**From:** Jian X. Zheng (*jian@zeland.com*)

**Date:** Tue May 08 2001 - 15:24:23 PDT

**Next message:**Inmyung Song: "Re: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Previous message:**Rede, James: "[SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**In reply to:**Rede, James: "[SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Next in thread:**Inmyung Song: "Re: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Reply:**Inmyung Song: "Re: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"

Hi, James:

I would like to give some comments:

1. I am not sure why you use the terminology "edge-coupled differential

stripline". Stripline normally means that you have a trace between top and

bottom ground plane. Do you mean the trace is inside the 62 mils thick

substrate? However, it does not seem that is what it should be. I assume the

traces are on one surface of the substrate.

2. Using our IE3D field solver, I can optimize the dimensions for you:

(a) If you want to keep the gap width to be 6-mils, the trace width will be

25-mils in order to achieve Zc = 100-ohms.

(b) If you want to keep the trace width to be 10-mils, the gap width will be

3-mils.

The above results assume the traces are on top of the one surface.

3. If the traces are inside the dielectrics:

(a) If you want to keep the gap width to be 6-mils, the trace width should

be 8-mils to get Zc = 100-ohms.

Any question, please feel free to let me know. Thanks!

Best regards,

-----------------------------------------------------------------------

Jian-X. Zheng, Ph.D

Zeland Software, Inc., 48890 Milmont Drive, 105D, Fremont, CA 94538, U.S.A.

Tel: 510-623-7162, Fax: 510-623-7135, Web: http://www.zeland.com

---------------------------------------------------------------------

*> -----Original Message-----
*

*> From: owner-si-list@silab.eng.sun.com
*

*> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Rede, James
*

*> Sent: Tuesday, May 08, 2001 2:18 PM
*

*> To: si-list@silab.eng.sun.com
*

*> Subject: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?
*

*>
*

*>
*

*> To the SI Good Guys,
*

*>
*

*> I have been asked to design an edge-coupled differential stripline with no
*

*> planes present
*

*> for FR-4. This design is necessary to pass a Hi-Pot requirement of 1500
*

*> volts.
*

*> The differential impedance is to be 100 ohms for T1 frequencies
*

*> (1.544MHz).
*

*> Four layers are present but no layers are power or ground. Let the board
*

*> thickness
*

*> be 62 mils +/-10%. Use 1/2 oz copper and assume that Er = 4.1.
*

*>
*

*> I cannot use my Hyperlynx field solver because THEY TOOK MY DONGLE.
*

*>
*

*> When I use an impedance calculator found on the web and specify 5-7-6 mils
*

*> (Trace-Space-Trace, TST) and a plane-to-plane separation of 30 mils, the
*

*> differential
*

*> impedance is 100 ohms. If I then widen my plane-to-plane spacing to
*

*> 30000000000 mils,
*

*> I get something like 255 ohms. By trial and error, I was able to
*

*> find a TST
*

*> of 20-6-20
*

*> that would produce a 100 ohm differential impedance at the 30000000000 mil
*

*> plane-to-plane
*

*> separation.
*

*>
*

*> Qs: Is this a reasonable way to approach this problem? Is there a better
*

*> way?
*

*> How should this problem be done, even a field solver will not
*

*> give an answer
*

*> without ground planes present? What about accounting for the
*

*> board thickness
*

*> then air?
*

*>
*

*> J.J. Rede
*

*> Signal Integrity Engineer
*

*> Taqua Systems
*

*> Hyannis MA
*

*>
*

*> **** To unsubscribe from si-list or si-list-digest: send e-mail to
*

*> majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
*

*> si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
*

*> si-list archives are accessible at http://www.qsl.net/wb6tpu
*

*> ****
*

*>
*

**** To unsubscribe from si-list or si-list-digest: send e-mail to

majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE

si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.

si-list archives are accessible at http://www.qsl.net/wb6tpu

****

**Next message:**Inmyung Song: "Re: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Previous message:**Rede, James: "[SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**In reply to:**Rede, James: "[SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Next in thread:**Inmyung Song: "Re: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"**Reply:**Inmyung Song: "Re: [SI-LIST] : Differential Impedance of a Stripline w/ No Planes?"

*
This archive was generated by hypermail 2b29
: Thu Jun 21 2001 - 10:11:52 PDT
*