Author Topic: How to get a clock signal from a crystal oscillator  (Read 4135 times)

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Offline igendel

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Re: How to get a clock signal from a crystal oscillator
« Reply #25 on: November 17, 2017, 12:09:45 pm »
If your happy with your probing technique, try upping that drive strength resistor to 4.7K,

No good - the ringing was a bit more pronounced with 4.7K than with 1K.

Hook up your probe to a Jim Williams pulse generator (see https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/) and see what the ringing looks like.  If its period is similar to that you are observing in your oscillator circuit, odds are, its a probe artefact.

For decoupling, try 1nF ceramic in a small SMD package, glued directly on top of the chip, and wired as directly as possible to its power and ground pins.   Put the 0.1uF leaded ceramic across the power input to the breakout board, and *PRAY*! 

Now where do I get that kind of pulse generator in a short notice?  :)

Soldering an SMD cap on that chip would be quite a challenge now... I'll give it a try later today. Thanks!


Maker projects, tutorials etc. on my Youtube channel: https://www.youtube.com/user/idogendel/
 

Offline StillTrying

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Re: How to get a clock signal from a crystal oscillator
« Reply #26 on: November 17, 2017, 12:30:06 pm »
the scope couldn't even find an alignment by itself, thought it was 30MHz or something

At least you now know the frequency of the ringing. :)
Why are you viewing a 5V signal on 5V/div. If you used the next sensitivity up 2V/div. you'd see more detail, triggering would be easier/more stable, and the Auto Max. Min. and Vpp numbers would be more accurate.
CML+  That took much longer than I thought it would.
 

Offline Ian.M

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Re: How to get a clock signal from a crystal oscillator
« Reply #27 on: November 17, 2017, 12:57:40 pm »
Hook up your probe to a Jim Williams pulse generator (see https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/) and see what the ringing looks like.  If its period is similar to that you are observing in your oscillator circuit, odds are, its a probe artefact.
Now where do I get that kind of pulse generator in a short notice?  :)
Build it Manhatten style on a scrap of copper clad FR4 - the 90V supply can be done with 10x really cheap zinc carbon PP3 batteries from the market, so you can discard the PSU circuit (the 10Meg-24K divider chain + everything to the left of it).   For the 50R emitter resistor, its best to use two 100R SMD resistors upside down either side of the output pad to minimise inductance.    Breadboard the circuit with 100pF for C2 and if you cant easily source a few 2N2369 transistors to try, try different low Vceo, high Ft transistors till you find one that pulses reliably.  RF transistors are more likely to avalanche than most switching transistors.  If you are using a through hole transistor, its probably best to drill a hole in the PCB and mount it up-side down for minimum lead length.  Caution: metal can transistors usually have the can connected to the collector  - you'll need to countersink the hole slightly to remove a ring of copper to avoid shorting it out.

See AN47, appendix D, page 93 of http://www.linear.com/docs/4138

Also note that C2 can be replaced by a long length of coax for a flat(ish) topped pulse.  10m of 66% velocity factor coax will give you a pulse duration of about 50ns,  which will resemble a half cycle of a 10MHz squarewave.
 


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