Phase to amplitude converting in analog stage

[aegis27]

Hi, all.

I am trying to measure phase changes according to difference materials.
I know the best way is to record applied and measured signal, but due to low sampling rate of ADC and high frequency of input sinusoidal waveform, I can not record them.
So, I wonder if there is a way to convert phase to amplitude, so I can easily record them with ADCs.
Measuring impedance is pretty simple but I can not figure out how to measure them in analog stage with op-amplifiers.
Could anyone advise me how to solve this problem?

Best,
SLee

 

[Prototyp_V1.0]

First thing I got to think of is to use two comparators and a simple latch to make a short spike that last the same period of time as from original signal zero crossing to the zero crossing of the phase shifted signal.
A possible problem is that if high frequency, the method may be less accurate.

 

[Warpspeed]

An exclusive OR gate makes a wonderful phase comparator, but first you need to convert your sine waves to square waves which is not difficult.

The output of the exclusive OR gate can then be averaged (with a resistor and capacitor) or a low pass filter, and you get a resulting dc voltage proportional to phase difference.

 

[KlausST]

Hi,

Read about "lock in amplifier" (LIA).
It is a solution to measure amplitude and phase angle (0..360°).
The output is low pass filtered and therefore you may see it as DC. = easy to read with an ADC.
You need at least two bipolar ADC inputs per channel.
***

The XOR solution is easy. You need reliable zero cross signals from a clean sine wave.
But it's impossible to calculate if the phase angle is positive or negative.
Negative phase angle 0° ... -180° ( = 360° down to 180°) will give the same result as positive phase angle 0° ... 180°

Klaus

 

[Warpspeed]

Klaus has a point, but is not 90 degree lagging the same as 270 degree leading ?

 

[KlausST]

Hi,

but is not 90 degree lagging the same as 270 degree leading ?

Exactely. That what I wrote:

0° ... -180° ( = 360° down to 180°)

Indeed it repeats every 360°...


Klaus