• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 2606 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DFE tap values?

Peter Monta
Prodigy 40 points
Other Parts Discussed in Thread: DS125DF111

We would like to know the values of the DFE taps in an absolute sense, as a function of the DFE tap register settings.  For example, for the DS125DF111, tap 1 has a five-bit field and taps 2-5 have a four-bit field, along with a polarity bit for each tap.  What is the actual value of the DFE tap as a function of these quantities, if the main (cursor) tap is normalized to +1 when presented to the DFE summing node?  Is the range of each tap from -1 to +1, and tap 1 simply offers higher precision than the others, or do they have different ranges?  Thanks.

  • 0
    TI__Mastermind 43795 points

    Hi Peter,

    All taps have equal weighting, each increment is equal to 6mV.  The first Tap has a five bit field so it has 2x the maximum range.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 40 points
    Thanks. What voltage does AGC set for the main tap? In other words, the first tap has a range from 6*31=186 mV to -186 mV, and taps 2-5 half of that. Is the main tap also 186 mV, so that the DFE could be manually configured for an impulse response of say (-1, -0.5, +0.5, -0.5, +0.5) for the five taps, as a proportion of the main tap of +1? We're considering channels that don't look like a large main pulse followed by small amounts of ISI, so we need to know the exact amounts of available DFE feedback.
  • 0 in reply to Peter Monta
    Prodigy 40 points
    After reading the data sheet again, it appears it's the CTLE auto-adapt that's playing the role of AGC here, and the adaptation looks for the most open eye, not for any particular voltage level. So the "strength" of the DFE is variable because it depends on the CTLE settings.
  • 0 in reply to Peter Monta
    TI__Mastermind 43795 points

    Hi Peter,

    Yes the DFE gives "absolute" levels of voltage adjustment.  So the overall DFE strength is based on the strength of the input signal and CTLE gain.

    Regards.

    Lee