Keysight oscilloscopes help you find the cause of glitches

Abnormal glitches, non-monotonic edges, and metastable signals are a few types of signal anomalies that often annoy engineers and keep them awake. Troubleshooting anomalies usually involves three steps:

1. Observe and identify; confirm the existence of abnormalities

2. Signal isolation; separate abnormal signals from good signals

3. Analyze and collect; find clues to the root cause (such as frequency anomalies, unique patterns, or other identifiers to diagnose the cause of the first anomaly.)

1. Confirm and isolate exceptions

If you suspect an anomaly exists in your design, the first thing you need to do, whether during product development, design verification, or failure analysis, is find the anomaly. Figure 1 shows an unusual glitch mixed in with a good signal. This burr can cause the design to experience intermittent operational failures. If a slower waveform capture rate (trigger update rate) is used like a traditional digital storage oscilloscope, the first step of observation confirmation will take a long time. However, with the 6000X Series' 450,000 waveforms per second capture rate (waveforms/second), you can see this unusual glitch immediately. In terms of time savings, if you use an oscilloscope with a capture rate of 450,000 waveforms/second to display a glitch, it may take 10 seconds, but if you switch to an oscilloscope with a capture rate of 1,000 waveforms/second, it will take 75 minutes to display the same glitch!

Now that you've identified the glitch, you'll want to isolate it from the good signal. Using advanced triggering is an essential method for isolating signals in modern oscilloscopes. However, setting up advanced triggers requires expertise and can be a challenging process, depending on the complexity of the anomaly you are trying to isolate. With InfiniiScan zone touch triggering, a hardware exclusive to the 6000X Series oscilloscopes, signal isolation is as simple as drawing a box around the signal or area of ​​interest and selecting whether the signal must cross or must not cross ". The oscilloscope will only display waveforms that meet these qualifications. Figures 2 and 3 are examples of using InfiniiScan area triggering to isolate unusual glitches in our sample signal. Because 6000X InfiniiScan zone triggering is hardware-based, it can scan with triggering speeds up to 160,000 waveforms per second. In comparison, software-based zone triggering can only view about 1,000 waveforms per second.

Figure 1. Fast update rate catches abnormal glitches faster.

Figure 2. Check this box to set up InfiniiScan area touch triggering.

Figure 3. Only the crossover waveforms outlined in Figure 2 are captured and displayed.

2. Collect and conduct in-depth analysis to determine the source of burrs

Once the anomaly is isolated, the next step is to collect and analyze the relevant information and try to find the root cause of the glitch. Using the dual cursors on the 6000X Series oscilloscope's multi-touch screen, we can quickly measure the size of the glitch, which in the case of Figure 4 is approximately 40 ns as shown in the graph. After knowing the width of this burr, we can now use the second method to isolate the burr.

Figure 4. Using dual cursors to determine burr size

What we really want to know is whether this glitch occurs multiple times, and if so, how often it occurs. Among the advanced triggers in this case, the pulse width trigger is the more ideal one. Pulse width triggering works by setting a pulse width condition of "greater than," "less than," or "between." The pulse width trigger setting shown in Figure 5 uses a pulse width of "less than 50 ns".

Figure 5. Set pulse width trigger

But how can we find out how often glitches occur? Segmented memory is a standard feature on InfiniiVision 6000X Series oscilloscopes, which allows you to selectively capture and store important signal activity or segments without capturing trivial ones. signal idle time. We provide each segment with a time stamp relative to the first triggering event. Segmented memory is an ideal solution because we suspect that such glitches occur very infrequently, separated by very long periods of idle time. We will use segmented memory and pulse width triggering to find out how many times this glitch occurs.

Figure 6. Fifty glitches captured in segmented memory. Sidebar list showing relative time stamps

Figure 6 shows the results of capturing 50 glitches. Using the scrollable sidebar event list, you can quickly find the time stamp for each segment. This listing shows that the glitch is periodic, occurring every 42ms, or a frequency of 23.8 Hz.

In other words, you can determine that the potential root cause of this glitch is a coupled signal from the source at approximately 23.8 Hz.

Using both segmented memory and colorimetric analysis allows for further in-depth analysis. When the colorimetric display is activated, the "Segment Analysis" function of the segmented memory is able to overlay all segments. By showing a three-dimensional quantitative view of the waveform, the colorimetric display can provide how often a specific event of interest occurs, so find out as shown in Figure 7

Figure 7. Colorimetric analysis of segmented memory can provide additional insight into the type of glitch you are dealing with.

For the abnormal waveform signal shown, this is an ideal solution.

Also note that segmented memory can capture 50 glitches in 2 seconds at 20 GSa/s. A traditional oscilloscope without segmented memory capability would require a memory depth of 40 Gpts to perform the same length of acquisition (2 sec / (1 pt / 20 GSa/s) = 40 Gpts).

10-bit counter/accumulator

The InfiniiVision 6000 Built-in 10-bit counters and accumulators count the number of edges and "qualified events". Figure 8 shows the use of a counter to measure the frequency of events whose pulse width meets the trigger condition. As expected, the counter found that the glitch occurred at 23.8 Hz.

Figure 8. Using a 10-bit counter and accumulator to determine the frequency of events that qualify as a trigger