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CC1120 AFC

KAZUHIKO TAKRYAMA
Prodigy 110 points
Other Parts Discussed in Thread: CC1120

We are developing a apparatus using CC1120.

Although we read specifications, we were not able to understand the right AFC setup.

Does the AFC operate for CC1120 correctly by the following register setup?
  FREQOFF_CFG.foc_en= 1 (ON)
  FREQOFF_CFG.foc_cfg = 11
  (FOC in Frequency Synthesizer Enabled, Loop Gain factor 1/128 .)

But I wonder that we do not command  "SAFC strobe".
Do we need to do "SAFC strobe" command with the FREQOFF_CFG setting ?

If we should command  "SAFC strobe" , do we need to set the "SAFC strobe" in the act of receiving the preamble signal?

When is the best timeing of SAFC strobe?

Thanks.

 

  • 0
    TI__Guru**** 317180 points

    AFC:

    From the user guide:

    “The estimated frequency offset value is available in the FREQOFF_EST status register. This can be used for permanent frequency offset compensation. By writing the value from FREQOFF_EST into FREQOFF, the frequency synthesizer will automatically be adjusted according to the estimated frequency offset."

    The frequency offset estimate is updated automatically but to use the estimate it has to be written into the FREQOFF1 and FREQOFF0 registers either by hand or using the SAFC strobe. The strobe can be issued at any time but will not take effect before next time the receiver enters RX.

  • 0 in reply to TER
    Prodigy 110 points

    Thanks for your advice.

    Let me reaffirm your advice.

    You said that we must command "SAFC strobe" in all of register settings , right?

     

    I think we need the "SAFC strobe"  with FREQOFF_CFG.foc_cfg=0.
    ( What's the difference between FOC in Frequency Synthesizer Enabled and disenable. )

     

    Thanks.

  • 0 in reply to KAZUHIKO TAKRYAMA
    TI__Guru**** 317180 points

    The difference between the two frequency compensation loops are given in section 5.5 in the User Guide.

    If frequency compensation after the loopfilter is used, the SAFC strobe is needed. If frequency compensation in the synth is selected the FREQOFF register is updated automatically.

  • 0 in reply to TER
    Prodigy 110 points

    Thanks for your informations.

    I understood that CC1120 has 2 type frequency compensation.

    One is " after the channel filter". This  compensation is needed to update FREQOFF by hand or using the SAFC strobe.

    Another is "the frequency synthesizer". This compensation is updated FREQOFF automatically.

     

    But I could not confirm that the compensation of  "the frequency synthesizer" updates FREQOFF automatically with TI evaluation board and SmartRF.

    Please tell me how to confirm "the frequency synthesizer" works well.

     

    And please let me know if I understand the following attitude correctly.

    If I set  the compensation of " after the channel filter" during a receipting a DATA packet, I need to update FREQOFF register by hand.

     

    Thanks.

  • 0 in reply to TER
    Intellectual 355 points

    TER said:

    AFC:

    From the user guide:

    “The estimated frequency offset value is available in the FREQOFF_EST status register. This can be used for permanent frequency offset compensation. By writing the value from FREQOFF_EST into FREQOFF, the frequency synthesizer will automatically be adjusted according to the estimated frequency offset."

    The frequency offset estimate is updated automatically but to use the estimate it has to be written into the FREQOFF1 and FREQOFF0 registers either by hand or using the SAFC strobe. The strobe can be issued at any time but will not take effect before next time the receiver enters RX.

    Dear TER,

    Do you mean "from the OLD user guide"? On revision B of the document, a lot of chapters "disappeared", and also the "frequency offset compensation" chapter you quoted.

    Maybe the "advance information" was "too advanced"?

    And just for information, on the new document the (newly added?) PDF bookmarks tab is not working properly... (e.g., try to find chapter 8.12...)