Hey again. One thing I noticed recently is whenever I extract a circuit (run

extract all

), it looks like no parasitic resistances are extracted. I am checking this by reading the resulting

.ext

file. Is there some additional setting I need to set? This happens in every example I have tested, but here I included my specific example. I open SSTL.mag, and run

select top cell; extract all

. Are there really no significant parasitic resistances in this design?

there is extra spets required. I think cthresh and rthresh is one of them. But for resistance extraction you also need extra steps

Here is a PEX script that can serve as reference. https://github.com/hpretl/iic-osic/blob/main/iic-pex.sh

@User: Using just "extract" will only extract parasitic capacitances (and "lumped" resistances, which, to my knowledge, no tool understands what to do with, although it's a pretty clever idea). Extracting resistances requires having magic annotate the extraction results. The sequence of commands goes like this:

flatten cellname_flat
load cellname_flat
extract all
ext2sim labels on
ext2sim
extresist tolerance 10
extresist
ext2spice lvs
ext2spice cthresh 0
ext2spice extresist on
ext2spice

A couple of notes: (1)

extresist

does not work well with hierarchy. Your best bet is to flatten the circuit before running parasitic extraction. The

flatten cellname_flat

command flattens the loaded cell and places it into a new cell called

cellname_flat

. This will make the top level subcircuit in the output called `cellname_flat`; there are ways to work around that but probably not worth worrying about. (2) I always like to use

ext2spice lvs

even when not doing LVS because it sets "sane" configuration; then I redo some settings like the capacitance threshold, for parasitic extraction.

Thanks everyone! I gave Tim's script a shot and it basically worked. Here is the script I finally settled on:

set NAME [cellname list self];
select top cell;
# (Flattening improves resistance extraction)
flatten "[list $NAME]_flat"
load "[list $NAME]_flat"
select top cell;
extract do resistance;
extract all;
ext2sim labels on;
ext2sim;
extresist tolerance 10;
extresist all;
ext2spice lvs;
ext2spice cthresh 0;
ext2spice extresist on;
ext2spice -o "pex_[list $NAME].spice";