Patent Application
20090213710
The present invention relates to an apparatus for reproducing information recorded on an information carrier.
The invention further relates to an information carrier for use in such an apparatus.
The invention also relates to a method for reproducing information recorded on an information carrier.
An apparatus for reproducing information from an information carrier having a waveform equalizer is known from European Patent application 0940811 A1. In the known apparatus an optical pickup unit reads recorded information from a recording disk. The recording disk is rotated by a spindle motor. The optical pickup unit supplies a read signal to an amplifier. The amplifier amplifies the read signal to a desired level and supplies an obtained read signal to a waveform equalizer. An amplitude limiting circuit present in the waveform equalizer converts a signal level of the read signal by limiting the amplitude of the read signal. The amplitude limited read signal is supplied to a high-frequency emphasizing filter. The high-frequency emphasizing filter emphasizes the level of high frequency components of the amplitude limited read signal and supplies a resultant signal as an equalization correction read signal to a binary value decision circuit. The binary value decision circuit discriminates whether the signal level of the equalization correction read signal corresponds to either one of the logical levels “1” and “0”, and generates a result of the discrimination as reproduction data.
The density of the information on the information carriers becomes higher and higher as the area of information recording is more developed. From DVD to Blu-ray Disc egalization of the read signal has therefore become more and more a necessity in order to reduce inter symbol interference. Egalization makes it possible to detect the smallest signals in the read signal properly. In the case of Blu-ray Disc the smallest signals are called the 12's. They represent the highest frequencies of the channel and have the smallest amplitude due to the optical MTF which has its cut off near to that high frequency. The so called limit equalizer described in EP-A-0940811 is better in reducing Inter Symbol interference and therefore performs very well to make the ‘eye’ in the read signal open (unequalized read signals may have closed ‘eyes’ because of the very small I2 signals). An important parameter of an equalizer is its gain; a measure of the ‘boost’ the equalizer gives.
When reading out the information carrier more or less noise is contained in the read signal. The characteristics of the noise are dependent on the type of information carrier. For instance, for Blu-ray Disc Rewritable there are defined three different capacities in the physical specification: 23.3 GB, 25 GB and 27 GB. Each of these three capacities have a different channel bit length which decreases for increasing capacities. The smaller the channel bit length, the more difficult the 12 signals become to detect. This is related to the noise in the read signal. The gain setting of the equalizer such that, given the noise characteristic, the 12's are optimally boosted is therefore dependent on the type of information carrier. For write once recording, such as Blu-ray disc Recordable, there are different media types which are suited. These media types are organic (dye) and inorganic types and Low to High (L2H) media. The different media types have mutually different noise characteristics or obtain less modulation at the highest frequencies as one can expect from the MTF and therefore need different optimal gain settings for the equalizer.
Thus, the optimal gain setting for the equalizer is dependent on the type of information carrier. For optimal reading the information carrier the apparatus for reproducing information on the information carrier needs to know the optimal gain setting for the equalizer. The known apparatus can not determine the optimal gain setting and does therefore reproduce information with a gain setting which may not be optimal. The noise and inter symbol interference in the read signal is consequently not suppressed optimally by the equalizer.
It is an object of the invention to provide an apparatus for reproducing information as described in the opening paragraph, which better suppresses the noise and inter symbol interference in the read signal.
It is a further object of the invention to provide a method for reproducing information as described in the opening paragraph, which better suppresses the noise and inter symbol interference in the read signal.
It is still a further object of the invention to provide an information carrier for use in the apparatus according to the invention.
Therefore, the apparatus according to the invention comprises:
a waveform equalizer for obtaining a corrected signal S′ by performing a waveform equalization to a read signal S read out from the information carrier, the waveform equalizer having an amplifying element with a gain K;
gain setting means for reading a numerical gain setting stored on the information carrier setting the gain K of the amplifying element to a value related to the numerical gain setting.
The method according to the invention comprises the steps of:
obtaining a corrected signal S′ by performing a waveform equalization to a read signal S read out from the information carrier using a waveform equalizer having an amplifying element with a gain K;
reading a numerical gain setting stored on the information carrier and setting the gain K of the amplifying element to a value related to the numerical gain setting.
On the information carrier in accordance with the invention the numerical gain setting is stored.
The optimal gain setting of the equalizer for a given information carrier can be determined in advance by analyzing the information carrier. By storing the determined optimal gain setting in the form of the numerical gain setting on the information carrier, the apparatus in accordance with the invention is able to read the optimal gain and setting the gain K of the amplifying element accordingly. The equalizer can subsequently perform optimally for that information carrier by optimally suppressing the noise and inter symbol interference in the read signal.
In an embodiment of the apparatus according to the invention the waveform equalizer comprises a FIR filter able to perform a filtering process to said read signal S, the FIR filter having tap coefficients
The abbreviation FIR stands for Finite Impulse Response. This filter thus has an impulse response which is finite. Such a filter consists of tap delays, amplifying units and an adder for adding the outputs of the tap delays and amplifying units. The amplifying units have an amplification of K, Depending on the value of K, the waveform equalizer has a certain frequency response. The gain K is set by reading the optimal gain from the information carrier and setting the gain K accordingly. This waveform equalizer can be used in run length limited, RLL, codes. RLL codes are indicated by parameters d and k. The d stands for a minimum run length constraint, and the k for a maximum run length constraint. A run length smaller than d+1 is not allowed, a run longer than k+1 is not allowed either. The described waveform equalizer is suitable for a RLL code where d=1.
This FIR filter is a 4-tap transversal filter with transfer function:
In an apparatus such as a Blu-Ray Disc writer the waveform equalizer can be followed by a limit equalizer.
A limit equalizer is described in EP-A-0940811. As is described in EP-A-0940811 the limit equalizer suppresses noise and inter symbol interference substantially.
In a further embodiment of the apparatus according to the invention the limit equalizer comprises:
a first FIR filter able to perform a filtering process to said read signal S, having tap coefficients [0,0,0,1];
amplitude limiting means able to obtain an amplitude limited read signal by limiting an amplitude level of said read signal S by a predetermined amplitude limitation value;
a second FIR filter able to perform a filtering process to said amplitude limited read signal, having tap coefficients [−m,m,m,−m], m being a suitable amplification factor;
an adder able to add the signals obtained by performing the filtering process by each of said first and second filters, and output the corrected signal S′. In case of the Blu-Ray Disc writer a suitable value of the amplification factor m would be m= 3/16. In an embodiment of the apparatus according to the invention the gain setting means 1 are adapted to read an additional numerical gain setting and to set an amplification factor of the limit equalizer a value related to the additional numerical gain setting.
An example of an information carrier is an DVD+R optical disc. The area of the disc on which information is or can be written is called the information zone. The information zone consists of an Inner Drive Area, a Lead-in Zone, a Data Zone, Lead-out Zone and an Outer Drive Area. The Lead-in Zone contains control information. The Lead-in Zone is located at the inner side of the Information Zone. The Lead-in Zone comprises a Control Data Zone. The Control Data Zone contains physical format information, disc manufacturing information and content provider information. The physical format information contains information such as disc size, recording density, maximum read power, parameter settings for recording etc. . . . . The numerical gain setting can be stored in the physical format information table.
These and other aspects of the apparatus, information carrier and method according to the invention will be apparent from and elucidated by means of the drawings, in which:
a shows an information carrier (top view),
b shows an information carrier (cross section),
The apparatus for reproducing information shown in
a shows a disc-shaped information carrier 11 having a track 9 and a central hole 10. The track 9, being the position of the series of (to be) recorded marks representing information, is arranged in accordance with a spiral pattern of turns constituting substantially parallel tracks on an information layer. The information carrier may be optically readable, called an optical disc, and has an information layer of a recordable type. Examples of a recordable disc are the CD-R and CD-RW, and writable versions of DVD, such as DVD+RW. Further details about the DVD disc can be found in reference: ECMA-267: 120 mm DVD—Read-Only Disc—(1997). The information is represented on the information layer by recording optically detectable marks along the track, e.g. crystalline or amorphous marks in phase change material. The track 9 on the recordable type of information carrier is indicated by a pre-embossed track structure provided during manufacture of the blank information carrier. The track structure is constituted, for example, by a pregroove 14 which enables a read/write head to follow the track during scanning. The track structure comprises position information, e.g. addresses, for indication the location of units of information, usually called information blocks. The position information includes specific synchronizing marks for locating the start of such information blocks. The position information is encoded in frames of modulated wobbles as described below.
b shows a part of a cross-section taken along the line b-b of the information carrier 11 of the recordable type, in which a transparent substrate 15 is provided with a recording layer 16 and a protective layer 17. The protective layer 17 may comprise a further substrate layer, for example as in DVD where the recording layer is at a 0.6 mm substrate and a further substrate of 0.6 mm is bonded to the back side thereof. The pregroove 14 may be implemented as an indentation or an elevation of the substrate 15 material, or as a material property deviating from its surroundings.
The information carrier 11 is intended for carrying information represented by modulated signals comprising frames. A frame is a predefined amount of data preceded by a synchronizing signal. Usually such flames also comprise error correction codes, e.g. parity words. A number of such frames constitute an information block, the information block comprising further error correction words. The information block is the smallest recordable unit from which information can be reliably retrieved. An example of such a recording system is known from the DVD system, in which the frames carry 172 data words and 10 parity words, and 208 frames constitute an ECC block.
n=10×vref (n rounded off to an integral value)
n=10×vref (n rounded off to an integral value)
n=Wavelength−600
Byte 36—Maximum read power, Pr at reference velocity.
n=20×(Pr−0.7)
Byte 37—PIND at reference velocity.
n=20×(PIND−5)
Byte 38—βtarget at reference velocity.
n=10×βtarget
Byte 39—Maximum read power, Pr at maximum velocity.
n=20×(Pr−0.7)
Byte 40—PIND at maximum velocity.
n=20×(PIND−5)
Byte 41—βtarget at maximum velocity.
n=10×βtarget
Byte 42—Ttop (≧4) first pulse duration for current mark ≧4 at reference velocity.
n=16×Ttop/TW and 4≦n≦40
Byte 43—Ttop (=3) first pulse duration for current mark =3 at reference velocity.
n=16×Ttop/TW and 4≦n≦40
Byte 44—Tmp multi pulse duration at reference velocity.
n=16×Tmp/TW and 4≦n≦16
Byte 45—Tlp last pulse duration at reference velocity.
n=16×Tlp/TW and 4≦n≦24
Byte 46—dTtop first pulse lead time at reference velocity.
n=16×dTtop/TW and 0≦n≦24
Byte 47—dTle 1st pulse leading edge correction for previous space =3 at reference velocity.
n=16×Ttop/TW and 4≦n≦40
Byte 49—Ttop (3) first pulse duration for current mark=3 at maximum velocity.
n=16×Ttop/TW and 4≦n≦40
Byte 50—Tmp multi pulse duration at maximum velocity.
n=16×Tmp/TW and 4≦n≦16
Byte 51—Tlp last pulse duration at maximum velocity.
n=16×Tlp/TW and 4≦n≦24
Byte 52—dTtop first pulse lead time at maximum velocity.
n=16×dTtop/TW and 0≦n≦24
Byte 53—dTle first pulse leading edge correction for previous space=3 at maximum velocity.
The Extended information blocks can be used to store the numerical gain setting of the waveform equalizer 6, byte 64 for example.
For an information carrier 11 with the Blu-ray Disc Recordable (BD-R) format the numerical gain setting can for instance be stored in the Permanent Information & Control data zone (PIC) of the information carrier 11. The PIC zone is located in the Lead-in Zone. The PIC zone contains a Disc Information table which is perfectly suitable for storing the numerical gain setting.
An example of the internal structure of the waveform equalizer 6 is shown in
The waveform equalizer 6 may be followed by a limit equalizer. This embodiment is shown in
The read signal S is fed to the same waveform equalizer 6 as shown in
The amplitude limiting circuit 62 counteracts an increase of inter symbol interference. Without the amplitude limiting circuit 62, if an excessive high frequency emphasis is made, inter symbol interference increases and, as a result jitter increases.
In
O
fl(n)=S(n−3) Equation 1
where Ofl(n) stands for the output of the first filter 61 at sampling instant n, and S(n−3) stands for the input of the first filter 61 at sampling instant n−3.
The second filter 63 is a FIR filter having tap coefficients [−m,+m,+m,−m]. This means that an input to this filter is delayed by three tap delays D4, D5 and D6, and there are four outputs fed to amplifying units A5, A6, A7 and A8 having an amplification factor of respectively −m, +m, +m and −m. The first amplifier A5 placed directly after the input SLIM, the second amplifier A6 is placed after the first delay tap D4, etc. The outputs of the amplifying units A5 to A8 are added by adder B2. The output Of2 of the second filter relates to the input Slim of the second filter 63 as expressed in equation 2:
O
f2(n)=−m.Slim(n)+m.Slim(n−1)+m.Slim(n−2)+−m.Slim(n−3) Equation 2
The total output S′ of this embodiment of the waveform equalizer 6:
S′=−m.S
lim(n)+m.Slim(n−1)+m.Slim(n−2)+−m.Slim(n−3)+S(n−3) Equation 3
The optimal value of the gains K and/or m is dependent on the noise characteristics of the information carrier 11. The optimal value of the gains K and/or m is therefore stored on the information carrier 11, read out by the gain setting means 1 and subsequently set to the read numerical gain setting.
After this description of the invention with reference to preferred embodiments thereof, it is to be understood that these are not limitative examples. Thus, various modifications will be apparent to those skilled in the art, without departing from the scope of the invention, as defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04105882.7 | Nov 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2005/053785 | 11/16/2005 | WO | 00 | 3/17/2009 |
