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Solving a differential equation using VerilogA Model

RFStuff

Dear All,

I need to solve a differntial eqaition in my VerilogA marco-model

The eqaution I want to solve is:-

 

 ddt(V(alpha)) = Vx * V(in)

V(in) is the input signal ( as a function of time 't')  to the model.

Vx is read from a "table_model" at (t + V(alpha) i.e (  $(abstime) + V(alpha)  )

To solve this  I did as below:-

 

 // define branches
branch (alpha) alpha1;
branch (alpha) alpha2;

I(alpha1) <+ -Vx * V(in);

I(alpha2) <+ ddt(V(alpha));

 

  The KCL at alpha forces I(alpha1) + I(alpha2) = 0  and solve the differntial equation.   

 

I went and checked the results.

At  $abstime = t1

     Vx * V(in)= x1

     V(alpha)= y1

At  $abstime = t2

     Vx * V(in)= x2

     V(alpha)= y2

 

I think y2 should be eqaul to 

         y2= [ x2 * (t2 - t1) ]  + y1.

But SPECTRE is showing something different than "y2" .

Can anybody please tell where I am going wrong ?

 

Kind Regards,

 

 

 

 

 

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