CA1213047A

CA1213047A - Method for the storage on and the reproduction from an optically readable record carrier, record carrier for use in the method and apparatus for use in the method

Info

Publication number: CA1213047A
Application number: CA000449683A
Authority: CA
Inventors: Constant P.M.J. Baggen
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1983-03-17
Filing date: 1984-03-15
Publication date: 1986-10-21
Also published as: ES530578A0; EP0119657A1; NL8300961A; KR840008871A; JPS59188840A; US4667317A; ATE28946T1; SG9788G; AU2564784A; EP0119657B1; ES8503879A1; DE3465390D1

Abstract

ABSTRACT:

Method for the storage on and the reproduction from an optically readable record carrier, record carrier for use in the method and apparatus for use in the method.

A method is described for storing and reproducing data words by means of a standard compact disk digital audio player. The bit groups in which said data words are contained are recorded at least three times, the analog output signal of the player being sampled and digitized during reproduction.

Description

.3~7 PHN. 10.626 The in~ention relates to.a method of storing groups of n bits on:and reproducing them from an optically readable record carrier, which groups each represent.an analog signal value, said groups being recovered from.a signal obtained by reading said:record carrier during reproduction,~after which said groups: are subjected to an interpolation process, in which:a group to he substituted for.an unreliable group is generated from groups situated on.both sides of the unreliable group by interpolation of ~aid groups, and subsequently to:a digital-to-analog conversion for converting said groups i.nto the correspond-ing analog signal.~alues.
The invention:also relates to:a record carrier for use in the method.
The invention.also relates to:a first.apparatus for use in the method, co~prising:a read:apparatus,:a decoding circuit:for.reco~ering groups of n bits which each:represent:an:analog signal.~alue from the signal read, .an interpolation cirauit for generating a substitute group for:an unreliable group by interpolation of the groups situated on.both sides of said unreliable group,.and a digital-to-analog con~erter for converting said groups into the corresponding.analog.signal.values.
Moreover, the invention relates to:a second 25 : apparatus for use in the method.
Such::a method, record :carrier:and:apparatus.are known.from Philips Techni:cal Review, Vol. 40, 1982, No~.6, the complete issue. Such::apparatuses:and rec~rd .carriers are commercially:a~ailab:le under the designation Compact 3Q Dick Digital Audio System and are used for reproducing : audio in~ormation which is:recorded on the optically read-:able record carr:ier in digi~ally coded form~

, ~.

PHN.10.626 2 22.8.83 In the same way as audio cassettes such a recorcl carrier may be usecl for the s-torage of o-ther da-ta, in par-ticu:Lar computer da-ta, such as computer programs and computer games. However, -the risk of an erroneous bi-t group is too great for this purpose~ In the case of ~igi-tal audio said errors are largely masked bysaicl in-terpolation, which is effecti-ve in the case of digi-tal audio because adjacen-t bi-t groups represent correla-ted signal values and the substitute signal value obtained through interpolation will generally be compatible witLl the original signal value.
~Iowever, if as in the case of said computer data, the bit groups are uncorrelated~ the interpolation will resu~t in a bit group ~hich has no relation with -the original bit group. Thus, for such a use interpolation is unlikely to improve the error probability.
~ t is the object of the invention to provide a method of the type mentioned in -tha opening paragraph which enables a simple storage and reproduc-tion with a - reduced error probability. Theinvention is embodied in the method, the record carrier in the two apparatuses.
The method in accordance with -the invention is charac-terized in that 2 (m ~ 1) analog signal values which are each re-presentative of a da-ta word of m bits correspond to the groups of n bits~ said data words are each stored on the record carrier in the form of k(lc ~ 3) groups representing said data word, andper period corresponding to k groups which are representative of said data word the analog signal obtained by digital-to-analog conversion is sampled at an instant which is situatecl from both limits of said period of k groups at least at a tima in~er~al corresponding -to the repetition period of the groups in the signal obtained after read-out.
The invention is based on the recognition that in this ~ay using a standard compact-disk digital audio player including the in-terpolation circuit it is yet possible to s-tore and reproduce data in a reliable manner because by repea-ting said groups a-t least -three times and - ~2~3~7 PllN.10.~26 3 22.~.83 subsequen-tly sampling -them at the correct instan-t erroneous in-terpolation canno-t be genera-ted by interpolating a-t the sampling instant.
The record carrier for use in the inventive methocl may be characterized in -that -the recorded signal comprises gro~lps of n bits which correspond to 2 (m ~ 1) analog signal values which are each represen-tative of a data word of m bits, said data words each being s-torecl in the form of k(k j 3) groups representing said clata word.
The firs-t apparatus o~ the type mentioned in -the introductory part ~or use in the method in accordance with the invention may be characterized ~!~y a sampling circuit for sampling the obtained analog signal per period corres-ponding to k groups representa-tive of said data word a-t an 15 instant which is situa-ted within both limits of said period of k groups at least at a time interval corresponding -to the repetition period of the groups in the output signal of the decoding circuit.
The second apparatus for use in the method in

2~ accordance with the invention may be characterized in that the apparatus is provided with an analog input for receiving a signal from a compact disk digital audio player?
a sampling circuit for sampling -the analogue signal re-ceived per periocl corresponding to k groups representative 25 of said data word at an instan-t which is situated from both limits of said period of k groups at least at a time interval corresponding to the repetition period of the groups? an analog-to-digital converter whose input is connec-ted to the output o~ the sampling circuit, and an 30 output for a digital signal~ which autput is connected to the output of the analog-to-digital converter.
This second apparatus has the advantage that a first apparatus is ob-tained by connection to -the ou-tput of an existing player for audio-signal reproduction.
The method and the record carrier may further be characterized in that the m most significant bits of the groups of n bits directly cons-titute the data word of m bits~

:~2~L3~7 PHN.10.626 4 22.8.83 In this way -the data words can be recoverecl very simply from -the ou-tpu-t signal of the sampling circ~tit by means of an A/D conver-ter~
In order to ob-tain clock informa-tion in a simple manner the methocl and the recorcl carrier in accorclance with the inven-tion may further be characterized in that a clock modulation ls inserted at one of the n bits which is less significant than -the m most significant bits.
In this respect it is advantageous tha-t the periocl of the clock modulation corresponds to the duration of k groups.
~ s a result of this step the frequency of this clock information is situated in a zero point of the data-information spectrum because the clock fraquency is -then 2 the repeti-tion frequeney of the data ~ords.
This version of the method and the record carrier may further be characterized in that k is an even number and the clock modulation is obtained in that the bit intended for the clock modulation alternately assumes one of two logic levels every k/2 groups.
Thus, a elock signal ot' a symme-trical shape~
which is simple to process electronically, is obtained in the analog signal.
Specifically, a preferred version of the method and the record carrier in accordance wi-th the invention may be characterized in that n='16 and m=10, the clock modulation is inserted in the 13 h bit, and -the 11 h and 12 h bit have a fixed logic value, and that after sampling the signal is su'bjected to an analog~to-digital conversion.
~ or the recovery of the digital data words the first apparatus may fur-ther be characterized in that an analog-to-digital converter is arranged af-ter thesampling circuit.
~ or -the recovery of a clock signal the first apparatus may further 'be charac-terized in tha-t the apparatus further comprises a filter which is tuned to the clock frequency and l~hich is connected to the output of -the ~3~7 PHN.10.626 5 22.8.83 digital-to-analog conver-ter, and a phase-locked loop ~or ~erlving a cloc~ frequency for controlling -the sampling cireuit from the analog signal, ancl the seeond apparatus may ~urther be characterized in -that -the appara-tus ~urtller comprises a filter which is tuned -to the clock ~requency and which is eonnec-ted -to the analog input~ and a phase-lockecl loop for cleriving a clock frequeney ~or controlling -the sampling circuit from the analog signal.
The inven-tion will now be described in more detail, by way o~ example, with re~erence to the accompanying drawings, in which Figure 1 shows an apparatus for carrying out the method in aceorclanee with the invention~
~ igure 2 shows some diagrams to illustrate the operation o~ the interpolation eireuit in said apparatus, Figure 3 shows some diagrams to e~plain -the operation o~ said apparatus.
Figure 1 shows an apparatus ~or earrying ou-t the method in aeeordanee with the invention. I-t eomprises an optieal read appara-tus 1 whieh reads a disk-shaped reeord earrier 3, clriven by a drive means 4~ by means of a laser beam 2~ The signal read is appliecl to a deeoder eireuit 5 in whieh the signal is modula-ted, arrangecl and subjected to an error eorreetion process in con~ormity ~i-th the standard eompaet-disk digital audio sys-tem. On the ou-tputs l6-bi-t digital audio signals appear ~or -the le~t-hand ehannel (output 6) and ~or -the right-hand ehannel (output 8), a reliabili-ty ~lag ~or the digital samples in the lefthand signal (output 7), a reliability ~lag for the digital samples in the right-hand ehannel (output 9~ and a eloek signal (output 10) representing the sampling ~re~ueney (44.1 k~Iz). These signals are applied to an interpolation eireuit 11 ~hieh generates a new sample ~hen the reliabili-ty

3 flag indica-tes that-tl-lis sample is unreliable. Moreover, the eireuit l 1 may be designed so tha-t the signal is suppressed temporarily when too many unreliable samples appear, whieh depending on the version, may already be the ease in -the 3~7 PHN.10.626 6 22.8.83 even-t of two consecutive erroneous samples. The output signal of the interpolation circuit 11, -together wlth the sampling frequency, is applied to a D/A converter 12, which procluces an analog signal on outputs 13 (lef-t-hancl channel) ancl 1L~
(right-hand channel), which converter also comprises a low-pass filter. So far the apparatus corresponds to a standard compact-disk digital auclio player.
Figure 2 illustrates the operation of theinter-polation circui-t 11 when, in accordance with the invention, l0 each sample is repeated at least three -times. Figure 2a shows these samples S1~ S2 and S3 ~ith corresponding analog signal values ~3 followed by three samples S4, S5 and S6 with the analog signal values A1. When the reliability flag indicates that sample S3 is unreliable a sample S30 i9 15 generated with a coresponding analog signal value A2 = ''(A1 ~ ~3) between the analog signal values of the samples S2 and S4. If as indicated in Figure 2b the sample S2 is unreliable, -the interpolation circuit substitutes it by the sample S20 of a corresponding signal value between 20 the signal values of the samples S1 and S3 and consequently icdentical to the sample S2. 11hen a sample is repeated three times the central sample is always correct in the case of interpolation of one erroneous sample, regarclless of which sample is obtained by in-terpolation.
Figures 2c and 2d represent a si-tuation in which -the samples are repeatecl four -times. Four identical samples S1 to SL~ are shown, followed by four identical samples S5 to S8 of corresponding signal values A3 and A1, respectively.
In Figure 2c it is assumed that the sample S4 is incorrect.
3C The in-terpolation circuit then generates a sample SL~o of the analog signal value ~2. In the situation of Figure 2d it is assumed that the sample S3 is not correct. The inter-polation circuit then genera-tes as identical-sample S30.
Both the sample S2 and S3 remain correct regardless of the 35 place of an incorrect sample.
In general-it is therefore correct to state that when each sample is repeated at least -three times the gL7 PHN.'10.626 7 22.8.~3 corresponcling analog signal values within each block of repea-tecl samples are correct in the range w'hich is situated within -the limits O:r each block at least at a time inter-val equal to the repetition period of -the samples provicled that -the num'ber of consecu-tive erroneous samples is not greater -than two~ although these situations may also -turn out to be correct in the case o-f a corresponding ex-tension of` the blocks and the interpolation period. For example, two consecutive incorrect samples upon insertion of the samples by interpolation do not present problems when each sample is repeatecl five times or more~
The invention is based on tha insights outlined in the foregoing. The apparatus shown in Figure 1 therefore comprises a sampling circuit 15 for sampling the analog ou-tput signals on outputs 13 and 1 ~r (in principle it is also possible to use only one of the two channels) at the correct instants. For this purpose a clock signal is derived from the analog signal on outpu-t 14, for example by means of a phase-locked loop 16. The output signal on the outpu-t 20 of the sampling circuit 15 is converted into a digital code by means of an analog-to-digi-tal converter 1~ hich code appears on output lS (left-hand channel) and '19 ~right-hand channel) together with the clock signal on output 20.
Figure 3 illus-trates the operation by means of 25 e~am7)le where 2-bit clata words are s-tored via ~-bit samples which are repeated three times, Figure 3a shows three con-secutive data words 1'l, 0-l and 10. They may be represen-ted by a selection of one out of four analog signal values Ao~ Al, A2 and ~3. ~n the case of a selection in accordance 3~ with a binary series the values Ao~ Al, A2 and A3 respect-ively correspond to the data words 00~ 01, 'lO and 11 and may therefore 'be recordefl directly on -the record carrier as two bits of samples ~ hen each sample is repeated three -times the pa-ttern shown in Figure 3b is obtained.
After read-out ancl digital-to-analog conversion the pattern, in conformity with the invention, should be sarnpled at the location of the samples S2, S5, s~ For this purpose a clock ~3~7 PHN.lo.626 8 22.~.83 signal as shown in Figure3c may be proviclecl, which signal comprises one bi-t which assumes -the logic value 1 at the location of the samples S2, S5, S . This bit ma-y be added to the samples S at some distance (for example, one bit) 5 as a less-significan-t bit~ so that four-bi-t samples are obtained. Af-ter read-out and demodulation this yielcls the signal shown in Figure 3cl on the output of the democlula-tor 5.
It is now assumecl that -the samples S3 and S8 are incorrect.
The interpola-tion circuit 11 then inserts a sample of the lO corresponding analogue signal value A2 instead of A1 for the sample S3, whilst of -the sample S~ the clock modulation disappears. Thus, a signal as shown in Figure 3e appears on the output of thein-terpolation circuit 11 ~ whicll signal is converted into a signal as shown in Figure 3f (when the filtration is ignored) by the n/A converter 12, which signal has the incorrect value A2 at the location of sample S3 and from which the clock modulation is rnissing at the location of the sample S8. By means of the filter andphase-locked loop circui-t 16 the clock signal is derived (Figure 3g), said pllase locked loop inserting the missing clock pulse at -the location ofthe sample S8 without any problems.
After sampling the signal shown in Figure 3h is obtained on the output of -this sampling circuit l5~ whic1l signal is con-verted into -t~ logic signal shown :in Figure 3i by the ~/D
converter l7~ the A/D converter in -the present example being a two-bit conver-ter because the two least-significant bits need no-t be converted. Thus, theerroneous samples S2 and S8 do not disturb -the reproduction of tne logic signal shown in Figure 3a.
In the present example a repetition of three times is used. In a practical example, in which 10-bit data words are accommodated in 16~bit samples as most significant bits, -the clock modula-tion being applied -to the 13 bi-t (note that the clock modulation must be added to only one of the two stereo chalmels when the information in the -two channels allows this), a repetition of four times is chosen because tllen a symme-trical clock may be used with a change Or the logic level after every 2 bi-t, i.e. in the exanlple ~Z~3~7 PHN.10.626 9 22~.83 shown in Figure 3c be-tween the samples S2 ancl S3, SL~ ancl S5~ S6 and S7, e-te., which simpli-ries -the logic. I-t is -to be noted tllat a repetition of four or more times is ad-vantageous in comparison with three times repetition beeause in -the case of three -times repetition sampling must be ef~ected exactly a-t the central bit group, which imposes stringent requirements on the s-tability of -theclock signal.
The choice of a clock with a frequency which is twice as high as the repetition frequency of` the data words (Figure 3i) moreover has the advantage that this clock then appears in a zero point of the frequeney speetrum of the data words.
In the manner described in the foregoing a standard compact-disl~ digital audio player may be adapted for the transfer of cda-ta signals, in particular non-intereorrelated data words, wi-thout modi~ying the player, in which case the error probability would be too high i~
no additional steps were taken. Because in general said player is already in use for audio purposes, it may be advantageous to clesign an adaptor comprising the sampling circuit 15, the phase-locked loop 16 and the analog-to-digital converter 17.
Obviously, it is possible to achieve an additional 25 error correetion in the eoding of -the da-ta worcLs themselves b~ means of parity bits and the like.
In the apparatus 5 the samples are provided with a reliabili-ty ~lag. In principle, it would therefore be possible to selec-t always a reliable sample from the groups 30 Or three or more samples wi-thout the use of` the inventive principle. ~Io~ever, then it is necessary -to equip the player with an output sueh that the interpolation circuit 11 has no undesired ef`fects, but this has the disadvantage that for this purpose standard compact-disk digital audio 35 players have to be modifiecl, By way o-f illustration Figure 1 shows such a modifieation. For this purpose the outpu-ts 6 to 9 o~ the decoder device 5 are connec-ted to a selec-tion device 21 in which from each group one reliable sample is ~2~3~7 PHN.10.626 10 22.8.83 selected, which directly iIl cligi-tal forrn is applied to an output 22 (le~t-hand channel) and 23 (righ-t-tland channel) respec-tively. All 16 bits of eaeh sample may then be utilized for the data word. For -the purpose of synchronization the sampling frequency on the output 10 of the demodulation circui-t is divicled by -the number of samples per da-ta 1~ord by means of a divider stage 22, steps being taken to ensure the correct phase relationship. This clock frequency is also applied to an output 25. The player -thus modified is suitable l0 ~or use wi-th record carriers in which all l6 bits are em-~
ployed for data storage.
The complete apparatus shown in Figure 1 may be advantageous because it is suitable for both sys-tems and, if desired, for audio reprodue-tion.
In prineiple, it is also possible to s-tore and reproduee one-bit data words. The A/D eonverter 17 is then a one-bit eonverter or discrimina-tor.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS

1. A method of storing groups of n bits on and reproducing them from an optically readable record carrier, which groups each represent an analog signal value, in which said groups are recovered from a signal obtained by reading said record carrier during reproduction, after which said groups are subjected to an interpolation process, in which a group to be substituted for an unreliable group is generated from the groups situated on both sides of the unreliable group by interpolation of said groups and sub-sequently to a digital-to-analog conversion for converting said groups into the corresponding analog signal values, characterized in that 2m(m ? 1) analog signal values which are each representative of a data word of m bits correspond to the groups of n bits, said data words are each stored in the record carrier in the form of k (k ? 3) groups repre-senting said data word, and per period corresponding to k groups which are representative of said data word the analogue signal obtained by digital-to-analog conversion is sampled at an instant which is situated from both limits of said period of k groups at least at a time interval corresponding to the repetition period of the groups in the signal obtained after read-out.

2. A method as claimed in Claim 1, characterized in that the m most-significant bits of the groups of n bits directly constitute the data word of m bits.

3. A method as claimed in Claim 2, characterized in that a clock modulation is inserted at one bit of the n bits, which is less significant than the m most significant bits.

4. A method as claimed in Claim 3, characterized in that the period of the clock modulation corresponds to the duration if k groups.

5. A method as claimed in Claim 4, characterized in that k is an even number and the clock modulation is obtained in that the bit intended for the clock modulation alternately assumes one of two logic levels every k/2 groups.

6. A method as claimed in Claim 3, 4 or 5, charac-terized in that n = 16 and m = 10, the clock modulation is inserted in the 13th bit, and the 11th and 12th bit have a fixed logic value.

7. A method as claimed in Claim 1, characterized in that after sampling the signal is subjected to an analog-to-digital conversion.

8. A record carrier for use in the method as claimed in Claim 1, characterized in that the recorded signal com-prises groups of n bits, which correspond to 2m(m ? 1) analog signal values which are each representative of a data word of m bits, said data words each being stored in the form if k (k ? 3) groups representing said data word.

9. A record carrier as claimed in Claim 8, charac-terized in that the m most-significant bits of the groups of n bits directly constitute the data word of m bits.

10. A record carrier as claimed in Claim 9, charac-terized in that a clock modulation is inserted at one of the n bits which is less significant than the m most significant bits.

11. A record carrier as claimed in Claim 10, charac-terized in that the period of the clock modulation cor-responds to the duration of k groups.

12. A record carrier as claimed in Claim 11, charac-terized in that k is an even number and the clock modula-tion is obtained in that the bit intended for the clock modulation alternately assumes one of two logic values every k/2 groups.

13. A record carrier as claimed in Claim 10, 11 or 12, characterized in that n=16 and m=10, the clock modulation is inserted in the 13th bit and the 11th and 12th bit have a fixed logic value.

14. An apparatus for use in conjunction with the method as claimed in Claim 1, comprising a read apparatus, a decoding circuit for recovering groups of n bits which each represent an analog signal value from the signal read, an interpolation circuit for generating a substitute group for an unreliable group by interpolation of the groups situated on both sides of said unreliable group, and a digital-to-analog converter for converting said groups into the corresponding analog signal values, characterized by a sampling circuit for sampling the obtained analog signal per period corresponding to k groups representative of said data word at an instant which is situated within both limits of said period of k groups at least at a time interval corresponding to the repetition period of the groups in the output signal of the decoding circuit.

15. An apparatus as claimed in Claim 14, charac-terized in that an analog-to-digital converter is arranged after the sampling circuit.

16. An apparatus as claimed in Claim 14 or 15, char-acterized in that the apparatus further comprises a filter which is tuned to the clock frequency and which is connected to the output of the digital-to-analog conver-ter, and a phase-locked loop for deriving a clock frequency for controlling the sampling circuit from the analog sig-nal.

17. An apparatus for use in conjunction with the method as claimed in Claim 1, characterized in that the apparatus is provided with an analog input for receiving a signal from a compact-disk digital audio player, a sampling circuit for sampling the analogue signal received per period corresponding to k groups representative of said data word at an instant which is situated from both limits of said period of k groups at least at a time interval corresponding to the repetition period of the groups, an analog-to-digital converter whose input is connected to the output of the sampling circuit, and an output for a digital signal, which output is connected to the output of the analog-to-digital converter.

18. An apparatus as claimed in Claim 17, charac-terized in that the apparatus further comprises a filter which is tuned to the clock frequency and which is connected to the analog input, and a phase-locked loop for deriving a clock frequency for controlling the sampling circuit from the analog signal.