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Design Languages >> Verilog-AMS >> smoothing transition function in transient analysis
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Message started by Dracon on Mar 7^th, 2009, 7:27am

Title: smoothing transition function in transient analysis
Post by Dracon on Mar 7^th, 2009, 7:27am

Dear All,

I have a problem with function that should smooth my output signal.
The transition(V(x), td,tr,tf) add to signal rise and fall times but only in linear way.
I have written following funkction based on Lagrange interpolation between three points (x1,y1) (x2,y2) , (x12,y12) and wanted signal, after smoothing to be more exponential, but I get convergence problem:
"internal timestep too small in transient analysis"
Note that points(x,y) are changing in time.

analog function real fsmooth;
input x,x1,y1,x12,y12,x2,y2;
real x,x1,y1,x12,y12,x2,y2;
real n1,n12,n2;
begin
n1 = ((x-x12)*(x-x2))/((x1-x12)*(x1-x2));
n12 = ((x-x1)*(x-x2))/((x12-x1)*(x12-x2));
n2 = ((x-x1)*(x-x12))/((x2-x1)*(x2-x12));
fsmooth = n1*y1 + n12*y12 + n2*y2;
end

endfunction
Perhaps there is some embedded function to do this??

Thanks for your answers.
Best regards,
Dracon

Title: Re: smoothing transition function in transient analysis
Post by pancho_hideboo on Mar 8^th, 2009, 9:47am

Dracon wrote on Mar 7^th, 2009, 7:27am:

I have written following function based on Lagrange interpolation between three points (x1,y1) (x2,y2) , (x12,y12) and wanted signal, after smoothing to be more exponential, but I get convergence problem:
"internal timestep too small in transient analysis"

Try other interpolation filter such as spline, raised-cosine, etc.

Dracon wrote on Mar 7^th, 2009, 7:27am:

Perhaps there is some embedded function to do this??

There is no built-in function provided for such purpose.
Everyone write own interpolation filter, if needed.

Title: Re: smoothing transition function in transient analysis
Post by Ken Kundert on Mar 8^th, 2009, 2:38pm

The reason why it is not built into the language is because in practice, it is very rarely needed. My experience is that people overuse smoothing, usually at great cost in modeling and simulation time. Can I ask why you think you need it?

-Ken

Title: Re: smoothing transition function in transient analysis
Post by Dracon on Mar 8^th, 2009, 3:01pm

I just begun my journey with modelling circuits and thought it maybe good idea to make signal transitions as it look like in specification. I needed it for driver de-emphasis model, but now if I look on that from a perspective of large simulation time I do not think this is my goal. I think the model have to be simple for functional verifications.
Thanks