); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY In a message dated 9/28/2007 17:28:15 Pacific Daylight Time, [EMAIL PROTECTED] writes:
>How stable is a typical well-designed DAC output over temperature and >whatever? Very stable. Our firmware analyzes this stability statistically, and adjusts for it. Can't get into too much details, suffice it to say that when the Fury is locking an external Rubidium prototype from Quartzlock there is very little thermal sensitivity of the combined unit when running on the lab bench with Airco going periodically etc. >What about a couple of extra op-amps? Different story. Never tried that, only one Opamp is needed to do this though. Linear Technology yesterday announced a new "super duper" CMOS opamp that would probably work quite well. Better to use an OCXO with 0V to 5V range, or mechanically tune it away from 0V to an offset of say 2.5V or so. Opamps will always introduce noise, drift, etc etc, so we do not typically use them. >Do any OCXO vendors offer the DAC inside the oven with a digital interface? >That seems like the obvious way to reduce temperature dependencies. Yes, but you have to include the DAC voltage reference as well. The drawback is that you need to run digital wires into the sensitive OCXO case. Second drawback: you have to run the chips at the Crystal temp, or near that; so that reduces the component lifetime. Third drawback: you need a big can for that. Fourth drawback: it's non-standard, so you don't get to pick-and-choose from a wide variety of OCXO manufacturers. Also, this requires the OCXO to have more than the usual number of (expensive) pins. Lastly: what format to support? I2C or SPI? According to Murphy you will always choose the wrong one... >From what I have seen on our Fury with Double Oven OCXO's and Rb's being locked, I think a well-tuned circuit is good enough to not require the DAC to migrate into the OCXO. Besides electronic compensation, there is also matching the tempco of the reference to cancel the tempco of the DAC etc etc to improve the circuits' performance. The Z3801A for example has low-pass filter Opamps, as well as DAC and reference etc outside of the OCXO case, and seems to work very well too even though it is an older design. Some manufacturers do integrate the DAC for special apps, we are under NDA so I cannot talk about it in more detail unfortunately. bye, Said ************************************** See what's new at http://www.aol.com _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
