Re: [SI-LIST] : Dual Stripline impedance

Ravinder Ajmani (ajmani@us.ibm.com)
Wed, 15 Apr 1998 11:56:34 -0400

Using the Engineering Solutions Impedance calculator, I get the followi=
ng
dimensions for obtaining a 100 Ohms differential pair:
Width of conductors: 5 mils
Thickness of conductors: 1.4 mils
Thickness of dielectric: 15 mils
Space between conductors: 4 mils
Dielectric constant: 4.6
However, based on my past experience with this software, the actual imp=
edance
value is always lower than the calculated value. The actual thickness =
of
dielectric may be in the range of 20 - 25 mils, other parameters being
constant. We always have to do 1 - 2 iterations before we can hit corr=
ect
impedance.

Regards,
Ravinder Ajmani

Always do right. This will gratify some people and astonish the rest. =
....
Mark Twain

owner-si-list@silab.Eng.Sun.COM on 04/15/98 07:56:18 AM
Please respond to owner-si-list@silab.Eng.Sun.COM
To: si-list@silab.Eng.Sun.COM
cc:
Subject: [SI-LIST] : Dual Stripline impedance

Hi all,

We're thinking about using a dual stripline for a differential
pair. The diff. impedance should be 100ohm.

Have anyone used this before? Or seen it in suggested? Come to think
of it, it does sound like a good idea (not mine). Now, the hard part
is getting the right geometry... Any help from various programs or
books? Any references would very helpful, the only one I found is in
"Transmission Line Design Handbook", and it is not very clear. Can you
analyze this with a field solver?

The concept goes like this (cut-through view of the board):

Plane
-----------------------

--------
| L1 |
--------

--------
| L2 |
--------

-----------------------
Plane

The Zdiff should be between L1 and L2.

Homann

=