# oscillator voltage

I've used mostly crystals with caps. Now thinking about using this oscillator and got to wondering how to calculate how much voltage it takes to drive it? Is there a maximum and/or minimum? Just never thought much about voltage relating to crystals.

Thanks/

Well, that's just screwy... No voltage on the datasheet! And, it's a datasheet from a reputable manufacturer! They also don't show a table of available frequencies... If you look at a [u]Fox datasheet[/u] you'll see a voltage.

I'd just buy from a different manufacturer.

Just never thought much about voltage relating to crystals

Bare crystals don't have any active electronics so like most passive components they'd only have a maximum voltage. ...I've never thought about crystals either. I assume they can handle fairly high voltages, but the 1st datasheet I found didn't have a voltage spec.

I'm thinking that FOX device you linked to is a Si-MEMS type with circuitry inside (seeing the E/D pad) that would be voltage specific, whereas the one I gave uses crystal strictly in fundamental mode - the kind of thing I usually do, but as with you, never really thought of voltage limits. Just always assumed that since everything I usually do is 1.8-5v, most were just fine within that range.

You can figure out the dissipation from the Q, but there isn't a power dissipation spec either.

You can assume such crystals are designed for logic levels at most.

Level of drive
200 μW Max.
Recommended: 1 to 100 μW

The OPs datasheet just shows a bare cystal, not an oscillator.

Hence the voltage is irrelevant.

Allan

I likely got this conversation off to a poor start by use of the "oscillator" word kinda defining what I was referencing as just a crystal in a can (which I already knew) as pointed out by allenhurst, when my real question was how much voltage a crystal (that particular one) can take within an oscillation circuit, which was shown on the datasheet as pointed out by aarg. So using that information I'm guessing at 5 volts, and considering the crystal's resistance of 60 ohm max at 16MHz, I'd need a total "minimum" resistance in a circuit of the type below of 125k passing a maximum of 40μA? Which could of course then just be applied to whatever voltage I was going to use. Seems to kinda all be "coming into focus" now.

These crystals are not designed for a general high voltage oscillator circuit, they are designed
for logic circuitry which is mainly 3.3V and below these days.

It may work in a 12V circuit, it may not, the manufacturer isn't going to worry about that. In general
a larger package would imply greater power handling, but it all depends on the details of what's inside.

You could try asking the manufacturer directly what the limits are, or you could try using it and
seeing if it works (which doesn't guarantee a long life or that other similar crystals will be happy).

My suspicion is that the materials used are robust, it can probably take it, but you might find
the frequency gets pulled a bit by overdriving it, and long-term drift may be greater than specified.

Okay MarkT - thanks. Makes sense. So likely 3.3v and below common, with 5 volts max, since that too is common logic so it seems the datasheet would say otherwise if not acceptable. After I wrote what I wrote last, I got to thinking that if the resistance was increased significantly to satisfy much higher voltage while still falling within the power handling parameters, that in itself would likely greatly impact oscillation efficiency.

BTW, what are you trying to do?

Good question MarkT, but not trying to do anything. Just got curious about min/max voltages that can be applied to a specific crystal without messing up it's efficiency.

Efficency?

Not sure what that means in this context.

A typical crystal in this region - 4- 40 MHz can be modelled as a largish inductor (5mH?) in series with a very small capacitor and resistance as specified.

Mess about in PSPICE, LTSPICE etc and see what currents and hence powers are involved at various voltage p-p involved.

Allan

Would help a bit to know what kind of purpose the crystal is for.
Most applications using crystals for microprocessors use a pierce oscillator which requires the crystal to operate in parallel resonant mode, so the crystal appears as a very high Q parallel resonant circuit.
Power dissipation in the crystal is tiny.

Maybe you can browse through this...

allanhurst:
Efficency?

Not sure what that means in this context.
Allan

Thanks Allan! Perhaps I used the wrong word, or maybe I'm thinking something that doesn't even happen. Seeing in the datasheet "200μW Max", I was wondering what happens if it's pushed above that a little or below that a lot. Does the crystal not perform as well, become less "efficient" as far as resonating well, or what?

Didn't think about modeling this in spice, but that's a good idea.

Hi mauried.

Responding to posts is a very slow process here, as I keep getting a notification that I have to wait 5 minutes to post again. In the meantime, someone else posts, or I walk away to do something and forget that I never replied.

mauried:
Would help a bit to know what kind of purpose the crystal is for.
Most applications using crystals for microprocessors use a pierce oscillator which requires the crystal to operate in parallel resonant mode, so the crystal appears as a very high Q parallel resonant circuit.
Power dissipation in the crystal is tiny.

The crystal is just being used for an atmega328.

Thanks southpark, I'll have a look at it.

"I keep getting a notification that I have to wait 5 minutes to post again"
That goes away after 100 posts.

Good crystal for '328Ps:
http://www.dipmicro.com/store/XC7-16000
Don't forget 22pF caps.
http://www.dipmicro.com/store/C1K22-50

Quartz crystals will fracture if the voltage is too high. In vacuum tube circuits back in the 1930-1940, etc. They were used with 300-400 volts, but were an inch square and perhaps 1/16 inch thick.

The crystals you buy today are tiny both in area and thickness. Open a can and take a look.

Paul

I should also add the crystals can vibrate in different modes. Look it up!

Too much power risks breaking the piece of quartz or de-bonding the contacts.- it is, after all, vibrating.

I'd stick to the specs.

If you're using it on a '328 , I woudn't worry. The power involved is very tiny.

Allan