[time-nuts] Linear voltage regulator hints...
kb8tq at n1k.org
Thu Dec 11 07:51:00 EST 2014
If your OCXO has a stability of +/-3x10^-10 over 0 to 60C (numbers picked to make math easy):
6x10^-10 / 60 = 1x10^-11 per C
If the OCXO is 10X better than that (unlike) you are at 1x10^-12/C
If the room temperature swings 1 C, you get a 1x10^-11 swing in the OCXO.
Keep in mind that the OCXO also responds to things like gradients as much as it does to absolute temperature.
If your EFC range is 1x10^-7 for 5V (pretty common):
Each 1 mv change is 2 x10^-11.
A 78L05 will hold 1 mv over 1C. Roughly 90% of them will hold that over 20C. That’s a cheap regulator for 2x10^-12.
A 10 ppm / C reference will get you to 1x10^-13 / C
You don’t *need* an EFC at 1x10^-7. Something 1/10 that size is probably good enough. Knocking it down to that level is just a couple of resistors. Way less money than fancy references.
> On Dec 11, 2014, at 7:13 AM, dan at irtelemetrics.com wrote:
> Yeah, I suffer from time-nuts digest lag, family lag, day job lag, among other things. So please excuse delayed responses...
> The oscillator has proven to be relatively immune to 'reasonable' changes in voltage, as would be expected. About the range of Numbers Bob Camp has suggested, or maybe even better. The EFC voltage is not an issue at this point. It was previously, and the solution to that was a low drift 'roll your own' design.
> It would be nice to replace it with a COTS part, but it looks like there aren't any available. Thus the reason for pinging the list. Sometimes you all pull things out of thin air... ;) That said, the LT3081 looks interesting. At the very least it's easily controllable from an external source. I've got a few on order, and if it pans out I'll report back here.
> What I'm after right now is in reality small. Temp cycles are somewhat apparent from looking at what the EFC voltage is doing locked with the GPSDO. It's on the order 10^-12 range, if I did my math right. It is visible, so it may be worth trying to fix. Of course, now that Bob has his new CS to play with anything I do is judged by a completely different standard! ;)
> Again, thanks for the responses!
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