Re: [ng-spice] Design Document Comments


To ng-spice@ieee.ing.uniroma1.it
From Paolo Nenzi <pnenzi@ieee.ing.uniroma1.it>
Date Fri, 8 Oct 1999 09:28:43 +0200 (CEST)
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On Thu, 7 Oct 1999, Manu Rouat wrote:

> Paolo Nenzi wrote:
> 
> > DIRECTORY ORGANIZATION
> > ======================
> > I like the structure organization you made, but how do you think to split
> > the existing code into the new structure ?
> 
> It's work, and it will take some time..... we can start as soon as we agree 
> on a tree - maybe we can do that now?
> The transition will most probably be a bit chaotic, but it can be done if
> we are well organised.

OK let's start. What about starting from an empty CVS tree ? 
We may call it tg-spice (transitional generatio spice) ???

> 
> - use the analog kernel for all components (thus they all have an analog 
> description) but it is possible to have different levels of precision
> for different blocks (ie high precision for pure analog blocks , low
> precision for digital blocks to speed things up)

Digital signals have sharp rising and falling edges, can this cause
instability for an analog kernel ?
 
> - use one program that is 'on top' of an analog and a digital simulator - 
> this is the method used by Mentor Graphics - it works, but it is really
> heavy. The program simulates the analog part and the digital part
> separately with the appropriate simulator and takes care  of the
> interaction between the two. I suppose that both simulators must be
> coded to allow  this.

Mhh, this seems too heavy and complex to do. 

> - use a true mixed-mode simulator like Avanti's Starsim - 
> it is a completely different method of simulation (transistor
> charateristics are 'precalculated' using an analog simulator, and put
> into tables - these tables are then used by the simulator instead
> of recalculating everything).
Is this the sparse-tableau method ???

> My feeling is that we should stick to a true analog simulator, 
> at least in the beginning.

Yes, I agree, we should realize a sort of "switching model with dealy" for
digital components, a sort of second order model. This can be sufficient
to start. 

I would like to hear Kev for this, I am not sure that it is what he would
like to do. 

When I think to a mixed mode simulator I am thinking at a tool that can
reliably simulate spice described subcircuits with verilog or VHDL
described ones. I know that there are may ways to to that but I am a
newbie in the filed and my ideas are not completely clear. 

Paolo    


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