Patent Publication Number: US-2011051575-A1

Title: Focus jump method and optical disc apparatus

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority from Japanese application JP2009-194959 filed on Aug. 26, 2009, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a focus jump method and an optical disc apparatus. 
     For a purpose of improving a recording capacity of an optical disc, there has been a practical use of the optical disc having a plurality of recording layers. For example, a two-layered DVD having an 8.5 GB recording capacity has been available in correspondence to a single-layered DVD having a 4.7 GB recording capacity, and a two-layered Blu-ray disc (hereinafter, referred to as BD) having a 50 GB recording capacity has also been available in correspondence to a single-layered BD having a 25 GB recording capacity. 
     Further, the two-layered DVD and BD are available for both a reproduction-only ROM disc and a recordable disc (hereinafter, referred to as R disc). The two-layered BD is available even for a rewritable disc (hereinafter, referred to as RE disc). 
     Furthermore, JP-A-2006-252771 has been opened to the public as a document in relation to another multilayer optical disc. 
     In this document, a claim  1  states that “a multilayer optical disc having a structure such that the converging light beam transmits through one side of the first and second recording layers to retrieve the other side of the first and second recording layers,” and also states that “a reproduction-only area, in which non-erasable information is recorded as a pit string on the first recording layer, is provided on an inner periphery of the multilayer optical disk, and another area except for the reproduction-only area is set to a first recording area to which information can be written by the converging light beam.” 
     In the JP-A-2006-252771, the first recording layer has a recordable area other than the reproduction-only area, however, it is possible to employ a structure such that the first recording layer is the reproduction-only area alone. The above-mentioned example is shown in  FIG. 2 . 
       FIG. 2  is a cross section schematic diagram of the multilayer optical disc. In  FIG. 2 , an optical disc  201  is configured to have a first recording layer  202  of the reproduction-only area and a second recording layer  203  of the recordable area. Presently, the multilayer optical disc having the structure shown in  FIG. 2  has not been turned into practical use, but it can sufficiently and technically be realized in consideration of a current condition where the two-layered ROM disc, R disc and RE disc are already turned into the practical use. In addition, the laser light used for reproducing and recording data is incident from the second recording layer  203 . 
     Hereinafter, a problem will be described with a case of performing a seek operation involved with a focus jump in the multilayer optical disc in  FIG. 2 . 
     When the focus jump is performed, it is required that an optical disc apparatus reads out address information from the optical disc to check layer information contained in the address information so that it is confirmed whether the focus jump is applied correctly. Data is recorded with concavity and convexity pits on the first recording layer  202  as a reproduction-only, and a pit string forms a track. The second recording layer  203  of the recordable area also forms a track by a so-called land/groove structure. Further, the track has a wobbling structure which is meandered through the track. 
     In addition, in the case of the first recording layer  202 , the address information is contained in the data configured by a pit group. In the case of the second recording layer  203 , the address information is recorded in the wobbling by a phase modulation. To this end, it is required that a tracking servo control is performed to read out the address information, and a laser spot follows the track to read out the information. 
     When the track is formed by the pit string, it has been known generally that a known DPD (differential Phase Detection) method is suitable as a generation method for a tracking error signal (hereinafter, referred to as TE signal). In contrast, when the track is formed by a land/groove structure, it has also been known that a push-pull method, which obtains a signal in response to a tracking error amount even though the recording layer is a non-recorded state, is suitable as the generation method for the TE signal. Hereinafter, the TE signal generated by the DPD method is referred to as a DPD signal, and the TE signal generated by the push-pull method is referred to as a push-pull signal. 
     When the focus jump is applied from a condition of performing a tracking servo control with use of the DPD signal in the first recording layer  202  to the second recording layer  203 , the tracking servo control can be performed without problem since the DPD signal can be generated correctly in response to a presence or absence of a recorded mark when a landing position on the second recording layer  203  is an already-recorded portion. In contrast, when the landing position is a non-recorded portion, the DPD signal cannot be generated correctly since the recorded mark is not present. To this end, the tracking servo control cannot be performed. 
     Further, when the focus jump is applied from a condition where the tracking servo control is performed with use of the push-pull signal in the second recording layer  203  to the first recording layer  202 , the push-pull signal cannot be generated accurately on the first recording layer  202 . This is because the amplitude of the push-pull signal depends on the height of pit. Normally, the pit height has been designed such that the amplitude of a reproduced signal of the data can be obtained more than a predetermined value, and that height is different from a height of which the amplitude of push-pull signal becomes maximum. In consequence, the push-pull signal is lowered than the ideal maximum amplitude, therefore, a noise is increased when amplifying the amplitude of push-pull signal by using a preamplifier and the like so as to obtain the predetermined value or more, and the quality of push-pull signal becomes deteriorated. To this end, the tracking servo control cannot be performed in high accuracy. 
     In the case of the existing focus jump method, as described above, it cannot be confirmed whether the focus jump is performed correctly since the tracking servo control is performed to not be able to read out the address information after performing the focus jump. 
     SUMMARY OF THE INVENTION 
     In order to solve the above-mentioned problem, the focus servo is decoupled once when switching over the recording layer to which tracking servo control is applied, and the generation method for the TE signal is switched over to a method suitable to a target layer to then couple the focus servo to the target layer once again, thereafter, the tracking servo control may be restarted. However, this method takes a long period of time to switch over the recording layer, therefore, a seek time period is increased. 
     An object of the invention is to provide a focus jump method and an optical disc apparatus that includes a multilayer optical disc having both a reproduction-only recording layer and a recording layer of the recordable area, present in the disc, therefore, an increase of time period can be constrained for performing the seek operation. 
     The above-mentioned object is achieved by the invention written in the claims, as an example. Further, the object can be achieved by switching over a generation method of a tracking error signal to either a first or second generation method in response to the target layer to which a focus jump is applied, for a time period during which a tracking servo loop is opened in association with the focus jump. 
     According to the invention, it is possible to provide the focus jump method and optical disc apparatus since the apparatus has the multilayer optical disc having both the reproduction-only recording layer and recording layer of the recordable area in the disc to thereby constrain the increase of seek operation. 
     The other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing an optical disc apparatus in a first embodiment of the invention; 
         FIG. 2  is a cross section schematic diagram showing a multilayer optical disc; 
         FIG. 3A  is a waveform schematic diagram showing a DPD signal; 
         FIG. 3B  is a waveform schematic diagram showing a push-pull signal; 
         FIG. 4  is a flowchart showing an operation in the first embodiment; 
         FIG. 5  is a waveform schematic diagram for explaining the first embodiment; 
         FIG. 6  is another waveform schematic diagram for explaining the first embodiment; 
         FIG. 7  is a configuration schematic diagram showing an optical disc apparatus in a second embodiment of the invention; 
         FIG. 8  is a flowchart showing an operation of the second embodiment; 
         FIG. 9  is a waveform schematic diagram for explaining the second embodiment; and 
         FIG. 10  is another waveform schematic diagram for explaining the second embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an optical disc apparatus in embodiments of the invention will be described with reference to the drawings. 
     Embodiment 1 
       FIG. 1  is a configuration schematic diagram showing an optical disc apparatus in a first embodiment. 
     A reference numeral  1  denote an optical disc or the multilayer optical disc already shown in  FIG. 2 . In addition, both the first recording layer  202  (already described in  FIG. 2 ) as a reproduction-only layer and the second recording layer  203  (already described in  FIG. 2 ) of the recordable area, can be reproduced and recorded by the same wavelength laser light, respectively. A data recording method uses the same format for both the recording layers  202 ,  203 . That is, the first and second recording layers  202 ,  203  are conformed to the same DVD format or BD format, for example. The second recording layer  203  of the recordable area, may also be either recordable or recordable. The optical disc  1  also corresponds to a so-called Intra-Hybrid. 
     A reference numeral  2  denotes a spindle motor for rotating the optical disc  1  in response to an output signal from a spindle driver circuit. 
     A reference numeral  3  denotes the spindle driver circuit for outputting a drive signal to rotate the spindle motor  2  on the basis of a spindle drive signal output from a control circuit  19 . 
     A reference numeral  4  denotes an optical pickup providing an optical component, such as a semiconductor laser, an objective lens, etc. for irradiating a laser light on the optical disc  1  to record and reproduce information. The optical pickup  4  also provides a plurality of optical detectors to output an electric signal in response to a reflected light from the optical disc  1 . It is configured that the optical pickup  4  further provides a focusing actuator and a tracking actuator (both not shown) to be able to drive the objective lens. In addition, the focusing actuator moves the objective lens in a focusing direction, that is, moves the objective lens in a substantially perpendicular direction with respect to the respective recording surfaces of the optical disc  1 . Further, the tracking actuator moves the objective lens in a substantially radial direction of the optical disc  1 . 
     A reference numeral  5  denotes a focusing error signal generation circuit for computing an output signal from the optical pickup  4  by using a known astigmatic method to output a focusing error signal (hereinafter, referred to as FE signal) which varies in response to a focusing error amount. 
     A reference numeral  6  denotes a focusing compensation circuit for outputting a signal which is compensated for a phase and a gain so that a stability and a follow-up capability of a focusing servo are improved in relation to the FE signal. 
     A reference numeral  7  denotes a jump signal generation circuit for generating and outputting a jump signal required for performing a focus jump in response to a control signal supplied from the control circuit  19 . 
     A reference numeral  8  denotes a switching circuit in which an output signal from the focusing compensation circuit  6  is supplied to an input terminal (a) and the jump signal from the jump signal generation circuit  7  is supplied to an input terminal (b). Further, the switching circuit  8  is controlled by a control signal FONT supplied from the control circuit  19  to be switched over to the input terminal (a) when the control signal FONT is set to a Low output. In contrast, the switching circuit  8  is switched over to the input terminal (b) when the control signal FONT is set to a Hi output. The output signal from the switching circuit  8  is a drive signal to be used for the focusing servo, and the drive signal is hereinafter referred to as a FOD signal. 
     A reference numeral  9  denotes a DPD generation circuit for generating the output signal from the optical pickup  4  by using a known DPD method to output a DPD signal which varies in response to a tracking error amount. The DPD generation circuit  9  also incorporates a gain circuit (not shown). The gain circuit is also set previously to such that the amplitude of DPD signal is varied to make a tracking servo loop gain into a predetermined characteristic. 
     A reference numeral  10  denote a push-pull generation circuit for generating the output signal from the optical pickup  4  by using a known push-pull method to output a push-pull signal which varies in response to the tracking error amount. The push-pull generation circuit  10  also incorporates a gain circuit (not shown), and the gain circuit is also set previously to such that the amplitude of push-pull signal is varied to make the tracking servo loop gain into a predetermined characteristic. 
       FIGS. 3A and 3B  are waveform schematic diagrams showing the DPD signal and push-pull signal, respectively. The following description will be concerned with these signals when a laser spot to be performed for the record/reproduction traverses a track of the recording layer on the optical disc  1 . 
     Specifically,  FIG. 3A  is a waveform example of the DPD signal when the laser spot traverses the track of the reproduction-only first recording layer  202 , and this signal shows a saw-tooth waveform signal.  FIG. 3B  is a waveform example of the push-pull signal when the laser spot traverses the track of the second recording layer  203  of the recordable area, and this signal shows a substantially sine waveform signal. A position indicated by a filled circle on both the waveforms indicates that the laser spot is located just on the track. 
     Referring back to  FIG. 1 , the following description will be concerned with a configuration of the optical disc apparatus. 
     A reference numeral  11  denotes a switching circuit in which the DPD signal is supplied to an input terminal (a) and the push-pull signal is supplied to an input terminal (b). The switching circuit  11  is also controlled by a control signal TESEL supplied from the control circuit  19  to be switched over to the input terminal (a) when the control signal TESEL is set to the Low output. In contrast, the switching circuit  11  is switched over to the input terminal (b) when the control signal TESEL is set to the Hi output. In addition, an output from the switching circuit  11  indicates a TE signal. 
     A reference numeral  12  denotes a tracking compensation circuit for outputting a signal which is compensated for a phase and gain so that the stability and follow-up capability of a tracking servo are improved in relation to the TE signal. 
     A reference numeral  13  denotes a switch for operating on and off by a control signal TCNT supplied from the control circuit  19 . The switch  13  becomes on-state, when the control signal TCNT is set to the Hi output, to output a signal supplied from the tracking compensation circuit  12 . In contrast, the switch  13  becomes off-state, when the control signal TCNT is set to the Low output, to output a reference potential. At this time, the position of objective lens in a tracking direction becomes a middle position to make a tracking servo control off. In addition, the output from switch  13  indicates a tracking drive signal (hereinafter, referred to as TRD signal). 
     A reference numeral  14  denotes a sled control circuit for outputting a sled drive signal (hereinafter, referred to as SLD signal) in response to an instruction from the control circuit  19 . 
     A reference numeral  15  denotes a driver circuit for amplifying the FOD signal and TRD signal to then be supplied respectively to the focusing actuator and tracking actuator in the optical pickup  4 . The driver circuit  15  also supplies an amplified signal of the SLD signal to a sled motor. 
     A reference numeral  16  denotes a sled motor  16  for rotating in response to the amplified signal of the SLD signal by the driver circuit  15 . 
     A reference numeral  17  denotes a lead screw, one end of which is coupled to the sled motor  16 , to be rotated by the sled motor  16 . Further, it is configured that the optical pickup  4  moves in the radial direction of optical disc  1  when rotating the lead screw  17 . 
     A reference numeral  18  denotes an address demodulation circuit for demodulating address information on the optical disc  1  by using the output signal of the optical pickup  4  to then output itself. In the case of the reproduction-only first recording layer  202 , the address demodulation circuit  18  demodulates the address information contained in data configured by a pit group to then output itself. In contrast, in the case of the second recording layer  203  of the recordable area, the address demodulation circuit  18  demodulates the address information contained in phase modulation information on a wobbling to then output itself. 
     The control circuit  19  controls the optical disc apparatus entirely. The control circuit  19  receives the FE signal and the address information output from the address demodulation circuit  18 , and also outputs a spindle drive signal, the control signal FCNT for controlling the switching circuit  8 , the control signal TESEL for controlling the switching circuit  11 , and the control signal TCNT for controlling the switch  13 . In addition, the control circuit  19  may be of a generally used CPU. 
     In the above-mentioned apparatus, the tracking compensation circuit  12 , switch  13  and driver circuit  15  function as a tracking servo control unit for controlling the tracking servo, for example. The control circuit  19  also functions a switching unit for making the tracking servo control unit on and off. Further, in the above-mentioned apparatus, the DPD generation circuit  9 , push-pull generation circuit  10 , switching circuit  11  and control circuit  19  function as a tracking error signal generation unit, for example. 
     Next, an operation of the focus jump provided in the above-mentioned optical disc apparatus will be described with reference to a flowchart in  FIG. 4  and a waveform diagram in  FIG. 5 . 
     In addition, the focus jump means an operation on a process of a layer-to-layer jump, that is, it means that a focus position of a light irradiated from the optical pickup  4  is moved from one recording layer to the other. Further, the layer-to-layer jump means an operation in such that the recording layer is altered for the record or reproduction of the optical disc  1 . 
     The optical disc apparatus before applying the focus jump is assumed to set a condition where the optical disc  1  rotates and the focusing servo control and tracking servo control are being operated in the reproduction-only first recording layer  202 . That is, the control signal FONT output from the control circuit  19  is set to the Low output, the switching circuit  8  is connected to the input terminal (a) to output the output signal, as the FOD signal, of the focusing compensation circuit  6 , and the focusing servo loop indicates a condition where it is closed. Further, the control signal TCNT output from the control circuit  19  is set to the Low output, the switch  13  closes to output the output signal, as the TRD signal, of the tracking compensation circuit  12 , and the tracking servo loop indicates a condition where it is closed. Furthermore, the control signal TESEL output from the control circuit  19  is set to the Low output, and the switching circuit  11  outputs the DPD signal, as the TE signal, to be supplied to the input terminal (a). 
     In addition, what the focusing servo loop is closed means that a focusing error signal is made closer to a zero-cross point on a S-shaped signal. This operation can also be rephrased to such that the focusing servo control is simply performed. Conversely, it can be rephrased to such that, what the focusing servo loop is opened means that the focusing servo control is made stopped. 
     In the above-mentioned condition, the focus jump starts toward the second recording layer  203  of the recordable area, at a step S 101 . The control circuit  19  makes the switch  13  off at a time T 0  in  FIG. 5  as the control signal TCNT is set to the Hi output, and the tracking servo loop is then opened. To this end, the tracking servo control is made off, at a step S 102 , and the TE signal indicated by (c) in  FIG. 5  is made into a DPD signal waveform of the saw-tooth waveform from the time T 0 . 
     In addition, it can be rephrased to such that, what the tracking servo loop is opened means that the tracking servo control is made stopped, and what the tracking servo loop is closed means that the tracking servo control is performed. It can also be rephrased to such that, what the tracking servo loop is closed means that it can be controlled such that the tracking error signal is made close to the zero-cross point on the S-shaped signal. In addition, the zero-cross point of the tracking error signal appears respectively at a positive polarity and a negative polarity on an inclination of the S-shaped signal. In this case, the zero-cross point indicates a zero-cross point on a polarity where the tracking servo control is made into a negative feedback control. 
     Next, at a time T 1  in  FIG. 5 , the control circuit  19  makes the switching circuit  8  connected to the input terminal (b) to open the focusing servo loop as the control signal FONT is set to the Hi output. At the same time, the control circuit  19  outputs an instruction to the jump signal generation circuit  7  at the time T 1 , to then output an accelerating voltage to be required for the focus jump to the FOD signal indicated by (e), at a step S 103 . The objective lens provided on the optical pickup  4  is accelerated by the accelerating voltage to then start to move, and the laser spot moves away from the first recording layer to make the amplitude of the DPD signal or TE signal indicated by (c) small. Further, a known S-shaped waveform appears on the FE signal indicated by (f) in  FIG. 5  in response to a moving amount of the objective lens. 
     The control circuit  19  outputs the accelerating voltage to monitor the FE signal indicated by (f) and detect whether the FE signal reaches a peak level, at a step S 104 . At the step S 104 , if the peak level is detected (or Yes), the process at the step S 104  is terminated. In contrast, if the peak level is not detected (or No), the monitoring for the FE signal indicated by (f) continues after returning the process to the step S 104 . In a peak detection method, it is determined that the peak is detected at a time T 3  at which the FE signal indicated by (f) is lower than a detection level Vth 1  in  FIG. 5  after the FE signal indicated by (f) is higher than the detection level Vth 1  at a time T 2 , as an example. In addition, the “peak level” in this embodiment is not necessarily limited to the level at which the FE signal indicated by (f) becomes maximum. For example, the peak level may be a value which becomes a relative maximum, among measured values. The peak level also includes an error range of a predetermined amount, for example, the error range of 1%. 
     At the step S 104 , if the peak is detected (or Yes), the control circuit  19  monitors the FE signal indicated by (f) to detect whether it is made zero-crossed, at a step S 105 . If the FE signal indicated by (f) is made zero-crossed (or Yes), the process at the step S 105  is terminated. In contrast, if the FE signal is not made zero-crossed (or No), the monitoring for the FE signal indicated by (f) continues after returning the process to the step S 105 . In  FIG. 5 , the FE signal indicated by (f) is made zero-crossed at a time T 4 . 
     Further, if the zero-cross is detected at the step S 104  (or Yes), the control circuit  19  outputs the instruction to the jump signal generation circuit  7  to output a decelerating voltage to be required for decelerating the objective lens at a step S 106 . In  FIG. 5 , the decelerating voltage is output to the FOD signal indicated by (e) at a time T 4 . 
     The control circuit  19  outputs the decelerating voltage to then monitor the FE signal indicated by (f) and detect whether the FE signal becomes the peak level having a polarity opposite of that detected at the step S 104 , at a step S 107 . At the step S 107 , if the peak is detected (or Yes), the process at the step S 107  is terminated. In contrast, if the peak is not detected (or No), the process returns to the step S 107  to continue to monitor the FE signal indicated by (f). In the peak detection method, it is determined that the peak of the reverse polarity is detected at a time T 6  at which the FE signal indicated by (f) is higher than a detection level Vth 2  in  FIG. 5  after the FE signal indicated by (f) is lower than the detection level Vth 2  at a time T 5 , as an example. 
     If the peak of the reverse polarity is detected (or Yes) at the step S 107 , the control circuit  19  monitors the FE signal indicated by (f) to detect whether the FE signal is made zero-crossed, at a step S 108 . If the FE signal indicated by (f) is made zero-crossed (or Yes), the process at the step S 108  is terminated. In contrast, the FE signal is not made zero-crossed, the process returns to the step S 108  to continue to monitor the FE signal indicated by (f). In  FIG. 5 , the FE signal indicated by (f) is made zero-crossed at a time T 7 . 
     If the zero-cross is detected at the step S 108  (or Yes), the control circuit  19  makes the switching circuit  8  switched over to the input terminal (a) as the control signal FCNT is set to the Low output. In consequence, the switching circuit  8  outputs an output signal, as the FOD signal, of the focusing compensation circuit  6 , therefore, the focusing servo loop is closed to thereby make the focusing servo on, at a step S 109 . 
     After the focusing servo is made on at the step S 109 , the control circuit  19  determines a type of a target layer to which the focus jump is applied, at a step S 110 . At this step S 110 , when the target layer to which the focus jump is applied is the reproduction-only recording layer  202 , the control circuit  19  makes the DPD signal to be supplied to the input terminal (a) of the switching circuit  11  into the TE signal as the control signal TESEL is set to the Low output, at a step S 111 . In contrast, when the target layer to which the focus jump is applied is the recording layer  203  of the recordable area, the control circuit  19  makes the push-pull signal to be supplied to the input terminal (b) of the switching circuit  11  into the TE signal as the control signal TESEL is set to the Hi output, at a step S 112 . 
     In addition, the target layer to which the focus jump is applied is the second recording layer  203  of the recordable area, in this embodiment. Therefore, the TESEL signal indicated by (a) is set to the Hi output at a time T 8  in  FIG. 5 , and the push-pull signal is selected as the TE signal. To this end, the TE signal indicated by (c) in  FIG. 5  becomes the push-pull signal having a substantially sine waveform from the time T 8 . 
     Thereafter, at a time T 9  in  FIG. 5 , the control circuit  19  makes the switch  13  on as the control signal TCNT is set to the Low output. In consequence, since the output signal of tracking compensation circuit  12  is output as the TRD signal, the tracking servo loop is closed to make the tracking servo on, at a step S 113 . 
     After the tracking servo loop is closed at the step S 113 , the address demodulation circuit  18  becomes a state such that the address information on the optical disc  1  can be output. Thus, the control circuit  19  obtains the address information from the address demodulation circuit  18  to check layer information contained in the address information to confirm and detect whether a landing layer, which operates the focusing servo control, is the target layer to which the focus jump is applied, at a step S 114 . As a result of the confirmation at the step S 114 , if the landing layer is not the target layer, it is desirable to perform a predetermined error process (which is not described in this embodiment). In contrast, as a result of the confirmation, the focus jump process is terminated if the landing is performed correctly on the targeted recording layer, at a step S 115 . 
     In the above-mentioned embodiment, the focus jump has been described with the case where it is applied from the reproduction-only recording layer  202  to the recording layer  203  of the recordable area. In the case where the direction of focusing direction is reverse, that is, when the focus jump is applied from the recording layer  203  of the recordable area, to the reproduction-only recording layer  202 , the above-mentioned embodiment is also applicable thereto. 
       FIG. 6  is a waveform diagram showing the case where the focus jump is applied reversely. 
     In an operation shown in  FIG. 6 , the optical disc apparatus before applying the focus jump is assumed to set a condition where the optical disc  1  rotates and the focusing servo control and tracking servo control are being operated on the second recording layer  203  of the recordable area. That is, the control signal FONT output from the control circuit  19  is set to the Low output, the switching circuit  8  is connected to the input terminal (a) to output the output signal, as the FOD signal, of the focusing compensation circuit  6 , and the focus servo loop indicates a condition where it is closed. Further, the control signal TCNT output from the control circuit  19  is set to the Low output, the switch  13  is closed to output the output signal, as the TRD signal, of the tracking compensation circuit  12 , and the tracking servo loop indicates a condition where it is closed. In other words, the condition indicates that the tracking servo control is being performed. Furthermore, the control signal TESEL output from the control circuit  19  is set to the Hi output, and the switching circuit  11  outputs the push-pull signal, as the TE signal, to be supplied to the input terminal (b). 
     In  FIG. 6 , the control circuit  19  makes the tracking servo off at the time T 0 , at the step S 102 , to thereby make the TE signal indicated by (c) into the push-pull signal of the substantially sine waveform. Further, the jump signal generation circuit  7  outputs the accelerating voltage of the reverse polarity against that shown in  FIG. 5  at the time T 1 , at the step S 103 , to thereby make the FE signal indicated by (f) into the S-shaped waveform of the reverse polarity against  FIG. 5 . 
     In addition, in the peak detecting process at the step S 104 , it is desirable that the detection level uses a detection level −Vth 1  of the reverse polarity against the detection level Vth 1  shown in  FIG. 5 . 
     The jump signal generation circuit  7  also outputs the decelerating voltage of the reverse polarity against that shown in  FIG. 5  at the time T 4 , at the step S 106 . 
     In a reverse peak detecting process at the step S 107 , it is desirable that the detection level uses a detection level −Vth 2  of the reverse polarity against the detection level Vth 2  shown in  FIG. 5 . 
     In the determination of the target layer type at the step S 110 , the control circuit  19  determines the reproduction-only recording layer  202  as the target layer, and the switching circuit  11  switches over the TE signal to the DPD signal at the time T 8 , at the step S 111 . To this end, the TE signal indicated by (c) is made into the DPD signal of the saw-tooth waveform at the time T 8 . 
     As described above, an aspect of the optical disc apparatus is that the generation method of the TE signal is switched over on a time period during which the tracking servo loop is opened in association with the focus jump. To this end, even when the focus jump is performed to then switch over the recording layer to which the tracking servo control is applied, the address information can be obtained by restarting the tracking servo control rapidly. Thus, it is possible to perform the seek operation rapidly. 
     In addition, the first embodiment is not limited to the above-mentioned method. 
     For example, the switching operation of the TE signal at the steps S 110 , S 111  and S 112  may be performed at a different timing by the optical disc apparatus. That is, the switching operation of the generation method for the TE signal may be performed at an arbitrary timing by the optical disc apparatus if a time period is ranged from the time T 0  to T 9  during which the tracking servo loop is opened in association with the focus jump. For example, the loop operation for the peak detection at the steps S 104  and S 107  is performed by plural times in the optical disc apparatus, and the loop operation for the zero-cross detection of the FE signal at the steps S 105  and  108  is also performed by plural times therein, therefore, the optical disc apparatus may be configured that the switching operation for the TE signal is performed on either the loop operation. 
     The optical disc apparatus may also be configured that the switching operation for the TE signal is performed in range of a time period from the time T 1  at which the accelerating voltage is output, to the time T 2  at which the FE signal indicated by (f) exceeds the detection level Vth 1 , or from the time T 4  at which the decelerating voltage is output to the time T 5  at which the FE signal indicated by (f) exceeds the detection level Vth 2 . 
     Further, the operation for making the tracking servo off at the step S 102  and the output of the accelerating voltage at the step S 103 , may be performed at the same time or substantially the same time. That is, a variation timing of the TCNT signal indicated by (b) at the time T 0  and the FONT signal indicated by (d) and FOD signal indicated by (e) at the time T 1 , may be the same or substantially the same. 
     According to the above-mentioned optical disc apparatus, the seek operation can be performed rapidly on a multilayer optical disc having the reproduction-only recording layer  202  and the recording layer  203  of the recordable area on the optical disc  1 . Particularly, it is remarkable to obtain an advantage from the multilayer optical disc having the reproduction-only recording layer  202  and the recording layer  203  of the recordable area, both of which are irradiated on the optical disc  1  by the laser light of the same wavelength. 
     Embodiment 2  
     A second embodiment of the optical disc apparatus will be described below. 
     In a BD (Blue-ray Disc), it is generally known that a spherical aberration occurs in response to a variation of a so-called cover layer thickness which is a distance from the surface of disc to the recording layer. The spherical aberration occurs deteriorating a reproduction performance as well as a record performance. Therefore, the optical disc apparatus for recording/reproducing the BD is configured that a spherical aberration correcting mechanism is provided in the optical pickup. For this purpose, it is known that a spherical aberration correcting amount is appropriately set to the cover layer thickness, as a method. Further, various methods are publicly opened to set the spherical aberration correcting amount appropriately to the target layer to which the focus jump is applied in a two-layered BD. In the second embodiment, a focus jump method will be described with the case applicable to the BD having both the reproduction-only recording layer and the recording layer of the recordable area. 
       FIG. 7  is a schematic diagram showing a configuration of an optical disc apparatus in the second embodiment. The configuration of the optical disc apparatus in  FIG. 7  different from the optical disc apparatus in  FIG. 1  described in the first embodiment is described below. 
     The control circuit  19  supplies a spherical aberration correcting drive signal SAD to the driver circuit  15 . The driver circuit  15  amplifies the supplied spherical aberration correcting drive signal SAD to drive the spherical aberration correcting mechanism (not shown) in the optical pickup  4 . The spherical aberration correcting mechanism in the optical pickup  4  corrects the spherical aberration in response to a drive signal supplied from the driver circuit  15 . In addition, the configuration of spherical aberration correcting mechanism can be employed as a so-called beam expander mechanism combined with generally known concave lens and convex lens or a liquid crystal correcting mechanism using a liquid crystal element. 
     Other elements in  FIG. 7  are the same as these shown in  FIG. 1 , therefore, the same elements are appended with the same reference numerals and omitted to these description. 
     Next, in the above-mentioned configuration, an operation of the focus jump in the second embodiment will be described with reference to a flowchart in  FIG. 8  and waveforms in  FIG. 9 . 
     There are two different points in the flowchart in  FIG. 8  compared with that in  FIG. 4  of the first embodiment. That is, the flowchart in  FIG. 8  is different in that a drive process for a 50% spherical aberration correction at a step S 116  is added after the process for making the tracking servo off at the step S 102  and another drive process for the 50% spherical aberration correction at a step S 117  is added before the process for making the tracking servo on at the step S 113 . The drive for the spherical aberration corrections will be described below. 
     In addition, in the existing two-layered BD, it is regulative that a distance from a disc surface to which the laser light is incident, to the recording layer on the side of the objective lens is set to 75 μm, likewise, a distance from one disc surface to the other recording layer is set to 100 μm. Therefore, assuming that a physical specification for the respective layers of the multilayer optical disc in  FIG. 2  is conformed to the BD specification, a distance from the disc surface to the second recording layer  203  of the recordable area is set to 75 μm, likewise, a distance from the disc surface to the reproduction-only first recording layer  202  is set to 100 μm. In consequence, a distance between the first recording layer  202  and the second recording layer  203  becomes 25 μm, therefore, the spherical aberration correcting mechanism should correct the spherical aberration corresponding to 25 μm in order to make the record/reproduction performance optimal. That is, the spherical aberration correcting amount to be optimal for the first recording layer  202  is different from that to be optimal for the second recording layer  203 . Assuming that a difference between these correcting amounts is 100%, a 50% amount of the spherical aberration is corrected at the step S 116 , and another remaining 50% of that is corrected at the step S 117 . 
     In the operation shown in  FIG. 8 , the optical disc apparatus before applying the focus jump is assumed to set a condition where the optical disc  1  rotates and the focusing servo control and tracking servo control are being operated in the reproduction-only first recording layer  202 . That is, the control signal FONT output from the control circuit  19  is set to the Low output, the switching circuit  8  is connected to the input terminal (a) to output the output signal, as the FOD signal, of the focusing compensation circuit  6 , and the focusing servo loop indicates a condition where it is closed. Further, the control signal TCNT output from the control circuit  19  is set to the Low output, the switch  13  closes to output the output signal, as the TRD signal, of the tracking compensation circuit  12 , and the tracking servo loop indicates a condition where it is closed. Furthermore, the control signal TESEL output from the control circuit  19  is set to the Low output, and the switching circuit  11  outputs the DPD signal, as the TE signal, to be supplied to the input terminal (a). The spherical aberration correcting drive signal SAD (indicated by (g) in  FIG. 9 ) output by the control circuit  19  is assumed to be a level S 0  in  FIG. 9 , and the spherical aberration correcting amount in this condition is assumed to be optimal for the recording layer  202 . In addition, a level S 2  in  FIG. 9  is assumed to be a condition where the spherical aberration correcting amount is optimal for the recording layer  203 . 
     The focus jump starts at the step S 101 . The control circuit  19  makes the control signal TCNT into the Hi output at the time T 0  in  FIG. 9  to then make the tracking servo off, at the step S 102 . The control circuit  19  drives 50% of the spherical aberration correcting amount at the time T 1  in  FIG. 9 , at the step S 116 . That is, the spherical aberration correcting drive signal SAD indicated by (g) varies from the time T 1  and reaches a level S 1  at the time T 2  to then terminate the drive of the spherical aberration correction at that time point. Here, the level S 1  is set to a middle level between the level S 0  and a level S 2 . In fact, at the step S 116 , the spherical aberration is corrected by 50% of the entire amount thereof by varying the spherical aberration correcting drive signal SAD from the level S 0  to S 1 . 
     Thereafter, the jump signal generation circuit  7  outputs the accelerating voltage required for the focus jump at the time T 3 , at the step S 103 . Likewise to the first embodiment, the process at steps S 104  to S 109  is performed, and the focusing servo loop is closed at the time T 9 . The process at the steps S 110  to  112  is also performed to switch over the generation method of the TE signal. In this embodiment, the target layer to which the focus jump is applied is the second recording layer  203  of the recordable area, and the TE signal indicated by (c) is the push-pull signal at a time T 10 . In addition, at this time, the level of spherical aberration correcting drive signal SAD indicated by (g) is S 1 , and the level S 1  is not optimal for the second recording layer  203 . Therefore, the amplitude of TE signal indicated by (c) for which the push-pull signal is selected is small. 
     Further, the control circuit  19  drives the remaining 50% of the spherical aberration correction, at the step S 117 . That is, the spherical aberration correcting drive signal SAD indicated by (g) starts to vary from a time T 11  to then reach the level S 2  at a time T 12 . The amplitude of TE signal indicated by (c) becomes larger than that at the time T 11  since the level S 2  is optimal for the second recording layer  203  as described above. 
     Thereafter, the control circuit  19  performs the process for making the tracking servo on at the step S 113  and the process for confirming the landing layer at the step S 114 , and the focus jump is then terminated at the step S 115 . 
     In the above-mentioned embodiments, the focus jump has been described for the case where it is applied from the reproduction-only recording layer  202  to the recording layer  203  of the recordable area. In a reverse direction of the focus jump, it is also possible to apply the focus jump from the recording layer  203  of the recordable area, to the reproduction-only recording layer  202 . 
       FIG. 10  shows a waveform diagram for the above-mentioned case. 
     In an operation shown in  FIG. 10 , the optical disc apparatus before applying the focus jump is assumed to set a condition where the optical disc  1  rotates and the focusing servo control and tracking servo control are being operated on the second recording layer  203  of the recordable area. That is, the control signal FCNT output from the control circuit  19  is set to the Low output, the switching circuit  8  is connected to the input terminal (a) to output the output signal, as the FOD signal, of the focusing compensation circuit  6 , and the focusing servo loop indicates a condition where it is closed. Further, the control signal TCNT output from the control circuit  19  is set to the Low output, the switch  13  closes to output the output signal, as the TRD signal, of the tracking compensation circuit  12 , and the tracking servo loop indicates a condition where it is closed. Furthermore, the control signal TESEL output from the control circuit  19  is set to the Low output, and the switching circuit  11  outputs the push-pull signal, as the TE signal, to be supplied to the input terminal (b). The spherical aberration correcting drive signal SAD (indicated by (g) in  FIG. 10 ) output by the control circuit  19  is assumed to be the level S 2  in  FIG. 10 , and the spherical aberration correcting amount in this condition is assumed to be optimal for the recording layer  203 . 
     The tracking servo is made off at the time T 0 , at the step S 102  to thereby make the TE signal indicated by (c) into a substantially sine waveform push-pull signal. 
     The control circuit  19  drives 50% of the spherical aberration correcting amount at the time T 1  in  FIG. 10 . That is, the control circuit  19  varies the spherical aberration correcting drive signal SAD indicated by (g) from the time T 1 . Thereafter, when the spherical aberration correcting drive signal SAD reaches the level S 1  at the time T 2 , the control circuit  19  terminates the drive of the spherical aberration correction at that time point. Here, the level S 1  is the middle level between the level S 0  and S 2 , therefore, the spherical aberration is corrected by 50% of the entire amount thereof, at the step S 116 . 
     Thereafter, the optical disc apparatus outputs the accelerating voltage to be required for the focus jump of the reverse polarity against  FIG. 9  at the time T 3 , at the step S 103 , the process at the subsequent steps S 104  to S 109  is performed, and the focusing servo loop is closed at the time T 9 . In addition, an S-shaped curve appeared on the FE signal indicated by (f) in association with the focus jump becomes a reverse polarity against the FE signal indicated by (f) in  FIG. 9  since the direction of the focus jump in  FIG. 10  is reverse against that in  FIG. 9 . 
     Furthermore, the process at the steps S 110  to S 112  is performed to switch over the generation method for the TE signal. In the embodiment of  FIG. 10 , the target layer for the focus jump is the reproduction-only first recording layer  202 , and the DPD signal is output as the TE signal indicated by (c) at the time T 10 . 
     Furthermore, the control circuit  19  drives the remaining 50% of the spherical aberration correction at the step S 117 . That is, the spherical aberration correcting drive signal SAD indicated by (g) starts to vary from the time T 11  and reaches the level S 0  at the time T 12 . 
     Thereafter, the control circuit  19  performs the process for making the tracking servo on at the step S 113  and the process for confirming the landing layer at the step S 114  to then terminate the focus jump at the step S 115 . 
     As described above, an aspect of the optical disc apparatus is that the generation method of TE signal is switched over for the time period during which the tracking loop is opened in association with the focus jump, for example. To this end, the tracking servo control restarts rapidly to obtain the address information even when the focus jump is performed to then switch over the recording layer to which the tracking servo control is applied, so that it is possible to perform the seek operation rapidly. 
     In addition, the second embodiment is not limited to the above-mentioned method. 
     For example, the entire drive amount (100%) of the spherical aberration correction is divided into a 50%-to-50% ratio at the steps S 116 , S 117  in  FIG. 8 , but it may be divided into a 30%-to-70% ratio, as a divided ratio. The process at the step S 116  may be omitted to be set to a 0%-to-100% ratio if the focusing servo control is not deviated from the process. Conversely, the process at the step S 117  may be omitted to then be set to a 100%-to-0% ratio. That is, the ratio can be changed arbitrarily in range where the accuracy of the focus jump can be maintained. 
     Further, the switching operation of TE signal performed at the steps S 110 , S 111  and S 112  may be performed at other timings. That is, the optical disc apparatus may perform the switching operation of the generation method for TE signal at an arbitrary timing if the timing is within a time period from the time T 0  to time T 13  during which the tracking servo loop is opened in association with the focus jump. For example, the optical disc apparatus may be configured to perform the switching operation of TE signal on the loop operation of the peak detecting operation at the steps S 104 , S 107  and the FE signal zero-cross detecting operation at the steps S 105 , S 108 , as described in the first embodiment. The optical disc apparatus may also be configured to perform the switching operation of TE signal at a time period from the time T 3  at which the accelerating voltage is output, to the time T 4  at which the FE signal indicated by (f) exceeds the detection level Vth 1  or a time period from the time T 6  at which the decelerating voltage is output, to the time T 7  at which the FE signal indicated by (f) exceeds the detection level Vth 2 . 
     Alternatively, the optical disc apparatus may be configured to perform the switching operation of TE signal for a vicinity of a time period, for a time period from the time T 0  to T 1 , for a time period from the time T 2  to T 3 , or for a time period from the time T 12  to T 13 , during which the spherical aberration correcting drive signal SAD is varied. 
     Furthermore, the optical disc apparatus may be configured to perform the switching operation of TE signal in parallel with the variation of the spherical aberration correcting drive signal SAD for the time period during which the spherical aberration correcting drive signal SAD is varied, that is, the time period from the time T 1  to T 2 , or the time period from the time T 11  to T 12 . In fact, the optical apparatus may be configured to overlap the time period of performing the switching operation for the time period during which the spherical aberration correcting drive signal SAD is varied. The optical disc apparatus may also be configured to overlap the time period during which the switching operation is performed, the time period during which the spherical aberration correcting drive signal SAD is varied and the time period during which the objective lens is driven in the focus direction. In consequence, an entire processing time can be shortened more. 
     In addition, the spherical aberration correcting drive signal SAD is set to the level signal in  FIG. 10  and  FIG. 11 , which is for sake of simplicity in the description, however, the spherical aberration correcting drive signal SAD is set to a pulse-shaped signal when using the stepping motor as a drive mechanism for the spherical aberration correction. 
     The FOD signal indicated by (e) in  FIGS. 5 ,  6  and  FIGS. 9 ,  10  is set to a signal output as a binary level of the accelerating voltage and decelerating voltage for the time period during which the focus servo loop is opened. However, this waveform is not limited to the embodiment, and a voltage for applying a uniform motion to the objective lens may be output for a time period during which the accelerating voltage is switched over to the decelerating voltage. For example, for a time period from the time T 5  at which the peak of the FE signal indicated by (f) is detected at the step S 104  to the time T 7  at which the FE signal indicated by (f) first exceeds the detection level Vth 2  in the reverse peak detection at the step S 107 , the FOD signal indicated by (e) is set to a middle point voltage for example to then apply the uniform motion to the objective lens for that time period. 
     According to the above-mentioned optical disc apparatus in the second embodiment, since the optical disc apparatus provides the configuration to correct a part at a time for the spherical aberration, the tracking servo control applies to both the layer before applying the focus jump thereto and the target layer when performing the focus jump, so that it is possible to obtain the tracking error signal having a sufficient amplitude. In consequence, it is possible to constrain an increase of a processing time period in association with the focus jump. 
     In addition, the multilayer optical disc in relation to the invention is not limited to the configuration shown in  FIG. 2 . A reverse layer configuration may be acceptable in comparison to the configuration shown in  FIG. 2 . That is, it is needless to say that, one recording layer close to the objective lens is the reproduction-only recording layer and the other recording layer is the recording layer of the recordable area in the multilayer optical disc, which is also applicable to the embodiments as described above. 
     Further, the multilayer optical disc described in the embodiment of  FIG. 2  is the two-layered structure optical disc. However, the number of layers is not limited to the two-layered. The multilayer optical disc having the two or more layers such as three or four layers, are applicable to the embodiments as described above. 
     And also, the recording layer  203  of the rewritable area is applicable. 
     The optical system in the optical disc apparatus used for the invention and the generation method of the servo error signal are not limited to the description in the embodiments. For example, a known knife-edge method etc. may be used as the generation method of FE signal. The generation method of TE signal for the recording layer  203  of the recordable area, may be acceptable any methods if the method can obtain the TE signal in response to the tracking error amount even in a non-recorded portion of the optical disc. For example, a known DPP (Differential Push Pull) method etc. may be used. 
     In addition, the DPD generation circuit  9  and push-pull generation circuit  10  in the embodiments are configured to respectively have the gain circuit, however, the setting of gain circuit may also be changed as common to the gain circuits when switching over the generation method of TE signal. 
     In the case of a disc having a first recording or reproducing layer and a second recording or reproducing layer each having a different physical specification, the invention is applicable to even the case where the tracking error generation method, which can obtain a larger TE signal by the optical disc apparatus, is different for the respective layers as a first and second generation method. In this case, the first layer may be either the recording layer of the recordable area or the reproduction-only recording layer, and the second layer may also be either the recording layer of the recordable area or the reproduction-only recording layer. 
     Besides, the invention is not limited to the above-mentioned embodiments, but includes various examples. For example, the above-mentioned embodiments are described in detail for explaining the invention to understand easily, and all of the configurations are not necessarily limited to the invention. Further, one of the configurations in an embodiment can be replaced with the other in the other embodiment, and one of the configurations in an embodiment can be added to the other in the other embodiment. One of the configurations in the respective embodiments can also be added to, deleted from or replaced with the other configuration. 
     Even though a part or entire of the above-mentioned configurations may be configured by the hardware, it may be configured so as to be achieved by executing programs in a processor. Further, a control line and information line are indicated as required for the explanation, but all of the control line and information line are not necessarily indicated on products. Practically, it may be considered that almost all configurations are connected mutually. 
     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.