Detector with common mode comparator for automatic test equipment

Abstract

A detector circuit for automatic test equipment samples and tests differential signals. The detector circuit includes a pair of impedances connected in series between first and second legs of a differential input signal. A signal is formed at the junction of the two impedances that equals the common mode voltage of the differential signal. The common mode signal is coupled to the input of a window comparator, which compares the common mode signal with predetermined thresholds. The window comparator generates an output indicative of whether the common mode signal is above, within, or below the predetermined thresholds. Using this approach, the detector circuit can detect errors in differential signals caused by mismatched amplitudes or by timing skew between the first and second input signals. According to one feature, the detector circuit also includes a differential mode detector that receives the first and second input signals. The detector circuit according to the invention thus separately extracts the common mode and differential components of a differential input signal for separate evaluation.