[SI-LIST] Re: SI effects for Stackup with GND plane but no VCC plane?
- From: <Wolfgang.Maichen@xxxxxxxxxxxx>
- To: <cuong@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 2 Nov 2012 08:34:03 +0000
With only two layers (signal traces above ground plane) what you have is
microstrip (not stripline). As for differences between microstrip and
stripline, microstrip do exhibit dispersion as well as far end crosstalk, but
their effect is minor unless you have extremely long traces and/or want to go
to multi-GHz speeds. A more detailed discussion is e.g. in Bogatin "Signal and
Power Integrity Simplified". Second, cross talk is more of an issue because
there is more fringe field - can be mitigated by increasing line-to-line
spacing (> 3...4 line widths for stripline, > 6 line widths for microstrip to
get <1% crosstalk, this applies to 50 Ohm single ended lines / 100 Ohm diff
lines).
That said, microstrip works very well up to very high speeds if designed right.
Things to watch out for would be breaks in the ground plane beneath a signal
trace (avoid at all costs!), Nickel plating (increases skin effect), solder
mask (makes line an embedded microstrip and as a result changes effective
dielectric constant and also dielectric loss tangent), and as mentioned
crosstalk.
Wolfgang
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Cuong Nguyen
Sent: Friday, November 02, 2012 12:37 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] SI effects for Stackup with GND plane but no VCC plane?
Experts,
A customer of mine is looking into doing SI analysis including extraction of
nets out to S-params and Spice models.
their stackup only has GND plane and no VCC plane (other than thick traces).
Does this "asymmetric" setup presents any potential issues? Inaccuracies?
Etc..? when doing SI analysis for
both Single-ended (I don't think so) and Differential (maybe?) signals?
The kind of analysis they're thinking of doing is basic SI quality,
Crosstalk, eye-diagrams, and loss analysis (S-param).
Their stackup is not complicated but does have analog components.
=== === === === === ===
Cuong Nguyen
Field Application Engineer
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