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 equal to

        y2= [ x2 * (t2 - t1) ]  + y1.

But SPECTRE is showing something different than "y2" .


Can anybody please tell where I am going wrong ?
Whether my line of thought is correct ?
or it may be some accuracy issue of Spectre lile Reltol, Vabstol,Abstol playing some rule ?

Also I solve the above differntial eqaution using MATLAB ODE45().
It is totally different from the SPECTRE result !



Kind Regards,