[SI-LIST] Re: Hspice Network Analysis
- From: "Mike Degerstrom" <degers@xxxxxxxxxxxxxxxxxxxx>
- To: Bill.Cohen@xxxxxxxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Thu, 13 Nov 2003 08:42:39 -0600
Bill,
The capacitance is dependant on bias voltage.
This should work:
1) Repeat your transient analysis with a ramp
starting at .9*VDD and stopping at 1.1*VDD.
2) Repeat your AC analysis but with the DC
voltage set to VDD.
Your results now should match. Your analysis is interesting as
I've modeled PDS on chips in the past. I didn't take the time
to see if series resistance makes a difference for on-chip
decaps but suspected it didn't. I actually didn't model
the decaps but used ideal capacitors to match the databook
specs. for the capacitance per sq/micron for the decap
cells.
Mike
On Wed November 12 2003 2:54 pm, Bill.Cohen@xxxxxxxxxxxxxxxx wrote:
> I have been analyzing on chip decoupling capacitors using hspice. I have
> extracted the capacitance of the decoupling capacitor using transient
> analysis. I ramped a voltage (slow Ramp 1ms) and looked for the current. I
> found the capacitance using the formula
>
> c=i*dt/dv
>
> Using AC analysis I then curve fit an external resistance to mimic my
> routing and transistor channel resistance using a reference ideal RC
> circuit.
>
> I then used the AC Network analysis package available in Hspice. I got good
> correlation to the resistance but I have bad correlation between the
> capacitance. Does anyone have experience with the Network analysis
> available in Hspice? Why would the Network analysis capacitance number vary
> widely from the transient analysis? I curve fit from 100K to 1Ghz and ran
> the network analysis at the same frequencies.
>
> Transient Analysis: C=18.6pF
> AC curve fitting of R=2.8 ohms
>
> Network analysis: R=2.86ohms, C=7.95pF.
>
> --------------------------------------------------------------
>
> | Bill Cohen
> | Toshiba America Electronic Components
>
> --------------------------------------------------------------
>
>
> -------------------------------------
--
Mike Degerstrom email: degers@xxxxxxxxxxxxxxxxxxxx
Advanced Signal Integrity Design, LLC http://www.advancedsidesign.com
Phone: 507-289-2900 Fax: 507-280-0052 Cell Phone: 507-254-4448
316 6th Street SW; Rochester, MN 55902
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