Hi Russell and Andy,

Thanks for the links. I've seen the old mchip xtal app note but I'll have
to take a look at the new one (and these links in more detail) when I have
some more time.

Specifically, the question I have never seen addressed to my satisfaction
is why it is justified to consider the two external caps to be "in series".
Under that idea, it should not matter what I choose for C1 and C2 as long
as their series combination is the same capacitance, I should get the same
oscillation frequency (assuming stray cap and all else is the same). It
seems to me that this is not true, and that even several values of C1,C2
which gave the same CL could result in different 180 deg phase points,
hence different oscillation frequencies.

The argument I've usually seen is to redraw the caps in series with a
ground point in the middle and then say that, as far as the crystal is
concerned, there is just one loop of current through all three components
and they are effectively in series. This ignores that you are going to
attach other things (the inverter input and output) to the ends of this,
making it not nearly so symmetrical.

Also, the first of the two links you sent, Russell, claims that the cap on
the output of the inverter, along with the drive limit resistor, form a
simple RC voltage divider, and you can compute the voltage level at this
point based on this. I don't think this is an accurate way of describing it
since it is also connected to the (inductive) xtal which may alter the
impedance at that junction considerably.

Sean

At 02:35 PM 2/25/2003 +1300, you wrote:
> > > Can someone point me to a detailed explanation of [crystal
> > > oscillator Load Capacitance specs?]
>
>Closish
>
>         http://www.eetkorea.com/ARTICLES/2001SEP/2001SEP06_AMD_AN.PDF
>
>Not quite what you want, but useful
>
>         http://pdfserv.maxim-ic.com/arpdf/AppNotes/app58.pdf
>
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