[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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