Re: [SI-LIST] : differential impedance....NEED your feedback

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From: Mike Jenkins (jenkins@lsil.com)
Date: Mon Jun 12 2000 - 18:27:37 PDT


Vairamuthu,

My only comment (aside from being impressed by a 3 mil etch width)
is that diff Zo = 2 x (single-ended impedance - Z12), where Z12
relates to coupling between the lines. That is, if the lines are
close, your "diff Zo" will be LESS than 2x75. They should
probably be 3-5 times farther apart than the distance to the
ground planes (i.e., 3-to-5 times 8 mils).

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Maybe that's conservative, but you probably ought to get someone
with a field solver to work it out, if the lines will be closer.

Regards,
Mike

"AYYANU,VAIRAMUTHU (A-Singapore,ex2)" wrote:
>
> Hi Jenkins,
>
> I have the same issue i.e. FC signals to have differential Zo = 150 ohms
> (stripline if possible?)
>
> Here is my thinking:
>
> >>>>> SHOULD USE "BT" MATERIAL or other equivalent material that has a
> diectric constant = 3.5. If you refer to
> http://swan.automata.com/cgi-bin/imped-sl, you get the follwing data
>
> I. Automata's Stripline Impedance and Capacitance Modeling
>
> You submitted the following name/value pairs:
> Er = 3.5
> h = 16 (i.e. ground plane to ground plane separation)
> t = .5 Oz
> w = 3
> The characteristic impedance = 74 Ohms (diff Zo = 2x75 = 150 ohm)
> The intrinsic line capacitance = 1.6 pF/inch
>
> >>>>> If we use FR-4, the dimensions are becoming out of limit for strip
> line. Let me know if you have any final configuration/recommendation.
>
> Regards,
> Vairamuthu
>
> Principal Development Engineer,
> HSIO dept, Agilent Technologies S'pore Pte Ltd.,
> SCO, 1150 Depot Road,
> Singapore 109673
>
> ****************************************************************************
> *************************
>
> Re: [SI-LIST] : differential impedance
> About this list Date view Thread view Subject view Author view
>
> From: Mike Jenkins (jenkins@lsil.com)
> Date: Thu Apr 20 2000 - 11:29:41 PDT
>
> Next message: MikonCons@aol.com: "Re: [SI-LIST] : 20-H Rule and
> Self-Resonant Frequency of Power Planes"
>
> ----------------------------------------------------------------------------
> ----
>
> Sean,
>
> Based on experience with Fibre Channel PCB layouts, 150 ohm dif'l
> striplines will require some pretty thick dielectrics and some
> pretty thin lines. I believe it's doable, but will dictate some
> trade-offs on the cross section.
>
> Good luck,
> Mike
>
> >
> > We currently have an application that requires some signals to
> > be 150 ohms (stripline if possible?); with them being routed as
> > differential pairs so that their impedance is 75 ohms. Anyone have any
> > experience with this as stripline. We have done them as microstrip
> > before and at 100/50 stripline, but never 150/75.
> >
> > Regards,
> > Sean Murray
> > Sales Manager
> >
> > M&M Specialties Inc.
> > 1236 W. Southern Ave. #106
> > Tempe, AZ. 85282-4518
> > Phone: (480) 858-0393 x105
> > Cell: (602) 684-7859
> > Fax: (480) 858-1882
> > Email: seandm@mmspec.com
> > WWW.mmspec.com
>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Mike Jenkins Phone: 408.433.7901 _____
> LSI Logic Corp, ms/G715 Fax: 408.433.7461 LSI|LOGIC| (R)
> 1525 McCarthy Blvd. mailto:Jenkins@LSIL.com | |
> Milpitas, CA 95035 http://www.lsilogic.com |_____|
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Mike Jenkins               Phone: 408.433.7901            _____     
 LSI Logic Corp, ms/G715      Fax: 408.433.7461        LSI|LOGIC| (R)   
 1525 McCarthy Blvd.       mailto:Jenkins@LSIL.com        |     |     
 Milpitas, CA  95035         http://www.lsilogic.com      |_____|    
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