The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design Languages >> Verilog-AMS >> Solving ODE in Verilog-AMS
https://designers-guide.org/forum/YaBB.pl?num=1301308727

Message started by Sumit Adhikari on Mar 28^th, 2011, 3:38am

Title: Solving ODE in Verilog-AMS
Post by Sumit Adhikari on Mar 28^th, 2011, 3:38am

Does anybody has any idea, if it is possible to solve an ODE in Verilog-AMS ? All my tries failed.
Regards,
Sumit

Title: Re: Solving ODE in Verilog-AMS
Post by boe on Mar 28^th, 2011, 8:18am

Sumit,

What do you want to achieve? It should be obvious how to solve an ODE if you use a time derivative, so I suppose that's not what you want.

B O E

Title: Re: Solving ODE in Verilog-AMS
Post by Sumit Adhikari on Mar 28^th, 2011, 8:52am

You are absolutely correct, I also thought that way. I am in need to solving current and voltage equations as the way I wish and add them with some other currents/voltages. I want to study transport equations modified quantum mechanical effects in DSM technology, for this Verilog-AMS is good, as I have good controllability. For a warm up I took SHM equation (ddt(ddt(V(p,n))) <+ -k * V(p,n), which should give me sinusoidal out put like a0*sin(wt). Following is the code :

`include "discipline.vams"
`include "constants.vams"

module oscillations_ode (p, n);

inout p ;
inout n ;
electrical p ;
electrical n ;
electrical d_1 ;
electrical d_2 ;

parameter real k = 10000.0 ;

real reff;

analog
begin//{
//@(initial_step)
@(initial_step("dc", "ac", "tran", "xf"))
begin//{
V(p,n) <+ 1.0 ;
V(d_1,n) <+ 0.0 ;
V(d_2,n) <+ 0.0 ;
end//}

V(d_1,n) <+ ddt(V(p,n)) ;
V(d_2,n) <+ ddt(V(d_1,n)) ;
V(d_2,n) <+ -k*V(p,n) ;

end //}

endmodule

output of this block (p) is driving a small parallel load of a resistor and a capacitor.

The solver is running, but I am always getting 0 output.

Do not understand why >:(

Regards,
Sumit

Title: Re: Solving ODE in Verilog-AMS
Post by boe on Mar 29^th, 2011, 7:39am

Sumit,

your code is wrong.

Code:

V(d_2,n) <+ ddt(V(d_1,n)) ;
V(d_2,n) <+ -k*V(p,n) ;

is equivalent to
Code:

V(d_2,n) <+ ddt(V(d_1,n)) - k*V(p,n) ;

which is not what you want. Correct would e.g. be
Code:

V(d_1,n) <+ ddt(V(p,n)) ;
V(d_2,n) <+ ddt(V(d_1,n)) ;
V(p,n) <+ -1/k*V(d_2,n) ;

This works with my simulator.

B O E

PS: You misused the contribution statement. It is not an assignment.

Title: Re: Solving ODE in Verilog-AMS
Post by Sumit Adhikari on Apr 1^st, 2011, 11:56am

Thanks for pointing out my mistake.
Regards,
Sumit

Title: Re: Solving ODE in Verilog-AMS
Post by Sumit Adhikari on Apr 1^st, 2011, 11:58am

Thanks for pointing out my mistake.
Regards,
Sumit