Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Oscillator with dual separate frequencies, is that possible?

Status
Not open for further replies.

neazoi

Advanced Member level 6
Joined
Jan 5, 2008
Messages
4,119
Helped
13
Reputation
26
Reaction score
15
Trophy points
1,318
Location
Greece
Activity points
36,918
Hi
I wonder if this circuit can operate giving two separate frequencies spaced apart 30Hz or so.
 

Attachments

  • Capture.PNG
    Capture.PNG
    7.1 KB · Views: 102

That circuit is not an oscillator. You could use a balanced mixer with 15 HZ mod frequency, will give Fc + 15HZ and Fc -15HZ on the same wire. It might be hard to filter off each component. The next step would be a phasing method of generating just one side band. The second side band could be generated using some of the common components (Fc+- 90 degrees, Fm +- 90 degrees).
Frank
 
  • Like
Reactions: neazoi

    neazoi

    Points: 2
    Helpful Answer Positive Rating
That circuit is not an oscillator. You could use a balanced mixer with 15 HZ mod frequency, will give Fc + 15HZ and Fc -15HZ on the same wire. It might be hard to filter off each component. The next step would be a phasing method of generating just one side band. The second side band could be generated using some of the common components (Fc+- 90 degrees, Fm +- 90 degrees).
Frank

This relates to my other post for generating a stable audio frequency, after mixing in that case. I opened it in another thread since this can be a completely different problem (RF related).
Half of this circuit IS an oscillator, I have tested it and in fact it is a really good one.
I wonder if two crystals can be used, as shown, each of them taking "energy" from the oscillator transistor, but resonate at a slightly different frequency, due to the slightly different crystal or tuning (a series capacitor maybe, that is not shown in the diagram).
Of course their outputs will be driven separately like shown.
 

Hi,

I have no good experience with two oscillators next to each other.
They usually influence each other resulting in clock jitter.

Many years ago i had two oscillators in one 74HC device, one was about 11MHz, the other 14MHz .. they always output the same frequency. Probably influenced by a not good pcb layout.


Klaus
 

I think the answer to the original question is "no", because the (necessary) nonlinearity of the oscillator doesn't allow independent oscillation modes to be build up. Particularly not with this low frequency difference which will most likely result in a single output frequency. In case of higher frequency difference you possibly get unstable behavior but unlikely two separate signals.

The diplexer method will work neither. Crystal Q isn't high enough to separate both frequencies (presumed they would be generated).

Obvious question, why not using two oscillator transistors? You still need to separate both oscillators thoroughly to avoid one signal "pulled" to the other frequency.
 

Hi,

I have no good experience with two oscillators next to each other.
They usually influence each other resulting in clock jitter.

Many years ago i had two oscillators in one 74HC device, one was about 11MHz, the other 14MHz .. they always output the same frequency. Probably influenced by a not good pcb layout.


Klaus

If they are two close, they usually lock to each other. They need good buffering to avoid this and maybe something like this output network

(http : // www . ab4oj . com/test/imdtest/images/fig9.gif )



The way I imagine the circuit in post #1, is that the oscillator provides energy to the one pin of the crystal, but each crystal resonates at a slightly different frequency.
Since the frequencies are close enough, no components change need to be done to the oscillator transistor and gain loop caps.
The output buffers should prevent locking of the oscillators.
However, I do not know if they could be locked on their input side (where the two crystals are connected together)

The reason I want to use a single oscilator with two resonators, is to eliminate different drifts, since any drift in the oscillator, will affect both output frequencies at a quite equal amount (asumming the crystals have relatively matched characteristics).

- - - Updated - - -

I think the answer to the original question is "no", because the (necessary) nonlinearity of the oscillator doesn't allow independent oscillation modes to be build up. Particularly not with this low frequency difference which will most likely result in a single output frequency. In case of higher frequency difference you possibly get unstable behavior but unlikely two separate signals.

The diplexer method will work neither. Crystal Q isn't high enough to separate both frequencies (presumed they would be generated).

Obvious question, why not using two oscillator transistors? You still need to separate both oscillators thoroughly to avoid one signal "pulled" to the other frequency.

We cross posted.
See my post #6 for the reason why I thought of a single oscillator.
I see your points you mention here.
 
Last edited by a moderator:

Hi,

what about using a (two) PLL to generate the two frequencies?


Klaus
 

Hi,
what about using a (two) PLL to generate the two frequencies?
Klaus

I should have specified it at the beginning. I am interested in relatively simple discrete components designs for the purpose.
 

If they are two close, they usually lock to each other. They need good buffering to avoid this and maybe something like this output network

(http : // www . ab4oj . com/test/imdtest/images/fig9.gif )




The reason I want to use a single oscilator with two resonators, is to eliminate different drifts, since any drift in the oscillator, will affect both output frequencies at a quite equal amount (asumming the crystals have relatively matched characteristics).

I think you are still missing the point ... the transistor is still only oscillate at a single freq. ( ignoring harmonics)

the dual oscillator in you attached image is one good way
or the dual PLL as KlausST suggested :)

Dave
 

That circuit is not an oscillator. You could use a balanced mixer with 15 HZ mod frequency, will give Fc + 15HZ and Fc -15HZ on the same wire. It might be hard to filter off each component. The next step would be a phasing method of generating just one side band. The second side band could be generated using some of the common components (Fc+- 90 degrees, Fm +- 90 degrees).
Frank
This is the solution.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top