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DS125DF111: Does DS125DF should be placed near MAC or close PHY in layout placement?

Smith Chao
Intellectual 255 points
Part Number: DS125DF111
Other Parts Discussed in Thread: DS100BR111,

Tool/software:

Hi TI expert,

I just wandering that I have a MAC which is support 10G KR but the ibis model doesn't contain 10G KR information but only XFI, and a Marvell 10G phy only support XFI, how can I place the retimer? close to MAC or close PHY?

As you know, in this case that 10Gphy(only XFI)-->MAC(can support 10G KR but ibis model without 10G KR information), which spec should I take?XFI or 10G KR? 

* I only place retimer in 10G phy RX side, the TX side without retimer, should I design on both side? during the PCB, the distance between MAC and 10Gphy is about 10,000mil

thanks

Smith 

  • +1
    TI__Mastermind 27980 points

    Hi Smith,

    10G-KR is a backplane interface which defines the connection between the MAC and the PHY. XFI is a front port interface which defines the connection between the PHY and an XFP optical module. Your PHY should have the capability to support both front port and backplane interfaces at the same time.

    Electrically, 10G-KR and XFI are identical. XFI includes strict eye mask requirements to ensure proper operation with optical modules. 10G-KR includes support for link training and auto-negotiation protocols.

    DS125DF111 does not support link training and auto-negotiation, as it is a protocol agnostic device and cannot transparently pass feedback protocols. DS125DF111 can still be used in 10G-KR use cases if LT and AN can be disabled by the MAC and the PHY. If LT and AN are required, then a redriver such as DS100BR111 is a better choice.

    I do not see any mention of 10G-KR or XFI in the DS1xxDF111 IBIS-AMI model. The model should only simulate high-speed electrical performance through the retimer.

    If you are only using the retimer in the MAC to PHY direction, I recommend placing the retimer close to the PHY. The majority of the retimer's equalization is performed on the Rx side of the device, so it is ideal to maximize channel length on the Rx side of the retimer.

    What is the EQ capability of your MAC Rx? If it incapable of compensating the link from PHY to MAC by itself, then the retimer should be used to support both directions of transmission. In this case, I recommend placing the retimer as close to the center of the link as possible, to balance equalization in either direction. I understand this may not be possible in backplane applications, so I recommend placing the retimer closer to the device with less EQ capability.

    Best,

    Lucas

  • 0 in reply to Lucas Wolter
    Intellectual 255 points

    Appreciate!! This help me a lot

    thanks you