Method and apparatus for detecting artifacts using common-mode signals in differential signal detectors

An apparatus analyzes a composite input signal to determine whether the amount of common mode signal in the composite signal is unacceptably high; thus, precluding an accurate diagnosis of the differential mode signal of interest. Method steps include separating the composite signal input into intermediate signals that are known functions of the differential mode signals of interest and common mode signals (or a suitable combination thereof). In one embodiment, the intermediate signals are cross-correlated to produce a measure of correlation between the intermediate signals. This measure is then compared with a threshold value. If the comparison is favorable, then the data is presumed to be uncorrupted and analysis of the signal representing the differential mode signal continues. Otherwise, the data is presumed to be corrupted and analysis of the signal data is inhibited. In another embodiment, the intermediate signal representing the common mode signal is itself compared against a threshold value without first cross-correlating with the intermediate signal that represents the differential mode signal. If the comparison is favorable, then it may be concluded that the potential for corruption is small and analysis of the intermediate or composite signal is continued.