The device for recovery of the clock frequency of a digital signal comprises a rectifier, a filter having a very narrow bandwidth coupled to the first input of a phase comparator of analog type, a controlled oscillator, the output of which delivers the recovered clock signal and is coupled to the second...http://www.google.com/patents/US4569064?utm_source=gb-gplus-sharePatent US4569064 - Device for recovery of clock frequency in digital transmission
