Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations KootK on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

unwanted oscillator synchronisation

Status
Not open for further replies.
Wedwin

Wedwin

Electrical
Aug 4, 2003
35
Hi all!

I want to create a few oscillators using Schmitt inverters and R and C to set frequency. I want them to run almost but not exactly at the same frequency. This because I want to conduct som interference experiments.

When I get close, bam, they get synchronised. The same thing have been rebuilt twice and several values have been tested

Has anyone else come across this phenomenon? Do anyone have any suggestions?

I am around or below 100 Hz, but am not afraid to try other ranges. It just "feel" alright to handle frequencies that fit into my mind.

Best regards, Wed
 
Replies continue below

Recommended for you

Sort by date Sort by votes
you are using the wrong sort of oscillator, try a LC type.
 
Upvote 0 Downvote
The cause is one osc. signal getting coupled into the
other. When this is close to the switching threshold,
its noise sensitivity is diminished so it gets triggered
prematurelly.

Solution:

Separate shielding buffering and decoupling, Run the osc.-s
at relative prime-times multiples ( e.g. 11*F1 and 13*F2 ) and divide them down.



<nbucska@pcperipherals.com>
 
Upvote 0 Downvote
I have done this on purpose many times to power combine oscillators. Another good one is even if the (multiple) oscillators are far enough away in frequency, they will remain at their frequency, but will become syncronized in (phase) called mode-locked condition, Producing a repeatable interfernce pattern.
 
Upvote 0 Downvote
Another way you can do it is to use two oscillators on quite different operating frequencies, and then digitally divide each frequency down by an appropriate division ratio.

There should then be no interaction or frequency pulling effects, because the oscillators are on totally different frequencies.
 
Upvote 0 Downvote
Hi warpspeed, relaxation oscillators will quite happily lock onto any hearby harmonic, back in the old tube days a multivibrator was used to divide by any number up to about 7.
 
Upvote 0 Downvote
Thanks a lot all of You for the information.

An LC solution would probably bring up the frequency a notch or two, but foremost in size.

The whole idea was a pretentionless experiment. That is why a common RC inverter osc would fit so well.

Since it doesn't work, I am happy to know why. And I will try to apply this newfound knowledge.

Best regards, Wed
 
Upvote 0 Downvote
cbarn24050

hehe, yes, but if one oscillator is divided by seven, and the other by eleven, there will be a continuously varying phase relationship between both oscillators.

The worst that can happen is a bit of pulling and jitter as they momentarily pass through instants of simultaneous switching. But the dividers will eliminate most of that from the outputs.

I can remember tweaking tube circuits with relaxation oscillators used for frequency division in commercial equipment many years ago.
 
Upvote 0 Downvote
Cbaarn: Yes, you R right, simpler circuit == more interaction.
Warp: Thanks for the support. Larger #s == less coupling.


<nbucska@pcperipherals.com>
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

EMET1970
  • Locked
  • Question
Understanding My Crystal Oscillator
Replies
18
Views
129
MagicSmoker
MagicSmoker
fg45
  • Locked
  • Question
wien bridge oscillator with op-amp buffer
Replies
1
Views
31
VEBill
VEBill
courtl
  • Locked
  • Question
HA7210 Low Power Crystal Oscillator
Replies
4
Views
51
sreid
sreid
skenn
  • Locked
  • Question
SAW resonator/oscillator
Replies
2
Views
43
jsolar
jsolar
kodabear
  • Locked
  • Question
Clock vs. Crystal Oscillator
Replies
9
Views
104
nbucska
nbucska

Part and Inventory Search

Sponsor

Back
Top Bottom