https://open-source-silicon.dev logo
#gf180mcu
Title
# gf180mcu
s

Stefan Schippers

02/07/2023, 11:05 AM
@Tim Edwards Are
nmoscaps
realized as poly over n-tap inside nwell ? or just as nmos (may be with some additional Vth adjusting implant)? Trying to figure out how
pmoscaps
are realized. From @Tom picture above (specifically the arrow) it seems that nmoscaps are implemented as nmos, possibly with a Vth correction.
t

Tim Edwards

02/07/2023, 1:56 PM
The GF180MCU documentation shows devices with a
_b
suffix that are the "true" varactors (poly over n-tap, and also poly over p-tap, which is not usually a characterized device). The ones without the suffix appear to be basic source-drain-tied FETs. But there is a separate device model for the source-drain-tied devices, which is why they have a separate device name. I'm not sure why a MOScap with a standard FET structure would need a distinct simulation model. So the MOScap FET devices are:
cap_nmos_03v3
,
cap_pmos_03v3
,
cap_nmos_06v0
, and
cap_pmos_06v0
, while the varactor devices are
cap_nmos_03v3_b
,
cap_pmos_03v3_b
,
cap_nmos_06v0_b
, and
cap_pmos_06v0_b
. (Then, to make life more complicated, there's the extended low-doped drain devices vs. the extended salicide-blocked drain devices. . .)
👍 1
1
r

Robin Tsang

02/12/2023, 4:40 AM
Looks like the moscap models are used to speed up spice sims. Inside the subckt definitions, ‘C’ is based on W*L of the transistor, and a Cox factor. It doesn’t simulate a mosfet.