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Simulators >> Circuit Simulators >> #nodes and #equations in Spectre
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Message started by leander on Apr 13^th, 2011, 6:56pm

Title: #nodes and #equations in Spectre
Post by leander on Apr 13^th, 2011, 6:56pm

I am doing a postlayout simulation for a PA. Their are a lot of parasitic Rs and Cs. The simulator reports insufficient memory when doing PSS analysis. I then notice from the inventory that the equations is much more than the nodes (>30X). Why this is the case? I thought the number of equations should equal the number of nodes plus independent sources and inductors.

Circuit inventory:
nodes 9929
equations 347049
iprobe 166629
ahdl simulator 1
bsim4 1400
bsource_1 313
capacitor 75946
diode 960
inductor 334
isource 2
port 2
resistor 83473
vsource 2

Title: Re: #nodes and #equations in Spectre
Post by boe on Apr 14^th, 2011, 3:58am

leander,

You have ~166 000 iprobes. I expect that the simulator solves those too. Also, you may have equations for derivatives of signals.

B O E

Title: Re: #nodes and #equations in Spectre
Post by Geoffrey_Coram on Apr 14^th, 2011, 8:22am

boe is correct; if iprobes are implemented as 0V voltage sources, then that would add a row for the branch current and an extra node, which gets you quite close to the number of equations.

BSIM4 can also add several internal nodes per device (up to 7: internal drain, internal source, two internal gate nodes, and four internal body nodes).

Title: Re: #nodes and #equations in Spectre
Post by boe on Apr 18^th, 2011, 10:43am

Geoffrey,

additional question: I'd expect the #nodes in the inventory to include the internal nodes of any (BSIM or other) models. Is that correct?

B O E

Title: Re: #nodes and #equations in Spectre
Post by Geoffrey_Coram on Apr 25^th, 2011, 6:01am

BOE -
I think #nodes generally does not include internal nodes of models.

Title: Re: #nodes and #equations in Spectre
Post by John O Donovan on Apr 25^th, 2011, 10:46am

Geoffrey is correct. Nodes are circuit nodes, not including any internal nodes of devices.

Regards,
John

Title: Re: #nodes and #equations in Spectre
Post by boe on May 6^th, 2011, 11:32am

Geoffrey and John,

Thanks!

B O E