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DS250DF210: Pre and Post cursor selection for Insertion loss

LALIT VERMA
Expert 1645 points
Part Number: DS250DF210

Hi,

We are planning to use DS250DF210 in one of our project.

There will be 8dB of insertion loss between DS250DF210 and the receiver IC at 20Gbps.

I know the insertion loss can be taken care by DS250DF210's TX equalization.

My question is:

1. How to select precursor and postcursor values based on insertion loss? Is there any equation which relates insertion loss, precursor and postcursor?

An early response will be highly appreciated. 

Thanks,

Lalit

  • 0
    TI__Expert 8585 points

    Hello Lalit,

    Please reference Section 8.3.9 Differential Driver With FIR Filter in the DS250DF210 data sheet for a description on how to select precursor and post cursor values.

    The image shown below (as in section 8.3.9.1 of the data sheet) shows typical cursor values we recommend for an insertion loss < 15 dB.

    The pre and post cursor de-emphasis values (in dB) can be determined using the equations below.

    Regards,

    Kia Rahbar

  • 0
    TI__Mastermind 19225 points

    Hi,

    The retimer Tx FIR pre-cursor and post-cursor values should be configured so as to optimize the bit error rate at the downstream receiver. In particular, the receiver IC most likely has some form of Rx equalization (either CTLE and/or DFE). Thus, the Tx need not have to compensate for the full output channel insertion loss for the link BER to be optimized. Ideally, you would sweep the Tx pre-cursor vs post-cursor values and evaluate BER at each point. You would then select the zero BER Tx FIR pre/post combination at the center of the error free region. Refer to the TI application note below for details on this "Green Box Analysis" Tx equalization optimization methodology.

    Green box testing: A method for optimizing high-speed serial links

    The DS250DF210 datasheet Table 2 shows example Tx FIR de-emphasis values in dB for a range pre and post coefficient settings.

    Thanks,

    Rodrigo Natal

    HSSC Applications Engineer