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LMK04208: VCO noise at VCC

Hirotaka Matsumoto
Guru 27525 points
Part Number: LMK04208

Hi all

Would you mind if we ask LMK04208?
On the customer's board, VCC line is overlapped VCO frequency noise.
According to the layout or the loop filter, might it occur(VCO frequency flows to VCC line)?
We clarify the cause of problem now.
If you have some experience, please let us know as the reference.

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Expert 5370 points
    Dear Matsumoto,

    I would like to clarify somethingl in your question.

    Are you asking about the design of the loop filter ? OR

    the transfer function of the noise going from the Vcc to the output?

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    Guru 27525 points

    Simon san

    Thank you for your reply.

    the transfer function of the noise going from the Vcc to the output?
    ->We ask this.

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 9920 points
    Hi Matsumoto,
    I think customer find there is VCO frequency on VCC plane. It is possible for internal VCO frequency leakage through power supply pins and power supply filters. It depends on layout and power supply filter design. What's current test result or impact on system? EMI? or SNR? How many dB we should improve for margin design? A measurement plot could help understand it.

    Regards,
    Shawn
  • 0 in reply to Shawn Han
    Guru 27525 points

    Shawan san

    Thank you so much for your reply.

    I think customer find there is VCO frequency on VCC plane.
    It is possible for internal VCO frequency leakage through power supply pins and power supply filters.
    It depends on layout and power supply filter design.
    ->Yes, we think so also.

    What's current test result or impact on system? EMI? or SNR?
    ->Our customer only would like to remove the VCO noise on clock out.
       Now, they board is in the development stage. So, it is not relation to EMI.

    We have one additional question.
    What number of VCCX is most closely connected with VCO?
    VCC13?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 9920 points
    Hi Matsumoto,
    We measured CLKout0 on our EVM and found your results as you did. The VCO is in close proximity to CLKout0 and is resulting in the crosstalk. That is why it appears that CLKout0_P has slightly more crosstalk than CLKout0_N. However when measured differentially, the crosstalk is reduced. I'm not aware of crosstalk at such a high harmonic of the desired output frequency causing any system issues.

    Pin10 Vcc1 Power supply for VCO LDO.

    Regards,
    Shawn