Hi Brian--
What Chuck says is true about HyperLynx BoardSim (enable Trace to Area Fill
Coupling), but if you are just mocking things up in HyperLynx LineSim you can
add reference conductors in the Transmission Line Editor.
To give you a frame of reference, I mocked up an example trace that was 8 mils
wide over a 5-mil dielectric, and the addition of two coplanar guard traces (5
mils wide, spaced 5 mils away) lowered the trace impedance by about 4 ohms.
To answer your question, yes, coplanar traces do make a difference in
characteristic impedance (Zo), and your field solver should be reporting that.
--Pat
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Chuck Corley
Sent: Thursday, November 05, 2015 11:56 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Characterizing PCB Impedance in Coplanar Structures
Hi Brian,
You didn't mention which 2D solver you're using, but Hyperlynx has an option
that must be enabled for it to consider coplanar traces and planes as a
reference. Try that option and see if that makes the difference you're looking
for.
In addition, the reference trace/plane must also be connected to a signal that
Hyperlynx has identified as a power supply (GND, etc.
normally qualify but other non-power supply traces may need to be manually
added to the power supply list).
Hope this helps.
Chuck
Chuck Corley
National Instruments
On 2015-11-05 14:51, Moran, Brian P wrote:
Hi Folks,------------------------------------------------------------------
Hopefully this is an easy one for someone out there, but I need some
insight. I'm using a 2D field solver to calculate the Zo of a
micro-strip which has both a traditional broadside reference plane and
ground guard traces on one or both sides.
The solver does allow me to define the guard traces as references.
However, even when I do, the field solver reports the same Zo as
without the guard traces. The only metric that does change is Zself,
but Zself does care if they are guard traces or normal signal traces.
So I'm wondering, should the solver include the coplanar reference
traces in its Zo calculation, or does Zo, by definition, only consider
the broadside reference.
Should I be looking at Zself to characterize the trace?
Or should I be looking for a different solver. How do people
generally characterize coplanar t-line structures?
Brian Moran
Intel Corporation
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