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Design >> Analog Design >> reference to Vth in macromodeling
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Message started by hossein_ml on May 27^th, 2005, 1:43pm

Title: reference to Vth in macromodeling
Post by hossein_ml on May 27^th, 2005, 1:43pm

Hi,

I have been trying to use the calculated value of Vth in Spectre DC analysis for my macromodels. Since in my macromodel, Vgs is sweeped, Vth will also be changed. Therefore, I need to use the real-time value of Vth in each step of parametric simulation in order to get accurate results. Anyone knows how I can reference to Vth parameter that is calculated by Spectre DC Analysis in the schematic when defining a value of say a resistor. I need to define this value based on accurate value of Vth. Is it possible at all?

Title: Re: reference to Vth in macromodeling
Post by Andrew Beckett on May 31^st, 2005, 10:41am

I initially thought you could do this with a bsource, something like:

Code:

//
model nch mos1 type=n vto=1 kp=16u gamma=1.3 lambda=0.01 \
phi=0.7 pb=0.80 mj=0.5 mjsw=0.3 cgbo=200p cgso=350p cgdo=350p \
cj=300u cjsw=500p ld=0.1u tox=80n \
af=1 kf=3.1e-24

m1 (drain gate 0 0) nch w=20u l=0.8u
vgs (gate 0) vsource dc=1
vds (drain 0) vsource dc=1

rmeas (rop 0) bsource r=m1:vth*1000
imeas (rop 0) isource i=1u

save m1:ids rop

parameters start=0 stop=5 step=20m gsv=1
vgssweep sweep dev=vgs param=dc start=0.6 stop=2.0 step=0.2 {
dcAnalysis dc dev=vds start=start stop=stop step=step
}

(bsource could have been "resistor" in the above example).

However, this doesn't work. I then remembered that there is:

PCR: 568208
Title: Allow passing device operating point to bsource

to get this to work.

So it's not possible right now (assuming I've understood the question properly!)

Regards,

Andrew.

Title: Re: reference to Vth in macromodeling
Post by aamar on May 31^st, 2005, 12:27pm

Hello,
Is the bsource, a generic dependent source? which I can use for example to define a current source, which is dependent on both current and voltage at the same time?
and if so, is there a symbol for it ? or must I edit the spectre netlist manually?

Thanks

Title: Re: reference to Vth in macromodeling
Post by Andrew Beckett on Jun 1^st, 2005, 1:20am

bsource is a generic dependent component, which can be a resistor, capacitor, inductor, voltage source or current source - dependent on expressions of voltages and currents. See spectre -h bsource for more details.

There is no component for it in analogLib - mainly because the expressions would confuse ADE - it tends to think that such expressions include design variables where you're actually referring to voltages at nodes in the design (say).

Mostly bsource gets used for device models - so you can create a subckt (or inline subckt) model and then include this as a model file, and have a corresponding symbol for that in DFII.

Regards,

Andrew.