[SI-LIST] Re: effects of pattern on transmission line - DDR2

Shane, in the end it is Vtt at the differential amplifier input.  But, most 
of us only get to see it on the PWB.

Steve.
At 01:57 PM 1/15/2004 -0800, San Miguel, Shane wrote:
>By VTT supply, do you mean on-die or external (supplied by the system or
>tester)?
>
>Shane San Miguel
>
>-----Original Message-----
>From: Steve Horne [mailto:sch@xxxxxxxxxxxxxx]
>Sent: Thursday, January 15, 2004 1:52 PM
>To: weirsp@xxxxxxxxxx
>Cc: San Miguel, Shane; silist
>Subject: Re: [SI-LIST] Re: effects of pattern on transmission line -
>DDR2
>
>
>Another issue that can affect this is what the other bits'
>transitions are doing to the VTT termination supply.  Having all
>the other bits have an opposite state than the victim (before,
>during and after the isolated 1) may yank the VTT supply in an
>unfavorable direction, affecting the victim bit.  At least this
>was the case in DDR1.  Your VTT decoupling is therefore an
>important variable in this analysis.
>
>Steve H.
>
>steve weir writes:
>  > Shane, what you are dealing with is group delay.  You can find it
>described
>  > in any filter literature.  The low frequency components of the long
>periods
>  > before and after the single pulse travel at a different rate than the
>high
>  > frequency components of the pulse.  This alters the pulse baseline
>and
>  > shape.  The isolated pulse will appear larger, and more unipolar than
>the
>  > later training pulses which will be almost uniform about the origin,
>and
>  > very close in shape to each other, as the system has stabilized.
>  >
>  > Steve.
>  >
>  > At 11:31 AM 1/15/2004 -0800, San Miguel, Shane wrote:
>  > >I have two data patterns of interest (I'll try text) both are a 4
>burst
>  > >of 4 type
>  > >
>  > >
>  > >----<xxxxxxxxxxxxxxx>----
>  > >
>  > >
>  > >
>  > >----_________| |______------
>  > >
>  > >
>  > >
>  > >In the first pattern we have an alternating 010101 type of pattern.
>The
>  > >second pattern is all zero's with a 1 in the middle.  The first
>pattern
>  > >(more traditional) is intended to stabilize the transmission line
>before
>  > >the measurement is made.  We forget the first and last couple of
>edges
>  > >and make rise/fall time measurements on each of the edges in the
>middle
>  > >of the train.
>  > >
>  > >
>  > >
>  > >My thinking is that the second pattern will produce a slower edge
>  > >because you have no activity and the BAM!  You have to fill up all
>this
>  > >trace capacitance and by the time you do that, the data is done.
>  > >
>  > >
>  > >
>  > >I guess my "rule of thumb" is what is stumping me.  I look at the
>first
>  > >pattern and go "ok, stable DC level, more repeatable results".  I
>look
>  > >at the second pattern and go "look at that inductive kick - what a
>  > >reflection" or "how much is that edge going to roll over"...
>  > >
>  > >
>  > >
>  > >Anyone care to educate me on the transmission line behavior with the
>two
>  > >patterns?
>  > >
>  > >
>  > >
>  > >Shane San Miguel
>  > >
>  > >
>  > >
>  > >
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