Apparatus and metod for correcting asymmetry in tical disk reproduction system

Abstract

In an apparatus and a method for correcting asymmetry in an optical disk reproduction system, an analog RF signal is received from an optical diode and an asymmetry-corrected signal is output as a digital EFM signal. The apparatus includes envelope detectors for detecting upper and lower envelopes of the RF signal, a level controller for controlling the level of the sum of the upper envelope and the lower envelope and for outputting signal having the controlled level, and a comparator for comparing the level of the signal output from the level controller with the level of the RF signal and for outputting the comparison result as the digital EFM signal.

Description

[0001] This application is a divisional application of Chinese patent application 98119229.7 with a filing date of September 10, 1998. technical field [0002] The present invention relates to optical disc reproduction systems, and more particularly to an apparatus and method for correcting the asymmetry of an RF signal output from a photodiode in an optical disc reproduction system. Background technique [0003] In an optical disc reproduction system, an asymmetry correcting device corrects the asymmetry of an RF signal and converts the RF signal into a digital eight to fourteen modulated (EFM) signal. That is, the asymmetry correcting means clips the RF signal output from the optical diode based on the clip reference level at which the asymmetry is corrected, and obtains a digital EFM signal. 'EFMcomparator (CXA12710)' (hereinafter referred to as a conventional asymmetry reference device) shown on page 89 of "SONY SEMICONDUCTOR IC DATABOOK" published by 'SONY' in 1990 is a...

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Problems solved by technology

Here, a hole defect is where the disc material is not good or the disc is drilled so deep that light passes through the disc without being reflected

Thus, the data cannot be detected

[0009] Then, in the portion where there is a scratch or a hole, since the asymmetry of the RF signal may be incorrectly corrected, an error correcting portion (not shown) connected to a conventional asymmetry correcting device cannot correctly correct the error.

[0010] Since the time constants of the resistors R5 and R6 and the capacitors C2 and C3 of the low-pass filter 16 are, for example, 5 ms, it is difficult for the clipping reference level to follow the RF signal much shorter than 5 ms at the portion where there are scratches or holes. mid level

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