Detection of an identification signal contained within a composite signal, without false signal recognition

摘要

A system for detecting the presence in a sampled composite signal of an identification signal having a predetermined frequency without falsely recognizing other sharp signal transitions in the sampled signal as the identification signal. The system includes a delay line for delaying the composite signal by one-half the cycle of the identification signal as defined by the predetermined frequency to thereby provide a delayed signal; a bias network for biasing the composite signal to provide a first biased signal that is biased a predetermined differential above the composite signal, and to provide a second biased signal that is biased the predetermined differential below the composite signal; a first comparator for comparing the first biased signal to the delayed signal to provide a first comparison signal that indicates when the delayed signal is above the first biased signal; a second comparator for comparing the second biased signal to the delayed signal to provide a second comparison signal that indicates when the delayed signal is below the second biased signal; and a signal processor for processing the first and second comparison signals to provide a flag signal that indicates when the delayed composite signals both periodically rises above the first biased signal at the predetermined frequency and periodically falls below the second based signal at the predetermined frequency, to thereby indicate detection of the identification signal.