Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
References: <firstname.lastname@example.org> <email@example.com>
Subject: Re: SPICE model of XTAL
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Tue, 10 Dec 2002 07:48:55 -0000
NNTP-Posting-Date: Tue, 10 Dec 2002 07:48:57 GMT
fred bartoli wrote:
> Tom Bruhns a écrit dans le message :
>> Paul Burridge wrote in message
>>> Well there's definitely a generic xtal in the parts list. I'd have
>>> thought one could have entered a value for resonant frequency, but
>>> strangely it appears not.
>> That would be a really thin model of a crystal! The one Kevin
>> mentioned, with a series RLC and a shunt C across it, is kind of a
>> bare minimum, and it can be helpful to actually use multiple series
>> RLCs to represent the various resonances (especially the overtones,
>> but perhaps also spurious resonances near the fundamental). These
>> are things they may not tell you when you buy the crystal, though.
>> There have been articles about how to measure crystals in the ARRL
>> literature. I think Wes Hayward is one of the fellows who put
>> together a crystal test set, and he's available on the web. He
>> frequents rec.radio.amateur.homebrew.
>> Be careful: SPICE is NOT a valid excuse for not understanding how
>> something works.
> IMO it's the worst excuse for not understanding how circuits works,
> as it allow you to play ad nauseum with parasitics and what-if
> scenarios. Spices limitations, as you tell bellow, are an invitation
> to clearly understand what is important and what is not because you
> can't model *all* the phenomenons and so are to be selective on the
> relevant ones.
However, spice allows you to *understand* and see effects that are
simply impossible to do by manual calculation. Sure, you need to
understand circuits to a reasonable extent independent of spice, but
there is no way that anyone can calculate even a 4 transistor circuit in
detail. Its nice to think that spice is just a number cruncher to do the
grunt work, but it isn't, its much more that this. For example, people
use TFlops computers to simulate atomic bombs. They do this because it
is *impossible* to *understand* what is exactly happening without it.
The world is simply too complicated to take the naive view that an
individual can understand all the details of phenomena without
simulation. In real life, simulation truly adds to ones understanding,
despite the fact that people don't like the idea.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.