Eye violation and excess jitter trigger

Abstract

An eye violation and excess jitter trigger for a digital signal uses a mask within a unit interval of the digital signal, such as a rectangular mask having corners defined by a high threshold, a low threshold, an early clock and a late clock, the early and late clocks being derived from a reference clock. The reference clock may be a recovered clock derived from the digital signal or from high and low threshold comparator outputs, or may be an external clock. For the excess jitter trigger, which is a special case of the eye violation trigger, the high and low thresholds are essentially equal. A status of the digital signal with respect to the mask is determined using the high and low thresholds and the early and late clocks, and a violation signal is output when the status indicates that a portion of the digital signal crossed into the mask. The violation signal may then be used to trigger data acquisition or for other purposes.