RE: Verilog-AMS question regarding retention

Arpad,

As I have read the LRM the subtle difference between ic being omitted and 
ic=0 is that in the first case the implicit DC provides the initial 
condition, while in the second one explicitly sets the initial condition 
to 0.

One example that I can think of is two identical capacitors in series: if 
a voltage is applied to the pair, you'd expect the voltage in between to 
be half of the total voltage: it's a capacitive voltage divider. Now if 
one is given an ic=0, the voltage in between would be either 0 or the full 
voltage, depending on which of the capacitors is connected to ground. Now 
what happens if both ic values are set to 0?

I've run this experiment with our in-house simulator which gives exactly 
the above results. With both capacitors having an ic=0, apparently the ic 
data are discarded.

Marq

owner-verilog-ams@eda.org wrote on 12-10-2005 18:26:02:
> Marq,
> 
> This is an interesting detail I missed.  According to this:
> "with the initial condition computed or assigned in DC analysis"
> if the idt statement is not part of the initial condition
> calculations, it should return results as if IC was omitted,
> i.e. IC=0?  So the two examples below are supposed to CORRECTLY
> return the same results?
> 
>   if (analysis("static"))
>     some stuff here;
>   else
>     V(cap) <+ idt(I(cap), V0) / Cap_value;
>   -------------------------------------------
>   if (analysis("static"))
>     some stuff here;
>   else
>     V(cap) <+ idt(I(cap)) / Cap_value;
> 
> Is this the intention of the LRM, and considered the correct
> behavior?
> 
> Arpad
> =================================================================
> 
> This is an excellent point: the LRM says that the idt() operator 
> should run from 0 to t, with the initial condition computed or 
> assigned in DC analysis. Now what happens if the simulation 
> starts at some other time, for instance to have some control logic 
> in a particular state? It should start from t0, where t0 is the 
> time value of the (implicit) DC analysis 
>