P
Paul Burridge
- Jan 1, 1970
- 0
Clearly, the AC gain of a buffered gate is a lot higher than that of an
unbuffered gate. But how exactly that leads to startup problems and
other trouble is not obvious to me. The application note Win has
mentioned does just note that without explanation. Another source is
Linear Technology's AN-12. Jim Williams writes there that the problem is
"the inability to reliably identify the analog characteristics of the
gates used as gain elements". He proceeds to describe the symptoms, but
without a deeper analysis of the causes.
I have since accepted it as common knowledge that unbuffered gates make
better crystal oscillators, but I admit that I still don't quite know
why it is so.
Hello, Stefan,
I've just read the app note Win pointed us to. It appears the argument
is that the buffered gates overdrive the crystal and can cause long
term damage to it. That's how I read it, anyway. Although it appears
from what is stated that such damage can be much mitigated if not
eliminated by the careful selection of the lower value resistor. I
wonder if ceramic resonators used in place of xtals in this type of
circuit are less susceptible to such damage?
I'm not altogether clear as to why the output of the 10Mhz oscillator
in the diagram is shown as being 0.5 - 40Mhz!
Incidentally, I just called Farnell to try to order some of these
devices but they've no record of the part number. :-(