Re: Missing Schmitt Gates??

John Larkin jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx posted to
sci.electronics.design:

On Tue, 04 Dec 2007 16:45:54 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Tue, 04 Dec 2007 15:40:47 -0800, D from BC
<myrealaddress@xxxxxxxxx> wrote:

On Tue, 04 Dec 2007 22:17:36 GMT, Rich Grise <rich@xxxxxxxxxxx>
wrote:

On Mon, 03 Dec 2007 19:07:08 -0800, John Larkin wrote:
On Mon, 3 Dec 2007 17:57:28 -0800, "Joel Koltner"
"D from BC" <myrealaddress@xxxxxxxxx> wrote in message

A crystal needs a good linear amp.

Everything is linear if you look closely enough...

I am being a little obtuse here -- the kind of oscillator I was
thinking of was your canoncial microcontroller/FPGA clock that
doesn't need to be particularly accurate -- it's common to use
50 or even 100ppm rocks in such systems; this is a completely
different league of oscillator than those you build for, e.g.,
fancy RF applications where you're after 2.5ppm or better.

I was never able to get the Schmitts to oscillate anywhere near
the supposed crystal frequency.


Maybe it's a little late in the thread to bring this up, but I'd
think that with the Schmitt characteristics of the input, the
crystal would have to be drastically overdriven, just to get the
gate to notice that there's a feedback signal.

But I wouldn't have any qualms about an HCU inverter or 3. ;-)

Cheers!
Rich

I think Ht for Logic with Schmitt inputs is about 1V @ 5V.

A crystal..well... isn't it just tiny jiggling piece of rock?
Ooops...I might be thinking piezo..
Damn..forgot all my crystal theory...cuts, shapes, modes and all
that jazz.
Anyways.. I can imagine that one has to be kind to a tiny piece of
crystal and not bash it with lots of drive.
However....depends on the precision required..
As someone posted, for clocking an uC or CPU ...who cares about
some drift..


D from BC

A crystal oscillator using an inverter with hysteresis WILL NOT
self-start.

...Jim Thompson


Of course it will self-start. It just won't run anywhere near the
crystal frequency!

John

Maybe in 1 in a trillion cases.

.

Relevant Pages

  • Re: Missing Schmitt Gates??
    ... I am being a little obtuse here -- the kind of oscillator I was thinking ... I think Ht for Logic with Schmitt inputs is about 1V @ 5V. ... A crystal oscillator using an inverter with hysteresis WILL NOT ... Of course it will self-start. ...
    (sci.electronics.design)
  • Re: Missing Schmitt Gates??
    ... I am being a little obtuse here -- the kind of oscillator I was thinking ... But I wouldn't have any qualms about an HCU inverter or 3. ... I think Ht for Logic with Schmitt inputs is about 1V @ 5V. ...
    (sci.electronics.design)
  • Re: Missing Schmitt Gates??
    ... I am being a little obtuse here -- the kind of oscillator I was thinking ... I think Ht for Logic with Schmitt inputs is about 1V @ 5V. ... A crystal oscillator using an inverter with hysteresis WILL NOT ... Of course it will self-start. ...
    (sci.electronics.design)
  • Re: Missing Schmitt Gates??
    ... I am being a little obtuse here -- the kind of oscillator I was thinking ... But I wouldn't have any qualms about an HCU inverter or 3. ... I think Ht for Logic with Schmitt inputs is about 1V @ 5V. ... Of course it will self-start. ...
    (sci.electronics.design)
  • Re: Missing Schmitt Gates??
    ... I am being a little obtuse here -- the kind of oscillator I was ... But I wouldn't have any qualms about an HCU inverter or 3. ... I think Ht for Logic with Schmitt inputs is about 1V @ 5V. ...
    (sci.electronics.design)