The invention relates to a device for measuring the phase angle between a sine wave or sinusoidal signal and a periodic or cyclic logic signal of the same frequency as the sine wave signal. It is applicable to synchronizer systems and more specifically to systems for controlling the synchronization of television lines in magnetoscopes.
In known devices, the phase angle, i.e. the displacement angle between two waves of the same frequency, is measured in an analog manner, which is less accurate than the device according to the invention which is based on a digital process. For example, the device according to the invention achieves an accuracy in the measurement of the phase angle such that a clock of above 1 GHz would be necessary in the case of a known device to obtain the same accuracy. Such measuring systems are not at present widely used. Through digitizing the measurements on the sine wave signal, it is possible to relatively easily obtain a very high degree of precision in the device according to the invention.
Fundamentally, the device according to the invention converts the sine wave signal at frequency F into a digital signal by means of an analog-digital converter sampled by the logic signal with which the phase angle is to be measured, said logic signal having a sampling frequency equal to 4 times that of the sine wave signal F. Two samples are measured on each sinusoidal half-cycle, the first sample giving a value representing the sine of the phase angle .0. and the second sample giving a value representing the cosine of the phase angle .0., displaced by .pi./2 and on the basis of which angle .0. can easily be calculated.
One of the original features of the device according to the invention is that the measurement of the angle .0. is independent of the amplitude of the sine wave signal, because the device either measures the tangent or the cotangent of angle .0. in absolute values, thus eliminating the amplitude A of the sine wave signal. Thus, the calculation of the tangent or cotangent of the angle .0., whilst forming the ratio of the sine to the cosine or vice versa, means that it is only necessary to take account of those parts in which the tangent or cotangent are linear functions. For this reason, the device according to the invention measures the absolute values of the sine and cosine of the angle and, as a function of the ratio obtained, it calculates either the tangent or the cotangent in such a way that it only works in the linear parts of these functions. Another original aspect of the device is that the precision obtained is only dependent on the number of bits of the analog-digital converter.