Abstract:
The present invention provides a focusing and tracking servo circuit used in an optical disk device that can maintain stability of the focusing and tracking servo at a time of recording or reproduction. This focusing and tracking servo circuit includes: a first storage unit that stores a parameter corresponding to light beam power at a time of recording; a second storage unit that stores a parameter corresponding to light beam power at a time of reproduction; and a selector unit that selects from the parameters stored in the first and second storage units upon switching between recording and reproduction, and sets the selected parameters in a detector unit. With this structure, the parameters can be instantly switched at the same time as the switching between recording and reproduction, and the stability of the focusing and tracking servo can be maintained.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a focusing and tracking servo circuit used in an optical disk device, and, more particularly, to a focusing and tracking servo circuit that performs recording and reproduction on a rewritable optical disk. 
     2. Description of the Related Art 
     There are two types of recording optical disks: one is a writing once type, and the other is a rewritable type. A CD-R (Compact Disk Recordable), which is a writing once optical disk, and a CD-RW (Compact Disk Rewritable), which is a rewritable optical disk, are both provided with a pregroove for guiding. Such a pregroove is very slightly wobbled in the radial direction with a center frequency of 22.05 kHz. Address information called ATIP (Absolute TimeIn Pregroove) for recording is multiplexed by FSK (Frequency Shift Keying) modulation with a maximum shift of ±1 kHz, and recorded on the pregroove. 
     A focusing and tracking circuit used in an optical disk device that performs recording and reproduction on such a recording optical disk emits optical beam on the optical disk, detects the reflection light from the optical disk by a plurality of detectors, generates a focusing and tracking error signal by performing a predetermined arithmetic operation, and drives a focusing and tracking actuator based on the focusing and tracking error signal. 
     In an optical disk device that performs recording and reproduction on a CD-R, which is a writing once optical disk, light beam power is used as read power at a time of reproduction. At a time of recording, the light beam power is switched between write power and read power (write power&gt;read power) in accordance with the value 0 or 1 of a recording signal. Accordingly, at a time of recording as well as reproduction, the reflection light is sampled at the timing of the light beam power being switched to the read power, thereby generating a focusing and tracking error signal. 
     In an optical disk device that performs recording and reproduction on a CD-RW, which is a rewritable optical disk, the light beam power is switched between write power and erase power (write power&gt;erase power&gt;read power) at a time of recording, in accordance with the value 0 or 1 of the recording signal. Accordingly, at a time of reproduction, the reflection light is detected at the timing of the light beam power being switched to the read power, thereby generating the focusing and tracking error signal. On the other hand, at a time of recording, the reflection light is sampled at the timing of the light beam power being switched to the erase power, thereby generating the focusing and tracking error signal. 
     Since the erase power has a higher output than the read power, the servo gain varies with the power. Therefore, it is necessary to change the sensitivity of each detector and the servo gain for recording and reproduction. 
     FIG. 1 is a block diagram of a conventional detector sensitivity switching circuit. This circuit is disposed inside a head amplifier IC. As shown in FIG. 1, a detector that detects a main light beam spot is divided into four detectors  10 A to  10 D, a detector that detects a preceding sub beam spot is divided into two detectors  10 E and  10 F, and a detector that detects a following sub beam spot is divided into two detectors  10 G and  10 H. 
     The head amplifier IC performs serial data transfer in order to reduce the number of pins. In compliance with a recording command or a reproduction command that instruct to switch between recording and reproduction, data SDATA consisting of address data and parameter data for setting detector sensitivity is serially transferred from a host device, and then stored in a shift register  12  at the timing of a clock signal SCK. An address decoder  14  decodes the address data stored in the shift register  12 , and transmits a write enable signal to one of detector sensitivity registers  16 A to  16 H corresponding to the address. The detector sensitivity register ( 16 B, for instance) that has received the write enable signal stores the parameter data supplied from the shift register  12 . Thus, the detector sensitivity of the detector ( 10 B, for instance) corresponding to the detector sensitivity register ( 16 B, for instance) can be switched. 
     Since the parameter data is serially transferred, a certain period of time is required until the detector sensitivities of all the detectors  10 A to  10 H are switched. FIG. 2 shows the switching timing of detector sensitivity in the prior art. Based on the ATIP information (timing information) of a wobble signal reproduced from the disk, a write gate is opened by a signal processing circuit, and recording is started. As shown in FIG. 2, the detector sensitivities of the detectors  10 A to  10 H are serially switched immediately before and after the opening of the write gate. As a result, there is a problem that the focusing servo and tracking servo become unstable. 
     This problem also arises in a case where the servo gain of the focusing and tracking servo is switched. While the servo gain is serially switched, the focusing servo and tracking servo become unstable. Furthermore, the offset varies with the switching of servo gain. If the switching of servo gain and the switching of offset are nor performed at the same time, the focusing servo and tracking servo become unstable. 
     SUMMARY OF THE INVENTION 
     A general object of the present invention is to provide a focusing and tracking servo circuit in which the above disadvantages are eliminated. 
     A more specific object of the present invention is to provide a focusing and tracking servo circuit that maintains stability in the focusing and tracking servo at a time of switching between recording and reproduction. 
     The above objects of the present invention are achieved by a focusing and tracking servo circuit used in an optical disk device, which performs recording by increasing light beam power applied onto an optical disk, and performs focusing and tracking servo. This focusing and tracking servo circuit comprises: 
     a detector unit that detects the light beam reflected from the optical disk; 
     a first storage unit that stores a parameter corresponding to light beam power at a time of recording; 
     a second storage unit that stores a parameter corresponding to light beam power at a time of reproduction; and 
     a selector unit that selects from the parameters stored in the first and second storage units in upon switching between recording and reproduction. 
     In the above focusing and tracking servo circuit, the selected parameter is set in the detector unit or in a corresponding one of a tracking servo gain switching unit, a tracking servo offset switching unit, a focusing servo gain switching unit, and a focusing servo offset switching unit. 
     Since the parameters selected from those stored in the first and second storage units at a time of switching between recording and reproduction are set in the detecting unit or in the focusing and tracking servo circuit, the parameters can be instantly switched at the same time as the switching between recording and reproduction, and stability can be maintained in the focusing and tracking servo. 
     In the above focusing and tracking servo circuit of the present invention, each of the parameters may be a detection sensitivity of the detector unit. 
     Also, in the above focusing and tracking servo circuit of the present invention, each of the parameters may be a servo gain and offset of the focusing and tracking servo circuit. 
     The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an example of a conventional detector sensitivity switching circuit; 
     FIG. 2 is a timing chart of detector sensitivity switching in the prior art; 
     FIG. 3 is a block diagram of one embodiment of an optical disk device to which a circuit of the present invention is applied; 
     FIG. 4 is a block diagram of a first embodiment of a focusing and tracking servo circuit in accordance with the present invention; 
     FIG. 5 is an illustration showing the relationship among a main light beam spot, a preceding sub beam spot, and a following sub beam spot, for a pregroove; 
     FIG. 6 is a block diagram of a second embodiment of the focusing and tracking servo circuit in accordance with the present invention; 
     FIG. 7 is a block diagram of one embodiment of a head amplifier; 
     FIG. 8 is a circuit diagram of one embodiment of an attenuator circuit; 
     FIG. 9 is a circuit diagram of one embodiment of a switching circuit of tracking servo gain and offset; and 
     FIG. 10 is a block diagram of a part of a modification of the focusing and tracking servo circuit of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is a description of embodiments of the present invention, with reference to the accompanying drawings. 
     FIG. 3 is a block diagram of one embodiment of an optical disk device to which a circuit of the present invention is applied. An optical disk (CD-RW)  20  is driven by a spindle motor to rotate. A controller  22  supplies an instruction to a servo IC  24 , in accordance with a record/reproduction command supplied from a host device. The servo IC  24  performs CLV (Constant Linear Velocity) servo for the spindle motor, and controls the rotation of a thread motor of an optical pickup  26 , so that the optical pickup  26  is moved to a desired block on the optical disk  20 , and focusing servo and tracking servo for the optical pickup  26  are performed. 
     Laser beam emitted from the optical pickup  26  is reflected by the recording surface of the optical disk  20 , and then detected by the optical pickup  26 . The reproduction signal obtained by the optical pickup  26  is supplied to a head amplifier IC  28 , which shapes the waveform of the reproduction signal. This reproduction signal is supplied to the servo IC  24  and to a following signal processing system, in which the reproduction signal is subjected to EFM demodulation and wobble signal separation. The demodulated signal synchronized in the signal processing system is decoded and subjected to error correction, and then is outputted as reproduction data. Meanwhile, the head amplifier IC  28  generates and supplies a focusing error signal FE and a tracking error signal TE to the servo IC  24 . 
     FIG. 4 is a block diagram of a first embodiment of the focusing and tracking servo circuit in accordance with the present invention. This circuit is disposed inside the head amplifier IC  28 , and performs sensitivity switching of detectors. In FIG. 4, the same components as in FIG. 1 are denoted by the same reference numerals. A main light beam spot  2 , a preceding sub beam spot  3 , and a following sub beam spot  4  are emitted onto a pregroove  1 . The reflection beam of the main light beam spot  2  is detected by divided detectors  10 A,  10 B,  10 C, and  10 D shown in FIG.  4 . The reflection beam of the preceding sub beam spot  3  is detected by divided detectors  10 E and  10 F shown in FIG.  4 . The reflection beam of the following sub beam spot  4  is detected by divided detectors  10 G and  10 H shown in FIG.  4 . It should be noted that the divided portions of each beam spot shown in FIG. 3 are denoted by alphabets corresponding to the detectors. 
     The head amplifier IC  28  performs serial data transfer in order to reduce the number of pins. Once the optical disk  20  is inserted into the optical disk device, the heat amplifier IC  28  determines the type of the disk (for instance, CD-R or CD-RW) and notifies the controller  22  of the type of the disk. The controller  22  calculates the detector sensitivities at the time of read power and write power in accordance with the type of the disk, and serially transfers SDATA that includes the parameter data for setting the detector sensitivities at the time of the read power and the write power, and address data, to the head amplifier IC  28 . 
     The SDATA is stored in a shift register  12  at the timing of a clock signal SCK. An address decoder  14  decodes the address data stored in the shift register  12 , and transmits a write enable signal to one of read detector sensitivity registers  17 A to  17 H and write detector sensitivity registers  18 A to  18 H, whichever corresponds to the address. The detector sensitivity register ( 17 B, for instance) that has received the write enable signal stores the parameter data transmitted from the shift register  12 . 
     In the above manner, the read detector sensitivity parameter data of the detectors  10 A to  10 H are set in the read detector sensitivity registers  17 A to  17 H, respectively, and the write detector sensitivity parameter data of the detectors  10 A to  10 H are set in the write detector sensitivity registers  18 A to  18 H, respectively. 
     The parameter data stored in the detector sensitivity registers  17 A and  18 A to  17 H and  18 H, which are paired by the detector, is supplied to data selectors  30 A to  30 H. In accordance with the output of an AND circuit  32 , at a time of reproduction, the data selectors  30 A to  30 H select the output data of the read detector sensitivity registers  17 A to  17 H. At a time of recording (when a write mode signal is high), when a high-level write gate signal is supplied, the data selectors  30 A to  30 H select the output data of the write detector sensitivity registers  18 A to  18 H. The data selectors  30 A to  30 H then supply the selected output data to the detectors  10 A to  10 H, respectively. 
     In the above manner, when the write gate signal becomes high at a time of recording, the detectors  10 A to  10 H are switched from the read detector sensitivity to the write detector sensitivity. Thus, the focusing and tracking servo at a time of switching between recording and reproduction can be stably performed. 
     FIG. 6 is a block diagram of a second embodiment of the focusing and tracking servo circuit of the present invention. This circuit is disposed inside the head amplifier IC  28 , and switches the detector sensitivities. The circuit shown in FIG. 6 also switches the servo gain and offset. In FIG. 6, the same components as in FIG. 4 are denoted by the same reference numerals. 
     Once the optical disk  20  is inserted into the optical disk device, the head amplifier IC  28  determines the type of the disk (CD-R or CD-RW, for instance), and notifies the controller  22  of the determined type of the disk. The controller  22  calculates the detector sensitivity corresponding to the type of the disk at a time of read power and at a time of write power, and servo gain and the offset of the focusing and tracking servo circuit. The controller  22  then serially transfers data SDATA that includes parameter data for setting the detector sensitivity at a time of read power and at a time of write power, the servo gain and offset, and address data, to the head amplifier IC  28 . 
     The data SDATA is stored in the shift register  12  at the timing of the clock signal SCK. The address decoder  14  decodes the address data stored in the shift register  12 , and transmits a write enable signal to one of a read tracking servo gain register  35 A, a write tracking servo gain register  35 B, a read tracking servo offset register  36 A, a write tracking servo offset register  36 B, a read focusing servo gain register  37 A, a write focusing servo gain register  37 B, a read focusing servo offset register  38 A, and a write focusing servo offset register  38 B, whichever corresponds to the address. The register that has received the write enable signal stores the parameter data transmitted from the shift register  12 . 
     In the above manner, the parameter data of the read tracking servo gain, the write tracking servo gain, the read tracking servo offset, the write tracking servo offset, the read focusing servo gain, the write focusing servo gain, the read focusing servo offset, the write focusing servo offset, can be set in the registers  35 A to  38 B, respectively. 
     The parameter data of the registers  35 A and  35 B to  38 A to  38 B is supplied to data selectors  40  to  43 . In accordance with the output of the AND circuit  32 , at a time of reproduction, the data selectors  40  to  43  select the output data of the read registers  35 A,  36 A,  37 A, and  38 A. At a time of recording (when the write mode signal is high), the data selectors  40  to  43  select the output data of the write registers  35 B,  36 B,  37 B, and  38 B when a high-level write gate signal is supplied. The data selectors  40  to  43  then supply the selected output data to a tracking servo gain switching unit  44 , a tracking servo offset switching unit  45 , a focusing servo gain switching unit  46 , and a focusing servo offset switching unit  47 . 
     The output of the AND circuit  32  is also supplied to an attenuator unit  48 . This attenuator unit  48  roughly switches the attenuation for the output of each of the detectors  10 A to  10 H at a time of recording or reproduction. After that, fine adjustment is carried out by the tracking servo gain switching unit  44 , the tracking servo offset switching unit  45 , the focusing servo gain switching unit  46 , and the focusing servo offset switching unit  47 . The offset switching is performed at a time of reproduction or recording, because the detector sensitivity is so roughly set that the offset value differs between a recording time and reproduction time, and the amplifier offset varies with the servo gain. 
     FIG. 7 is a block diagram of an example structure of the head amplifier IC  28 . As shown in FIG. 7, terminals  50 A to  50 H receive output signals A to H from the detectors  10 A to  10 H, respectively. Attenuator circuits  52 A to  52 H that constitute the attenuator unit  48  roughly set each detector sensitivity, and then supply the signals A to H to a sample holding circuit  54  that holds each signal at predetermined timing. 
     The signals A to H outputted from the sample holding circuit  54  are supplied to a matrix circuit  56 , which obtains a focusing signal FEO=(A+C)−(B+D), a tracking signal MPP=(A+D)−(B+C), and a signal SPPO=(F+H)−(E+G). 
     The signal FEO is supplied to the focusing servo gain switching unit  46  via a low pass filter  58 . The focusing servo gain switching unit  46  is accompanied by the focusing servo offset switching unit  47 , so that gain and offset operations are performed on the signal FEO. As a result, a focusing error signal FE is generated and outputted. 
     The signal MPP and the signal SPPO are mixed by a mixing circuit  59 , which generates a signal TEO=(A+D)−(B+C)−k·[(F+H)−(E+G)] (k is a predetermined coefficient). The signal TEO is supplied to the tracking servo gain switching unit  44  via a low pass filter  60 . The tracking servo gain switching unit  44  is accompanying by the tracking servo offset switching unit  45 , so that gain and offset operations are performed on the signal TEO. As a result, a tracking error signal TE is generated and outputted. 
     FIG. 8 is a circuit diagram of an example of the attenuator circuit  52 A. The other attenuator circuits  52 B to  52 H have the same structure as the attenuator circuit  52 A. As shown in FIG. 8, the parameter data from the shift register  12  is set in D-type flip-flops  62  and  63 . At a time of activating, a switch  64  selects a 0 DB amplifier  65  for the reproduction mode. After the determination of the disk based on reflection beam from the optical disk  20 , the parameter data in accordance with the type of the disk is transmitted from the controller  22  and set in the flip-flop  63 . The gain of an amplifier  67  is then switched. 
     When a recording command is inputted at a time of recording, parameter data for switching the switch  64  to a −20 dB amplifier  66  is transmitted and stored in the flip-flop  62 . A write gate is then opened, so that the sensitivity of the detector  10 A is instantly switched to the recording mode. 
     FIG. 9 is a circuit diagram of an example of a tracking servo gain and offset switching circuit. It should be understood here that a focusing servo gain and offset switching circuit has the same structure. In FIG. 9, the same components as in FIG. 6 are denoted by the same reference numerals. 
     As shown in FIG. 9, D-type flip-flops  35 A 1  to  35 A 4  constitute the read tracking servo gain register  35 A, D-type flip-flops  35 B 1  to  35 B 4  constitute the write tracking servo gain register  35 B, D-type flip-flops  36 A 1  to  36 A 4  constitute the read tracking servo offset register  36 A, and D-type flop-flops  36 B 1  to  36 B 4  constitute the write tracking servo offset register  36 B. Switches  40   1  to  40   4  constitute the data selector  40 , and switches  41   1  to  41   4  constitute the data selector  41 . 
     The tracking servo gain switching unit  44  varies the gain of an amplifier  44   5  switches  44   1  to  44   4  that are switched on and off in accordance with the output of the switches  40   1  to  40   4  of the data selector  40 . The tracking servo offset switching unit  45  varies the offset, which is added by an adder  45   5 , by switches  45   1  to  45   4  that are switched on and off in accordance with the output of the switches  41   4  to  41   4  of the data selector  41 . 
     After the determination of the type of the disk in accordance with the reflection beam from the optical disk  20  at a time of activation, the parameter data based on the determined type of the disk is transmitted from the controller  22 . Accordingly, the parameter data of the read tracking servo gain is set in the D-type flip-flops  35 A 1  to  35 A 4 , and the parameter data of the read tracking servo offset is set in the D-type flip-flops  36 A 1  to  36 A 4 . Likewise, the parameter data of the write tracking servo gain is set in the D-type flip-flops  35 B 1  to  35 B 4 , and the parameter data of the write tracking servo offset is set in the D-type flip-flops  36 B 1  to  36 B 4 . The tracking servo gain switching unit  44  sets the gain in accordance with the output of the D-type flip-flops  35 A 1  to  35 A 4  transmitted via the switches  40   1  to  40   4  of the data selector  40 . The tracking servo offset switching unit  45  sets the offset in accordance with the output of the D-type flip-flops  36 A 1  to  36 A 4  transmitted via the switches  41   1  to  41   4  of the data selector  41 . 
     When the write gate is opened at a time of recording, the tracking servo gain switching unit  44  sets the gain in accordance with the output of the D-type flip-flops  35 B 1  to  35 B 4  via the switches  40   1  to  40   4  of the data selector  40 . The tracking servo offset switching unit  45  sets the offset in accordance with the output of the D-type flip-flops  36 B 1  to  36 B 4  via the switches  41   1  to  41   4  of the data selector  41 . In this manner, the sensitivity of the detector  10 A is instantly switched to the recording mode. 
     FIG. 10 is a block diagram of a part of a modification of the focusing and tracking servo circuit shown in FIG.  4 . FIG. 10 only shows the part related to the detector  10 A, but the other detectors  10 B and  10 H each have the same structure as the detector  10 A. In this modification, a plurality of write detector sensitivity registers  18 A 1  to  18 A 15  are employed. In a recording operation in which write power and erase power are alternately applied, a data selector  50  switches the write detector sensitivity corresponding to the erase power. 
     In a CD-RW, before recording is performed on the optical disk, test write is performed in a power calibration area (PCA) on the inner periphery of the disk, so as to determine the optimum recording power. This is called an optimum power control (OPC) operation. In this operation, the write power and erase power are varied in 15 steps, with a power value stored in advance in the optical disk device being the center value. With the 15-step varied write power and erase power, test write is performed. Prior to switching of the OPC, the detector sensitivities corresponding to the 15-step varied power values are stored in the write detector sensitivity registers  18 A 1  to  18 A 15 , and the detector sensitivities of all the detectors  10 A to  10 H is at once switched in 15 steps, based on the timing of changing the erase power. 
     Also, in order to accommodate a running OPC for changing the optimum recording power in a few steps during a recording operation, the detector sensitivities corresponding to 5 steps power values consisting of the optimum recording power as center value and two values each below and above the center value are stored in the write detector sensitivity registers  18 A 1  to  18 A 5 . Based on the timing of changing the erase power during the recording operation, the detector sensitivities of all the detectors are switched at once. Although the detector sensitivity switching is shown in this modification, the switching of the servo gain and offset may of course be performed in the same structure. 
     The embodiments of the present invention have been described by way of examples using a CD-RW, but the present invention can also be applied to other types of rewritable optical disks such as MD (MiniDisk). 
     The present invention is not limited to the specifically disclosed embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 11-271163, filed on Sep. 24, 1999, the entire contents of which are hereby incorporated by reference.