Time-domain Measurements of Frequency Stability

The frequency stability´s definition in time domain is briefly introduced and four measurement methods are discussed in this paper, including direct counters, frequency difference multipliers, heterodyne method and dual mixer time difference method. Some detailed calculations on accuracies are given for a better comparison. What´s more, for making precise measurements, an attempt to combine these four methods with the latest TDC and TAC techniques is made, and a block diagram is presented. Finally, we estimate the accuracies of these combinations: direct counters combined with the dual arctangent technique can reach 4 E-12/S, frequency difference multipliers with multi-phase clock TDC 2.5 E-13/S. When the multi-phase clock TDC technique applied on heterodyne method and dual mixer time difference method, the measurement accuracy respectively can reach 1.25 E-16/S and 2.5 E-17/S.