A Technique for Measuring Picosecond Delays using Phase Modulation

This paper presents a delay measurement technique leveraging the high accuracy in the amplitude/frequency measurements of a spectrum analyzer. The two signals whose phase difference is to be measured are combined to generate a single output that can be fed to the spectrum analyzer. The delay information is embedded in the form of phase modulation in this output signal, resulting in a spur at one-fourth of the input signal frequency. The magnitude of this spur is used for estimating the input delay. Monte Carlo simulations of the proposed method for an input delay of 10 ps gives an estimated delay with a mean of 10.25 ps and a standard deviation of 1.17 ps.