[sdiy] oscillator jitter / phase noise

[Czech Martin]

> exact frequency doesn't really matter that much). Preferably using a
> quality audio interface (I'm assuming consumer soundcard 
> crystals are not
> very stable).

Why? It is very hard to get a bad crystal today.
Thus it is more a matter of the oscillator circuit
and even more of it's power supply.
Nearly all CMOS ICs have the standard pierce configuration,
i.e. a inverter serves as amplifier. The more sophisticated
have a servo loop that will control amplitude and
delivers very soft drive of the crystal (thus letting it
doing it's job without disturbation).
The jitter will be intruduced mainly by:
-having a pll (RC type VCO has very large jitter compared to crystal)
-saving power pins and operating the inverter from dirty I/O
 supply

An on top of all: you can build the best chip and still some
manufacturer invents a crap application that will spoil
the performance completely. 
The application board is the real performance killer.


m.c.