Mike Reagan wrote:

> source termination allows the signal to reflect off the load and
> > travel back to the source, where is absorbed by series termination. > > >
>
> And I will bet his analysis was done with  sine wave reflections not  a
> rising edge of a pulse.   Try  a simple experiment,   pick a design you
> already have on the bench,  replace the resistor with  10 ohms then replace
> it with 50,   Get a high speed scope and measure the leading edges.
> If you apply his theory you are playing games with bouncing spikes back and
> forth.. which .equals a very noisy board.  The name of the game is to keep
> the spikes from being generated in the first place   not spike management.
> I guess you could do spike management but I prefer  the first method.    Try
> the bench test   and look at the edge.  I had a very good rf engineer
> explain then he showed me.

Yes, but once we get down to specifics with line length and Tr, the picture
changes.  If the Tr is less than the one-direction Tp (propagation delay)
of the line, then the reflection problem is a bear, and must be dealt with.
If the Tp is MUCH less than the Tr (as it was in this particular case) then
the reflection is 'distributed' across many reflections of the partial rising
(or falling) edge.  This makes for wave shape distortion, but the reflection
is much smaller.  In between these two cases, the reflection is in between
minimal and full scale.

Jon

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