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LMX2572LPEVM: Side bands at modulating sampling rate

FATHAH A R
Prodigy 20 points
Part Number: LMX2572LPEVM
Other Parts Discussed in Thread: LMX2572LP

Hi TI Experts,

I am working with LMX2572LPEVM, and facing the issue of side bands, offset from carrier at multiple of modulating sampling rate.

The pictures of output spectrum while modulating and non modulating situation are in attachment section.

The working conditions are:

>OSCinP is from Reference PRO board (100MHz)

>Fpd = 100MHz, PLL_DEN = 0x44AA2000, FSK_DEV_SCALE = 32, CHDIV = 32

>Programming of LMX2572LP is from a custom host via SPI(FSK SPI FAST)

>Modulating sampling rate = 96KHz

>Modulating signal frequency = 1KHz

>Expected deviation = 2KHz

>All other registers are at reset values

There are side bands at multiple of sampling rate(96KHz) offset from carrier, how can reduce it.

Thanks in advance.

Best regards
Fathah A R

  • 0
    TI__Guru* 81400 points
    Hi Fathan,

    The only way to reduce the level of this kind of spurs is use a higher sampling rate. The higher the sampling rate, the smaller is the spurs.
    Please note the spurs level will also increase if the frequency deviation is bigger.