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AFE7500 Fref clock specification

David Park
Expert 7070 points

Hi,

In AFE7500 datasheet, phase noise of Fref is -135dBc/Hz.

1. What is this value for? is this minimum requirement for input of Marconi?

Could you let me know where this value come from?

2. What value can we see in Marconi EVM?

Thanks in advance.

 

  • 0
    TI__Expert 8895 points

    Hi, David

    It has to be -135dBc/Hz (or below) for 10/100KHz offset from 122.88MHz of reference. This is also aligned with LMK device's typical number. 

    This mathematical calculation { 20*log10(Frf/Fref)} is only valid for Phase Noise at close in frequency offset from carrier frequency.  

    Our measured in-band phase noise @ 100KHz offset  @ 3.5G from AFE7500EVM is -101 dBc/Hz.

    20*log10(3.5GHz/122.88MHz)=29dB.

    -135dBc/Hz + 29dB = -106dBc/Hz.

    This number is the calculated one from AFE7500 output, and we got -101dBc/Hz which is 5dB higher than our desired in-band phase noise @ 3.5GHz. Considering majority degradation of error vector magnitude, measured -101dBc/Hz @ 100MHz offset @ 3.5GHz should be fine because we got 0.7~0.8% of error vector magnitude from AFE7500EVM.

    As we don't have AFE7500 official forum for now, you can reach me directly for this device for the time being. We will have official one soon, and I'll let you know once ready.

    Thanks,

    KW