Hi Olin.

One can drive Xtal in with precise clock generator and load the
Xtal out with several different values of precise resistors with
low inductance and low capacitance ( say recommeneded for 1GHz designs )
Phase shift ( delay ) and output impedance can be measured for let's
say 20 samples for difference frequecnies, oscillation modes, etc.


WBR Dmitry.


Olin Lathrop wrote:
> 
> Spehro Pefhany wrote:
> > The output acts like a *current* source.
> 
> That's the same as saying it has inifinite impedence.  As I said, I agree
> that the capacitors are in series for calculating the load capacitance in
> this case.
> 
> However I don't agree that the driver has infinite impedence.  It has CMOS
> high/low output drive transistors, and will look roughly resistive.  And, I
> think there is a good chance that this resistance is about the same or lower
> than the impedence of the capacitor on the pin at that frequency.
> 
> Do you at least agree that if the driver has finite impedence, then just
> adding the two capacitors is not valid?
> 
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