Polarity switching signal generator, method of the same, and optical disk drive

A polarity switching signal generator able to stably generate a suitable polarity switching signal for inverting the polarity of a tracking error signal, wherein a reference value stored in a reference value storage circuit is updated by a rotational angle indicated by a rotational angle signal at a switching position of a land and groove captured by a capture circuit when an address decode signal is normal and wherein, further, a comparator compares the reference value stored in the reference value storage circuit with the rotational angle indicated by the rotational angle signal and generates a polarity switching signal instructing the switching of the polarity when they match.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a polarity switching signal generator able
 to stably generate a suitable tracking error signal, a method of the same,
 and an optical disk drive.
 2. Description of the Related Art
 Digital versatile disk-random access memory (DVD-RAM) and other rewritable
 optical disks are now in use.
 Such rewritable optical disks include ones which use for example a land
 groove system as a disk format. In this case, the recording surface of the
 optical disk is provided with data areas in which only guide grooves for
 recording and reproducing any information and address areas in which
 absolute positions on a disk are stored by pits.
 The formats of the land-groove system can be roughly divided in a double
 spiral format and a single spiral format.
 In the double spiral format, as shown in FIG. 1, a land track 50 and a
 groove track 51 are located next to each other. Further, in the single
 spiral format, as shown in FIG. 2, a land track 52 and a groove track 53
 are located one after the other for every circuit to form one track as a
 whole.
 Below, the tracking servo control of a recording and reproduction apparatus
 of the related art for recording and reproducing data to and from a
 DVD-RAM of the single spiral format will be explained.
 FIG. 3 is a block diagram of an optical disk drive 1 of the related art for
 realizing the tracking servo control of a recording and reproduction
 apparatus of a DVD-RAM disk.
 As shown in FIG. 3, in the optical disk drive 1, a DVD-RAM disk 2 is driven
 to rotate by a spindle motor 15. A laser beam from a laser 3 is fired
 through an object lens to a position on the recording surface of the
 DVD-RAM disk 2 under the control of a tracking coil 4. The reflected laser
 beam is received by a photoreceptor 5.
 The photoreceptor 5 converts the reflected laser beam from the DVD-RAM disk
 2 to a tracking error signal S5a indicating the deviation of tracking and
 a sum signal S5b indicating the amount of the light of the reflected laser
 beam and outputs these to A/D converters 6 and 7 respectively.
 The tracking error signal S5a and the sum signal S5b are converted to a
 digital tracking error signal S6 and a sum signal S7 and output to a
 normalizer 8.
 The normalizer 8 normalizes the tracking error signal S6 so that its level
 does not change and outputs the normalized tracking error signal S8 to a
 polarity switch 9.
 On the other hand, the address S5c read from the DVD-RAM disk 2 is output
 from the photoreceptor 5 to the last sector detector 13. The last sector
 detector 13 detects a last sector signal S13 indicating a sector just
 before the land and the groove are switched on the basis of address S5c.
 Next, a one-sector delay unit 14 delays the last sector signal S13 by
 exactly one sector's worth of time to produce a polarity switching signal
 S14 and outputs the polarity switching signal S14 to the polarity switch
 9.
 Based on the polarity switching signal S14, the polarity switch 9 inverts
 the polarity of the tracking error signal S8 in accordance with need to
 produce a tracking error signal S9 of a controlled polarity. It outputs
 the tracking error signal S9 to a phase compensation digital filter 10.
 It is necessary to control the polarity of the tracking error signal SB in
 this way because the polarity of the tracking error signal becomes
 inverted between when tracing a land and when tracing a groove.
 The tracking error signal S9 is phase-compensated and converted to an
 analog signal in the D/A converter 11 to produce a drive signal S11.
 The drive signal S11 is amplified by a drive amplifier, then output to the
 tracking coil 4 as a drive signal S12 to drive the tracking coil 4.
 Summarizing the problems to be solved by the invention, in the optical disk
 drive 1 of the related art shown in FIG. 3, as describe below, the
 polarity switching signal S14 is not suitably produced, so if suffers from
 the disadvantage that the tracking servo control becomes unstable.
 Specifically, when the recording surface of the DVD-RAM disk 2 becomes
 dirty and the last sector cannot be detected, when starting to trace a
 track after a seek operation, when using a zoned constant linear velocity
 (CLV) format where the number of the address areas 60 present in one turn
 of the disk differs for each zone as shown in FIG. 4 and the rotating
 speed of a spindle motor 15 will not stabilize at the point of change of
 zones, etc. the polarity switching signal S14 is not suitably produced.
 Note that in a DVD-RAM of the CAV format, as shown in FIG. 5, the address
 areas 70 and the data areas 71 are arranged radially.
 When the polarity switching signal S14 is not suitably produced and the
 timing of the polarity switching becomes off, a suitable tracking error
 signal S9 is not produced while the polarity is wrong and the tracking
 servo control becomes unstable state.
 Further, during a seek operation, since an optical pick-up is moving over
 the tracks, the last sector cannot be detected and the polarity cannot be
 suitably controlled in the polarity switch 9. Therefore, during a seek
 operation, the tracking error signal S9 becomes discontinuous at the
 boundary between a land and a groove, so there is the disadvantage that a
 count error occurs in the traverse counter which counts the number of
 tracks being traversed.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide a polarity switching
 signal generator and method able to stably generate a suitable polarity
 switching signal for inverting the polarity of a tracking error signal and
 an optical disk drive able to realize stable tracking servo control.
 According to a first aspect of the present invention, there is provided a
 polarity switching signal generator for generating a polarity switching
 signal for use in switching a polarity of a tracking error signal in
 accordance with a switching position between a land and groove during
 tracking servo control of an optical disk in which lands and grooves are
 alternately arranged in a radial direction, comprising a rotational angle
 generating means for generating a rotational angle of said optical disk on
 the basis of a rotation signal based on rotation of said optical disk
 input from a driving means for driving the rotation of said optical disk;
 a switching position detecting means for detecting a switching position
 between a land and groove on the basis of an address signal read from said
 optical disk; a rotational angle determining means for determining said
 rotational angle generated by said rotational angle generating means at a
 timing in accordance with the detection of the switching position between
 a land and groove; a reference value storing means for storing a reference
 value to be compared with said rotational angle generated by said
 rotational angle generating means; a reference value setting means for
 updating the reference value stored in said reference value storing means
 with the rotational angle determined by said rotational angle determining
 means when said address signal is correct; and a comparing means for
 generating a polarity switching signal instructing the inversion of the
 polarity of the tracking error signal when the rotational angle generated
 by said rotational angle generating means matches with the reference value
 stored in said reference value storing means.
 Preferably, said reference value storing means holds the stored reference
 value when error has occurred in said address signal.
 Preferably, said rotation signal comprises an FG signal.
 Preferably, further provision is made of a phase synchronization circuit
 for receiving as input the rotation signal based on the rotation of said
 optical disk from said driving means and generating a new rotation signal
 improved in resolution from the input rotation signal and said rotational
 angle generating means generates a rotational angle of said optical disk
 on the basis of said new rotation signal input from said phase
 synchronization circuit.
 Preferably, the optical disk is a rewritable optical disk.
 According to a second aspect of the present invention, there is provided an
 optical disk drive for driving an optical disk where lands and grooves are
 alternately arranged in a radial direction, comprising a rotational angle
 generating means for generating a rotational angle of said optical disk on
 the basis of a rotation signal based on rotation of said optical disk
 input from a driving means for driving the rotation of said optical disk;
 a switching position detecting means for detecting a switching position
 between a land and groove on the basis of an address signal read from said
 optical disk; a rotational angle determining means for determining said
 rotational angle generated by said rotational angle generating means at a
 timing in accordance with the detection of the switching position between
 a land and groove; a reference value storing means for storing a reference
 value to be compared with said rotational angle generated by said
 rotational angle generating means; a reference value setting means for
 updating the reference value stored in said reference value storing means
 with the rotational angle determined by said rotational angle determining
 means when said address signal is correct; a comparing means for
 generating a polarity switching signal instructing the inversion of the
 polarity of the tracking error signal when the rotational angle generated
 by said rotational angle generating means matches with the reference value
 stored in said reference value storing means; a polarity switching means
 for switching the polarity of a first tracking error signal generated on
 the basis of the result of the reception of the reflected light of said
 optical disk on the basis of the polarity switching signal generated by
 said comparison means to produce a second tracking error signal; and a
 driving means for driving the optical disk on the basis of said second
 tracking error signal.
 According to a third aspect of the present invention, there is provided a
 polarity switching signal generation method for generating a polarity
 switching signal for use in switching a polarity of a tracking error
 signal in accordance with a switching position between a land and groove
 during tracking servo control of an optical disk in which lands and
 grooves are alternately arranged in a radical direction, comprising the
 steps of generating a rotational angle of said optical disk on the basis
 of a rotation signal based on rotation of said optical disk input from a
 driving means for driving the rotation of said optical disk; detecting a
 switching position between a land and groove on the basis of an address
 signal read from said optical disk; determining said generated rotational
 angle at a timing in accordance with the detection of the switching
 position between a land and a groove; updating a reference value with the
 rotational angle determined when said address signal is correct; and
 generating a polarity switching signal instructing the inversion of the
 polarity of the tracking error signal when the generated rotational angle
 matches with the reference value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Below, a DVD-RAM recording and reproduction apparatus of an embodiment of
 the present invention for recording and reproduction on and from a DVD-RAM
 of the single spiral format will be explained.
 The DVD-RAM recording and reproduction apparatus of the present embodiment
 is characterized by its tracking servo control.
 FIG. 6 is a block diagram of an optical disk drive 21 for realizing
 functions related to a tracking servo control of a recording and
 reproduction apparatus of a DVD-RAM disk according to the present
 embodiment.
 The optical disk drive 21 performs the tracking servo control of a DVD-RAM
 disk 2 of the single spiral format driven by the spindle motor 15.
 As shown in FIG. 6, the optical disk drive 21 comprises a polarity
 switching signal generator 29, a digital signal processor 19, a spindle
 controller 40, an address decoder 41, and a tracking coil 4.
 The spindle controller 40 generates a spindle drive signal S40a which it
 outputs to the spindle motor 15 and generates a spindle lock signal S40b,
 indicating whether the spindle motor 15 is stable at a target number
 rotating speed (that is, if the spindle motor 15 is in a locked state) on
 the basis of a periodicity of a FG signal S15 from the spindle motor 15
 shown in FIG. 7A, which it outputs to a reference value setting circuit
 36.
 The address decoder 41 generates an address signal S41b on the basis of an
 RF signal S5c input from a photoreceptor 5 and outputs the address signal
 S41b to a last sector detector 13. Further, the address decoder 41
 generates an address decode error signal S41a indicating whether a decode
 error has occurred in the read address on the basis of the RF signal S5c
 input from the photoreceptor 5 and outputs the address decode error signal
 S41a to the reference value setting circuit 36.
 Digital Signal Processor 19
 The digital signal processor 19 is basically the same as the digital
 processor of the optical disk drive 1 shown in FIG. 3 described above.
 That is, the digital signal processor 19 comprises A/D converters 6 and 7,
 a normalizer 8, a polarity switch 9, a phase compensation digital filter
 10, and a D/A converter 11.
 The A/D converter 6 converts the analog tracking error signal S5a from the
 photoreceptor 5 to a digital tracking error signal S6 and outputs the
 tracking error signal S6 to the normalizer 8.
 The A/D converter 7 converts the analog sum signal S5b from the
 photoreceptor 5 to a digital sum signal S7 and outputs the sum signal S7
 to the normalizer 8. the normalizer 8 normalizes the tracking error signal
 S6 so that its level does not change on the basis of the sum signal S7 and
 outputs the normalized tracking error signal S8 to the polarity switch 9.
 The polarity switch 9 inverts the polarity of the tracking error signal S8
 in accordance with need based on the polarity switching signal S29 to
 produce the tracking error signal S9. The tracking error signal S9 is
 output to the phase compensation digital filter 10.
 The phase compensation digital filter 10 performs phase compensation on the
 tracking error signal S9 and outputs the phase compensated tracking error
 signal S10 to the D/A converter 11.
 The D/A converter 11 converts the digital tracking error signal S10 to an
 analog tracking error signal S11 and outputs the tracking error signal S11
 to a drive amplifier 12.
 Polarity Switching Signal Generator 29
 As shown in FIG. 6, the polarity switching signal generator 29 comprises a
 PLL circuit 30, a rotational angle counter 31, a comparator 32, a capture
 circuit 35, a reference value setting circuit 36, a reference value
 storage circuit 37, a last sector detector 13, and a one-sector delay unit
 14.
 The last sector detector 13 and the one-sector delay unit 14 are the same
 as the last sector detector 13 and the one-sector delay unit 14 of the
 optical disk drive of the related art shown in FIG. 3 described above.
 The last sector detector 13 generates a last sector signal S13 indicating
 the sector immediately before the point where a land and a groove are
 switched on the basis of the address signal S41b input from the address
 decoder 41 and outputs this to the last sector detector 13.
 The one-sector delay unit 14 delays the last sector signal S13 by one
 sector's worth of time and outputs the result to the capture circuit 35 as
 the last sector signal S14a shown in FIG. 7C.
 The PLL circuit 30 performs PLL processing with respect to the FG signal
 shown in FIG. 7A input from the spindle motor 15, then outputs the same as
 an FG signal S30 shown in FIG. 7B to the rotational angle counter 31.
 The rotational angle counter 31 counts the pulses included in the FG signal
 S30, generates a rotational angle signal S31 indicating the rotational
 angle of the DVD-RAM disk 2 on the basis of the result of the count, and
 outputs the same to the comparator 32.
 The capture circuit 35 captures a rotational angle value indicated by the
 rotational angle signal S31 from the rotational angle counter 31 in
 accordance with a timing of reproduction of the last sector on the basis
 of the last sector signal S14a from the one-sector delay unit 14.
 The reference value setting circuit 36 functions to determine whether or
 not the rotational angle value captured by the capture circuit 35 is
 correct and updates the reference value stored in the reference value
 storage circuit 37 only when it determines it is correct.
 Specifically, the reference value setting circuit 36, in the case where the
 spindle lock signal S40b indicates a state of lock and error has not
 occurred in the address decode error signal s41a, reads out the rotational
 angle value captured in the capture circuit 35 as an effective value,
 calculates the average value of the read rotational angle value and a
 plurality of rotational angle values read from the capture circuit 35 in
 the past, and updates the reference value already stored in the reference
 value storage circuit 37 by using the average value as a new reference
 value. In this way, the reference value stored in the reference value
 storage circuit 37 can be stabilized by finding the average value of the
 rotational angle values by the capture circuit 35 even in the case where
 the rotational angle values captured in the capture circuit 35 change
 slightly.
 The comparator 32 compares the rotational angle value indicated by the
 rotational angle signal S31 from the rotational angle counter 31 and the
 reference value stored in the reference value storage circuit 37,
 generates the polarity switching signal S29 which generating a pulse at
 the time when the result of the comparison indicates coincidence as shown
 in FIG. 7E, and outputs the polarity switching signal S29 to the polarity
 switch 9.
 Below, the operation of the optical disk drive 21 shown in FIG. 6 will be
 explained.
 Here, an explanation will be given of mainly the operation of the polarity
 switching signal generator 29 for the case where the address decoder 1 has
 suitably decoded the address and for the case where it has not.
 Case Where Address Has Been Correctly Decoded
 In this case, the address decoder 41 has correctly decoded the address read
 from the DVD-RAM disk on the basis of an RF signal S5c in accordance with
 the result of reproduction from the DVD-RAM disk 2 and outputs a valid
 address signal S41b to the last sector detector 13. Further, it outputs an
 address decode error signal S41a indicating that the address has been
 correctly decoded to the reference value setting circuit 36.
 Next, the last sector detector 13 generates a last sector signal S13
 indicating the sector immediately before the point where a land and a
 groove are switched on the basis of the address signal S41b and outputs
 the last sector signal S13 to the last sector detector 13.
 The last sector signal S13 is delayed by exactly one sector's worth of time
 in the one-sector delay unit 14, then is output to the capture circuit 35
 as the last sector signal S14a generating a pulse at, for example, the
 timing A shown in FIG. 7C.
 Next, the capture circuit 35 captures a rotational angle value indicated by
 the rotational angle signal S31 at a timing in accordance with the last
 sector indicated by the last sector signal S14a.
 Next, since the spindle lock signal S40b indicates the lock state and the
 address decode error signal S41a indicates that the decoding has been
 performed correctly, the reference value setting circuit 36 uses the new
 reference value of the average value, calculated using the rotational
 angle value captured by the capture circuit 35, to update the reference
 value stored in the reference value storage circuit 37.
 Next, the comparator 32 compares the updated reference value stored in the
 reference value storage circuit 37 and the rotational angle value
 indicated by the rotational angle signal S31 and switches the polarity
 switching signal S29 when they match, that is, at the timing B shown in
 FIG. 7E.
 Case Where Error Occur in Decoding of Address
 In this case, in the address decoder 41, error occurs in the decoding of
 the address read from the DVD-RAM on the basis of the RF signal S5c in
 accordance with the result of the reproduction from the DVD-RAM disk 2 and
 the address signal S41b output to the last sector detector 13 becomes
 erroneous. Further, an address decode error signal S41a indicating error
 is output to the reference value setting circuit 36.
 The last sector detector 13 does not detect the last sector and a pulse is
 not generated in the last sector signal S14a output from the one-sector
 delay unit 14 at the timing C shown FIG. 7C where a pulse should be
 generated.
 As the result, the capture circuit 35 does not capture the rotational angle
 value indicated by the rotational angle signal S31.
 Further, since the spindle lock signal S40b indicates a lock state and the
 address decode error signal S41a indicates error, the reference value
 setting circuit 36 does not update the reference value stored in the
 reference value storage circuit 37.
 Next, the comparator 32 compares the reference value which has been stored
 in the reference value storage circuit 37 and the rotational angle value
 indicated by the rotational angle signal S31 and switches the polarity
 switching signal S29 when they match, that is, at the timing D shown in
 FIG. 7E.
 In this way, according to the optical disk drive 21, even when no pulse is
 generated in the last sector signal S14a at the timing C shown in FIG. 7C,
 the polarity switching signal S29 output from the polarity switching
 signal generator 29 can be appropriately switched at the timing D shown in
 FIG. 7E. Accordingly, the polarity switching signal S29 is not disturbed
 even when the recording surface of the DVD-RAM disk 2 is dirty and the
 last sector cannot be detected or when a spot cuts across tracks.
 Further, since the rotational angle value indicated by the rotational angle
 signal S31 corresponds to the revolution of the DVD-RAM disk 2, in the
 case where a DVD-RAM disk 2 of a zoned CLV format is used, even in the
 transient state in which the rotating speed changes, the polarity
 switching signal S29 can be switched appropriately at the point where disk
 is switched.
 According to the optical disk drive 21, therefore, the polarity of the
 tracking error signal read from the DVD-RAM disk 2 and the polarity to be
 actually controlled can be kept matched at all times and stable tracking
 servo control can be realized.
 FIGS. 8A to 8C are views for explaining the tracking error signal and the
 polarity switching signal in a seek operation moving across tracks of the
 DVD-RAM disk 2.
 Here, FIG. 8A is a waveform diagram of a tracking error signal of the
 related art where the polarity is not controlled, FIG. 8B is a waveform
 diagram of the tracking error signal shown in FIG. 6 where the polarity is
 controlled, and FIG. 8C is a waveform diagram of the polarity switching
 signal S29 shown in FIG. 6.
 As shown in FIG. 8A, when the polarity is not controlled, the tracking
 error signal becomes discontinuous at the disk switching timings a, b, and
 c. Accordingly, the traverse counter counting the number of tracks
 traversed cannot correctly count, error occurs in the result of the count,
 and the accuracy of the seek operation is reduced.
 As opposed to this, according to the optical disk drive 21 of the present
 embodiment, as shown in FIG. 8C, the level of the polarity switching
 signal S29 is switched at the disk switching timings a, b, and c, and the
 polarity of the tracking error signal S8 is inverted in the polarity
 switch 9. As a result, the waveform of the tracking error signal S9
 becomes continuous as shown in FIG. 8B. Therefore, the traverse counter
 can obtain the proper count and a high precision seek operation can be
 realized.
 As described above, according to the optical disk drive 21, a high
 precision polarity switching signal S29 can be generated in the tracking
 servo control at the time of reproduction from a DVD-RAM disk 2 of the
 single spiral format. That is, according to the optical disk drive 21,
 even in the case where the recording surface of the DVD-RAM disk 2 becomes
 dirty and the last sector could not be detected or in the case where a
 spot cuts across tracks, a high precision polarity switching signal S29
 can be generated.
 Further, according to the optical disk drive 21, when a DVD-RAM disk 2 of
 the zoned CLV or other format is used, even in the transient state in
 which the rotating speed is changing, a high precision polarity switching
 signal S29 can be generated.
 As a result, according to the optical disk drive 21, the tracking servo
 control can be performed stably and the precision of the seek operation
 can be improved.
 The present invention is not limited to the embodiment described above.
 For example, in the embodiment described above, a DVD-RAM was given as an
 example of an optical disk, but the optical disk of the present invention
 may also be another optical disk of the land-groove system.
 Further, in the embodiment described above, a PLL circuit 30 was provided
 for achieving a high resolution of the angle of the FG signal S15,
 however, when a high resolution of the angle is not required or when the
 FG signal S15 has a high resolution of angle, it is possible to configure
 the invention without the PLL circuit 30.
 Summarizing the effects of the invention, according to the polarity
 switching signal generator and method described above, a suitable polarity
 switching signal for inverting the polarity of the tracking error signal
 can be stably generated.
 Further, according to the optical disk drive described above, stable
 tracking servo control can be realized.