Adding Delay to the Trigger NI-5670

[maeri]

I'm working with a DUT (device under test) unit where the RF antenna is located remotely from the DUT connected via optical fiber up to 40 km in length.

As an example, the 40km length adds about 211 uSec delay in the RF path. Since the NI-5670 is triggered directly from the DUT, I need a way to add delay in the trigger path.

How would NI engineers suggest doing this?

[kirsch]

That's a lot of delay!

My suggestion would be to pad the data in the Signal Generator, inserting (211us - trigger reaction delay) worth of silence at the beginning of the waveform. You may need to play with the exact amount of padding you need. Keep in mind that the NI 5670 has an inherent delay of 64 Sample Clocks + 110 ns (NI 5421) + ~250 ns (NI 5610) between Start Trigger and data coming out of the front panel connector. That adds up to ~6.76 us when running at 100MS/s.

Hope this is helpful.

Marcos Kirsch
Staff Software Engineer
Signal Generators Group

[maeri]

Thanks Marcos,

I fought about adding delay to generation script (digital script trigger will be used) with WAIT statement. Does it make sense ?

Padding waveform with 0 is interesting. But I also need different test scenarios (variable fiber length), so it wouldn't be so simple to add 0's to all my cases.

You've mentioned about delays in NI-5670 AWG and UpConv, could you point me to the right location of those infos? Think it'd be very usefull to have exact information about delays since I'm using 3GPP freqz.

Thanks
maeri

[maeri]

btw. great home site 😉 I was in TX once (Ft. Worth) - nice place to live

[kirsch]

Yeah, you can use the Wait instruction as well. I did not know if you were using a script or not. Also, you could do the padding by generating the waveform and using the subset instruction or the finite repeat instruction, this way you don't need to change your waveform data.

For example:

script myScript
    wait until ScriptTrigger0
    generate myPadding subset(0, 10000)
    generate myWaveform
end script

Just change the 10000 with the actual number of samples that you need. The waveform named myPadding needs to be larger, of course.

Another option (a simpler one too!), like you said, is to use the wait statement:

script myScript
   wait until ScriptTrigger0
   wait 10000
   generate myWaveform
end script

Do you mind posting the script you were planning on using? Hope this helps

[maeri]

In my case I use VI from NI Dev site:

http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=073647F70ABF3152E0440003BA7CCD71

What was changed in my case is vector type: I/Q with IQ data file sample rate at 15,36MS/s and vector samples size
~1228776. Whole repeated sentence lasts ~80ms, and trigger is working at 80ms too.

My script part:

script triggerFiniteGeneration
repeat forever
wait until scriptTrigger0
wait %samples%
generate triggeredWaveform
end repeat
end script

where %samples% is swap with actual delay (in samples) calculated from formula:desired delay (211u) * IQ data file sample rate. When %samples% was swapped with 3241 DUT wasn't syncing. I'll try to decrease overall %samples% size with H/W delay added by 5670.

[kirsch]

You can find the delays added by the NI-5421 in the NI 5421 Specifications document installed in NI-FGEN. Look under:
Start Menu\Programs\National Instruments\NI-FGEN\Documentation\Hardware Specifications

To find the delays added by the NI-5610, loog at the NI_567x_Specifications.pdf document in
Program Files\IVI\Drivers\niRFSG\Documentation

Marcos