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[SI-LIST] Re: Broadside coupled line vertical registration
- From: Martyn Gaudion <martyn.gaudion@xxxxxxxxxxxxxxxxxxxx>
- To: Dennis.Han@xxxxxxxxxxx
- Date: Fri, 06 May 2005 23:27:29 +0100
Hello Dennis,
I have recently seen some quite tightly coupled broadside pairs
where a small Rogers core is in the center of a mostly FR4
stackup. The pair is closely coupled and the closest ground
planes may be several layers away. I guess to ensure most
of the field is carried in the low loss Rogers material.
Kind regards
Martyn Gaudion
www.polarinstruments.com
At 23:14 06/05/2005, you wrote:
>I bet it's because most broadside-coupled line designs aren't truly =
>coupled.
>They are really two 50 ohm transmission lines, if 100 ohms differential =
>is
>the target. There is usually a large dielectric thickness between the =
>lines
>and a small amount of dielectric between the lines and ground. To get =
>truly
>coupled lines requires a thick board.
>
>Dennis
>
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>On
>Behalf Of Grasso, Charles
>Sent: Friday, May 06, 2005 4:50 PM
>To: 'tony_dunbar@xxxxxxxxxx'; 'si-list@xxxxxxxxxxxxx'
>Subject: [SI-LIST] Re: Broadside coupled line vertical registration
>
>
>Broadside coupled diff pairs tend to be less susceptible
>to vertical registration issues than one would initially
>think.
>
>Best Regards
>Charles Grasso
>Senior Compliance Engineer
>Echostar Communications Corp.
>Tel: 303-706-5467
>Fax: 303-799-6222
>Cell: 303-204-2974
>Pager/Short Message: 3032042974@xxxxxxxx
>Email: charles.grasso@xxxxxxxxxxxx; =20
>Email Alternate: chasgrasso@xxxxxxxx
>=20
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
>On
>Behalf Of Dunbar, Tony
>Sent: Thursday, May 05, 2005 10:24 AM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Broadside coupled line vertical registration
>
>
>In the past, if memory serves me right, Scott McMorrow has contributed
>valuable information on this topic and it should be locatable in the
>archives, along with other folk's inputs on the thread. Scott may also =
>have
>a paper on this, but I'm less sure of that.
>
>Regards,
>Tony
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Bill Wurst
>Sent: Thursday, May 05, 2005 10:07 AM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Broadside coupled line vertical registration
>
>Mark,
>
>While you are evaluating the effects of copper registration, don't =
>forget to
>also include the effect of manufacturing variations in the thickness of =
>the
>three dielectrics: top plane-to-trace, trace-to-trace, and bottom
>plane-to-trace. Each one will have an impact, the degree of which is
>dependent upon the relative spacing and the amount of variation relative =
>to
>the nominal thickness, as well as the width of the traces.
>
>Regards,
>
> -Bill
>
>
> /************************************
> / billw@xxxxxxxxxxx /
> / /
> / Advanced Electronic Concepts, LLC /
> / www.aec-lab.com /
> ************************************
>=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
>3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D
>=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
>3D=3D3D=3D3D=3D3D
>Ed Sayre III wrote:
> > Mark,
> > Try using a free ware field solver for this. It is a simple=3D20
> > experiment and you will surprised by the results.
> > We have done some substantial investigations into this and =
>found=3D20=20
> > that the broadside registration is not as sensitive to variations=20
> > as=3D20 edge coupled spacing and dielectric thicknesses. Of course =
>the=20
> > issue=3D20 is the level of coupling for the lines. The tighter the=20
> > mutual=3D20 coupling the more critical the registration. Thus try =
>your=20
> > stack and
>see.
> >=3D20
> > Regards
> > -Ed
> >=3D20
> >=3D20
> >=3D20
> >=3D20
> > At 02:37 PM 5/5/2005 +0100, Mark Burford wrote:
> >=3D20
> >>I have an interesting query, I would like to know what you guru's=3D20
> >>think about the effect of the vertical alignment of a broadside=3D20=20
> >>coupled trace and the error it could potentially introduce to 2D field
>
> >>solvers and the traditional transmission line approximation
> >>formulas=3D20 for calculating Z0, C and L. To clarify: a perfect=20
> >>alignment I am=3D20 classing as both lines exactly stacked one above =
>the=20
> >>other with with=3D20 core material in the centre an no over hang, =
>worst=20
> >>case would be one=3D20 line being offset to the left or right by 50=20
> >>percent.
> >>
> >>Could the potential error introduced be described to a first order
> >>by=3D20 decreasing the capacitance by at worst case 0.5? What would =
>be=20
> >>the=3D20 2nd order effects?
> >>
> >>Your thoughts I am sure will be as diverse as they are interesting.
> >>
> >>Thanks guys
> >>
> >>Mark Burford=3D3D20
> >>EngD Research Engineer
> >>
> >>------------------------------------------------------------------
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