[time-nuts] Mems oscillators

Bob Camp lists at rtty.us
Sat Feb 23 17:47:10 UTC 2013


Hi

MEMS has the advantage of starting at a very high frequency. That lets you divide down and get pretty good broadband phase noise. That translates into good jitter performance over the normal telecom 12 KHz and up type of jitter masks. If you plan on putting in a very high shock / vibration environment (think 155mm projectiles) it will survive better than a chunk of quartz. 

Quartz has a higher resonator Q than MEMS and is rarely (if ever) seen in multiple resonator oscillator configurations. MEMS commonly shows up in multi resonator configurations. The lower Q means you will have worse close in phase noise on the MEMS. The multi-resonator stuff means the phase noise will get a bit nutty looking once you are inside the cluster of resonators (multiple peaks in the noise close to carrier). 

If your jitter requirement drives you to a mask with a low end limit below 100 Hz, the MEMS won't look very good for jitter compared to an XO. As you go lower still, an OCXO will look much better than either the XO or the MEMS.

Aging wise, XO's are not something that people get real excited about aging on. If your $1 oscillator that is spec'd to 0.01% drifts 0.001% vs 0.0001% people rarely care. Not a lot of attention gets paid to that end of things. The same thing applies to MEMS. They are plenty good enough for the intended use.

If you start looking at OCXO type aging, then no. MEMS is not going to do the same sort of <1.0x10^-10 per day / <1.0x10^-9 per month stuff that a modern chunk of quartz will do. 

Bob

On Feb 23, 2013, at 12:07 PM, Darren Grist <darren.grist at gmail.com> wrote:

> Has anyone done any comparision between MEMS and quartz oscillators ?
> Is the long term stabilty (aging) of MEMS better than quartz ?
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