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LMX2571 SPI Fast Mode Sampling Rate

ufukt
Prodigy 220 points
Other Parts Discussed in Thread: LMX2571

Hi,


I want to use LMX2571 for creating arbirtary level FSK signal (typically FM signal) in my application. I have a message signal with approximately 50ksps . I will oversample this signal and then give it to the LMX2571 in SPI Fast Mode. Does this mode provide the rate of changing arbitrary frequency level at 250kHz (or more) ? What is the limit?


Thank you,

  • 0
    TI__Guru** 107110 points
    Hi Ufuk,
    Each SPI programming word is 24-bit long. For 250kHz sampling rate, the SPI clock rate will be 6MHz. This is fine, our SPI interface can support up to 100MHz.
  • 0 in reply to Noel Fung
    Prodigy 220 points
    Hi Noel,

    I knew that SPI can reach 100MHz but I was not quite sure about the rate of changing frequency levels. Thank you for the clarification.

    I want to be sure about one more thing: In the data sheet, it says there is a relationship between loop bandwidth and FSK baud rate and the loop bandwidth must be set at least 2 times of baud rate. What about in my application, how to relate loop bandwidth with arbitrary level changing frequency rate? For example, like in my application, for 250kHz rate should the loop bandwidth be 500kHz or more?

    Thank you,
  • 0 in reply to ufukt
    TI__Guru** 107110 points
    Hi Ufuk,
    Right, 500kHz loop bandwidth will be good enough.