[sdiy] Black Magic oscillator cans

[Glen]

At 05:56 AM 7/20/03 , Tim Ressel wrote:

>Does anyone have experince with programmable
>oscillators? ECS and Cardinal make these little
>oscillators that look like normal clock oscillators,
>but are programmable.

I just visited the ECS web site and viewed the data sheets for a few of
these devices. I also viewed the page about the dedicated programmer you
would need to program these devices. Considering the need for a programmer,
it seems somewhat expensive to get started with these devices, if you only
need to program one or two it's going to be too expensive, but if you are
doing thousands it wouldn't be bad.

There is one thing that bothers me even more than needing a programmer. I
could not find any reference to the *Precision* with which these devices
could be programmed. I could only find reference to the frequency ranges
they would operate over. For example, if I want an oscillator set to
2.00024 MHz, can I actually program that particular frequency? It's
possible that the closest frequency you could program would be 2.0002 MHz;
or even worse, 2.000 MHz might be the closest frequency this device
provides for. I would definitely want to know how fine I could adjust the
frequency before I got into working with these devices.

If all you want is to feed a TOG, why not do what has been done
commercially for several years. Use an LC oscillator containing a variable
inductor. These can be fairly stable, and they have the advantage of being
*continuously* tunable. This is especially handy if you have more than one
TOG in an instrument and you want to detune one very slightly from the
other one.

If you really want crystal stability, wouldn't it be fairly simple to have
some custom crystals made? There are crystal houses that do this sort of
thing all the time. I don't think it costs all that much, and it will
probably provide you with even more stability and less jitter than these
programmable devices. I know that most of the typical fixed-frequency
crystal oscillators are not quite as accurate or stable as a good discrete
crystal oscillator design, using a high-quality crystal.


later,
Glen Berry