Ultrahigh resolution frequency measurement scheme based on phase relationship between period groups

To achieve high resolution in frequency measurement, an depth analyzing of the group phase relationship between two signals with different frequencies is done, on which an ultrahigh resolution measurement scheme by detecting the optimal group phase coincidence is presented. The method is implemented on a CPLD chip, and the actual measurement data of the prototype shows that its resolution is approximately 10^-13/tau order of magnitude. This scheme is simple in circuit, high in measurement resolution, and low in cost. So it shows a wide promotion and application value.