Assura Question-Cap Extraction

Dear all,
I am using Assura to carry out extraction.
In the 'Extraction' form, there is an option called 'Cap Extraction Mode'
and we can choose 'coupled' or 'decoupled'.
My question is what is the difference? I have read the manual, but i still
not understand. How to conside the choice? Also, it said it will extracted
the capacitance on SELECTED net, but how to select? It seem that there is no
selection required.
Before using Assura, i was using Diva and i only need to choose 'Cap ALL'
then. So, i would like to share your experience on Assura.

Thank you very much!

Best Regards,
Raymond

 

Raymond,

Decoupled will take any capacitance between different nets and
decouple it so that all capacitors are to ground. Obviously this is
less accurate, but results in a smaller network and can be fine for
simple modelling. Coupled keeps the capacitors between nets so that
they are output between those nets (although if you specify a minimum
capacitor value, smaller capacitors get decoupled and then summed up,
and then filtered out if the total decoupled sum is less than the
minimum).

If you're choosing to extract the capacitance of selected nets, you
can (in Assura 3.1) pick the nets from the schematic which it will
extract. There's something on the form which shows that (I'm running
Windows at the moment so can't quickly remind myself what the form
looks like - to be honest the form is completely different depending
on which Assura version you're running).

There's far more flexibility with Assura RCX than Diva, which is why
you have more choices.

Regards,

Andrew.

 

Hi,

In any layout, there will be parasitic capacitances from nets to
underlying substrate, and from nets to other wires in the layout.
Assura gives you the option of how you want to report these different
capacitances.

With "coupled" caps, capacitances between nets in your design will be
extracted.

With "decoupled", the capacitances are still extracted, but they are
represented as a lumped capacitance for each net to substrate, rather
than between nets.

The number of capacitors extracted in "decoupled" mode will be smaller
than for "coupled".

Your design will dictate the right one to choose - if you are worried
about cross-coupling between switching nets and high-impedance nets in
a high-frequency design, "coupled" will be important to you.

Assura allows you to either extract all nets, or to select those nets
you want to extract, and ignore the others. You can either supply a
list of nets you wish to extract, or you can select the nets from the
schematic, when you set-up the RCX run (from the Virtuoso Layout GUI,
go to Assura/Run RCX/Extraction, in Assura av3.1.2).

If you use RCX option "selected nets proper" (also on the "Extraction"
form) the netlist, (or av_extracted view), will contain all your
drawn devices, plus extracted parasitics on the selected nets only.

Good luck,

Paul