February 13, 2025 - Creating Tail Pulses Using the Sequencer on an Arbitrary Waveform Generator

This script is authored by BNC electrical engineer Edgar Guzman. It is an excerpt from a video that is linked [here]

I'm Edgar, one of the engineers here at Berkeley Nucleonics and I'm going to go over how to use our Model 670C or any of our arbitrary waveform generators to generate a sequence of pulses. In this case, I'm going to mimic the pulse that would come out of our BH-1 as that unit is now no longer manufactured. I will demonstrate how to duplicate that signal using an arbitrary waveform generator.

On display here is the UI of our 670C on default settings - it is now doing a standard sine wave. I'm going to turn channel one on so it's outputting a standard sine wave. Now I am going to add an entry so that there are two entries in the sequencer. The sequencer can have up to several thousand waveforms. It depends on what your application is, but today I am going to show how to build a tail pulse using the exponential rise and the exponential fall or decay.

These waveforms are built into the 670C and any of the other model 600 ARBs, like the 675 and 685. Here is a typical exponential rise and decay at one volt to negative one volt. I’ll now demonstrate what that looks like on the screen. It’s a standard exponential rise, exponential decay. Now to get the required timing - if a specific frequency is needed - I will need to set the unit to advanced settings then go into the trigger. This is what will be the period of interval, which will come into play later. Right now it's set to one millisecond. I'm going to keep it at that. Roughly with frequency it's going to be one kilohertz.

In order to actually get that to take effect I go to Edit Entry. Here is where I can pick how I want to jump between sequences. For this particular example it's going to be a fairly straightforward sequence: sequence one to sequence two and then back. Now set this to timer. This will cause it to wait for the timer one millisecond to reset each time before it starts outputting the next waveform. Close this to be able to start outputting. You can see my period has changed to one millisecond. Now it’s outputting at roughly one kilohertz even though it's the same exponential rise and exponential decay wave forms.

At this point, I set the lengths and durations of the exponential rise and exponential decay depending on what kind of rise time and fall time I want. It's not going to be exact. It's roughly a 50 nanosecond rise time - it's roughly 4.5 times that to get what I need.

I’ll pick a random number now - I’ll choose 450 nano and make sure this is set here. I want this to be interpolation and decimation so it keeps its standard wave shape. When I start outputting that, it’s apparent that the waveform has gotten significantly smaller - so I have a smaller rise time. The same can be done with the exponential decay.

Let’s say I want 100 microsecond fall time and I’ll set it to 500 micro to see what I get. It gives me roughly 100 microseconds full time. I’ll have to play with it a little bit, because this unit is an arbitrary waveform generator. I am dealing more with how many points and how long a waveform is going as opposed to the frequency, like I would with a pulse generator or a dedicated delay generator.

That wraps up the demonstration and is only one of the many ways that an AWG can generate a tail pulse. I also created parametric waveforms that align more with what I wanted to see. This generally depends on the goal and the application of the user. The point is that Arbitrary Waveform Generators are extremely versatile.

If you are an end-user and have any type of waveform that you need to see, if you need to mimic any of BNC's outdated equipment, or if you need the function of equipment that is no longer in production, reach out via phone or email. We can see if your desired application is feasible on our Arbitrary Waveform generators or any other products that we may make. We want our equipment to work for you and are excited to push the boundaries of our units alongside your work. Thank you.

Questions? The Berkeley Nucleonics team is proud to be able to speak to our existing and new customers one on one. Call in or email us with questions - ask for Ed!