how to obtain phase difference between two signals?

[oahsen]

phase between two signals

I want to obtain two sine waves that have same frequency and 90degree phase difference. I have two signal generators for this purpose(stanford research systems DS345) whose operation manuel is given at ;

https://www3.imperial.ac.uk/pls/portallive/docs/1/7293214.PDF

But i couldn't figure our how to achieve my purpose. There should be a way to trigger the other signal generator with the output of one signal generator, so that i can give a 90 degree phase to the other one. Have anyobody tried to achieve such an phase difference and is there any other way (rather than using two signal generators) to do it? thx in advance

 

[LvW]

phase difference between two signals

Instead of using two separate generators you can integrate the signal of one generator. The output of the integrator is phase shifted by 90 deg.

 

[Borber]

phase difference between signals

Using only one generator the required phase shift is best acheived with RC integrator in first and CR differentiator in second branch of signal splitter. Phase difference or shift between branches outputs is 90°. Both RC constants must be equal for exact phase difference (can be trimmed). Ideally both signal amplitudes are allso equal at -3dB and T=RC.

 

[LvW]

phase difference in two signals

Using only one generator the required phase shift is best acheived with RC integrator in first and CR differentiator in second branch of signal splitter. Phase difference or shift between branches outputs is 90°. Both RC constants must be equal for exact phase difference (can be trimmed). Ideally both signal amplitudes are allso equal at -3dB and T=RC.

I don´t understand the purpose of a signal splitter.
By integrating and - at the same time - differentiating a sine wave you get two signals which are out of phase by 2x90=180 deg.
Or did I misunderstand something ?

 

[Borber]

all pass filter two signal with 90 phase shift

One signal is divided in two by splitter. First branch has ph. shift +45°and second -45°. Integration in one branch and differentiator in other but never cascaded. Shift between branches is 90°. And this is exactly what oahsen need.
Or did I misunderstand something?

Phase shift between branches is frequency independent and only signal amplitudes are changing.

 

[nl5]

how to calculate phase between two signals

Please note that RC-CR solution works only at fixed frequency f=1/(2*pi*R*C). If frequency changes, the amplitudes and phase shift also change.

Integrator always has 90 degrees phase shift, but the amplitude will change as well.

 

[Borber]

calculate phase difference between signals

Phase shift of a particular branch regarding signal generator is changing but phase shift of one branch regarding other is frequency independent and that is what is needed.

 

[nl5]

90 degree phase shift frequency independent

Phase shift of a particular branch regarding signal generator is changing but phase shift of one branch regarding other is frequency independent and that is what is needed.

Oh yes, you right! Just amplitudes change in opposite directions...

 

[LvW]

phase difference 2 signals

One signal is divided in two by splitter. First branch has ph. shift +45°and second -45°. Integration in one branch and differentiator in other but never cascaded. Shift between branches is 90°. And this is exactly what oahsen need.
Or did I misunderstand something?

Phase shift between branches is frequency independent and only signal amplitudes are changing.

OK, I see what you mean. The misunderstanding was because you have called your branches "integrator" resp. "differentiator" - and that´s not correct !
Your solution contains simply one RC-lowpass and one CR-highpass.

 

[Borber]

circuit for intagrator & diferentiator

After all a low-pass is integrator and high-pass is diferentiator on certain parts of theirs transfer functions if you want it or not.

 

[LvW]

lpf and integrator

After all a low-pass is integrator and high-pass is diferentiator on certain parts of theirs transfer functions if you want it or not.

An integrator has a phase shift of 90 deg. - and an RC lowpass approaches this phase only at infinity (and NOT on "certain parts" of the transfer function.
The same (with a neg. sign) applies to an CR-highpass.
A lowpass is simply a lowpass and nothing else. Don´t you agree ?

 

[kspalla]

rc phase difference

I would like to add few comments.
I agree that LPF is integrator and high pass filter as differntiator but the conditions are missing in this statement.
The missing par t is the time constant of the filter to the applied signal.
If the time constant is very large when compared to the applied signal then LPF acts as integrator.
If the time constant is very small when compared to the applied signal then HPF acts as differentiator.
But at this application they are equal.
So one can not call it as combination of integrator and diferentiator in this application.
You can get the same shift of +45°and -45° with LC circuit also.
This will fulfill the requirement of 90° phase shift.
May I know the frequency of operation, if it is in the microwave range then a 4 port hybrid branch line can do the same.

 

[LvW]

diferences between differentiator and integrator

I would like to add few comments.
........
If the time constant is very large when compared to the applied signal then LPF acts as integrator.
If the time constant is very small when compared to the applied signal then HPF acts as differentiator.
............

Yes, I agree. It is completely correct to say that a first order lowpass can "act" as an integrator (or better: approaches an integrating function) for frequencies far above its corner frequency. This especially is true as we all know that an ideal integrating function cannot be realized.
However, I don´t like formulations like "an RC lowpass is an integator". This discussion is a very good example for misunderstandings which arise if not the proper wording is used.

 

[big_boleros]

An old thread I know, but I found it via Google.

So, reading through this thread an integrator can be used to phase shift a signal a constant 90 degrees, but the amplitude will be affected.

Could someone be so kind to suggest some CR values fora circuit, I'm thinking an opamp arrangement with the capacitor in the negative feedback loop like this...
am!)
(ignore the actual values - it's not my diagr
**broken link removed**

....where the phase shift will be a constant 90 degrees, but the amplitude not too impacted between say 80Hz & 5kHz?

Is it just as simple as ensuring the corner frequency is well above 5Khz. I observe in the resulting amplitude plot, that the slope starts just before the corner frequency....

**broken link removed**

So if I say pick 10Khz as my corner frequency...at the risk of labouring the point (but I want to make sure!)....then all frequencies *will* be a constant 90deg phase shift & yet the amplitude will not be impacted upto my required 5Khz?

 

[lurchman]

oahsen,

There are numerous ways you can do it with a triggerable signal generator.

The first choice is analog or digital.

As others have noted the analog methods have some (but not insermountable) problems.

Have you considered generating a digital trigger that is in phase quadrature?

It can be fairly easily done with two Dtypes and putting 4f in as the clock.

The resulting output is very nicly in quadrature and will stay that way across just about any frequency range you can get into the circuit (so near DC to many MHz).

It's a bit of kit I have in my toolkit (along with a FLL frequency multiplier) that I find very usefull when syncing up osciliscopes and the likes when looking at various modulation waveforms.

The FLL is a bit of a cheat in that it uses a "digital" oscillator which is effectivly a DDS chip.

 

[big_boleros]

Apologies I wasn't clear in my last post - I probably should have started a new thread ....I don't want to generate a phase shift between two signals ...I merely want to cause a 90 deg phase shift on one incoming signal ...an audio signal...but without impacting its magnitude (alas, I have no control over the source)....ie I simply want to phase shift all audio frequencies 80hz thru 5Khz by 90 degrees.

Is my understanding correct (wrt my last post) of being able to use that simple circuit?