Hi <@U01819B63HP> I have a quick question regarding the parameter `mf` of `mimcap` , I looked into t...

Chris

07/05/2023, 11:14 PM

Hi @Stefan Schippers I have a quick question regarding the parameter

mf

mimcap

, I looked into the SKY130 spice model of

mimcap

and see there is a definition of

mf

, but when using xschem to export the netlist, there are both

and

mf

defined for the capacitor. I noticed that these two parameters are generally the same. What is the difference between

and

mf

here? Or is this some sort of artifact to avoid some script conversion error? And what if these two parameters are not with the same value? Thanks!

Stefan Schippers

07/06/2023, 7:18 AM

When you specify a value for

mf

in xschem for a mimcap (example:

mf=2

) it will emit a netlist line with

m=2

and

mf=2

. the

mf

is just a copy of he

instance multiplier. It is created to make this multiplier parameter available inside the mimcap model. For some unclear reason the multiplier

parameter can not be used inside a model equation. This is done also for mosfets, where

mult

and

are set to the same value,

mult

only present to make it available inside the model definition. see in below

cap_mim_m3_1

spice model the mf
parameter used in capacitance mismatch estimation:

* SKY130 Spice File.

.subckt  sky130_fd_pr__cap_mim_m3_1 c0 c1 w=1 l=1 mf=1

.param wc = 'w+m3_dw*1e6+tol_m3*1e6'

.param lc = 'l+m3_dw*1e6+tol_m3*1e6'

.param via3_spacing = '(0.17+0.25+0.140)*(0.17+0.25+0.140)'

.param num_contacts = '(wc*lc/via3_spacing)'

.param r1 = 'rm3*(lc)/(wc)'

.param r2 = 'rcvia3/num_contacts'

.param carea = 'camimc*(wc)*(lc)'

.param cperim = 'cpmimc*((wc)+(lc))*2'

.param czero = 'carea + cperim+MC_MM_SWITCH*AGAUSS(0,1.0,1)*0.01*2.8*(carea + cperim)/sqrt(wc*lc**mf*)'

c1 c0       a 'czero' tc1 = 0 tc2 = 0.0

rs1 a        b1 'r1' tc1 = {tc1rm3} tc2 = {tc2rm3}

rs2 b1        c1 'r2' tc1 = {tc1rvia3} tc2 = {tc2rvia3}

.ends sky130_fd_pr__cap_mim_m3_1

Chris

07/06/2023, 6:00 PM

Thanks for the clarification!

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