G3RUH used an LT1006 with good results for the IsoTemp OCXO. http://www.jrmiller.demon.co.uk/projects/ministd/dcamp.gif
cheers, ian > Date: Thu, 14 Jan 2010 06:57:39 -0500 > From: John Foege <john.fo...@gmail.com> > Subject: [time-nuts] GPSDO Design > To: time-nuts@febo.com > Message-ID: > <888d55281001140357s6021cfa9i4227741eedb2f...@mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > Hi All, > > Quick question for the more experienced members here with GPSDO > design/operation. Let's assume I'm using a 4096 phase comparator chip > followed by some kind of long time constant lowpass loop filter, > whether it be analog or digital, is not of concern for the following > question. > > Obviously using a 74HCT4096 would mean that my EFC voltage range would > be approx. 0-5V. If I wanted to use an OCXO with say a 0-8V EFC > voltage range, then I would be inclined to simply use an op-amp > amplifier with a gain of 1.6 to scale the EFC voltage accordingly. > > But not just any op-amp would do I take it? High-speed would of course > be of no concern. Also low-offset would be of little concern, as the > PLL would work to correct this, and it therefore seems to be > negligible. However, the part that's got me thinking is noise. > Obviously any noise at the ouput of the amp would adversely affect the > frequency stability of the OCXO. > > I thought the best way to control this would be to use an extremely > low noise op-amp employing a rather large compensation cap to give me > a rather small bandwidth, perhaps only a few hundred hertz. > > Anyone have experience with this? Assuming I have an OXCO with a max. > pulling range of 1ppm or 1e-6 over a 10V range, then I effectively can > pull 1e-7 per volt. This translates to 1e-10 per millivolt and 1e-13 > per microvolt. Assuming that is a logical conclusion, then for a good > OCXO, in which I can at best hope for 5e-12 stability for tau=1s (e.g. > HP10811A), I would strive to to keep the noise at such a level that it > is an order of magnitude better than the best short term stability > figure. Accordingly, then I should shoot to keep any noise under 1 > microvolt? > > I don't have much experience with noise calculations. I know it is > specified in nV/sqrt(Hz) generally. Translating this to something > practical is basically the assistance I'm looking for here. > > I would appreciate anyone being able to teach me a bit more about this. > > Thank you in all in advance. > > Sincerely, > > John Foege _________________________________________________________________ Search for properties that match your lifestyle! Start searching NOW! http://clk.atdmt.com/NMN/go/157631292/direct/01/ _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.