Output a 10 usec TTL HIGH through PFI port on AWG Waveform Generator

[Denn_Mann]

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Dear LV Community,

I would like my waveform generator (PXI-5422) to output a 10usec pulse through its PFI1 line whenever CH0 output a wave.  The pulse repetition frequency of both CH0 and the PFI1 port is 10 kHz.  Is it possible for the waveform generator to automatically generate this TTL HIGH signals for 10 usec on the PFI1 line while simultaenously outputting a waveform that is 100 usec long?

Another approach I am considering is to re-route a RTSI1 pulse (10usec) coming from an FPGA and outputting this through the PFF1 port of the AWG; however, I doubt this is possible as the HELP MENU for the AWG states that the rerouting can only take place when the AWG is in idle mode.

Any help will be greatly appreciated!

Have a nice day 🙂  I attached a functional diagram which hopefully explains what I am trying to do a little better.  Once again thank you for looking!

-Daniel

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[Travis_Ann_N]

Hi Denn_Mann,

I'd like you to take a look at the FGEN Shipping example titled "Fgen Arb Waveform Marker.vi". In step 4 of this example, you could use the PFI 1 line as your marker and set the position of it. You can also set other properties such as "Marker Event Pulse Width Units" and "Marker Event Pulse Width Value" to set the width of your pulse. The rest of that example isn't necessarily important for the set up you described, just focus on Step 4. 

Also, you might want to take a look at some additional Marker Event information. 

Regards,

Travis Ann

[Denn_Mann]

Hi Travis,

Thank you very much for making me aware of the Marker function in my AWG.  I tried to get it to work, unfortunately, I was only able to generate a 320 nsec TTL HIGH signal when the Output Behavior option in the Method Node was set to "Pulse." When I changed the Output Behavior to "Toggle," a really strange decaying exponential which lasts about 1 usec (Vout> 0.7V) was recorded. I recorded the screenshots shown below using the same Digitizer included in my PXI system by using the "NI 5761 - Getting Started.proj" example file.  Now, I make it clear here that I am using a 4dB attenuator at the input of my Digitizer (NI 5761) so as to not damage it because when I looked at the amplitude of the PFI output line on my oscilloscope I noticed that it was 3.2 V which means that when this is dropped across a 50-Ohm impedance (which is what the Digitizer input channel has) it comes down to 1.6V (i.e. half as much).  This 1.6 V exceeds the rated 1Vp and thus care must be taken.

I have included pictures below of the two outputs I received and have put a pink stripe on the graphs to show which graph represents the "Pulse" and "Toggle" Scenario.   I am starting to think we will need to purchase a "Triggering and Synchronization" card that will be able to output the 10usec pulse which I require.  I will list my equipment list here in the bottom to see if anyone else has ideas as to how to get this working with the equipment I have available.  Cheers!

-Daniel

Equipment:

Chassis: PXI-1031 DC

Controller: PXI-8102

AWG: PXI-5422

FPGA: 7954r

Digitizer: NI 5761

"Pulse" Configuration Screenshot showing 320 nsec TTL HIGH marker

"Toggle" Configuration for PFI1 Line

[Denn_Mann]

I forgot to state that if I try to make the "Pulse" any longer than 320 nsec at 200 MS/sec rate on my AWG I get an error.  The "Toggle" case does not give this error.  Clearly, if I lower the rate of my AWG the time duration of the pulse increases, however, for my application, this is not a viable option as the chirp we are generating needs to be as defined as possible.

Thanks for stoppping by.

Have a nice day!

-Daniel

[Denn_Mann]

All,

I figured out what the "Toogle" function is supposed to do: This setting sets the PFI line to TTL HIGH for the duration of the transmission of CH0.  Once this wave has been transmitted and the next wave is sent, the PFI line sets the output to TTL LOW and this is repeated.  I have included a screenshot that shows the display of the oscilloscope. The 10 usec chirp is shown as a sideways trapezoid and the PFI line is shown as the square wave.  Note that the chirp duration is only 10 usec, but technically I am zero padding the CH0 output with 90 usec of data such that I can attain a 100usec transmission which is how I am able to get my PRF of 10 kHz.  Thus, when the 100usec of CH0 output data is finished, the PFI line TOGGLES to the alternate TTL value.  I am still quite confused as to why the Digitizer would show a decaying exponential instead of the square wave my oscilloscope shows.

[Henrik_Volkers]

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@Denn_Mann wrote:

.  I am still quite confused as to why the Digitizer would show a decaying exponential instead of the square wave my oscilloscope shows.

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Highpass filter 🙂

AC coupling mode in the digitizer?

[Travis_Ann_N]

Hi Denn_Mann,

I ran the code on my end and verified that there is a limit of 320ns. I'm going to do some more research and see if there is another way to do this with your current hardware. 

Regards,

Travis Ann

[Travis_Ann_N · Accepted solution]

Hi Denn_Mann,

To get around the 320ns limit, you should be able to use scripting with markers on the FGEN to achieve your goal. What you'll want to do is use scripting with markers in Toggle mode. You will want to toggle high then toggle low after the number of samples that you want to the pulse to be high while your signal is present. I've linked some information below that should be good scripting resources for you if you are unfamiliar. 

Advanced Waveform Sequencing and Triggering on Arbitrary Waveform Generators

Creating a Marker Event in Script Mode

Script Mode

Shipping Example: "Fgen Arb Script.vi"

Regards,

Travis Ann

[Denn_Mann]

Hi Traivs,

I am extremely thankful for your guidance.  I was able to get the PFI1 line to output the required trigger for the duration that I needed.  I have attached both the code and screenshots of this code generating a 3 usec chirp + 3 usec PFI HIGH as well as a 10 usec chirp + 10 usec PFI HIGH.  Hope this helps other programmers out there!  btw, these AWG are extremely powerful 🙂  

-Daniel

3 usec Chirp (15 -35 MHz) shown as the sideways trapezoid and its "TOGGLE" PFI1 Line output

10 usec Chirp (15 -35 MHz) shown as the sideways trapezoid and its "TOGGLE" PFI1 Line output