# Phase difference measurement of a 100 kHz tone

I would like to measure the phase difference of a 100 kHz tone. The tone is transmitted and then received.

The received tone is sampled using an 1 MHz 12 bit ADC(IQ) and the SNR is at least 35 dB.

Our aim is to measure the phase difference in at least 360/500= 0.72 degree steps.

• Is this possible?
• Should I use a PLL or a FFT based approach?
• "phase difference of a tone": a difference (and a phase) is always a relative thing. So, difference to what? – Marcus Müller Mar 5 at 15:29
• Sorry. You are right. The tone is transmitted and then received. – Kurtul Mar 5 at 16:11

The achievable rms accuracy is approximately the reciprocal of the SNR as an rms quantity, specifically $$10^{-35/20}$$ in your case assuming the small angle criteria, if your noise is all phase noise. It is likely your SNR is equally phase and amplitude noise, so the phase result as limited by your noise would be 3 dB better after hard limiting the signal to eliminate the AM component.