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CC1120: Manually frequency compensation with FREQOFFx registers

luis.lopez
Expert 1050 points
Part Number: CC1120
Other Parts Discussed in Thread: CC1101,

Hello guys!

I have been using CC1101 for many years and its frequency compensation was done as the document "DN015 Permanent Frequency Offset Compensation" said.

Because now we are migrating to CC1120, my question is about the use of an accumulate signed variable for the FQY compensation. Is it necessary to accumulate the estimated offset (FREQOFF_ESTx) given by CC1120 or I must assign directly the estimated offset to FREQOFF1 and FREQOFF0? I don't want to use the command SAFC because there are a lot of radios in a local net so I will do manually the compensation.

Many thanks in advance!

Best regards,

Luis J

  • 0
    TI__Guru**** 317180 points
    I'm not fully sure what you mean.

    The content of FREQOFF_EST is the frequency offset estimate the chip made for the last received packet. The RF frequency is set by the FREQ and FREQOFF registers.

    How you want to use the FRQOFF registers is a bit up to you. You can either use the SAFC stobe to move the content in the FREQOFF_EST registers into the FREQOFF registers or, if you have a fixed offset or want to have control over the value in the FREQOFF register, you can write whatever value you want directly to these registers.
  • 0 in reply to TER
    Expert 1050 points

    Thank you for your attention, TER

    As you can read in your document SWRA159, the permanent frequency compensation executed on CC1101 should use a variable which accumulates the offset values when receiving, and use this accumulate when transmiting.

    Well, what i want to know, is if CC1120 needs this performance to compensate the frequency using the correct registers for it.

    Thanks again and best regards, 

    Luis J.

  • 0 in reply to luis.lopez
    TI__Guru**** 317180 points
    This is not chip dependent.

    Typically a accumulated frequency will give better performance.

    If you find the offset at time 0 and place this offset in the FREOFF registers you will get good performance. But over time the center frequency both on the RX and TX side will change over time due to xtal drift (both temp and aging). Hence reading the frequency offset estimate for each received packet and adjust the the content of the FREQOFF register accordingly will give better performance over time.
  • 0 in reply to TER
    Expert 1050 points
    Thank you, TER.
    Now I have clear the action that I must do for fqy compensation on CC1120.

    Best regards,

    Luis.