Re: Missing Schmitt Gates??

On Mon, 03 Dec 2007 11:55:07 -0800, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Mon, 3 Dec 2007 10:47:27 -0800, "Joel Koltner"
<JKolstad71HatesSpam@xxxxxxxxx> wrote:

"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:p1f6l3laoaebkm8i6pihgthn4do0l00cem@xxxxxxxxxx
Tiny schmitts can do analog-like stuff, too, like being the basis for
a boost regulator, or acting as a frequency-counter front end.

By now you've probably used one as a crystal oscillator too, right?


No. I don't design XOs any more. It's too easy to buy a packaged
surface-mount thing that just works, usually within a couple of ppm,
right out of the tube.

Incidentally, Schmitts make rotten XO's, at least the couple of times
I tried it.

A lot of the Tiny gates will pull huge currents if their inputs are
much off the rails. I have thermal images to prove it.

John


If I got this right....???

XO oscillators work ideally with one magic phase.
Kinda like a phase shift oscillator.
The energy within the XO has to be allowed to rock back and forth
sinusoidally (linearly) and oscillation sustained by linear
regenerative feedback.
Nonlinear elements like clipping, xover and nonlinear transfer in the
feedback path mess up the frequency stability.
I don't see how all these linear requirements can be achieved with
digital parts meant for digital applications.
A crystal needs a good linear amp.
A shaper cct. then makes sq wave. This can be a Schmitt.


D from BC
.

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