[sdiy] Measuring phase diff between sines

[DSL FODA01]

I was thinking you could maybe normalize the amplitudes of the two waves and
then sum them, the result correlating to the phase angle... or you could buy
a commercially-made phase angle meter.

Dave


----- Original Message -----
From: "Fredrik Carlqvist" <Fredrik.Carlqvist at iar.se>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, May 09, 2006 10:10 AM
Subject: [sdiy] Measuring phase diff between sines


>
>
> Hello all!
>
> I have two sine sources and wish to measure the phase difference with at
> least 14 bits accuracy, preferrably 16 bits. The frequency of one of
> these sources is fixed at 10kHz, the other comes from an inductive
> pickup. The maximum phase difference change in one period of the
> reference is 3.6 degrees, that is 1% of a period.
>
> Directly measuring the time between zero-transitions is not good enough
> since there is also noise and DC offset on the picked up signal.
>
> My first thought was to use a PLL-type filter, using two comparators to
> get two square signals, followed by some logic (IN1 & !IN2) to derive a
> phase difference in a capacitor. Then use the reference to determine
> which half-plane we're in (leading or trailing?). This is too slow
> though, as the time constant for the RC filter must be very long to
> allow 14-bit precision (1.5 s, 6 s for 16-bit precision).
>
>        ______        ______
> Sine1 |      |______|
>         ______        _____
> Sine2 _|      |______|
>
> Comb  ||____________||_____ into RC filter
>
>
> It would be ideal to remove all amplitude dependence from the system.
> This would be accomplished by only looking at zero transitions. By using
> integrated and differenciated versions of the picked up signal, we could
> have eight zero-transitions per period.
>
> As the maximum change in phase diff is limited, one could use a DCO to
> compare to the picked up signal, keeping guesses of both the next value
> and the derivative of the phase difference, and using the DCO phase to
> compare to the reference signal.
>
> Does anybody have any better ideas?
>
>
> Fredrik C
>