[SOLVED] RE: Damping Freq of Oscillation cadence

[kenambo]

RE: Damping Freq of Oscillation cadence

Hi All,

I have simulated a ideal LC oscillator without damping in cadence with L= 2nH and C=1pF. The natural frequency of oscillation is Fn = 3.56G.
Now I have added a damping resistor value of 10 Ohm and still the output is oscillating at the same frequency and dies out eventually.

Damping Ratio = 0.11

According to theory, the oscillation frequency should decrease and settle to the final value right?

Damping changes the natural frequency of oscillation. So the changed frequency(Damping frequency) is constant or gradually reducing to zero?

 

[pancho_hideboo]

Re: Damping Freq of Oscillation cadence

I have simulated a ideal LC oscillator without damping in cadence with L= 2nH and C=1pF.

What do you menan by "in cadence" ?
Are you Cadence's Employee ?
Use correct terminology.

According to theory,
the oscillation frequency should decrease

Yes.

and settle to the final value right?

No, since steady state oscillation can not exist.

So the changed frequency(Damping frequency) is constant or gradually reducing to zero?

Constant, since your circuit is linear.

 

[LvW]

Re: Damping Freq of Oscillation cadence

According to theory, the oscillation frequency should decrease and settle to the final value right?

No - in general, that is not correct.
A damping resistor in parallel to an LC-tank circuit does not modify the resonant frequency.

 

[kenambo]

Re: Damping Freq of Oscillation cadence

Constant, since your circuit is linear.

So if the system is non linear then there is no specific damping frequency right? The oscillations start at natural frequency and the frequency decreases gradually as the oscillations die out. Am I
right?

 

[pancho_hideboo]

Re: Damping Freq of Oscillation cadence

No - in general, that is not correct.
A damping resistor in parallel to an LC-tank circuit does not modify the resonant frequency.

Eigen Frequency changes.
Eigen Frequency is also called as Free Oscillation Frequecy or Natural Frequency.

 

[kenambo]

Re: Damping Freq of Oscillation cadence

No - in general, that is not correct.
A damping resistor in parallel to an LC-tank circuit does not modify the resonant frequency.

We are talking about series RLC cicruit.

It wont change the resonant frequency as long as the energy lost in each cycle is compensated.

And it does change with damping ratio. And for underdamped system.. this is called as damping frequency of oscillation. The circuit has the same natural frequency but due to added resistor(damping resistor) the oscillation frequency will get changed.

 

[pancho_hideboo]

Re: Damping Freq of Oscillation cadence

I have simulated a ideal LC oscillator without damping in cadence with L= 2nH and C=1pF.

What do you mean by "in cadence" ?
Are you Cadence's Employee ?

So if the system is non linear then there is no specific damping frequency right?

It depends on amplitude.

The oscillations start at natural frequency
and the frequency decreases gradually as the oscillations die out.
Am I right?

Of course, Wrong.

It wont change the resonant frequency as long as the energy lost in each cycle is compensated.

Wrong.
Resonant frequency has no relation to energy compensation.

You can not understand followings at all.
- Resonant Frequency
- Eigen Frequency
- Free Oscillation Frequency=Natural Frequency=imag(Eigen Frequency)
- Steady State Osciilation Frequency

The circuit has the same natural frequency

Wrong.

but due to added resistor(damping resistor) the oscillation frequency will get changed.

Wrong.

Both natural frequency and free oscillation frequency change.

Too many wrongs.

 

[LvW]

Re: Damping Freq of Oscillation cadence

We are talking about series RLC cicruit.

This information was missing from the beginning.

When you have a specific question related to a working (or non-working) circuit, it is best (no - it is necessary)

(1) to show us the circuit
(2) to specify your requirements
(3) to tell us what looks weird.

Otherwise, you cannot expect any helpful answer.

 

[kenambo]

Re: Damping Freq of Oscillation cadence

What do you mean by "in cadence" ?
Are you Cadence's Employee ?

That's none of your concern. I used it to mention I am simulating it using cadence virtuoso ADE L. Yeah, I used wrong terminology and will correct it hereafter. You have the right to say "use correct terminology". But asking "Are you a Cadence's Employee?" is completely irrelevant. Mind your own business before asking this to anybody hereafter.

It wont change the resonant frequency as long as the energy lost in each cycle is compensated.

This needs some clarification. What I am saying is as long as the energy dissipated is compensated the circuit oscillates at same Resonance Frequency. And Resonance Frequency doesn't depend on damping. I can prove it. So it is not wrong.

Resonant frequency has no relation to energy compensation.

Right. But to sustain oscillations we need energy compensation in case of energy loss.

You can not understand followings at all.
- Resonant Frequency
- Eigen Frequency
- Free Oscillation Frequency=Natural Frequency=imag(Eigen Frequency)
- Steady State Osciilation Frequency

Maybe I am not clear about some of this. And I think You too. Natural Frequency never changes for a RLC circuit. It is always 1/sqrt(LC). What changes is Damping frequency. Which changes according to damping ratio.

Both natural frequency and free oscillation frequency change.

I disagree natural frequency remains constant only free oscillation frequency changes depending on the damping ratio.

Too many wrongs.

Somethings need more clarification. So nothing is wrong here as long as you look in different perspective.

NOTE: Please be polite while answering threads.

- - - Updated - - -

This information was missing from the beginning.

When you have a specific question related to a working (or non-working) circuit, it is best (no - it is necessary)

(1) to show us the circuit
(2) to specify your requirements
(3) to tell us what looks weird.

Otherwise, you cannot expect any helpful answer.

Hi

It is a simple series RLC circuit. Nothing is weird. Just trying to understand some terminologies. Sure add circuit description in future

Thanks.

 

[pancho_hideboo]

Re: Damping Freq of Oscillation cadence

No.
You are misunderstanding resonant frequency and natural frequency.
Resonant frequency is 1/sqrt(L*C) regardless of R.

LvW says this in his post#3.

Natural frequency is imaginary part of Eigen frequency.
This is no more than Eigen value problem mathematically.

Anyway, your knowledges are too many wrong.

 

[LvW]

Re: Damping Freq of Oscillation cadence

What changes is Damping frequency. Which changes according to damping ratio.

What is "damping frequency" ? When you are using such a term, I suppose you know what it means? Me not!

More than that, in your first post you speak about an "ideal LC oscillator". From this, I have derived that it is a working oscillator circuit (including amplifier) for sustained oscillation.
Now, I`ve got the impression that you speak about a passive RLC circuit, correct?
To me, this is not an "oscillator"......but, of course, it is a matter of definition.
Therfore, to avopid such a misunderstanding, a circuit diagram is necessary.
For example, even in such a passive circuit, the loss resistances can have several positions (in series, in parallel or both).

 

[kenambo]

Re: Damping Freq of Oscillation cadence

What changes is Damping frequency. Which changes according to damping ratio.

What is "damping frequency" ? When you are using such a term, I suppose you know what it means? Me not!

More than that, in your first post you speak about an "ideal LC oscillator". From this, I have derived that it is a working oscillator circuit (including amplifier) for sustained oscillation.
Now, I`ve got the impression that you speak about a passive RLC circuit, correct?
To me, this is not an "oscillator"......but, of course, it is a matter of definition.
Therfore, to avopid such a misunderstanding, a circuit diagram is necessary.
For example, even in such a passive circuit, the loss resistances can have several positions (in series, in parallel or both).

It is a simple passive series RLC circuit.

Ok let me be clear about this.

Damped Frequency is the frequency at which an underdamped system oscillates when excited. It is denoted as Omega_d

There is a relation between Undamped frequency (or resonance frequency or natural frequency) and damped frequency Omega_d.

Omega_d = omega_n*sqrt(1 - square of damping_ratio).

SO Omega_n which is 1/sqrt(L*C) is the natural frequency which is independent of R.

and Omega_d is the damped/damping frequency which depends on R (Through Damping_ratio).

- - - Updated - - -

No.
You are misunderstanding resonant frequency and natural frequency.
Resonant frequency is 1/sqrt(L*C) regardless of R.

LvW says this in his post#3.

Natural frequency is imaginary part of Eigen frequency.
This is no more than Eigen value problem mathematically.

Anyway, your knowledges are too many wrong.

Yes. Resonant frequency is independent of R. I am assuming this from textbooks, omega_n is the natural frequency (also resonance frequency). What you are trying to say is underdamped frequency which is omega_d.
I think, the names have gotten us into this confusion.

And you are right. It is the imaginary part of eigen frequency or pole frequency. But it is underdamped frequency, which is always less than natural frequency Omega_n.

Maybe yours need some attitude, regarding knowledge.