Re: gEDA-user: series terminators

[ldoolitt@xxxxxxxxxxxxxxx]

DJ -

On Thu, Sep 21, 2006 at 12:18:46PM -0400, DJ Delorie wrote:
> Double sided, 0.062.

How quaint.  ;-)

The board I'm in the middle of bringing up is 6-layer, 0.045.
I've probably linked to it before:
 http://recycle.lbl.gov/llrf4/
So the distance between a trace and its ground plane is
an order of magnitude smaller than what you have.

And yes, it's laid out with Gnu/PCB.

> I figured that; they're going on the SRAM side of the DIN connector,
> about in the middle of the run.

On the board above, I have some 100-ohm series resistors [*] on
digital traces.  Signalling rate could be as high as 105 MS/s, and
the longest traces are about 4.5 cm.

> I have a 32 Ms/s scope and a 500MHz logic analyzer, neither of which
> is great for this kind of test, but might be close enough.

Only if you work with slow parts.  Edge speeds faster than 1ns are
fairly common these days.

    - Larry

[*] On the board photo, look in the center of the board, to
the left of the "big" FPGA.  There is a vertical line of eight
resistor packs, in series with the data pins from the four
high speed ADCs just to their left.


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