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CC1200: Relationship between symbol rate and RF bandwidth

Aidan Hunt
Prodigy 50 points
Part Number: CC1200

Hello,

I know that the CC1200 User Guide has a helpful table on page 30 that describes the relationship between Data Rate (in kpbs) and Symbol Rate (in ksps), which depends on the encoding selected. What I don't understand is the relationship between the symbol rate and the RF bandwidth needed. For example, if I have am designing for a licensed application with a 20 kHz authorized bandwith, how would I know what to set the symbol rate to to get the maximum allowable data rate? For example on page 25 it shows a frequency analyzer graph of the transmitted signal--how can I tell the chip how wide I want that waveform to be? I see how to set that for receive, but I'm not sure how to do it for transmit.

Thanks,

Aidan

  • 0
    TI__Guru**** 317180 points
    The minimum required RX bandwidth to ensure reception is given by:

    RX BW = Signal Bandwidth + 4*ppm Crystal * RF Frequency of Operation

    For FSK the signal bandwidth can be approximated as data rate + 2*frequency deviation (Carson’s rule)
  • 0 in reply to TER
    Prodigy 50 points
    Thanks! The first equation makes sense but I am a little confused about the second one. When I googled Carson's rule, it gives the formula CBR = 2(freq dev + peak freq), so I am assuming there is another rule stating that data rate = 2(peak freq) to transform that into your equation? Does that work for 4FSK or just 2FSK? And just to clarify, that is data rate and not symbol rate?
  • 0 in reply to Aidan Hunt
    TI__Guru**** 317180 points
    The last equation is for 2-FSK. Since this is just a approximation and normally GFSK is used that gives a lower OBW (signal bandwidth), you should basically measure the signal bandwidth to be safe.