Optical information reproduction device and signal processing circuit used therein

A signal processing circuit of an optical information reproduction device for reproducing information from an optical disk medium on which an identification information area including first identification information shifted radially outward with respect to the center of a recording track by a specified distance and second identification information shifted radially inward with respect to the center of a recording track by a specified distance, and a user information area disposed along the center of a recording track are disposed in concentric or spiral form, and including an optical head illuminating the optical disk medium with a light beam, and including a split photodetector having at least two light-receiving parts disposed on opposite side of a track tangential line in the far field of the optical disk medium and receiving light reflected from the optical disk medium, said signal processing circuit comprising:

• an adder adding the outputs of the split photodetector;
• a subtracter which obtains a difference between the outputs of the split photodetector;
• a difference signal processor which makes the output of said subtracter similar to the output signal of said adder in waveform pattern;
• a signal selecter which selectively outputs the output of said adder and the output of said difference signal processor;
• and
• a waveform shaper which detects the information recorded on said disk medium from the output signal of said signal selecter;
• said signal selecter selecting the output of said difference signal processor or the output of said adder when said identification information area is being scanned and selecting the output of said adder when said user information area is being scanned.

An device reproducing information from an optical disk medium being scanned, said device comprising:

• an adding circuit having at least two inputs, each of said at least two inputs being operatively connected to one of at least two outputs of an optical head, said adding circuit having as an output a first signal related to the sum of the at least two outputs of the optical head;
• a subtracting circuit having at least two inputs, each of said at least two inputs being operatively connected to one of said at least two outputs of the optical head, said subtracting circuit having as an output a second signal related to the difference between the at least two outputs of the optical head;
• a signal processing circuit having at least one input operatively connected to said output of said subtracting circuit, said signal processing circuit having as an output a third signal that is either related to the second signal or that is related to the selectively modified second signal, said processing circuit ensuring that said third signal is similar in waveform pattern to said first signal;
• a signal selecting circuit having at least two inputs, one of said at least two selecting circuit inputs operatively connected to said output of said adding circuit and the other of said at least two selecting circuit inputs operatively connected to said output of said signal processing circuit, said signal selecting circuit having as an output a fourth signal selectively related to said first signal or selectively related to said third signal;
• and
• a waveform shaping circuit having at least one input operatively connected to said output of said signal selecting circuit, said waveform shaping circuit at least obtaining information recorded on the disk medium from said fourth signal.