Phase/Magnitude Detector - RF Cafe Forums

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eeboy
Post subject: Phase/Magnitude Detector Posted: Sun Oct 14, 2007 10:41 am

Lieutenant

Joined: Sun Oct 14, 2007 10:35 am
Posts: 2
Hello,

I am looking for a simple phase magnitude circuit. I have a few references which have a straight forward solution for obtaining the magnitude but the phase seems to be overly complicated (involving a diode ring modulator).

Any suggestions?

Thanks,
Jason

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nubbage
Post subject: Posted: Tue Oct 16, 2007 3:57 am

General

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi eeboy
If you can down-convert the channels to HF (maybe the signal frequency is already <50MHz?) then an XOR logic followed by an integrator will measure phase fairly accurately. With the two channels squared off to logic levels and fed to a 74LS exclusive OR, the output will contain a narrow spike when the channels are in phase, and will be a logic 1 when they are 180 out of phase. Any in-between state gives a pulse whose width is proportional to the phase difference. The integrator is a pulse width to analog level low-pass filter.

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eeboy
Post subject: Posted: Tue Oct 16, 2007 4:34 am

Lieutenant

Joined: Sun Oct 14, 2007 10:35 am
Posts: 2
That's a beatiful solution... very simple!

One more issue though... this would give a good indication as to when the phase angle is zero however, it does not give an indication as to wether it's lagging or leading. I can't think of an easy method to accomplish this. I could always calculate the time between the voltage and current peak but this becomes not trivial. Any suggestions?

FYI, the frequency is 27MHz.

Thanks!

Posted 11/12/2012