US Patent 7123547 Time delay measurement

A time measurement system for measuring the delay between first and second signals comprises means for detecting the times of upcrossings when the first signal crosses a predetermined level (preferably substantially different from the average level) with a positive slope and the times of downcrossings when the first signal crosses the predetermined level with a negative slope. These events are transmitted to a remote device receiving the second signal, which uses the events to define respective staggered segments of the second signal, to sum said segments and to detect a predetermined feature in said sum, the position of said feature representing the delay between the first and second signals.