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DS90UH947-Q1: EMI issue in 95-105MHz frequency

Roy Chou1
Genius 16190 points
Part Number: DS90UH947-Q1

Hi Team,

We meet EMI issue in 95-105MHz frequency as below. As you saw, the noise could be improved by using 948Patgen. Also, we tried to add core on FPD-link cable near RX(948) side and the noise energy also can be reduced. 

Can you let me know if I want to implement the core on FPD-link cable via layout, how should we do?

In addition, do you have any method by using software that can reduced the noise? We tried to adjust the BC speed, but useless.

We zoomed in the noise and found that there is 500kHz noise on it. But in our system, we didn't use 500kHz chip. Is it possible that the noise generated by FPD-link transmission?

Thank you.

Regards,

Roy

  • 0
    TI__Guru** 108380 points

    Hello Roy,

    1) you can't use a core on the layout. what you can use is an CMC right after the connector on the 948 board. Also you can use an CMC on the 947 layout but right after the AC-coupling capacitors very close to the SER.

    2) Via software or registers we can't do anything, unfortunately!

    Other improvements that can/should be done on the layout:

    - You need to check the Power Supply & Voltage regulators on the boards.
    - Make sure all Power Supply Decoupling capacitors/Filtering are having the right size and placed closest to the power pins.
    - Keep the traces from decoupling caps to GND as short (and thick) as possible and go immediately down into the power and ground planes.
    - Ensure bypass caps are on same layer as the device for best results; if not place caps on the opposite layer closest to the power pins.
    - Use inductor or ferrite beads to split power rails to minimize noise coupling (IC power from the rest of the supply system)
    - Do NOT place vias between bypass caps and device.
    - Place the capacitor positive pad directly on the power traces (DC current flow)

  • 0 in reply to Hamzeh Jaradat
    TI__Genius 16190 points

    Hi Hamzeh,

    Honestly, we had modified many times layout and also reviewed by your team. Now we may need to figure to the root cause to see if we can use software or any other way to fix the issue.

    In addition, is it possible to let 947 continuously transmit FPD-link signal(include timing information), but not connect to 948? 

    Regards,

    Roy

  • 0 in reply to Roy Chou1
    TI__Guru** 108380 points

    Hello Roy,

    as I said, via software or registers we can't do anything, unfortunately!

    Roy Chou1 said:
    In addition, is it possible to let 947 continuously transmit FPD-link signal(include timing information), but not connect to 948? 

    It should be possible if you power-up your system normally and in the middle of the streaming just unplug the 948 borad. But I am not sure why is this question? If you unplug the 948 board, you will have an open link and all of the signal will be reflected!