Method for Detecting Starting Position of Data Recording Block

The present invention relates to a method for detecting a starting position of each data recording block on a data recording medium such as an optical disk, and more particularly to a reliable method for detecting a starting position of each data recording block.

Heretofore in an optical disk apparatus, as shown in FIG. 4(1) of the accompanying drawings, there are provided on a recording medium chiefly ID areas in which respective track numbers, respective sector numbers and other data necessary for recording-reproducing are recorded in advance, and DATA areas in which user data are to be recorded.

At the starting position of each ID area, a pattern called "a sector mark" (SM) indicating the starting position of a sector (or data recording block) is recorded in a manner different from a data modulating manner. Each sector mark is placed between a gap (GAP) area and an ID area. In the accompanying drawings, symbol `A` designates a sector.

Since a detection signal of a sector mark is used as a timing signal for reading and writing, a very high degree of reliability is required for the detection of the sector mark. To secure such high reliability, according to conventional prior art methods, the GAP area ahead of a sector mark is detected to generate a gate signal which predicts the position of the sector mark following the GAP. The sector mark would be detected during a period of time designated by the gate signal.

From the view point as to whether or not the frequency of a recording/reproducing clock is variable, the optical-disk recording/reproducing method can be classified into a CAV (Constant Angular Velocity) method in which the frequency of an optical-disk recording/reproducing clock is unchanged over the entire surface of the disk, as shown in FIG. 4(2) of the accompanying drawings, and an MCAV (Modified CAV) method in which the recording surface of the optical disk is divided into some concentric zones and the frequency of the recording/reproducing clock in an outer zone is higher than that in an inner zone so that the recording capacity of the disk can be increased.

Also, from the view point as to how data bits `1` and `0` are recorded on the disk, the recording/reproducing method is classified into a pit-position recording/reproducing method in which `1` is represented by the position of a pit, as shown in FIG. 3(1), and a pit-edge recording/reproducing method in which `1` is represented by an edge of a pit, as shown in FIG. 3(2).

The foregoing prior art system is effective for detecting the sector mark in the pit-position recording/reproducing system regardless of which of the CAV method or the MCAV method is employed therein. However, in the pit-edge recording/reproducing system, the sector mark pattern area would be larger than that in the pit-position recording/reproducing system. In order to make the sector mark pattern different from any of the data patterns, the pits of the sector mark pattern would be elongated in the pit-edge recording/reproducing system as seen from FIG. 3, causing the following problems:

(1) The data formatting efficiency would be lowered. This is because the available storage capacity is lowered by the amount of increase of the sector mark pattern area which causes reduction of the writing area of the user's data.

(2) Automatic focusing accuracy and tracking accuracy would be lowered. This is because the sector mark pattern area in the form of elongated pits reflects a remarkably less amount of light, compared to other areas in the automatic focusing for automatically focusing a light spot on a recording surface of the disk and in the tracking control of the light spot onto grooves of the disk, thus impeding the stability of a servo system.

The present invention provides a method for highly reliable detection of a starting position of a data recording block.

A first aspect of the present invention relates to a method for detecting a starting position of a data recording block on a data recording medium on which a VFO pattern and a CRC code are recorded at a starting position of each of the data recording blocks. The starting position of the data recording block is detected by utilizing at least one of the result of detection of the VFO pattern and the result of operation of the CRC.

Preferably, the starting position of the recorded data block is detected such that firstly in a pull-in state the VFO pattern is detected several times, and then in a steady state the result of operation of the CRC is utilized.

According to a second aspect of the invention, there is provided a recording/reproducing apparatus of a recording medium having an address area performatted at a starting position of each of the sectors, comprising: means for detecting a predetermined pattern of data pulse train; means for creating a reading timing, at which an associated address is to be read, according to the detection of the predetermined pattern of data pulse train; means for discriminating whether the address thus read is correct or not; and means for creating recording/reproducing timings, for the sector of the address and an address reading timing for the next sector based on the time point when the address is read.

Preferably the apparatus further comprises means for generating a mask signal which prohibits the detection of the predetermined pattern of data pulse train for a predetermined period from the time point when the address was correctly read.

Likewise the apparatus may further comprise means for storing the time point when the address was read; means for calculating a difference between the time point for the previous sector and the time point for the current sector, based on the content of storage of the storing means; and means for generating an address reproducing timing for the next sector based on the calculated difference.

The recording medium may have a plurality of address data at the starting position of each of the sectors, and the difference calculating means may be capable of calculating an immediately previous inter-sector distance from the time point when any of the addresses in the previous sector was read and the time point when any of the addresses in the current sector was read.

In general, at a starting position of a data recording block at a sector on a recording medium such as an optical disk, a VFO pattern for creating a synchronizing clock and a CRC (Cyclic Redundancy Check) code for discriminating whether an address was read correctly or not. In this invention, for detecting the starting position of a sector, the result of detection of a VFO pattern and/or the result of calculation of a CRC code are used, without a dedicated pattern such as a sector mark pattern. Further, highly reliable detection of the starting position of a sector can be realized by additionally using a gate signal to eliminate any misoperation.

Accordingly it is possible to prevent the formatting efficiency from lowering, while maintaining the accuracy of automatic focusing and tracking. Regarding the formatting efficiency, not only since the lowering of the formatting efficiency is prevented, but also since the sector mark itself can be removed, it is possible to positively increase the data writing area.

FIG. 1 is a circuit diagram showing a detecting system for detecting a starting position of a sector in which the present invention is incorporated;

FIG. 2 is a timing chart showing the operation of the detecting system of FIG. 1;

FIG. 3 is a pit diagram showing a pit-position recording/reproducing method and a pit-edge recording/reproducing method; and

FIGS. 4(1), 4(2) and 4(3) are diagrams showing a sector format, a form of CAV disk and a form of MCAV disk.

One embodiment of the present invention will now be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a circuit diagram showing a detecting system for detecting a starting position of a sector in which the present invention is incorporated, and FIG. 2 is a timing chart showing the operation of the detecting system of FIG. 1.

In FIG. 1, reference numeral 1 designates an optical disk; 2, an optical head; 3, a preamplifier; 4, a data reproducing circuit; 5, an analog-to-digital (A/D) converter; 6, a CRC operating circuit; 7, a VFO pattern detecting circuit; 8, a selector; 9, a counter; 10, a gate signal generating circuit; and 11, a control circuit for controlling the detection of the starting position of a sector.

A signal read from the optical disk 1 by the optical head 2 is input through the preamplifier 3 to the A/D converter 5. An amplified signal 102 output by the preamplifier 3 is also input to the data reproducing circuit 4. The data reproducing circuit 4 outputs a reproducing signal 103 and a CRC operation data signal 104. In the meantime, the VFO pattern detecting circuit 7 receives a digital signal 105 output from the A/D converter 5 and detects, at the start of detection of the starting position of a sector, a VFO pattern prerecorded in an ID area, and then outputs a detection signal 109. At that time, a selector control signal 110 causes an output signal 111 of the selector 8 to output the VFO pattern detection signal, with the selector 8 being controlled to be in a mode selecting the VFO pattern detection signal. As shown at a time point t1 in the timing chart of FIG. 2, this signal resets the output 113 of the counter 9 to "0" to initiate counting clocks (not shown) of a constant frequency. Based on this output 113 of the counter 9, the gate signal generating circuit 10 generates a VFO pattern detection mask gate signal 116. This gate signal 116 is a signal that enables the VFO pattern detection signal only during a period of time during which the VFO pattern of the next sector will be predicted to be detected.

When a VFO pattern is detected at the next sector, the output 113 of the counter 9 is reset (time point t2) again to "0" to initiate new counting, to instruct the control circuit 11 to switch the mode from a VFO pattern detecting mode to a CRC1 detecting mode in response to a gate signal control signal 114, while causing the gate signal generating circuit 10 to output a detection gate signal 106 for gating the result of operation of CRC1. Thus a pull-in mode has been completed and this system proceeds into a steady mode.

The CRC operating circuit 6 receives a CRC operation data signal 104 to perform CRC operation. If the result of operation of CRC is OK while the detection gate signal 106 is "1", it turned out in the CRC1 operating circuit 6 that the result of operation of CRC1 is correct, and the circuit 6 outputs a CRC1 OK signal 108. At that time, the selector control signal 110 selects the mode for selecting the CRC1 OK signal 108 to output the CRC1 OK signal as the output signal 111 of the selector 8. This signal 111 causes the output 113 of the counter 9 to be reset (time point t3) again to "0", initiates new counting based on the CRC1 OK signal 108, and then the result of operation of CRC1 of the next sector is monitored.

If the result of operation of the next sector is OK, the CRC1 OK signal 108 is dealt with as a sector's starting position detection signal, so that the signal can be a reference to create various timing signals needed for writing and reading. Creating these various timing signals can be realized by using the counter 9 and the gate signal generating circuit 10.

While monitoring the result of operation of the CRC1, when the result of operation of the CRC1 does not become OK (time point 14) during a period of time during which the CRC1 OK detection gate signal 106 is "1", the gate signal generating circuit 10 reports to the control circuit 11 by a CRC1 NG signal 115 that the result of operation of CRC1 was NG. Upon receipt of this signal, the control circuit 11 outputs to the gate signal generating circuit 10 an instructing signal 114 which causes the circuit 10 to output a gate signal 107 for gating the result of operation of CRC2. The control circuit 11 also outputs to the selector 8 an instructing signal 110 which causes the selector 8 to output the result of operation of CRC2. According to these instructions, the CRC operating circuit 6 operates CRC2 based on the CRC2 operation data signal 104.

If the result of operation of CRC2 is OK while the detection gate signal 107 is "1", it turned out in the CRC2 operating circuit 6 that the result of operation of CRC2 was correct, and outputs a CRC2 OK signal 108. Upon receipt of this signal, the control circuit 11 outputs (time point t5) a correction instructing signal 112 for correcting the output value 113 of the counter 9 by the amount of interval "X1" from CRC1 OK to CRC2 OK. Upon completion of the correction, the counter 9 starts counting and then the result of operation of CRC1 (or the result of operation of CRC2 in the case of CRC1 NG as mentioned above) of the next sector is monitored. Also in this case, the starting position of a sector is regarded to be detected in a pseudo manner with the corrected value of the counter output 113, so that timing signals necessary for writing and reading can be generated without intermission.

If the results of operation of both CRC1 and CRC2 are NG, the gate signal generating circuit gives CRC1 NG and CRC2 NG signals 115 to the control circuit 11, whereupon the control circuit 11 outputs a correction instructing signal 112 to the counter 9 to correct the output value 113 of the counter 9 by the amount of interval "X2" from CRC1 OK to CRC2 NG (time point t6). Also in this case, the starting position of a sector is regarded to be detected in a pseudo manner with the corrected value of the counter output 113, so that timing signals necessary for writing and reading can be generated without intermission.

Detection of the GAP (FIG. 2) ahead of the VFO by the VFO pattern detecting circuit 7 may be prerequisite for detection of a VFO pattern. In this case, instead of gating the VFO pattern detection, the GAP detection may be gated.

Further, if the VFO pattern detecting circuit 7 detects any abnormal number of rotations per unit time from the result of measurement of interval of the CRC1 OK detection (the counter output value 113) or if it is detected that a pair of operations of CRC1 and CRC2 happened to occur successively a predetermined number of times or more, it may effect the generation of correct timing signals necessary for writing and reading. Consequently, it may be done over again from detecting the starting position of a sector in the pull-in mode (VFO pattern detection) so that timing signals necessary for normal writing and reading can be provided.

In the pit-edge recording/reproducing method, the leading edges and trailing edges of a read signal could be reproduced separately. In this case, detection of a VFO pattern is performed from data 117, 118 (FIG. 1) respectively from the leading edge and the trailing edge, and the mode is then shifted to a mode for monitoring the result of operation of CRC, so that timing signals necessary for writing and reading can be provided.

In the illustrated embodiment, in the mode (steady state) for monitoring the result of operation of CRC, the monitoring is performed on the basis of measuring the interval between CRC1 OK and CRC1 OK. Alternatively, the starting position of a sector may be detected on the basis of measuring the interval such as between CRC1 OK and CRC2 OK, between CRC2 OK and CRC2 OK, or between CRC2 OK and CRC1 OK, so that timing signals necessary for writing and reading can be provided.

The detecting system may be further provided with a storage means for storing the time point at which the address was correctly read according to the result of operation of CRC, and another storage means for storing the difference (i.e., the interval between adjacent sectors) between the time point at which the address of the previous sector was read and the time point at which the address of the current sector was read. Based on this stored sector interval, a timing signal for reading the address of the next sector may be issued. If both CRC1 and CRC2 of the sector are NG, it is impossible to calculate the sector interval, in which event the previously stored value can be utilized.

In the case of pit-edge recording/reproducing, detections of a data pulse and a GAP may be performed by a first-order differential signal of the reproduced signal. In this case, detection of a data pulse or the like may be performed for the signal after the gain of the reproduced signal has been controlled (AGC: Automatic Gain Control).

Though the present invention is suitable when incorporated in an optical disk apparatus implementing edge recording/reproducing, it is a feature of the present invention to detect the starting position of a data recording block, without a sector mark. In the present sense, this invention may also be adopted to the pit-position recording/reproducing method and then to a recording medium other than an optical disk.

As mentioned above, according to the present invention, it is possible to detect a VFO pattern in an ID area, and to secure the high reliability in detecting the starting position of a sector by regarding the result of operation of CRC as the result of detection of the sector's starting position without a pattern such as a sector mark dedicated for detecting the starting position of a sector. Therefore, if the present invention is incorporated in an optical disk apparatus adopting pit-edge recording/reproducing, it is possible to improve the data formatting efficiency while maintaining the automatic focusing and tracking accuracy.