19.500 Mhz Oscillator/Crystal (or 39.000 Mhz)

[Derek Simmons]

I'm looking for either an oscillator or crystal for an oscillator with
a clock frequency of 19.5 Mhz either a 3.3 or 5 volt, 50%, in either a
8 or 14 pin package or leads for the crystal. I took a quick look at
Digi-Key and Mouser websites and I didn't find anything that came with
those exact specifications. It turns out that 19.5 Mhz isn't a common
frequency.

Most of the projects I've worked on in the past use a frequencies of
readily available parts. I've also checked for 39.0 since I could
easily divide it down but still not a common value.

What I did find were programmable oscillators. Are they an
electrically erasable or fuse like devices? Some of the specifications
led me to believe over a period of time the frequency could change, is
this true?

I'm looking for something that is expected to work in a device upto 10
ten years.

I'm looking for suggestions or any advice...

Thanks in advance,
Derek

 

[Hal Murray]

What I did find were programmable oscillators. Are they an
electrically erasable or fuse like devices? Some of the specifications
led me to believe over a period of time the frequency could change, is
this true?

The ones I'm familiar with are programmed at the factory or
distributor. After that, you are supposed to think of them
as normal parts.

There is one catch. They have a PLL inside so there will be
more junk on the spectrum than a crystal cut for the exact
frequency that you want. In the digital world, that would
be a bit of jitter. It's probably not enough to worry about
unless you are using it for something like an A/D where
jitter turns into error.

--
These are my opinions, not necessarily my employer's. I hate spam.

 

[Michael Black]

On Fri, 21 May 2010, Derek Simmons wrote:

I'm looking for either an oscillator or crystal for an oscillator with
a clock frequency of 19.5 Mhz either a 3.3 or 5 volt, 50%, in either a
8 or 14 pin package or leads for the crystal. I took a quick look at
Digi-Key and Mouser websites and I didn't find anything that came with
those exact specifications. It turns out that 19.5 Mhz isn't a common
frequency.

Most of the projects I've worked on in the past use a frequencies of
readily available parts. I've also checked for 39.0 since I could
easily divide it down but still not a common value.

What I did find were programmable oscillators. Are they an
electrically erasable or fuse like devices? Some of the specifications
led me to believe over a period of time the frequency could change, is
this true?

I'm looking for something that is expected to work in a device upto 10
ten years.

I'm looking for suggestions or any advice...

You go to a crystal manufacturer, and have them grind a crystal to your

frequency and specs (ie they will grind it to fit the oscillator you
are using).

It's only fairly recently that crystals have become commodity items.
Initially, all crystals were custom ground, with the rare exception
being something like 100KHz crystals for frequency calibrators.

When WWII ended, that changed things a bit, since so many crystals
were manufacturered for the war that for decades there were lots of
crystals already ground, useful so long as you could live with
what was available, or find one close enough to frequency that you
could grind it yourself (the cases back then were phenolic and were
screwed together, making it very easy to open the case and get the
quartz blanks out to do some mild grinding). So at least for
hobby purposes, a lot of things were built around those available
crystals, you'd find the cheap crystal first and if it wasn't quite
where you needed it, you'd change the design to fit it.

Color TV came along, and that meant color subcarrier crystals were
manufactured in large quantities, useful if you could figure out
something else to use them for. CB came along, and that caused
a lot of crystals to be manufactured before demand, so you could
drop by your local store and get a pair of crystals for another
channel off the rack.

Then digital ICs came along. That did two things. First, it was often
simpler to use crystals for clocking than an RC circuit, besides the
obvious of frequency stability. If you can get crystals cheap, they
can be cheaper than the multiple components of an RC oscillator, and
of course it means fewer parts on board. Second, once you had a digital
IC of fairly good integration, the frequency of the crystal often
didn't matter, you could divide down or whatever to get it.

So that brought a number of popular frequencies to the catalogs, really
odd looking frequencies until you started dividing them down and saw
what lower freuquencies they'd generate. So a new set of commodity
crystals came to the catalogs, those that popular ICs were designed
around.

A lot more digital equipment came along, and it just became so
common that the commodity crystals kept coming. Add more crystals
to the catalog to generate baud rates, add more crystals for popular
tone dialer ICs, and so on.

Anyone who came to electronics in recent years or decades might
believe that you just ordered what crystals were in the catalog,
the number that can be ordered off the shelf has greatly increased.
But then they wonder how they are supposed to get a frequency
that isn't in the catalog.

Nothing really has changed, except there are more frequencies
common enough to warrant making crystals for that frequency
as a commodity part. You still have to get a crystal ground
to frequency and specs if you can't get it out of the catalog.

Michael

 

[Tilmann Reh]

Michael Black schrieb:

Nothing really has changed, except there are more frequencies
common enough to warrant making crystals for that frequency
as a commodity part. You still have to get a crystal ground
to frequency and specs if you can't get it out of the catalog.

But if you need only very small quantities (or just samples), it's quite
comfortable (and cheaper) to use those programmed oscillators.

Tilmann

 

[Derek Simmons]

On May 22, 6:52 am, Michael Black <et...@ncf.ca> wrote:

On Fri, 21 May 2010, Derek Simmons wrote:
I'm looking for either an oscillator or crystal for an oscillator with
a clock frequency of 19.5 Mhz either a 3.3 or 5 volt, 50%, in either a
8 or 14 pin package or leads for the crystal. I took a quick look at
Digi-Key and Mouser websites and I didn't find anything that came with
those exact specifications. It turns out that 19.5 Mhz isn't a common
frequency.

Most of the projects I've worked on in the past use a frequencies of
readily available parts. I've also checked for 39.0 since I could
easily divide it down but still not a common value.

What I did find were programmable oscillators. Are they an
electrically erasable or fuse like devices? Some of the specifications
led me to believe over a period of time the frequency could change, is
this true?

I'm looking for something that is expected to work in a device upto 10
ten years.

I'm looking for suggestions or any advice...

You go to a crystal manufacturer, and have them grind a crystal to your
frequency and specs (ie they will grind it to fit the oscillator you
are using).

It's only fairly recently that crystals have become commodity items.
Initially, all crystals were custom ground, with the rare exception
being something like 100KHz crystals for frequency calibrators.

When WWII ended, that changed things a bit, since so many crystals
were manufacturered for the war that for decades there were lots of
crystals already ground, useful so long as you could live with
what was available, or find one close enough to frequency that you
could grind it yourself (the cases back then were phenolic and were
screwed together, making it very easy to open the case and get the
quartz blanks out to do some mild grinding).  So at least for
hobby purposes, a lot of things were built around those available
crystals, you'd find the cheap crystal first and if it wasn't quite
where you needed it, you'd change the design to fit it.

Color TV came along, and that meant color subcarrier crystals were
manufactured in large quantities, useful if you could figure out
something else to use them for.  CB came along, and that caused
a lot of crystals to be manufactured before demand, so you could
drop by your local store and get a pair of crystals for another
channel off the rack.

Then digital ICs came along.  That did two things.  First, it was often
simpler to use crystals for clocking than an RC circuit, besides the
obvious of frequency stability.  If you can get crystals cheap, they
can be cheaper than the multiple components of an RC oscillator, and
of course it means fewer parts on board.  Second, once you had a digital
IC of fairly good integration, the frequency of the crystal often
didn't matter, you could divide down or whatever to get it.

So that brought a number of popular frequencies to the catalogs, really
odd looking frequencies until you started dividing them down and saw
what lower freuquencies they'd generate.  So a new set of commodity
crystals came to the catalogs, those that popular ICs were designed
around.

A lot more digital equipment came along, and it just became so
common that the commodity crystals kept coming.  Add more crystals
to the catalog to generate baud rates, add more crystals for popular
tone dialer ICs, and so on.

Anyone who came to electronics in recent years or decades might
believe that you just ordered what crystals were in the catalog,
the number that can be ordered off the shelf has greatly increased.
But then they wonder how they are supposed to get a frequency
that isn't in the catalog.

Nothing really has changed, except there are more frequencies
common enough to warrant making crystals for that frequency
as a commodity part.  You still have to get a crystal ground
to frequency and specs if you can't get it out of the catalog.

    Michael- Hide quoted text -

- Show quoted text -

This might be wishful thinking but did they manufacture oscillators
with dual clocks?

Any recommendations on where I can economically order a small quantity
of 10 to 25?

Derek