TIMING RECOVERY FOR CHANNELS WITH BINARY MODULATION

摘要

For (re)writable and read-only optical disc systems the data clock is recovered by a phase locked loop (PLL), where the error signal is generated by comparing the actual zero-crossing with the zero-crossing of the generated clock signal. Given an optical system with a laser wavelength lambdalaser and a numerical aperture NA, the cut-off wavelength of the Modulation Transfer Function is given by lambda0 = lambdalaser/(2.NA). With decreasing bit length the amplitude of the minimum wavelength will decrease and is zero for wavelengths below lambda0. Consequently, the phase error signals generated by zero-crossing of these signals are disturbed by noise. The idea of the invention is to use the zero-crossings with sufficient performance only in deriving phase information for the clock recovery.