Design of a digital frequency discriminator using least squares based phase calibration

A digital frequency discriminator (DFD), i.e., a frequency measurement device with delay-line discriminators, has been developed for accurate measurement of the instantaneous frequency from received signals. In this paper, a new DFD with unwrapped-phase calibration in each correlator is proposed by reconsidering the basic operating principles of the DFD from a signal processing point of view, which enables us to reduce memory spaces. More specifically, the proposed approach utilizes (i) phase calibration to find the unwrapped phase in each delay time in consideration of integer multiples of 360° and (ii) estimation of the instantaneous frequency by fitting the unwrapped phase into the least-square straight-line. Finally, it is also demonstrated indirectly that the proposed approach can reduce frequency estimation ambiguity in a noisy environment, since it is shown that the proposed design is robust to additive phase noise ±30° under a specific case of the 1:4 ratio DFD, while the conventional DFD designs are restricted to ±22.5°.