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stary

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model of capacitor, controlled with voltage need
Oct 06^th, 2006, 6:13am

Gurus, please, help me!
I want to use a voltage-controlled capacitor of type:
c = c0 + k*V(vc1, vc2)
here c0 and k are constants; vc1, vc2 - controlling nodes. So I try to describe it as:

I(vp,vn) <+ ddt( (c0 + k*V(vc1, vc2)) * V(vp,vn)); � // (vp and vn are own nodes of capacitor)

But the compiler puts an error (rather long message). The main reason, as I understood, is mix of controlling and own voltages in one exepression. How it can be written in other form?

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Ken Kundert

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Re: model of capacitor, controlled with voltage ne
Reply #1 - Oct 6^th, 2006, 10:30am

If you are asking us to interpret an error message for you, it is helpful if you include the message in your post. Even better would be to include your model and perhaps a test circuit that exhibits the problem as well.

Have you taken a look at http://www.designers-guide.org/Modeling/varactors.pdf?

-Ken

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stary

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Re: model of capacitor, controlled with voltage ne
Reply #2 - Oct 8^th, 2006, 10:54pm

Hi, Ken

I want to simulate a capacitor, linearly controlled with a voltage:
c = c0 + k*V(vc1,vc2)
here:
c0 - initial capacitance,
k - a constant
vc1, vc2 - the controlling nodes of capacitor
and this capacitor placed between nodes vp and vn. According to your paper I changed model of this capacitor on:

I(vp,vn) <+ ddt(c*V(vp,vn)+k*V(vc1,vc2)*V(vp,vn)*V(vp,vn)*0.5)

(i.e., I(vp,vn) is calculated via charge-based model.)
Again I get an compiler' error:

dynamic quantities must be linearity accessible.

What is the reason of error and how it can be fixed?

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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: model of capacitor, controlled with voltage ne Reply #3 - Oct 8^th, 2006, 11:38pm I don't know. Your model seems fine to me. What does your vendor say? -Ken
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stary

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Re: model of capacitor, controlled with voltage ne
Reply #4 - Oct 9^th, 2006, 12:29am

Oh, Ken, you don't sleep?!
Unfortunately, no access to vendor.
If it can help, the full text of model is:
`include "discipline.h"
`include "constants.h"
model cap1 (vp, vn, vc1, vc2);
inout vp, vn;
input vc1, vc2;
electrical vp, vn, vc1, vc2;
parameter real c = 0;
parameter real k = 0;
analog
I(vp,vn) <+ ddt (c*V(vp, vn) + k*V(vc1, vc2)**V(vp, vn)*V(vp, vn)*0.5);
endmodule

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Geoffrey_Coram Senior Fellow Offline Posts: 1998 Massachusetts, USA	Re: model of capacitor, controlled with voltage ne Reply #5 - Oct 9^th, 2006, 6:09am stary wrote on Oct 9^th, 2006, 12:29am: model cap1 (vp, vn, vc1, vc2); s/model/module ? Quote: I(vp,vn) <+ ddt (cV(vp, vn) + kV(vc1, vc2)*V(vp, vn)V(vp, vn)0.5); Did you intend the * in there? My compiler has no problem with the module.
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stary New Member Offline Posts: 5	Re: model of capacitor, controlled with voltage ne Reply #6 - Oct 9^th, 2006, 6:21am Yes, I did mistake when typing this text here, valid line is: I(vp,vn) <+ ddt (cV(vp, vn) + kV(vc1, vc2)V(vp, vn)V(vp, vn)*0.5); Version of software is: Virtuoso 5.1041_USR3.27.30 I cannot say exactly - s/model/module. It is a model of one of circuit's block.
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Ken Kundert

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Re: model of capacitor, controlled with voltage ne
Reply #7 - Oct 9^th, 2006, 8:06am

This appears to be a bug in the simulator. I was able to work around it by assigning the argument of ddt() to a local variable, and then applying ddt() to that variable. So in particular, I used
Code:

`include "discipline.h"
`include "constants.h"

module cap1 (vp, vn, vc1, vc2);
inout vp, vn;
input vc1, vc2;
electrical vp, vn, vc1, vc2;
parameter real c = 0;
parameter real k = 0;
real q;
analog begin
    q = c*V(vp, vn) + k*V(vc1, vc2)*V(vp, vn)*V(vp, vn)*0.5;
    I(vp,vn) <+ ddt (q);
end
endmodule

and it compiled without finding any errors.

-Ken

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