CWS generation with Delay and Triggering

[Zarrar]

Hello, I want to generate two CWS , sine waves on 5644R, I have two 5644R, I have to generate One sine wave with 75ps dely from other. I want to know will it be generated using Instruments design libraries or using Example provided in VSG/VST sample project. For both of them, what will be role of I/Q Sampling. I have to do syncronization as well. 

[ashley_gee]

Hi Zarrar,

It sounds like you'll need to synchronize your two 5644R's, and then implement a delay in one. At a high level, the following article talks through synchronization of VSTs.

Trigger Synchronization Overview

http://zone.ni.com/reference/en-XX/help/373680C-01/rfvst/trigger_synchronization_overview/

However, the 5644R cannot use TClk synchronization. Therefore, you'll use the low-level properties and attributes to implement synchronization, all of which is described in the help documentation below.

Synchronization Using NI-RFSA and NI-RFSG

http://zone.ni.com/reference/en-XX/help/373680C-01/vstdevices/5644_rfsa_gsynchronization/

Feel free to post back with additional questions!

[Zarrar]

I have to implement 75ps delay in two cws in 5644R. Kindly provide solution is it poosible for 5644R to give 75ps delay in TWO CWS.

[ashley_gee]

Hi Zarrar,

Could you please clarify what you're trying to do? Each 5644R only has a single RF out port, so you can only generate one waveform from each. 

Also, what is your 75ps delay in reference to? Is there some sort of external trigger?

If you can provide a clearer picture of what you need and what your overall application is, we may be able to advise a more clear path forward. 

[Zarrar]

Thank you,

             I have two VSTs 5644R, in which I have installed 2012 LabVIEW, FPGA and RF drivers. I have to generate TWO cws on RFOut1 on both VSTs. My application is custom , so I want to generate one CW delay from other by 75ps with syncronization. I have currently used 5644R syncronization VI but delay is 499ps between CWS. I want to gain control of Phase. Please let me know is it possible on 5644R to achieve this delay. I have to to do sweep also from 1GHz to 6GHz after this delay implementation. I also want to know wheather I should do development on Instrument design libraries or VSG/VSA sample project as a starting point.

[ashley_gee]

Hi Zarrar,

Thanks for clarifying, that's helpful! It sounds like you're trying to do a multitone generation, so I'd recommend using the example RFSG Multitone Generation.vi.  This will allow you to explicitly control the phase of each tone, which is exactly what you need to do.

This is example installs with the RFSG driver, and can be found at the following path on disk (assuming you kept defaults during installation):

C:\Program Files (x86)\National Instruments\LabVIEW 2015\examples\instr\niRFSG

Once you get this set up for a single VST, you can use the synchronization info in my previous posts to sync the two VSTs together.

[shawn.t]

I think Zarrar is trying to start generation of a waveform (or CW tone---is that what CWS is?) with a difference of 75 ps. If that's right, that is pretty tight synchronization. I see you're able to reach a synchronization of around 500 ps. Is that consistent, or is that +/- 250 ps each initiate?

Hopefully, the offset is consistent. If it is, then there are two RFSG attributes that you can use to fine tune your synchronization. If you're not worried about when exactly the waveform starts (if 500 ps off is ok) but you need the waveforms to be exactly 75 ps out of phase, then you can use the RFSG Phase Offset attribute. To convert time to degrees, you'll need to consider the IQ rate of your waveform.

If you need the waveforms to begin exactly 75 ps apart, then you can use the Interpolation Delay attribute. This will allow you to shift the waveform up to half of the period of your IQ rate. It's units are in seconds so this is probably the easiest attribute for you to use. Try setting 425e-12 on the leading device and let us know what happens.

Two more things to consider: when synchronizing two devices like this, you need to consider your reference clock and LO. For phase coherency, I believe you need to share both. Export the ref clock and TX LO from one 5644 and import it on the other. (You can also use the PXI clock on both for a quick test, but I think the 5644 ref clock is more accurate.)

[Zarrar]

Hi,

  Thankyou, I have shared LO like in example, Currently PXI_CLK is selected,if I have to select Ref_Clk what shoulD I do?

Is it possible to achieve 75ps delay in cws using 5644R? I used example shared with you. How will I know about the I/Q rate of a CW? How will I extract I/Q samples in roder to put delay

[Zarrar]

Currently I am using this VI as a starting point. Let me know if have to generate delay How will I access I/Q samples

[shawn.t]

Is your 500 ps offset consistent? Or does it change on every run?

If it it changes every run, then you may not be able to get a consistent 75 ps offset. If there's very little jitter, then you should be able to fine tune your synchronization. I've seen offsets as tight as 40 ps, but I can't remember the jitter. 

I think CW mode still uses the IQ rate attribute, but to make things easier just try changing the interpolation delay attribute to compensate for your offset.