Abstract: An apparatus and method for determining the quality of a digital signal. The incoming digital signal is sampled with a number n of samples per defined pulse width, where N is greater than or equal to one, using clock cycles. An edge detector detects the edge position of a pulse of the sampled digital signal and a counter counts the clock cycles between at least a first edge and a second edge detected by the edge detector. A deviation detector then compares the counted clock cycles with a prestored reference-value in order to provide a deviation value as a measure for the instantaneous quality of the digital signal. The deviation value is then fed to a rework unit that outputs a value that is a measure for the quality of the digital signal.