to be integrated into a powerful analysis tool.