[SI-LIST] Re: Coplanar waveguide propagation delay
- From: "burke_ipc" <burke@xxxxxxxxxxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 19 Jan 2005 01:42:55 -0000
I'd like to offer two resulting options to your question: (text
references, and field solvers)
(1)In terms of text which include calculation methods for coplanar
models, I believe the:
(a) Handbook of microwave technology, 1995, Acedemic press
(b) Handbook of microwave and optical components Vol I, 1989, John
Wiley
Contain several examples that will help you.
(2) In terms of using a conventional 2D field solver approach (using
boundary elements for example)
You have a couple of options:
(a) A coplanar model can be thought of as a stripline model with the
ground planes infinitely far away.
The reason for this is simple:
A reference is necessary in order to correctly solve the problem
(you require a return path). Hence, using a ground plane reference
far enough away where there is no coupling works well.
So... a couple of questions follow:
(a.1) How do I define infintely far away in real useable terms?
Answer: The answer lies within the Height to Pitch ratio, where
height is the distance from the ground plane to signal broad side
surface and Pitch is the edge to edge distance between signals (can
also be thought of as center to center distance).
The Height to Pitch ratio is usually an exponential function, so it
is easy to get to where the height to pitch ratio does not matter
(e.g. the ground plane is not coupled to the signals). Hence you
have a coplanar design. So, what tends to work well for this method
is a Height which is 5-10 times the Pitch.
(a.2) Why would I use a ground reference when a coplanar design
would dictate some ground to signal ratio
within the pins?
Answer: If you do this, and subsequently create a SPICE model, you
give yourself the flexibility of varying
the ground to signal ratio (number of grounds to number of signals,
e.g. ...G S S G....) during simulation
without having to build several models (one for each G:S run). This
in turn reduces your workload in order to
come up with the least use of real estate, therefore the least cost
(from this particular perspective).
Finally, Interactive Products has various downloads (paper and
software at no cost) that can help you with this question. The
reports we produce contain a wealth of information which include the
prop delay you are looking for.
Hope this was helpful,
Brian Burke
Interactive Products Corporation
Signal Integrity Software Solutions
http://www.interactive-products.com
--- In si-list@xxxxxxxxxxxxxxx, Martyn Gaudion <martyn.gaudion@xxxx>
wrote:
> Hi Pawel,
>
> If you would like to try a field solver, there is
> a two week free evaluation on the Polar
> SB8000 at present... You can download, or
> find an installer disk on January Circuitree
> magazine. You will find both coplanar waveguide
> and coplanar strips with and without soldermask...
>
> www.polarinstruments.com/products/stackup/SB8000.html
>
> Kind regards
> Martyn Gaudion
> www.polarinstruments.com
>
>
> At 18:43 18/01/2005, you wrote:
>
> >Hello all,
> >I have short but vital for me question - Does anyone know some
formula or
> >relations for calculation of the propagation delay through
coplanar
> >waveguide? I found many articles about microstip and stripline
but nearly
> >null about coplanar waveguides.
> >Thank You in advance
> >
> >Pawel Rulikowski
> >
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