Have you ever set up your oscilloscope without a proper trigger? If so, you probably experienced something a little bit like this:
In this case, I had an edge trigger and the level was set above my waveform. The oscilloscope could not find any waveform data at that threshold and therefore, didn’t know what waveform data to display on screen.
When you have a trigger set up, the oscilloscope is looking at the acquisition data to see when your trigger conditions are met. If they are met, the oscilloscope will display the waveform data centered around the trigger event, thus stabilizing your display.
The easiest way to set up a quick trigger and stabilize your display is to hit Auto Scale. That will take care of your vertical and horizontal scaling, and sets up the most common trigger type (Edge) at an appropriate level. This gets you straight to basic troubleshooting.
Below is a trigger diagram showing the conditions for Edge trigger:
Figure 1- edge trigger diagram
But triggering isn’t just used to obtain a stable display. It can also help you find events in your waveform. And there are many different triggers to help you find many kinds of events – even the tricky, hard to find events like glitches, runts, patterns, and sequences. Keysight’s Infiniium oscilloscopes provide both hardware and software triggers. Hardware triggers are quick and address the most common use cases. They are looking for events happening in real-time acquisition data. Software triggers are used when the event you want to trigger on is just too complex for hardware alone. To perform a software trigger, first the oscilloscope triggers in hardware to acquire the waveform data. Then analysis and event searching happens in software before the waveform is displayed for that trigger. Perhaps a more accurate name for software triggering is event identification software.
Below, you’ll find a quick reference guide for all the hardware and software triggers available on Keysight’s Infiniium oscilloscopes. This will help you understand what triggers are available and determine what triggers you want to use when.
What it Does / When to Use
looks for slope and voltage level of the selected source - mostly used for general purpose viewing and trouble shooting
looks for a pulse that is narrower than other pulses in your source - used to capture infrequent glitches
looks for a pulse that is either wider or narrower than other pulses in your source based on the pulse width and polarity you set - used to capture pulses that are too short or too long in time
looks for a user specified pattern - used when you want to find a specific pattern across analog and/or digital channels
looks for a pulse that is smaller in amplitude than other pulses with low and high thresholds - to find pulses that are too low in voltage
Setup and Hold
looks for violations of setup time, hold time, or both setup and hold time based on a reference clock waveform
looks for edges that do not rise or fall across two voltage thresholds in the amount of time you specify - used to find violations in rise/fall time
Edge Then Edge
looks for the two events you specify delayed by the number of events or time you set
looks for a pulse that is lasting too long either at a high or low level - to find potential timeout errors
looks for an event of the waveform exiting, entering, or remaining outside a voltage range as specified to use when you want to view a waveform either within or without certain thresholds
looks for certain packets or patterns in protocol-based data. (Hardware protocol is only available on some Keysight oscilloscopes, the S-Series being one of them, with others performing protocol trigger in software).
any two of the above performed in sequence used when you want to capture the signal based on two trigger events
Software Triggers (Available with InfiniiScan N5414B):
What it Does / When to Use
After hardware triggering and the waveform data is acquired, the specified measurement is performed, and then if the measurement condition is met, the InfiniiScan trigger condition is set to true and the waveform is displayed on screen
create up to 8 zones and combine them with logic expressions to set triggering conditions
capture packets of customized protocols or generic patterns
capture small glitches or edges that may be hidden by hysteresis
capture runts that they may be hidden by hysteresis
I’m hoping as you advance past Auto Scale and try out a couple of these triggers, you’ll be a wiz and won’t even need this lookup table!
So how do you set up these different triggers? Easy. Here are the two simple steps:
- Choose the Trigger Menu, then select Setup
- Choose the trigger you want from the list on the left and set your desired conditions
Now you’re rockin’ and rollin’! You’re ready to find all sorts of different anomalies that could exist in your waveforms and find the root causes of your malfunctioning DUT faster.
If you have any interesting test conditions in which you used one of these triggers, we’d love to hear about it in the comments. Happy Triggering!