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TUSB551: EQ,DE,OS pin function check

Jessica Wu74
Expert 5120 points
Part Number: TUSB551

Hi Team,

Could you please kindly help to share some comments for EQ,DE,OS function, from datasheet, we can't know how would those pin help to improve the eye diagram quality? For EQ,DE,OS pin, would these pin impact the eye width or height or some other parameter? Or could you please kindly help to share some test report which could share to customer for reference, thus they could know how to fine-tune the EQ,DE,OS parameter in a more effective way, thanks a lot for your support.

Thanks a lot for your support.

Best regards

Jie

  • 0
    TI__Mastermind 20760 points

    Hi Jie,

    Equalization (EQ) will "boost" the signal moving through the re-driver. This can be helpful to keep your signal integrity when moving through a long PCB trace or cable. EQ will only compensate for loss on the receiving (RX) side of the TUSB551. You can see the eye diagram before and after 3dB of EQ is added to a signal in the TUSB551 datasheet. Notice that the eye width and height are both increased by adding EQ:

    De-emphasis (DE) will attenuate consecutive bits without affecting transition bits. Put simply, this will compensate for loss on the transmitting (TX) side of the TUSB551. If you have a long trace after the re-driver, it can help to add DE to maintain your signal integrity. See the eye diagram in the 551 datasheet when 3.5dB of DE is added to a signal with a long channel after the re-driver:

    Output swing (OS) will increase or decrease the differential amplitude of your signal. I recommend starting with the high OS setting if you add DE to the signal. Using the low OS setting combined with DE can attenuate the signal and hurt the signal integrity.

    Jessica Wu74 said:
    For EQ,DE,OS pin, would these pin impact the eye width or height or some other parameter?

    EQ and DE will affect the eye height and width. OS will affect the amplitude of the signal, which may affect your eye height.

    Jessica Wu74 said:
    Or could you please kindly help to share some test report which could share to customer for reference, thus they could know how to fine-tune the EQ,DE,OS parameter in a more effective way, thanks a lot for your support.

    To fine tune your EQ and DE settings, you should calculate the loss (in dB) of your PCB trace before and after the re-driver. This usually depends on your trace material, width, and length. Once you know the loss, you can set the 551 to the EQ value closest to the loss before the re-driver, and the DE value closest to the loss after the re-driver.

    I hope this helps. Let me know if you have any questions.

    Best,

    Shane