J
Jim Thompson
- Jan 1, 1970
- 0
Anyone have a reasonably accurate spice model for a 70MHz crystal?
(FUNDAMENTAL)
...Jim Thompson
(FUNDAMENTAL)
...Jim Thompson
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
Anyone have a reasonably accurate spice model for a 70MHz crystal?
(FUNDAMENTAL)
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:
http://www.kvg-gmbh.de/pdf/Crystals/Introduction.PDF
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
Jim said:Anyone have a reasonably accurate spice model for a 70MHz crystal?
(FUNDAMENTAL)
...Jim Thompson
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.
AWA is now merged with US Airways... how do you like that... America's
Worst (delays) Airline merges with America's most financially unstable
;-)
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
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 :-(
Maybe the scheduling reflects that everyone is leaving Sacramento, but
few are returning ;-)
Anymore I avoid flying as much as possible. All the security delays
really are a pain.
Jim said: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
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!
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
Jim said:The end customer IS the crystal manufacturer.
...Jim Thompson
Tim said: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.
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 ,,,
Winfield said:[email protected] wrote...
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.)