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Permanent Frequency Offset Compensation

Chad Christensen
Expert 1670 points
Other Parts Discussed in Thread: CC2530

Should the permanent frequency offset compensation (adding FREQEST into FSCTRL0) be performed for each channel, or will this value be constant for all channels?

Thanks,

Chad C.

  • 0
    TI__Expert 3205 points

    Hi

     

    The frequency offset estimate in FREQEST calculates the offset for the particular transmission currently being received. Hence the offset estimate is only valid for this one device that sent this message. Using FREQEST it is impossible to know if the correction is due to a frequency offset on the sending or receiving side, hence using this as a fixed device offset is not recommended

     

    If you are using a CC253x device and want to compensate for a permanent frequency offset in the current device I recommend looking into FREQTUNE register. XOSC32M_TUNE[3:0] allow you to effectively reduce synthesizer frequency. If you need to make a larger corrections than allowed by this register or you need to shift the frequency upward then I suggest you focus on tuning the off chip crystal load capacitances (CL). This tuning is described in CC2530 data sheet p.26 equation 1. HW tuning and FREQ_TUNE corrections are effective for al channels.

     

    Tor-Inge

     

  • 0 in reply to Tor-inge
    Expert 1670 points

    Thank you for the response. I'm sorry, but I don't think I did a good job explaining my question.

    I would like to calibrate the frequency offset of all devices when first manufactured. Everything on the assembly line will be calibrated to a single "master" transmitter, so that everything starts with the same frequency when leaving the factory. This calibration value is stored in flash along with all of our other calibration parameters. Should we perform this calibration for each channel, so that we have an array of offset parameters stored in flash; or is it safe to assume that any frequency offset between 2 devices will be consistent over a small frequency range?

    Is this even something that is recommended, or is this relatively trivial?

    Any advice or info would be appreciated. Thank you - 

    Chad C.

  • 0 in reply to Chad Christensen
    TI__Expert 3205 points

    Hi

     

    If crystal load capacitances are tuned to a nominal crystal frequency that is slightly above wanted, the FREQTUNE register can be used to perform production line calibration reducing this frequency offset.

    Note measure the frequency on RF output. A measurement probe on the crystal pins will shift the frequency.

     

    Tor-Inge