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Design Languages >> Verilog-AMS >> How to implement ODEs using Verilog-A
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Message started by shu on May 17^th, 2004, 5:18pm

Title: How to implement ODEs using Verilog-A
Post by shu on May 17^th, 2004, 5:18pm

I am wondering whether I can implement coupled odinary differential equations using Verilog-A and simulated by Spectre?
The equations look like
dx/dt=x*y
dy/dt=x/y

Thanks a lot.

Title: Re: How to implement ODEs using Verilog-A
Post by Geoffrey_Coram on Jul 9^th, 2004, 9:13am

Shu -
The equations you wrote could be implemented by two coupled simple circuits, each consisting of a 1-Farad capacitor and a dependent current source. In Spectre, I don't believe you can have a dependent source with a division, so it will have to be Verilog-A.

---- ode.va ----
`include "disciplines.h"
module ode(x,y);
inout x,y;
electrical x,y;
analog begin
I(x) <+ V(x)*V(y) - ddt(V(x));
I(y) <+ V(x)/V(y) - ddt(V(y));
end
endmodule
----
---- ode.netlist ----
*
simulator lang=spectre
ahdl_include "ode.va"
X1 (x y) ode
ic x=1 y=1
tran1 tran stop=1u skipdc=yes
----

As written, the only DC solutions of your equations are {x=0, y=anything but 0}, and when x=0, the transient analysis is boring.

To get something interesting, I have set "skipdc=yes" and provided initial conditions for both nodes.

-Geoffrey