US Patent 8005370 Reference clock rate detection for variable rate transceiver modules

A system and method are provided for determining an optical signal frequency range in an optical/electrical transceiver. The method receives an optical receive signal having a non-predetermined data rate via a network interface, and also receives an electrical reference clock signal having a non-predetermined frequency via a framer interface. The reference clock signal frequency is cross-referenced to an optical receive signal frequency. In one aspect a clock and data recovery (CDR) voltage controlled oscillator (VCO) is selected having an output frequency matching the cross-referenced optical receive signal frequency. The optical receive signal is converted to an electrical receive signal. Initially, the VCO is frequency-locked to the reference clock. Subsequent to frequency-locking the VCO output frequency, the converted optical signal is phase-locked, generating a receive data clock. The CDR supplies a converted optical receive signal and receive data clock to the framer interface.