); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi all,
being more than 30 years in the Frequency Control business, I want to comment on what Hal Murray wrote: > My first guess is that it's a backwards compatibility mess. Ages ago > somebody made a part with a single ground pin and somebody used it in some > telco gear and everybody has been using the same footprint ever since. If > that's the case, I'd expect there would also be a variation with a second > ground pin to get better performance. Look for example to the very popular "Eurocase" package CO 08, as used in the MTI 260 (and many OCXO from other manufaturers - like the AXIOM40 & 45 series of AXTAL). This package originated from a TCXO package, and was first used to make OCXO (as TCXO replacements) in the early seventies. The connection scheme for the 5 pins was given and included only one ground pin. Next generation in OCXO miniaturization (in Europe) was the 20x20 mm package CO15 (as AXIOM30 & 35), which has the similar legacy, i.e. the 5 pins were defined for TCXO, i.e. with one ground pin, and later (in the late 80's) used for OCXO. The next smaller THD OCXO was in the 4-pin DIL14 package (AXIOM20 & 25), and it's clear that the 4 pins do not allow 2 GND pins. Any additional pin means more cost - and as such special versions would run in much smaller quantities - the cost are even higher. And - the accuracy and stability requirements for those small OCXO was (and is) less stringent in most applications such as for telecomms. The cost situation changes, when it comes to SMD packages (like the 22x25 mm package CO 28 - AXIOM10). For those packages you can indeed find a few specs on the market, which have two separate ground terminals for oscillator and heater circuit. Such specs are written by people who know about the effects of ground loops. However I do not know any "modern" catalog or standard parts on the market with two ground terminals. In fact the impact on stability is mostly neglectable under stationary operation conditions with rather constant environmental temperature. For applications where temperature changes are an issue _and_ highest stability is required, there is no other way than having two separate grounds. > Are they running temperature tests with the EFC pin open so they don't see > any problem as the heater current changes? (or something like that) Indeed, many (if not most) OCXO manufacturers run OCXO temp tests (and aging tests with the EFC pin grounded. The undesired ground loop effect can be reduced if the connection is made very close to the pin, and if the inside connection to the PCB ground has low impedance. Regards Bernd DK1AG __________________ AXTAL GmbH & Co. KG Facility MOS Wasemweg 5 D-74821 Mosbach / Germany fon: +49 (6261) 939834 fax: +49 (6261) 939836 www.axtal.com _______________________________________________ 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.