In Reply to: Re: Crystal circuit posted by Greg Lynch on 03/27/01 at 8:12 PM:
I'll admit that I was being a bit hyperbolic about using gates to construct a crystal oscillator, but I was absolutely in earnest that I consider trying to do so to be a very, very bad idea!
I'd venture a guess that someone may have done some "math" for gate based oscillators, but that math would depend on component models which would have parameters outside of the specifications of the devices themselves, especially so for logic gates. I would be very hesitant to base a design on that work.
Therefore, if you really and truly cannot see your way clear to purchasing a commercially offered oscillator module, consider instead the possibility of making a Pierce crystal oscillator. The Pierce oscillator is a realatively simple circuit and can be made with one or two of 2N2222 or 2N3904 or similar devices. You'd need to level shift to get logic-level compatibility, but I think it would be worth it.
If you can't find a suitable circuit, please let me know.
John Dunn - President