[SI-LIST] Re: SI models at MGH speeds

Hassan,

There may be several reasons for inaccuracies in SPICE.

1)  Bad process file.  Many times the process files are developed
    for the smallest transistor size, and at other sizes (such as
    in the larger I/O buffers) they are all over the place.
2)  Larger companies have their own proprietary SPICE tools,
    which usually have process parameters which are incompatible
    with commercial tools.  Converting these process files to
    something that commercial tools can do results in loss of
    accuracy.  Kind of like if you wanted to convert a level=3D13
    MOSFET model to level=3D3.
3)  I also hear a lot lately that the small geometries we are
    using these days are starting to push the SPICE equations
    to the edge where they are not all that accurate or valid
    any more.
4)  For various reasons vendors release reduced "equivalent"
    circuits to the customer, which is not as accurate as the
    full design.

There may be more, but I could only remember these right now...

Arpad
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Hassan O. Ali
Sent: Thursday, May 26, 2005 2:17 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: SI models at MGH speeds


On May 26, "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx> wrote:
>=20
> On the other hand, the reason people turn to encrypted SPICE
> models is simply because they do not have the time (or don't
> want to take the time) to figure out how to make behavioral
> models.  If IBIS models were hard enough to make, writing
> macro models and *-AMS models are even harder.  However,
> SPICE may not be the solution either.  For one, it is slow,
> but I also hear issues with its accuracy (contrary to the
> popular belief that it is accurate).

Arpad,

What did you hear about the source of SPICE errors? Are the errors due =
to the failure of=20
SPICE to accurately handle multi-GHz SPICE device models or something =
else?

Thanks.

Hassan.
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