Jim said:Anyone have a reasonably accurate spice model for a 70MHz crystal?
(FUNDAMENTAL)
...Jim Thompson
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.
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 ,,,
Mesa etching.
John
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 ,,,
Keerect !-)
The fab has now agreed to get a crystal model from the manufacturer.
As is usual with most of my projects, I come on-board when the shit
has already hit the fan... the original design team has floundered ;-)
So the fab has to keep "tight cheeks" while they request data they
should have gotten long ago ;-)
...Jim Thompson
Only got to fly JetBlue once, from Long Beach to Boston. Got stuck inJoerg said: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
On Fri, 31 Mar 2006 09:08:57 -0700, Jim Thompson
[snip]As is usual with most of my projects, I come on-board when the shit
has already hit the fan... the original design team has floundered ;-)
So the fab has to keep "tight cheeks" while they request data they
should have gotten long ago ;-)
...Jim Thompson
Sounds like great fun. I love to swagger in, in a modest sort of way,
after somebody else has flubbed it. Especially if the somebody else is
their in-house crew. You get to say out loud, in a
kindergarten-teacher voice, the things they were afraid to mumble. The
real trick is to wind up friends with the guys you're trashing.
No time left and big-budget consequences are icing on the cake.
John
The end customer IS the crystal manufacturer.
Hello Jim,
Then they should be the experts on this and be able to furnish all the
model parameters. After all, they probably want the best oscillator in
town and that first silicon is a success.
Regards, Joerg
Jim said:"First silicon" WASN'T a success. That's why I've been brought in...
fix the screw-ups ;-)
...Jim Thompson
"First silicon" WASN'T a success. That's why I've been brought in...
fix the screw-ups ;-)
"Welcome to the project -- you're late and over budget"?
Not necessarily. There have been 70 MHz fundamental tourmaline crystals forJoerg said: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
Yep, I love it!
"The real trick is to wind up friends with the guys you're trashing."
So true.
Hello Jim,
In Asia that is even more touchy. You see a messed up design, something
that would never have worked and never did. Then you have to do the
dance of extreme politeness. "Well, there are some wonderful ideas in
this great design. Here is how we can add to those ideas to achieve an
improvement". Meaning in reality most of it had to be scrapped and
started from a blank sheet.
Regards, Joerg
Jim Thompson said:I certainly can roll my own, but I'm trying to get a model as close to
"real" as I can find.
Tom said:Fred, do folk ever tell you that you have a rather strange sense of
humor? I didn't get it the first time I read it, but now I do. ;-)
Thanks.
Cheers,
Tom
Fred said:Okay- well that might have been a stretch, but JT does need to watch for
the traps, like exciting various crystal vibration modes close to the
4th harmonic but not the 4th harmonic, or some tendency to chaotically
switch into a different mode. The previous people cannot be complete
incompetents and these kinds of issues are widely none thanks to authors KNOWN
like Parzen, so there must be something up with this particular crystal
cut that makes a reliable design particularly challenging. If he doesn't
get into the crystal physics on this one, his product will be no more
than a hunch.