The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Mar 29th, 2024, 1:57am
Pages: 1
Send Topic Print
Regarding conservative and non-conservative systems (Read 4994 times)
AMS_ei
Community Member
***
Offline



Posts: 67

Regarding conservative and non-conservative systems
Aug 28th, 2016, 6:41am
 
Hi,

I am a new with verilog-AMS.  I've developed a behavioral model of a lowpass filter.

//-----code begins here-----------//

`include “disciplines.vams”
`include “constants.vams”
module lp_filt_beh (sig1, sig2, gnd);
     inout sig1, sig2, gnd;
     electrical sig1, sig2, gnd;
     parameter real res = 1K;
     parameter real cap = 1u;
analog begin
     I(sig1,sig2) <+ V(sig1, sig2) / res;
     I(sig2,gnd) <+ ddt(V(sig2,gnd) * cap);
end
endmodule

//-------code ends here-----------------//

I am not sure whether it is a conservative system or a non-conservative systems.
How can I distinguish between them from the above example?

Explanation would be great helpful.

Thank you.

Warm regards,
Back to top
 
 
View Profile   IP Logged
Ken Kundert
Global Moderator
*****
Offline



Posts: 2384
Silicon Valley
Re: Regarding conservative and non-conservative systems
Reply #1 - Aug 29th, 2016, 7:26pm
 
Systems that satisfy both KCL and KVL are referred to as conservative systems. This is because of Telegan's Theorem, which states that if both KCL and KVL are satisfied, then the system conserves energy. Circuit simulator employ KCL and KVL to formulate their systems, so by definition anything you simulate with a circuit simulator is a conservative system.

However, it is common to refer to models that are written in terms of both voltage and current, as yours is, as conservative models. This distinguishes them from models that are just written in terms of voltage. Such models tend be be more abstract and referred to as signal-flow models.

These are really distinctions without a difference though. Nothing you need to worry about.

-Ken
Back to top
 
 
View Profile WWW   IP Logged
Geoffrey_Coram
Senior Fellow
******
Offline



Posts: 1998
Massachusetts, USA
Re: Regarding conservative and non-conservative systems
Reply #2 - Aug 30th, 2016, 11:04am
 
Back to top
 
 

If at first you do succeed, STOP, raise your standards, and stop wasting your time.
View Profile WWW   IP Logged
JayOcad
New Member
*
Offline



Posts: 8

Re: Regarding conservative and non-conservative systems
Reply #3 - Sep 8th, 2016, 12:17am
 
Thanks for all the guidance on this website and documents- with regards to conservative and non-conservative systems/ signal-flow systems, I had a question about potential signal-flow versus flow signal-flow.

Are there any differences between a signal flow system with a discipline defined with potential Efield only,  versus a discipline defined with flow Efield only?  If their access, idt, ddt, and all other definitions are exactly the same, does using a "flow" nature differ from using a "potential" nature?

I read in the AMS manuals that in a potential signal-flow system, there is no conservation of charges and, and no sum of *flows* condition (KFL not enforced), but is there a sum of potentials condition in a potential signal-flow system?  i.e. If I model Electric field with the "potential" nature declaration, and I need it to disregard conservation/ KPL, is that valid? In a circuit loop with device d1, d2, d3.., does the solver/Spectre try to enforce that the sum of the Electric field across d1,d2,d3.. = 0?

Conversely in a flow signal-flow system, where no potential is defined, I read there is no condition on sum of potentials, does this mean there is neither KPL nor KFL when Spectre sees that only a flow nature is defined? Or is only KPL not enforced and KFL is still enforced(and then Efield is a flow nature, then the Efield  into a node must equal the Efield out of a node?).

Thanks for the help,
Best regards,
J
Back to top
 
 
View Profile   IP Logged
Ken Kundert
Global Moderator
*****
Offline



Posts: 2384
Silicon Valley
Re: Regarding conservative and non-conservative systems
Reply #4 - Sep 9th, 2016, 12:00am
 
The only difference between full conservative descriptions and signal flow descriptions is that the models written with signal flow descriptions do not have access to the missing nature. Thus, if you use voltage signal flow, the model can neither observe or specify current. If you use current signal flow, the model can neither observe of specify voltage. Other than this there is no difference. That is why you can freely interconnect conservative and signal flow models.

With signal flow models there is some opportunity to simplify the formulation and therefore speed the simulator up a bit, but it is my understanding that there are no simulators that do that.

-Ken
Back to top
 
 
View Profile WWW   IP Logged
AMS_ei
Community Member
***
Offline



Posts: 67

Re: Regarding conservative and non-conservative systems
Reply #5 - Jan 18th, 2017, 7:57am
 
Hi Ken,

Thank you for the explanation.
How will you decide whether your design should be of modeled in conservative or in signal flow?

Thank you.

Kind regards,
Back to top
 
 
View Profile   IP Logged
Ken Kundert
Global Moderator
*****
Offline



Posts: 2384
Silicon Valley
Re: Regarding conservative and non-conservative systems
Reply #6 - Jan 18th, 2017, 4:38pm
 
Quote:
These are really distinctions without a difference though. Nothing you need to worry about.
Back to top
 
 
View Profile WWW   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2024 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.