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Crystal Oscillators

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It was pointed out to us that Wenzel Associates has a great web page on crystal oscillators, including some great downloads. Check them out by clicking here to see the Wenzel Library!

Here is an amazing, 40 minute video on the manufacture of deadly-accurate piezoelectric plates for radio communications from raw crystals during WWII. Thanks to Kerry for sharing this! If you think crystal direction alignment, wafer sawing and polishing were all developed in the "modern" silicon era, you're mistaken. Watch this video and if don't learn anything, please contact the Unknown Editor and he will refund your remaining Microwaves101 subscription fees.

Check it out, no one in the video is supersized like most would be if you filmed a US factory today (especially if you made a film at the Cheesecake Factory...)

Crystals Go to War

Here are some safety comments from Steve who viewed the video:

Besides the average mass of the workers, the other thing I find interesting in the video is is the nearly complete lack of any concern for industrial safety.  For example, the Chromic Acid used at 28:00 into the video, the stuff in the open bath on the hot-plate (guaranteeing outgassing, etc.) is carcinogenic.  Not just a little carcinogenic, but so carcinogenic that it is virtually unused in any industrial production today.  We are talking positive-pressure ventilator bunny-suit toxic / carcinogenic.  The girl pictured was just working over a vat of the stuff with no protection at all.  Eeek!

I do not even want to imagine where their waste-water went...

Yes, we agree. And everybody in that factory should have safety glasses on, no exceptions.

We will start this page with some definitions:

Crystal oscillator (XO)
A crystal oscillator without any bells or whistles, can provide maybe 100 ppm frequency stability over a moderate temperature range. The problem is that crystal oscillators by nature are temperature sensitive.

Ovenized crystal oscillator (OXO)
Using specialized heating elements, controllers and temperature chambers, the stability of a crystal oscillator can be improved to 10-10 (0.0001 PPM).

Voltage controlled crystal oscillator (VCXO)
This is a crystal oscillator that allows you to tune its frequency using an external voltage control. This is that heart of many a phase-lock loop, automatic frequency control and frequency-modulation scheme. The element that does the tuning is a varactor (voltage-variable capacitor).

Temperature-compensated crystal oscillator (TCXO)
Similar to a VXCO in that a varactor is used to vary the frequency of oscillation. An internal temperature compensation network using thermistors or other temperature sensors is used to provide a shaped voltage control signal to the device over temperature, so that stable frequency operation is provided.

Voltage controlled temperature-compensated crystal oscillator (VCTCXO)
Here an external voltage control is provided, but the signal is "reshaped" by the temperature compensation network so that stability over temperature is high but frequency is still controlled by an externally applied voltage.

Author : Unknown Editor

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