[SI-LIST] Re: [SI-LIST]: Design a shielded differential line

I have to ask this..

I noticed that Wadells book is referenced. How
many people have actually USED the equations
in the book ?? For example for the equation
for the shielded broadside coupled pair,
he uses k,K and K prime. In defining k he
has the unknown on the LHS of the equation.
If anyone knows how to decipher the equation
can they please let me know?


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of john lipsius
Sent: Tuesday, May 28, 2002 5:10 PM
To: si-list
Subject: [SI-LIST] Re: [SI-LIST]: Design a shielded differential line





1. I would use a field solver, like Apsim RLGC or Ansoft.
2. I would not use broadside, as you show.  I would use edge-coupled,
instead, due
    to manufacturing problems (difficult to maintain the geometry, therefore
the Z).
3. Reference:  "Transmission Line Design Handbook",  Brian Wadell.  See
    sec. 4.6.
4. A shielded pair would have contiguous reference copper around all 4
    sides.  Your diagram doesn't show this.
5. Not sure why you specify "minimum capacitance between the differential
line
    and the ground" since that's fairly well set by your choice of FR4 and
W,
    unless you're doing something exotic like minimizing electrical length
or
    maximizing phase velocity, which aren't of concern, I believe, in normal
    digital interconnect.



----- Original Message -----
From: "PRIEUR, Olivier" <Olivier.PRIEUR@xxxxxxxxxxxxxxxxx>
To: "si-list" <si-list@xxxxxxxxxxxxx>
Sent: Tuesday, May 28, 2002 7:15 AM
Subject: [SI-LIST] [SI-LIST]: Design a shielded differential line


>
> Dear All,
>
> I want to design a shielded differential line in a PCB.
> Nominal characteristic impedance of the differential line is 70 to 85 ohms
> The recherched struture is
> ______________            GND
>        ___                  h1
>        ___                  h
> ______________    h1   GND
> I have the added constraints:
> minimum width W of trace is .216 mm
> thickness h, h1 of dielectric is 0.1/0.2/0.3/0.4/0.5
> substrate dielectric constant about 4.7 (FR4)
> I look for h, h1 and W.
> I want a minimum capacitance between the differential line and the ground.
> Do you know a formula, an article about this topic?
>
> Best regards,
>
> ------------------------------------
> Olivier PRIEUR
> e-mail: olivier.prieur @astrium-space.com
> ------------------------------------
>
>
>
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