Patent Application
20060023604
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-223725, filed Jul. 30, 2004, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a signal processing apparatus and method for a recording medium which is suitable for a process of adequately processing a signal read out from an optical disk or hard disk with high recording density, for example.
2. Description of the Related Art
Recently, as an optical disk, an optical disk which is subjected to a recording/reproducing operation by use of a bluish-purple laser has been developed in addition to an optical disk which is subjected to a recording/reproducing operation by use of a red laser. In the case of an optical disk on or from which data is recorded or reproduced by use of a bluish-purple laser diode, the recording density can be enhanced since the wavelength of bluish-purple laser light is shorter than that of red laser light.
In a recording/reproducing apparatus which records or reproduces information with respect to the optical disk by use of the bluish purple laser, a readout signal is subjected to the reproducing process using a Partial Response and Maximum Likelihood (PRML) identification system and the readout precision is enhanced. As an explanatory material about PRML, Jpn. Pat. Appln. KOKAI Publication No. 2003-16733 is provided.
In recent years, when a reproducing apparatus is considered, various types of optical disks are provided and some of the optical disks have a region with high recording density and a region with low recording density. In the reproducing apparatus, it is desired to reproduce both of the optical disk with high recording density and the optical disk with low recording density. However, in the signal reproducing process using the PRML system that designed for high recording density, there occurs a problem that it cannot be attained at the time of reproduction of a region with low recording density.
An object of the embodiments is to provide a signal processing apparatus and method which can flexibly cope with both of signal reproducing processes for regions with low and high recording densities.
According to one aspect of this invention, there is provided a reproducing circuit which reads out a signal from an optical disk with high recording density by use of a bluish-purple laser and comprises a PRML processing function for a region with high recording density, a PRML processing function for a region with low recording density, and means for selectively switching the processing functions. Specifically, the reproducing circuit includes a waveform equalizing circuit which waveform-equalizes data read out from an optical disk, a plurality of PRML processors of different classes supplied with an output signal of the waveform equalizing circuit, a switch which selects one of output signals of the plurality of PRML processors and supplies the selected output signal to a decoder, and a controller which controls the switch according to high-density and low-density regions with different recording densities of the optical disk to set a selection state in which a corresponding one of the output signals of the plurality of PRML processors is selected.
By use of the above means, it becomes possible to adequately reproduce a signal in each of the regions with high and low recording densities.
Additional objects and advantages of the embodiments will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
There will now be described embodiments of this invention with reference to the accompanying drawings. In
The adaptive learning circuit 34 performs a control operation to set an optimum characteristic of the adaptive filter 33 based on input and output signals of the adaptive filter 33 and an output signal of the Viterbi decoder. Output signals of the adaptive filter 33 and selection switch 51 are fed back to the adaptive learning circuit 34.
In
Binary data is detected by the Viterbi decoders 40 and 41. One of the binary data items is selected by the selection switch 51 and input to the decoder 50. The binary data is subjected to a demodulation process in the decoder 50 and output as user data.
Recently, a portion with high linear recording density in which normal data is recorded and a portion with low linear recording density called a system lead-in area are provided on the same medium used as an optical disk.
In
In
Therefore, in this invention, the reproducing operation is performed by use of a partial response of Class 11, for example, in the area (system lead-in area) with low recording density.
Therefore, when data with normal density is reproduced, the Viterbi decoder 40 is selected by the selection switch 51 shown in
Thus, data recorded with different recording density can be reproduced by performing the waveform equalizing process to attain a partial response waveform of a different class according to the recording density of data to be reproduced and performing the Viterbi decoding process suitable for the selected class. In
The controller 55 can evaluate the reproduction signal by use of a decoded signal from the decoder 50 or a decoded output signal. Whether the Viterbi decoder used at present is suitable or not can be determined based on the evaluated value. If it is not suitable, the switch 51 is controlled to use an output signal of the other Viterbi decoder. Further, it is also possible to control the switch 51, evaluate the decoded output signals of the Viterbi decoders 40 and 41 and select the decoder corresponding to a suitable output signal. When the quality of a decoded output signal is determined, the determination can be made based on an error rate in the decoder 50. For example, the decoded output signals of the Viterbi decoders 40 and 41 are subjected to an error correction process. Then, it is determined that the decoder corresponding to an output signal having a lower error rate is suitable.
Various methods can be used as the control method of the switch 51. For example, in the case of the optical disk 11, since the physical addresses thereof are determined, the controller 55 determines data read time of the system lead-in area 13 based on the physical address, controls the switch 51 and sets the selection state of the Viterbi decoder 41 when data in the system lead-in area 13 is reproduced.
The recording density may be different depending on the disk and it becomes necessary to switch the class of the decoder according to the recording density. In such a case, for example, when BCA information is read out, the type of the disk is determined and an adequate Viterbi decoder can be selected according to the thus determined type.
This invention is not limited to the above embodiment.
In the case of the optical disk 11, data is recorded with different density depending on the type of a medium in a normal data area. That is, the reproduction signal spectrum has good matching with the partial response of Class 3443 in a reproduction-only medium and the reproduction signal spectrum has good matching with the partial response of Class 12221 in a rewritable medium. Therefore, when data in the data area of the reproduction-only medium is reproduced, the data reproduction process is performed by use of the partial response of Class 3443 and when data in the data area of the rewritable medium is reproduced, the data reproduction process is performed by use of the partial response of Class 12221. Further, when data in the system lead-in area of each of the reproduction-only medium and rewritable medium is reproduced, the data reproduction process is performed by use of the partial response of Class 11.
As described above, according to this invention, since the configuration of the signal processing apparatus which switches the classes of the partial response to match with the frequency characteristic of the reproduction signal according to the recording density of the recording medium is used, data items of media with a plurality of recording densities can be reproduced.
By the above means, signals in a region with high recording density and a region with low recording density can be adequately reproduced.
This invention is not limited to the above embodiments and can be embodied by modifying the constituents without departing from the technical scope at the embodying stage. Further, various inventions can be made by adequately combining a plurality of constituents disclosed in the above embodiments. For example, some constituents can be omitted from all of the constituents. Further, the constituents lying over the different embodiments can be adequately combined.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-223725 | Jul 2004 | JP | national |
