[SI-LIST] Re: Need your Opinion and expertise
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: Amir.Nader-Tehrani@xxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 Jul 2006 15:09:20 -0400
Hello Amir,
Always the basic (and seemingly easy) questions are the most interesting to
discuss on
this forum. So let me be among the first to respond. Please see my response
inline below.
Best regards.
Hassan.
On Jul 18, "Nader-Tehrani, Amir - ES/RDR -Gil" <Amir.Nader-Tehrani@xxxxxxx>
wrote:
>
> Hello Everyone,
>
>
> I am a recent graduate trying to get some insight into signal integrity.
> My first task is to model a connector using SPICE. It seems like the
> easiest approach considering what I have available is to first find the
> S-Parameters for the connector using a Network Analyzer and then use the
> S-Parameters to go from the parameters to a SPICE model using a software
> tool. I would appreciate it if you could give me some insight on the
> following.
>
>
>
> 1- Is this a valid and reliable approach and if you can propose
> better approaches to me.
Yes, it's a valid approach but not necessarily reliable or even appropriate
depending on
the circumstances. A couple of points to consider:
- With a VNA you'll need SMA connectorization on your connector probably
through a
special test fixture. To obtain accurate S-parameters for the connector only,
you'll
have to use an accurate s-parameter de-embeding scheme which can be quite
challenging if
you have a multi-channel connector with substantial inter-channel coupling. The
challenge is essentially in defining the appropriate connector boundary - i.e.
the
location where the test fixture ends and the connector begins. Most de-embeding
schemes
require that boundary to be away from discontinuities.
- Existing VNA's offer up to 4-port S-parameter measurement. In other words,
you can
only measure two lines at a time - again not so appropriate for multi-line
connectors
with substantial coupling between the lines.
- When you cannot use a VNA, you can use 3D electromagnetic field simulation
tools
which, among other things, allow you to extract s-parameters of a much higher
number of
lines. But those tools require you to obtain accurate geometrical and material
information of the connector.
> 2- If this is a valid approach, are there any special facts I need
> to keep in mind to avoid problems or to smoothen the process
See my response to (1) above.
>
> 3- Can you suggest any software (preferably evaluation software)
> that I can use to go from S- Parameters to SPICE model
I've used Agilent ADS before to perform SPICE equivalent circuit creation
through
optimization. For that, you need to have an idea of the kind of lumped and/or
distributed elements your connector should have and come up with a good initial
guess of
the associated values.
3D EM solvers like Ansoft HFSS and CST Microwave Studio also have SPICE
equivalent
circuit creation options. However, last time I tried them (more than 2 years
ago) I
wasn't very pleased.
> 4- What tool should I use to simulate the SPICE model for high
> speed signal integrity tests (what software) and what should I try to
> achieve from this simulation and what kind of data should I gather
With accurate models, you should be able to use any reputable SPICE software
out there.
Most commercial customers I think use Synopsys HSPICE but there are a number
of "packaged" SPICE simulators out there that come with other PCB tools.
Cadence Allegro
SI and Mentor HyperLynx are in that category. PSPICE too can do the job and
even the
free Berkeley Spice. Just have accurate models for the etire signal chain.
> I would highly appreciate your sharing of expertise and ideas.
>
>
>
> Sincerely
>
>
>
> Amir Nader-Tehrani
>
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