Hi, When comparing with AT-cut, we all know that the SC-cut crystal gives better warmup without overshoot, better 2nd order temperature performance, fewer dips, lower acceleration sensitivity and better short-term stability. However, nothing's been said in any of the literature I've seen whether this depends on running the crystal at/near a turnover point, or whether these advantages APPLY AT ALL TEMPERATURES. I am particularly interested in post-correction by electronic means in low power applications, rather than temperature compensation (TCXO), as an uncompensated oscillator tends to have lower phase noise and is cheaper to make. In some applications (such as the one of interest here), absolute oscillator frequency is unimportant, but knowing all about its environmental behaviour is important. The biggest problem with using a polynomial temperature fit approach is that with an AT-cut crystal, it is very difficult to mathematically correct for the second order temperature effects. Would using an SC-cut crystal in this type of application provide a measure of freedom from second order temperature and acceleration effects over a wide (-40°C to +85°C) temperature range, or does it only apply at or near turnover? Regards, Murray Greenman

A lot of work has been done in this area under the designator "Microprocessor Controlled Crystal Oscillator" MCXO, which is probably not a really great name. Anyway, they are non ovenized and use SC cuts. I believe the original FCS paper on them was around 1990. Regarding turnover specifically: many 10811 crystals do not have turnovers. Instead they have a broad range of very low (but not zero) tempco. There is nothing magic about being at a turnover other than zero tempco. Rick Karlquist N6RK Murray Greenman wrote: > ); SAEximRunCond expanded to false > Errors-To: time-nuts-bounces+richard > Hi, > > When comparing with AT-cut, we all know that the SC-cut crystal gives > better warmup without overshoot, better 2nd order temperature performance, > fewer dips, lower acceleration sensitivity and better short-term > stability. However, nothing's been said in any of the literature I've seen > whether this depends on running the crystal at/near a turnover point, or > whether these advantages APPLY AT ALL TEMPERATURES. > > I am particularly interested in post-correction by electronic means in low > power applications, rather than temperature compensation (TCXO), as an > uncompensated oscillator tends to have lower phase noise and is cheaper to > make. In some applications (such as the one of interest here), absolute > oscillator frequency is unimportant, but knowing all about its > environmental behaviour is important. The biggest problem with using a > polynomial temperature fit approach is that with an AT-cut crystal, it is > very difficult to mathematically correct for the second order temperature > effects. > > Would using an SC-cut crystal in this type of application provide a > measure of freedom from second order temperature and acceleration effects > over a wide (-40°C to +85°C) temperature range, or does it only apply at > or near turnover? > > Regards, > Murray Greenman > > _______________________________________________ > 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. > >

From: "Rick Karlquist" <richard@karlquist.com> Subject: Re: [time-nuts] Dumb question about SC-cut crystals Date: Mon, 22 Oct 2007 14:32:51 -0700 (PDT) Message-ID: <10280.192.25.142.225.1193088771.squirrel@webmail.sonic.net> > ); SAEximRunCond expanded to false > Errors-To: time-nuts-bounces+magnus=rubidium.dyndns.org@febo.com RETRY > > A lot of work has been done in this area under the > designator "Microprocessor Controlled Crystal Oscillator" > MCXO, which is probably not a really great name. > Anyway, they are non ovenized and use SC cuts. I believe > the original FCS paper on them was around 1990. I found the use of the different tempco dependence of the 1st and 3rd modes an interesting way of measuring the temperature-dependent shift. By having a dual-mode oscillator setup and then mix the 1st mode frequency with the divided down version of the 3rd and then measure the beat-frequency. This can then be used in various ways such as resynthesis etc. It's in a long presentation of Vig. He shows a number variants of this scheme. I am not yeat convinced it is the best of methods, but for smaller volume oscillators it is certainly an interesting approach. Cheers, Magnus