Improved digital dual-mixer time-difference technique and its applications

• Robust time-difference measurements at level 100 fs carried out by the described method. • Evaluations of the temperature sensitivity on the time difference. • Effect of cable assemblies on the frequency dispersion. The dual-mixer time-difference (DMTD) technique is used for precise low-noise time comparisons. Its digital version (D-DMTD) was also already developed. The paper describes a simple digital improvement of the method that allows to compare phases of harmonic signals with similar frequencies using a digital oscilloscope with mutually phase-locked sampling. The stability of the achieved time difference measurements is below 100 fs for averaging times from one second to almost one day. The presented applications are, for example, comparisons of 10 MHz references or precise measurements of the dispersion in coaxial cables.