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CC1125: PWM protocol, CC1125 working mode, clock accuracy

Part Number: CC1125


Section 4.3 of document AN122 reads as follows:

(using the FB2PLL feature greatly reduces the required crystal accuracy compared to many competing solutions.)

However, in section 5 of the document Feedback to the PLL, we can see that FB2PLL requires "leading codes" and "synchronization words".

(The receiver consists of dedicated DSP hardware capable of finding the frequency of the signal in the preamble and synchronisation word.)

That's fine with the FSK protocol,

From the FSK protocol document, each frame of message contains 12Bytes of leading code and 4Bytes of synchronization word,

However, PWM, another protocol that needs to be compatible, does not contain leading codes and synchronization words, so FB2PLL cannot be utilized.

Therefore, for the PWM protocol, the precision of crystal oscillator 10ppm is not to meet the work requirements of CC1125?

In PWM, there is no leading code for data transmission, so a high-precision clock is needed.

I need to confirm whether this is the mechanism. If it works like this, it needs the clock accuracy of 2ppm.


  • The required RX BW independent of phy and is given as 

    RX BW has to be larger than the maximum SBW plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal errors on TX and RX side to be of opposite signs.

    RX BW > SBW + 4∗XTALppm∗fRF

    where XTALppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading, and ageing. fRF = is the RF operating frequency

    FB2PLL improves this by the factor stated in he documentation. Since you don't have preamble/ sync you have to comply with the equation above.