Alright, this tool may not actually be helpful in your search for dinosaurs if someone really were to figure out how to bring them back, but this makes a great example to help explain the concept of oscilloscope segmented memory.
So, let’s begin our journey to the greatest theme park of all time – we’ll call it “Dinosaur Island” for lack of a better name... Naturally you’re going to want as much footage as possible of your favorite dino so you can always remember this grand adventure (assuming it has a better outcome than in the movie). Let’s say you’re a huge T-rex enthusiast, so you want to capture them (and only them) running around the park each day. To do this, you can set up a video camera in a tree and retrieve the footage at the end of the day.
But when looking at the footage from the first day, not only do you see your beloved T-rex, but you also see all of the velociraptors, triceratops, diloposaurus, and whatever other Jurassic creatures were running through the park that day. Your camera only has so much memory, and it filled up half way through the day. So you’ve wasted the majority of the memory on these other dinos you don’t even care about. You only have two days left in the park and you really want more T-rex footage. What do you do now?
What if you could set up a sensor condition (or trigger condition) that tells the camera to only record when there is T-rex running by? Now, when you collect your camera at the end of the trip, the memory will only consist of T-rex footage! Not only do you save memory and use it more efficiently, but you also save yourself loads of time by not having to sift through all the footage you don’t care about.
Sadly, your amazing trip has come to an end and it is time for you to return to the real world as an engineer. However, you did learn some new skills that can be applied to making oscilloscope measurements. The concept of capturing T-rex footage using a sensor condition directly correlates to using segmented memory on an oscilloscope. Let’s say you have a signal that has infrequent pulses – like an RF burst (image below). There are about 4ms of dead time (miscellaneous dinosaurs) between each RF pulse while the pulses themselves (your T-rex) are about 700ns. If you were to acquire this signal as-is, including all dead time, you would use 0.0175% of that memory capturing the actual pulse (T-rex) and 99.98% of it on that dead time (misc. dinosaurs)! THAT’S INSANE! Almost all of your memory is being used on something that you don’t even want to see.
To solve this problem, you could always just buy an oscilloscope with significantly more memory, but that gets very expensive very quickly. A much cheaper solution would be to utilize the segmented memory tool, which is already integrated into Keysight oscilloscopes. This application comes standard on the 4000 and 6000 X-Series and all Infiniium oscilloscopes, and can be activated via software license on the 2000 and 3000T X-Series. With this application, you can set a specific trigger condition and tell the oscilloscope to only capture the waveform when that condition is met. So, once you set the trigger and segment parameters, your scope will only capture the pulses in the signal and ignore the dead time (image below). This means that 100% of your memory is being used to capture the pulses and 0% capturing dead time. It allows you to capture a long time span while still digitizing at a high sample rate. This way, you aren’t losing any signal detail for those pulses and you’ll be able to make even more accurate measurements.
As I previously mentioned, this method will also save you a lot of time. Once all of the segments are acquired, you can easily scroll through a list of these segments and select which one you want to view (shown below). This list includes a time-tag of each of the segments which will give you insight into the frequency of each of the pulses. You can also view real-time and date information along the bottom of the screen, so you can see precisely when the pulse occurred. When using segmented memory for serial applications, the oscilloscope will automatically provide protocol decode for each of the captured packets.
Segmented memory can be especially helpful for many different applications, such as measuring an RF burst, decoding serial buses, finding glitches in repetitive signals, seeing the timing of single-shot events, the list goes on. This method gives you deeper insight in your design and helps you debug faster.
Want more detail? Check out these resources to understand how the segmented memory application works and how to set it up.