For other common crystal frequencies, let's not forget 3.579545 MHz and 4x that - NTSC TV color burst
and others listed here... https://en.wikipedia.org/wiki/Crystal_oscillator_frequencies On Tue, Mar 14, 2017 at 3:39 PM, Attila Kinali <att...@kinali.ch> wrote: > On Tue, 14 Mar 2017 13:39:02 +0100 > Magnus Danielson <mag...@rubidium.dyndns.org> wrote: > > > Some claims that MEMS will kill crystals. It will surely eat a good > > market share, but I think there is applications where MEMS is not mature > > enough compared to crystals. > > MEMS is quite mature, it's just that it is playing a different game. > While with quartz (and other piezoelectric crystals) we know how > to design a crystal to frequency, things aren't so simple for MEMS. > Simply scaling the design doesn't work apparently. > > What they instead do is to use the MEMS oscillator as a reference > for a PLL locked VCO. As the whole thing is going to be a few mm^2 > of silicon anyways, reserving some µm^2 for the PLL and VCO don't > cost much. And it gives the ability to "tune" the oscillator > for the frequency needed after production (the same technique is used > with "programmable" crystal oscillators). Of course, having a PLL, > mostly a fractional-N PLL, causes a lot of spurs in the output, > which can cause problems, depending on the application. > > The big promise of MEMS oscillators was, that they'd be cheaper (due to > integration in silicon) and used less power. As far as I am aware, > neither promise could be upheld. MEMS need a quite different production > process than normal digital electronics, hence it's usually more economic > to have the oscillator on a different die than the digital chip. As for > power consumption, the low power MEMS are about at the same level as the > low power 32kHz crystal oscillators (and also in the same frequency). > One place where MEMS are exceedingly good is temperature characteristics. > Silabs demonstrated an oscillator, which, prior to any compensation, > exhibited only <5ppm shift over the full temperature range. > > > As for the demise of single quartz crystal units, I think that is not > going to happen any soon. It is rather that the economics shift. Most > of the single crystals are used as reference oscillators for digital > and analog/RF chips. Ie most these chips have an internal oscillator > that uses an external crystal to drive their internall VCO+PLL. > As the crystal frequency is dictated by the frequencies these chips > have to generate, there is a kind of standardization going on due to > the limited number of protocols that need special frequencies. Two very > common frequencies are 12MHz, for USB, and 25MHz, for Ethernet. > 16MHz is base for CAN, some Wifi chipsets and USB as well. Then there > are a couple of frequencies that are related to GSM, UMTS and the various > other telephone standards. There are maybe a handfull of these frequencies, > which "everyone" needs (ie are used in many high volume products). These > are > the crystals we will be able around for the forseeable future. There are > other frequencies that are less used, which you will still get, but need > to pay more or are made to order. Frequencies for protocols that are > not used much anymore, or can be easily generated from another frequency > that is more common, are bound to die out (as has happend with all those > UART crystals, which are only used in legacy systems or for historical > reasons). > > > For specialized applications, where the crystal is not directly interfaced > to a chip that provides the oscillator, it is more convenient for the > designer to just use a complete oscillator than to design his own > oscillator > with all the problems that it involves. Getting such a device reliable to > work in production volumes is nothing an average engineer without prior > experience in can just pull off. Heck, I design my stuff to use oscialltors > instead of crystals, because that's one thing less I have to care about. > But even with these oscillators, there is only a limited number of > frequencies > that are easy to get. Those are again the standard frequencies from above, > and a couple of round numbers (like multiples of 10MHz) > > > Attila Kinali > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > _______________________________________________ > 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. > -- --Jim Harman _______________________________________________ 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.