[SI-LIST] Re: How to build a variable resistor in HSPICE

Steve,

I am trying to use the gpmos model that you have suggested
for SSO simulations and it is very useful, but I would like
veifying some issues:

1) implementing this model I noticed a mismatching beetwen
pmos spice and gpmos model: is this caused by pmos threshold voltage
(Vt) approximation?

2) what is exactly the flow that you use to extract the (x, y) data 
which are
inserted in the gpmos list?

3) how you extimate the pgain value?

The flow that I put in act is the following:

I simulate the pmos lieing the sorce pin to Vdd=3V, the drain pin to GND
and I apply a dc sweep on the gate pin over the range [0, 3V]. I extract 
the (Vg,Isd)
data and calculate the (x, y) values for Gpmos model putting
 x=Vg and y= Vsg=(Vdd-Vg)/Isd.

Is this flow correct or I am doing some errors?

Thanks and best regards,

                                         Antonio


swldstn@xxxxxxxxxxxx wrote:

>David,
>
>Below is a Voltage Controlled Resistor (Gxxx) that I use to
>emulate a simple Pmos Pullup to speed up some SSO work.
>This is from Hspice.
>
>This one has piece wise linear control to emulate the IV curve
>but you can simplify it to a simple linear equation
>
>Gpmos     psource   drain       VCR NPWL(1) pgate  die_vss  LEVEL=1
>0.25v,'150g/(pgain*psso)'
>+ 0.5v,'10meg/(pgain*psso)' 1v,'50k/(pgain*psso)' 2v,'4k/(pgain*psso)',
>3v,'2k/(pgain*psso)'
>
>This is the gate voltage control used to turn on the VCR.
>
>Vpgate    pgate     die_vss    PWL  0n 0V  7.5ns 0V  8.0nS 3V 15.0ns 3V
>15.5ns 0V
>
>Hope this helps. The pgain and psso are just parameters I use
>to set the drive strength and number of Pmos in parallel.
>
>
>Steve Waldstein
>swldstn@xxxxxxxxxxxx
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Beal, Weston
>Sent: Tuesday, October 14, 2003 7:38 PM
>To: 'david.kaiser@xxxxxxxxxx'; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: How to build a variable resistor in HSPICE
>
>
>David,
>
>I'm pretty sure that Hspice has an element called a voltage controlled
>switch that will do this.  It takes ON and OFF resistances as parameters.
>
>Later,
>Weston
>
>
>-----Original Message-----
>From: David Kaiser [mailto:david.kaiser@xxxxxxxxxx]
>Sent: Tuesday, October 14, 2003 3:55 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] How to build a variable resistor in HSPICE
>
>
>
>Can anyone show me how to build a resistor in HSPICE that varys in value=
> from 1000 Ohms to 1 ohm in about 1ns and visa-versa?
>I suppose I could use a FET, but I don't have enough experience with=
> transistors in HSPICE to do this myself.
>Thanks in advance.
>
>David Kaiser
>4 McDATA Pkwy.
>Broomfield, CO 80021
>(720) 558-4431
>david.kaiser@xxxxxxxxxx
>
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