how to measure a really small phase difference?

[freewing]

how to measure phase difference

I want to measure the phase difference between two signals. The phase difference is only 0.002 rad. So I think a binary PD is a good choice since it has a high gain when the phase difference is small. Since the two signals are ~100MHz signal, then half-rate binary PD can make it. But for normal half-rate binary PD, I/Q reference signals are needed. This will make things complex. So is there any other simple way to measure such a small phase difference?

 

[IanP]

measure phase difference

You can consider another option:

Have a look at Analog Devices AD8302.
This IC allows you to measure phase difference between two RF signals up to 2.5GHz with sensitivity 10mV per 1deg.
A comprehensive article on this issue you can find here:
https://www.analog.com/library/analogDialogue/archives/35-05/AD8302/

Good luck ..

 

[echo47]

measuring phase difference

Wow, that's a time delay of only one millimeter at the speed of light. What on earth are you measuring?

If you have two RF mixers and a 100.001 MHz oscillator, you could mix your two signals down to 1 kHz where the phase difference would be much easier to measure. You'll need to carefully balance the line lengths.

How about measuring *changes* in phase difference instead of trying to measure the absolute phase difference? Then you wouldn't need to balance the lengths or worry about drift.

 

[freewing]

measure phase difference rf

Actually, the two signals are on the chip and my phase detection circuit is also on-chip. When the phase difference is expressed in time domain, it's roughly 10ps. So I still think it's doable. Think about the CDR circuit for serial link and backplane communications. Now I just don't know which kind of phase detector is better.