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AWR2243: pfVcoSelect in cascade devices

Dave Ochs
Prodigy 250 points
Part Number: AWR2243

The value of pfVcoSelect is 2 in the MMWAVELINK_CASCADE_EXAMPLE/mmwaveconfig.txt file from the mmwave DFP. In reading the radar interface control document for the corresponding API, I would have thought that the FORCE_VCO_SEL should be set to 1 (Forced external VCO selection) on the slave devices, but not on the master. I don't see anywhere in the example code where that happens, though. It looks like it's being set to 2, so FORCE_VCO_SEL=0, for all of the devices. Am I misunderstand the meaning of the FORCE_VCO_SEL field? If so, what are the circumstances where that field would ever need to be set to 1?

Thanks,

Dave

  • 0
    TI__Mastermind 31680 points

    Hello Dave, 

    Yes, you're right, in cascade, to make the entire cascaded system operate as a single radar system, the Master is designated to generate a common Local Oscillator (LO) signal (19 GHz to 20.25 GHz) and that is shared on two different output pins through two different delay matched amplifiers. 

    The FORCE_VCO_SEL is to basically to choose between external and Internal VCO. You cannot use an external VCO here because you need to synchronize the FMCW ramp to the AWR devices framing engine. You cannot determine the start of the ramp, end of the ramp etc. in the external VCO. 

    As I mentioned, in case of slaves, LO is internally routed internally through the output pins from the master. 

    Figures 3 and 4 of the below document can help you understand this mechanism. 

    AWR2243 Cascade (Rev. B)

    Hope this helps.

    Regards,

    Ishita

  • 0 in reply to Ishita Kochar
    Prodigy 250 points

    Thanks for the quick response. Are you saying that the LO and the VCO are just completely separate, unrelated, things? Under what circumstances would an external VCO be used, then?

  • +1 in reply to Dave Ochs
    TI__Mastermind 31680 points

    Hello Dave, 

    Extremely sorry for the delay and thankyou for your patience. 

    I think there was a slight confusion on my part as well regarding the "FORCE_VCO_SEL" option, but I reached out to the team internally for this. 

    So the "FORCE_VCO_SEL" is choosing between internal or external "selection" between VCO1 and VCO2. 

    Internal means based on the chirp frequencies used, the firmware will internally select the VCO. In case of "External", the USER selects the VCO (VCO1 vs VCO2) to be used rather than firmware automatically selecting internally. 

    Hope this makes much more sense now. 

    I again apologize for the confusion earlier and the inconvenience caused because of that. 

    Regards,

    Ishita