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#sky130
Title
# sky130
s

Stefan Schippers

03/07/2022, 12:17 AM
@User while editing capacitor symbols to show the capacitance value based on W and L, i see the
cap_var_hvt
is not loaded in open_pdks spice models. if you see the file
.../share/pdk/sky130A/libs.tech/ngspice/all.spice
it loads:
.include "../../libs.ref/sky130_fd_pr/spice/sky130_fd_pr__cap_var_lvt.model.spice"
but does not load the
cap_var_hvt
high voltage capacitor, although that file exists in libs.ref (
sky130_fd_pr__cap_var_hvt.model.spice
). May be this capacitor is blacklisted /DNU for some reason? EDIT: Looking at the models these 2 capacitors have the same
tox
, so i believe there is no need to have both. the capacitance per area is indeed almost identical, and the
cap_var_lvt
has lower
vth
so behaves closer to an 'ideal' capacitor at low voltages, better than the
cap_var_hvt
t

Tim Edwards

03/07/2022, 1:57 PM
These are varactors, so the MOS threshold voltage changes the voltage range over which the device goes from minimum to maximum capacitance. I already have a script in open_pdks that modifies
all.spice
to include missing devices. I didn't notice before that the HVT varactor was missing, but it is trivial to expand the script to add it. There are probably more missing devices in
all.spice
, so just let me know when you find one.