[SI-LIST] Re: trouble simulating with AC coupling capacitors in topology
- From: "Beal, Weston" <Weston_Beal@xxxxxxxxxx>
- To: prathap sirishe <prathapsirishe@xxxxxxxxx>, Andy Haas <andyhaas@xxxxxxxxxxx>
- Date: Fri, 8 Jul 2011 17:58:49 +0000
The problem with this approach is that a good S-parameter model has the very
same behavior as the simple capacitor model. If the S-parameter model doesn't
show the same charging effect then I question the validity of that model. I
believe you could make an S-parameter model that would accurately represent the
high frequency impedance of the capacitor and avoid the low frequency charging,
but it would take care and understanding to generate that model. S-parameters
are like power tools. A skilled craftsman can get a lot of work done with them,
but in an unskilled hand they can do a lot of damage.
My preference for the series capacitor problem is to use a resistor with the
value of the capacitive reactance at the bit frequency of the signal on the
channel.
Weston
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of prathap sirishe
Sent: Friday, July 08, 2011 10:49 AM
To: Andy Haas
Cc: Newbie Pugal; Roopesh Badala; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: trouble simulating with AC coupling capacitors in
topology
Hello Roopesh,
I remember facing same issue before. From what I recollect, apart from all the
solutions mentioned so far, you can try to generate a s-parameter model for an
ac coupled differential trace pair using another simulation tool like Hyperlynx
and use the resultant ".s4p" file in Cadence tool set, replacing differential
trace segment with 4-port s-parameter model.
Hope this helps!
Regards,
Prathap
On Fri, Jul 8, 2011 at 11:31 AM, Andy Haas <andyhaas@xxxxxxxxxxx> wrote:
> Hi guys,
>
> There should be no issue in simulating nets with series caps within
> the Cadence SI environment. Initial conditions can also be used if you
> use the right model. Feel free to contact me offline and I'd be happy to help.
>
> Regards,
> Andy
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Newbie Pugal
> Sent: Friday, July 08, 2011 9:50 AM
> To: Roopesh Badala; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: trouble simulating with AC coupling capacitors
> in topology
>
> Hi Roopesh,
> I have faced similar problem in the past and went to cadence for the
> support but did not worked out. With the AC caps in the cadence the P
> and N waveforms will not come as expect. Later I simulated using
> HSPICE with initial condition settings or else you need to run a long
> bits for the settled waveforms.
>
> Regards
> Pugal
>
>
> ________________________________
> From: Roopesh Badala <roopesh.badala@xxxxxxxxx>
> To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
> Sent: Friday, 8 July 2011 4:54 PM
> Subject: [SI-LIST] trouble simulating with AC coupling capacitors in
> topology
>
> Hi All,
> I am trying to simulate a topology which has AC coupling capacitors in it.
>
> Using Cadence Allegro PCB SI tool set , i am unable to get the
> expected output.
>
> but when I simulate the same topology by removing the AC coupling
> capacitors in signal path, I get a perfect waveform.
>
> Is this a tool limitation..? can some body suggest me if they have
> faced similar issue.
>
>
> Thank you
>
> Roopesh
>
>
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