Patent ID: 7154305

Claim:
A system for monitoring frequencies of periodic electrical signals, comprising: a plurality of counters clocked by respective periodic electrical signals, each of the plurality of counters having a respective associated threshold; and a threshold detector configured to detect, for each of the plurality of counters, crossing of each threshold associated with the counter by the count of the counter, and to determine whether a frequency error has occurred based on whether the counts of the plurality of counters cross their respective thresholds in other than a particular sequence with respect to each other, wherein the threshold detector comprises: a plurality of threshold detection elements for detecting the crossing of each threshold associated with a respective counter by the count of the counter; and an error detector coupled to receive threshold crossing information from the plurality of threshold detection elements and configured to determine, based on the threshold crossing information, whether the counts of the plurality of counters cross their respective thresholds in other than the particular sequence.