Spice Crystal Model - 70MHz

Jim, seems to me it depends on just what you mean by "reasonably accurate." For a first pass, I'd use the standard one with a series inductance, capacitance and resistance and a shunt capacitance. You can measure the crystal parameters to get a good estimate of the values of Cs, Ls, Rs and Cp. Crystal manufacturers will commonly spec a typical and/or maximum Rs and a typical and/or minimum Q and a holder capacitance which is essentially the Cp. Rs and Q and frequency can easily be used to find Cs and Ls.

If you want to improve on that, you can add more parts to account for the inevitable minor parasitic resonances near the fundamental--I think the usual way is additional series LCRs in parallel with the main one. And you can add parts to account for the mechanical overtones at nominally 3x, 5x, ... the fundamental.

If you don't drive the crystal too hard, such a linear model should be OK, but real crystals, just like real resistors, capacitors and inductors, are not perfectly linear, and of course they also have a small temperature variation which depends on the cut angle.

Cheers, Tom

Hi Tom,

As usual I'm tasked with designing an on-chip oscillator with no data/model for the crystal :-(

I certainly can roll my own, but I'm trying to get a model as close to "real" as I can find.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Bad news. Motional parameters can be all over the place. It's a non-trivial task to, say, design a 5 MHz oscillator circuit that will work with *any* 5 MHz parallel-mode crystal. Series mode is maybe a little easier, but most crystals are designed for parallel.

John

Hello Jim,

Sorry, I don't. But high-end crystal manufacturers like these guys can usually provide the correct RLC values:

It's been a very long time but they have helped me out with SPICE data before.

OT: Checking for flights in and out of PHX. Why is it that Southwest has many nonstop flights from Sacramento to PHX in the morning but most late afternoon/evening return flights are lengthy stopover flights?

AWA is the other option but they impose a hefty change fee when the meeting goes longer than planned and I vaguely recall that you didn't like to fly with them for some reason.

Regards, Joerg

I have the advantage of being able to have components for AGC, so that'll help some.

I've just not done one at 70MHz fundamental before.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Thanks, Joerg! Looks like a good reference.

Don't know, I haven't flown Sacramento/PHX since Silicon Systems got bought out.

AWA is now merged with US Airways... how do you like that... America's Worst (delays) Airline merges with America's most financially unstable ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

If it's for a specific application can you contact the crystal manufacturer that the customer plans on using?

70MHz is way out there for a fundamental mode crystal, by the way -- I think if it were me I'd be making sure I knew how to make it work for a 3rd or even 5th overtone so when the customer calls you back in a panic you can save the day for them.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

It's one of the mesa-etch devices... used in a low distortion multiplier scheme, to get output at 280MHz.

Part of the problem is that I'm not working for the end customer, I'm working for a fab... so I'm anonymous :-(

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Hello Jim,

Didn't know that, I used to only fly long-haul. Southwest is pretty good. They are somehow always full to the brim but on time. They let you print your own boarding pass from the web so you can walk right to the gate and line up. Went to LAX last week with them. PHX will be a bit tight time-wise this time but if it leads to a longer term deal maybe we could have a Hefeweizen some day.

One domestic airline that I really like is JetBlue. IMHO they are the best. No food but everything else just clicks.

Regards, Joerg

Maybe the scheduling reflects that everyone is leaving Sacramento, but few are returning ;-)

That'd be great!

I've not flown them.

Anymore I avoid flying as much as possible. All the security delays really are a pain.

On March 4 we actually drove to Whittier instead of flying. Our schedule was tight... picked up "N" at Girl Scout camp at 7AM (MST) with a fully loaded car, arrived Whittier at 12 Noon (PST), checked into hotel (prearranged for early arrival), showered, dressed, and made the wedding at 3PM.

I doubt we'd have made it in time by air, considering parking at PHX, check-in, fly, arrive Ontario (John Wayne is WAY over-priced), get bags, rent car, drive :-(

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Hello Jim,

I'd still request the crystal data or mfg and P/N via the fab. Tim is right, anything past 40MHz on the fundamental is iffy. Maybe you could include some nifty circuitry that kind of forces it to run around 70MHz.

Regards, Joerg

Hello Jim,

ROFL! Seriously, before the voters kicked Gray Davis out of the governor's office neighbors moved out of state and the trucker said that his company had a problem. It was all the empty rides back.

I got used to it. Driving 8+ hours to places like L.A. is no fun. But last Thursday the security check line at LAX went all the way out into the street :-(

One of the things that I really miss from Europe is their fast train network. The lack of such transportation is a real damper for long-stretched states like California.

Regards, Joerg

I found "mesa etch" on altavista -- interesting. I agree with Joerg -- ask the fab to get you data. I suspect every manufacturer does their process differently, which is going to result in different crystal parameters. I think I'd even ask for the data, and the data from their second source candidate!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Hello Tim,

2nd sourcing a 70MHz fundamental crystal is going to be a real challenge. Almost like trying to copy the Stradivari violin.

Regards, Joerg

The end customer IS the crystal manufacturer.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Well, maybe asking for a 2nd source isn't politic then.

OTOH, they should be highly motivated to get the motational parameters right!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

You can get fundamental mode crystals out to 300MHz - to quote Douglas Dwyer from here back on Sat, Nov 4 2000 10:00 am - but it used to depend on using chemical etching or ion-beam milling to reduce the thickness of the crystal below the levels you can get by grinding.

Thin crystals used not to be cheap or easily available, but if someone is paying Jim Thompson to design an oscillator circuit, it may be that that someone has made a breakthrough - or found a reliable way to avoid making a break through the crystal ,,,

--
Bill Sloman, Nijmegen

Yes, and manufacturers talk about 200MHz fundamental mode crystals.

Har-de-har... I've read that overtone crystals have much higher Q than fundamental mode crystals at high frequencies, so why would it be so important to make a fundamental rather than overtone type at 80MHz, er, excuse me 70MHz? (I have 80MHz on my brain right now.)

--
 Thanks,
    - Win

Fundamental mode provides superior phase and jitter noise performance. Vectron is now boasting high frequency fundamental mode crystals with less than 150 fs (femto sec) jitter.