Re: 1 chip 1KHz xtal osc?

From: Ben Bradley (ben_nospam_bradley_at_mindspring.com)
Date: 07/09/04 

Date: Fri, 09 Jul 2004 16:17:40 -0400

On Fri, 09 Jul 2004 11:35:47 +1000, Mark Roberts <markrob789@aol.com>
wrote:

>I need a lowest possible parts count 1KHz square wave oscillator.

   [this is like a game show "Design That Circuit" in the spirit of
"Name That Tune"] I can do that with an op-amp, a capacitor and three
resistors.

>Must use crystal timing with accuracy as good as reasonably attainable
>without use of oven..

   Oh, well that's different...
   That would be a temperature-compensated crystal oscillator (TCXO).
Dallas makes one that oscillates at 32.768kHz, in fact that's almost
the part number. :)

>To do this, I assume it is best to start with the highest frequency
>crystal possible, as each divide down increases resolution.

   No it doesn't, if the crystal changes frequency, the divided down
signal changes frequency by the same percentage. Higher frequency
crystals are pretty much as stable, or unstable, as lower frequency
ones.

>Power requirements are open.
>
>Can anyone please advise regarding the most suitable circuit design?

   Do you need exactly 1kHz, or would a very stable signal at 1024Hz
or 992.9696...Hz? If either of those would work, you can use the
Dallas part and a 4024 to divide the oscillator output by 32 or 33.
   If you need exactly 1kHz, there are plenty of other TCXO's at
higher frequencies that will divide down to exactly 1kHz.

>With appreciation,
>
>Mark

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