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generation of gm/Id curves help needed

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f2003588

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the gm curve

i hav to design a fully diff amp...using gm/Id method to meet the specifications...
generated gm/Id curves for nmos(SOURCE connected to GND,DRAIN and GATE shorted and swept the DC voltage from 0 to 3.3v).....but facing problem how to generate the gm/Id curves for the pmos using spice cud anyone plzz tell the connections n how to perform it clearly its urgent.....it may be basic but i just started learning
 

gm v/s id curve

Ordinary Spice, even commercial, shows only currents and voltages in DC sweep analysis. Plotting gm over Id curves is very easy when you have Spice3/Nutmeg simulator. There is a very reliable SpiceOPUS, a modern investigation of the Spice3/Nutmeg -- just find it in the Internet. It is an interesting project at the University of Ljubliana, Slovenia.
The code may look like here:

save @mn[id] @mn[gm]
foreach voltage -4 -3 -2 -1 0
alter vbs = $voltage
dc vgs $Vmin $Vmax $Delta
let gmid = @mn[gm] / @mn[id]
end
plot all.gmid xlabel 'Vgs [V]'
+ylabel 'gm/Id [S/A] for Vbs = -4, -3, -2, -1, 0V'

A.
 

id curves

f2003588 said:
i hav to design a fully diff amp...using gm/Id method to meet the specifications...
generated gm/Id curves for nmos(SOURCE connected to GND,DRAIN and GATE shorted and swept the DC voltage from 0 to 3.3v).....but facing problem how to generate the gm/Id curves for the pmos using spice cud anyone plzz tell the connections n how to perform it clearly its urgent.....it may be basic but i just started learning
Click to expand...
 

gm/id method hspice

yeah i am nt directlly expecting the gm/Id curves first i will plot voltage n current curves then diff the voltage curve then divide by the current to get the required curve...but the thing is tht i am facing problem with the connections of pmos..(net list)cud plzz give the netlist (pspice) for tht r else the connections of drain source gate
 

how to plot gm/id in spice

*The following is the pmos.sp files simulated by Hspice.
*Size pmos device by plotting Id versus V*=2*Id/gm
mp dp dp 0 0 p33 w=10u l=1u m=1
vdp 0 dp dc 1v
.dc vdn 10mv 3.3v 10mv

*Note that vs is v*..
.probe vs=par(`-2*i(mn)/gmo(mn)`)
.probe Id=par(`-i(mn)`)
.option post probe list node dccap brief ingold=2 measdgt=6 numdgt=8
.lib
`./ms018_v1p6.lib` TT
.op
.temp 25
.end


Run dc analysis,and you can get the individual curve(I vs V,etc) using the calculator(wavescan or cosmoscope).Also you can sweep the L or W when running dc analysis.
 

gm/id +pmos

If you do not have HSpice, try this network in your PSpice :)
The rest is the same as for your nMOSFET.
 

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    f2003588

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