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Simulators >> Circuit Simulators >> Netlist reduction question
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Message started by Paul H on Nov 22^nd, 2010, 8:17am

Title: Netlist reduction question
Post by Paul H on Nov 22^nd, 2010, 8:17am

Hi,

In my AMS Designer log file I'm seeing ...

Parasitic resistor `rs' has been deleted because its
value of 24.6 mOhm ( R / (Area * MFactor) ) was smaller than `minr'.

and this is repeat a few times.

What is going on here ? To me it looks like spectre is doing some sort of netlist optimisation by default that I'm not expecting.

Thanks
Paul

Title: Re: Netlist reduction question
Post by Geoffrey_Coram on Dec 1^st, 2010, 8:33am

Do you actually care about a 24mOhm resistor? Generally, these resistors are in series with much larger nonlinear resistance (eg, the junction of the diode), and 24mOhm is irrelevant, but removing it makes the circuit matrix smaller (and less prone to numerical problems).

Title: Re: Netlist reduction question
Post by Paul H on Dec 1^st, 2010, 8:50am

No I don't care about resistors which are this small. I'm just trying to understand what spectre is doing to the input netlist before the numerical analysis part of the simulation starts.

Thanks
Paul

Title: Re: Netlist reduction question
Post by Ken Kundert on Dec 1^st, 2010, 10:18am

Spectre is not doing anything to the netlist. The message indicates that the MOS model itself considers the resistor to be negligible and so is ignoring it. If you feel the resistor is significant, there are steps you can take to assure it is included in the simulation, but that is very unusual. In almost all cases you are safe in allowing the resistors to be neglected.

-Ken