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Low jitter oscillators - special frequencies

H

Hal Murray

Jan 1, 1970
0
Most special order crystal oscillator packages now have a
PLL in them. When you order a special frequency, they take
an unprogrammed unit off the shelf and program in the PLL
parameters. Delivery in a few days.

The problem is that you get the jitter specs of the PLL rather than
the crystal. The jitter turns out to be important for high speed A/D
applications. It's probably important in most RF work too.

Anybody know a good place to get real crystal oscillators made to order
in small volumes? I need 10 or 20 but the first try came up with
a min order of 250. I'm expecting 10-12 week delivery. I can live
with that.

Many crystal/oscillator companies used to be in the business
of making small runs to a specified frequency. How many are
left?


Anybody familiar with the details of the PLL setup? I assume
somebody did the math and figured out what frequencies they
have to stock in order to cover all the target frequencies they
might want to produce. How many different frequencies do they
have to stock? What sort of ratios are they using in the PLL?

When did everybody switch to PLLs?
 
M

mc

Jan 1, 1970
0
Can you make your own crystal oscillators? Custom-made individual crystals
are abundant, of course, and always will be, as long as there's such a thing
as ham radio.

What does International Crystal (in Oklahoma City) offer these days?
 
M

Michael Black

Jan 1, 1970
0
Hal said:
Most special order crystal oscillator packages now have a
PLL in them. When you order a special frequency, they take
an unprogrammed unit off the shelf and program in the PLL
parameters. Delivery in a few days.

The problem is that you get the jitter specs of the PLL rather than
the crystal. The jitter turns out to be important for high speed A/D
applications. It's probably important in most RF work too.

Anybody know a good place to get real crystal oscillators made to order
in small volumes? I need 10 or 20 but the first try came up with
a min order of 250. I'm expecting 10-12 week delivery. I can live
with that.

Many crystal/oscillator companies used to be in the business
of making small runs to a specified frequency. How many are
left?
You're complicating matters by insisting on an actual oscillator.
An oscillator is really simple, so there's not a lot of advantage to
buying an oscillator module, certainly not if they are giving you problems.

You aren't likely to get custom frequency oscillator modules, because
they will be too costly to manufacture unless you are buying large quantities.
The modules you've seen are a tradeoff, allowing a wide range of frequencies
without the manufacturing cost. But they have to use a synthesizer, because
otherwise they are dealing with crystal grinding, and that's where the cost
lies.

Just order crystals. Newcomers don't realize that up till thirty or
so years ago, except for a handful of frequencies, crystals were not a
commodity. They were ground on demand, and of course you paid for them.
The only mass-produced crystals were for frequencies that were used
a lot.

That hasn't really changed, the crystals you see in the catalogs are
mass produced because they are commonly used frequencies. But those
common frequencies are more numerous now, since digital devices caused
a rise in the use of crystals in electronic equipment.

So if the frequency you want isn't a common frequency, you send the specs
to a crystal manufacturer, and they grind a crystal for you.

Michael
 
M

mc

Jan 1, 1970
0
Just order crystals. Newcomers don't realize that up till thirty or
so years ago, except for a handful of frequencies, crystals were not a
commodity. They were ground on demand, and of course you paid for them.
The only mass-produced crystals were for frequencies that were used
a lot.

I agree. I remember when 3.58 MHz was the only commodity crystal...
So if the frequency you want isn't a common frequency, you send the specs
to a crystal manufacturer, and they grind a crystal for you.

And this costs only a few dollars.
 
M

Marko

Jan 1, 1970
0
Depending upon the frequency you need, try Pletronics. Part of the
problem is that they aren't interested in selling a few dozen or even
a few hundred. They will provide samples at no cost if you can
convince them there is some possibility of larger volume. This is
assuming you are dealing with a reasonable frequency for them.

Also, if it is possible to taylor your design to some common
frequency, you should have more options. Check Digikey for some
common frequencies.

What frequency are you looking for and what are your jitter specs?

Marko
 
D

dd

Jan 1, 1970
0
Hal Murray said:
Most special order crystal oscillator packages now have a
PLL in them. When you order a special frequency, they take
an unprogrammed unit off the shelf and program in the PLL
parameters. Delivery in a few days.

The problem is that you get the jitter specs of the PLL rather than
the crystal. The jitter turns out to be important for high speed A/D
applications. It's probably important in most RF work too.

Anybody know a good place to get real crystal oscillators made to order
in small volumes? I need 10 or 20 but the first try came up with
a min order of 250. I'm expecting 10-12 week delivery. I can live
with that.

Many crystal/oscillator companies used to be in the business
of making small runs to a specified frequency. How many are
left?


Anybody familiar with the details of the PLL setup? I assume
somebody did the math and figured out what frequencies they
have to stock in order to cover all the target frequencies they
might want to produce. How many different frequencies do they
have to stock? What sort of ratios are they using in the PLL?

When did everybody switch to PLLs?
There is approx 10:1 price variation between crystals from Tiwan etc and
locally made in yhe US or UK.I was an XO designer for 25 years but all
by designd went to the Far East for volume manufacture.
Vectron and Fox make locally in the US but at a price.
I note that PLL is not the only means for flexibility there is also the
direct systhisis route which will provide better close in jitter but far
out sidebands.
Note also that the low cost crystals employ low Q quartz (generally)
which will influence close in noise.
 
F

Frank Moe

Jan 1, 1970
0
I think it will be difficult to find a manufacturer for only 10 crystals.
Maybe Quarz Technik (www.quarz-technik.de) still makes single custom crystals.
KVG (www.kvg-gmbh.com) also used to accept small quantity orders.
Do you need 10 forever or 10 for first series and 100 later?
Of cause you can have a single one but what would you want to pay?
What frequency are you looking for? Maybe it is not as uncustom as you think...
Frank
 
M

Marc H.Popek

Jan 1, 1970
0
Hal,

Can can make you real xtal oscillator on any (reasonable) frequency you
choose) and free running oscillator for the unreasonable choices :)

Marco
 
H

Hal Murray

Jan 1, 1970
0
[from my message of a month ago - looking for non PLL oscialltors]
Anybody know a good place to get real crystal oscillators made to order
in small volumes? I need 10 or 20 but the first try came up with
a min order of 250. I'm expecting 10-12 week delivery. I can live
with that.

Thanks for all the comments and suggestions to roll my own...

I was looking for a half-size can because I wanted to change
frequencies on an existing design with a socket.


If companies make to-order crystals, why don't they also make
to-order oscillators? (maybe with slightly longer lead times)
All they have to do is make the crystal and drop it into an
osc package rather than a crystal package.



I got an email suggestion to:
Try Cal Crystal / Comclox (www.calcrystal.com).
They had what I needed in stock. Thanks.
 
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