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100 KHz Crystal Oscillator

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floobydust:
ST app note AN5073 on SPDIF receivers, 2.2.1 the guy measures the open-loop gain of SN74LVC1GU04 at 36, and finds instability with SN74LVC1G04 with slow signals. Interesting to note.

vk6zgo:

--- Quote from: rcbuck on March 25, 2019, 04:18:24 am ---I've been experimenting with a 100 KHz crystal oscillator with some success. I know these are really not crystals but are tuning fork oscillators at these frequencies.
--- End quote ---
Then you "know" wrong -------100kHz crystals are as common as dirt!
--- Quote ---
I am using a Mouser part number 815-ABS25-100KT part. I can get the part to oscillate by adjusting the trim cap after powering the circuit up. I can bring it on frequency to exactly 100.000 KHz. However, if I power the circuit down and back up, the oscillator will not start without adjusting the trimmer until it starts. I can then adjust it back on frequency.

Circuit I am using is attached. Is there a better circuit that I can use?

--- End quote ---

Edit:-OK, I can see where you are coming from with the "tuning forks" terminology.
Yes, low frequency crystals are often cut into tuning fork form, but they are not tuning forks, & are several orders of magnitude more accurate & stable than real versions of those devices.
In any case, 100kHz crystals are not among this group, & are cut like other higher frequency crystals are.

As I pointed out, they are very common, as are stable oscillator circuits which use them---- Google for "100kHz calibrator" circuits.

szoftveres:
I found so many people suggesting to use of unbuffered inverters, versus buffered (like the 74HC04).
I had similar experience; a low frequency pierce crystal oscillator I built ran just fine with 4069UB, but it didn't start at all with 74HC04.
Why is that? What makes the (presumably higher gain) buffered HCMOS ICs such a bad choice for building an oscillator? I would be curious about the explanation.

edavid:

--- Quote from: vk6zgo on March 26, 2019, 07:10:33 am ---Edit:-OK, I can see where you are coming from with the "tuning forks" terminology.
Yes, low frequency crystals are often cut into tuning fork form, but they are not tuning forks, & are several orders of magnitude more accurate & stable than real versions of those devices.
In any case, 100kHz crystals are not among this group, & are cut like other higher frequency crystals are.

As I pointed out, they are very common, as are stable oscillator circuits which use them---- Google for "100kHz calibrator" circuits.

--- End quote ---

The device OP is using is definitely a tuning fork crystal.  It is much too small to be 100kHz AT cut.  (I have a few of those, and they are in oversize HC-6 cans about 2 inches long.  I don't think they have been a standard product for many years.)

schmitt trigger:

--- Quote from: szoftveres on April 08, 2019, 03:18:41 am ---I found so many people suggesting to use of unbuffered inverters, versus buffered (like the 74HC04).
I had similar experience; a low frequency pierce crystal oscillator I built ran just fine with 4069UB, but it didn't start at all with 74HC04.
Why is that? What makes the (presumably higher gain) buffered HCMOS ICs such a bad choice for building an oscillator? I would be curious about the explanation.

--- End quote ---

The way it was explained to me, is that unbuffered devices consist of a single NMOS/PMOS stage, which can be biased in "class A", necessary for the operation of this circuit.

I am sure other posters will add to this explanation.

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