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CDCE813-Q1: EMI issue

Cera Wei
Intellectual 2010 points
Part Number: CDCE813-Q1


Hi Team,

My customer is now using our CDCE813-Q1, but has the EMI issue, could you help check the diagram and give some suggestions? Thanks!

The clock is 83MHz and the schematic is as below:

Here's the test condition(near field test):

This is the spectrum with CDCE813:

And here is the spectrum without CDCE813:

We also tried SSCG, but with only 0.25% SSCG, the signal is too bad to display normally.

Thanks,

Cera

  • 0
    TI__Expert 5370 points
    Dear Wei,

    Looking at the spectrum on the picture, I see multiple peaks with Marker 1-4. None of them correspond to an harmonic of 83 MHz. I am not sure I understand what is going on.

    Could you please share the configuration file of the device?

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    TI__Intellectual 2010 points
    Hi Simon,

    Here's the register dump:
    [ 0.364079] **one***-----reg list-----*****the reg 0x80 value is 0x81
    [ 0.364705] **one***-----reg list-----*****the reg 0x81 value is 0x9
    [ 0.365329] **one***-----reg list-----*****the reg 0x82 value is 0x9c
    [ 0.365952] **one***-----reg list-----*****the reg 0x83 value is 0x1
    [ 0.366572] **one***-----reg list-----*****the reg 0x84 value is 0x0
    [ 0.367195] **one***-----reg list-----*****the reg 0x85 value is 0x0
    [ 0.367814] **one***-----reg list-----*****the reg 0x86 value is 0xe
    [ 0.368434] **one***-----reg list-----*****the reg 0x90 value is 0x0
    [ 0.369053] **one***-----reg list-----*****the reg 0x91 value is 0x0
    [ 0.369670] **one***-----reg list-----*****the reg 0x92 value is 0x0
    [ 0.370293] **one***-----reg list-----*****the reg 0x93 value is 0x0
    [ 0.370911] **one***-----reg list-----*****the reg 0x94 value is 0x61
    [ 0.371532] **one***-----reg list-----*****the reg 0x95 value is 0x0
    [ 0.372149] **one***-----reg list-----*****the reg 0x96 value is 0x80
    [ 0.372768] **one***-----reg list-----*****the reg 0x97 value is 0x0
    [ 0.373389] **one***-----reg list-----*****the reg 0x98 value is 0x1f
    [ 0.374008] **one***-----reg list-----*****the reg 0x99 value is 0xf0
    [ 0.374635] **one***-----reg list-----*****the reg 0x9a value is 0x2
    [ 0.375254] **one***-----reg list-----*****the reg 0x9b value is 0x10
    [ 0.375872] **one***-----reg list-----*****the reg 0x9c value is 0x1f
    [ 0.376494] **one***-----reg list-----*****the reg 0x9d value is 0xf0
    [ 0.377115] **one***-----reg list-----*****the reg 0x9e value is 0x2
    [ 0.377737] **one***-----reg list-----*****the reg 0x9f value is 0x10
  • 0 in reply to Cera Wei
    TI__Mastermind 28021 points
    Wei,

    The crystal is the largest potential cause of EMI. I note that the spurs for the markers are at 866, 778, 692, and 950 MHz. I also note that these are all close to multiples of 86.5 MHz. I know your input was 83 MHz, but the spectrum analyzer with 1 GHz span might not record these numbers very accurately and I don't see anything for multiples of 83 MHz. So perhaps these are 83 MHz spurs. If not, perhaps there is something else running around 86.5 MHz.

    Regards,
    Dean