JP2005056511A - Servo control method, servo control circuit, and optical disk drive provided with servo control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a servo control method capable of reducing an influence of a time lag existing in a failure detecting signal when the servo control of a pickup is carried out, and to provide a servo control circuit and also an optical disk drive provided with this servo control circuit. <P>SOLUTION: A servo error signal and the failure detecting signal are generated from an output signal of the pickup, and also a servo control signal and a hold signal are generated from the servo error signal, and when the servo control of the pickup is carried out by a changeover to either one of the servo control signal and the hold signal in accordance with the failure detecting signal, the servo error signal generated a predetermined time prior to the timing for changing over to the hold signal from the servo control signal is used as a servo error signal for generating a hold signal. This requires a delay circuit to be prepared at the input side of a hold signal generating circuit for generating the hold signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a servo control method, a servo control circuit, and an optical disc apparatus having the servo control circuit.

  Conventionally, in an optical disc apparatus, in order to perform feedback control of a reading point in a pickup, a servo control signal is generated from an output signal of the pickup, and a servo control voltage for servo adjustment of the pickup is output based on the servo control signal A servo control circuit is provided, and control is performed by inputting a servo control voltage to the servo (see, for example, Patent Document 1).

  This servo control circuit prevents the servo control based on the abnormal output signal when the pickup output signal itself is abnormal due to scratches on the disk or dust adhering to the disk. For this reason, when an abnormality occurs in the output signal of the pickup, there is provided holding means for setting the servo in a hold state.

  Specifically, referring to FIG. 6, the RF signal read from the disk 200 by the pickup 100 is input to the reproduction circuit 300 while being input to the servo control circuit 400.

  The servo control circuit 400 includes an error signal generation circuit 410 that generates a servo error signal from an RF signal that is an output signal of the pickup 100, a defect detection signal generation circuit 420 that generates a defect detection signal from the RF signal, and a servo error signal. A servo control signal generation circuit 430 that generates a servo control signal based on this, and a hold signal generation circuit 440 that generates a hold signal holding a constant value obtained from the servo error signal whose waveform is adjusted in the servo control signal generation circuit 430, The servo control voltage output circuit 450 outputs a servo control voltage based on a servo control signal or a hold signal.

  The servo control voltage output circuit 450 is configured so that either the servo control signal or the hold signal is input by the changeover switch 460 based on the defect detection signal. In particular, the output signal of the pickup 100 is abnormal. When this occurs, the servo is put into a hold state by inputting a hold signal to the servo control voltage output circuit 450.

Here, as shown in FIG. 7, the defect detection signal generation circuit 420 includes an A / D converter circuit 421 that converts an analog RF signal that is an output signal of the pickup 100 into a digital RF signal, and a primary peak of the digital RF signal. Based on a first peak hold circuit 422 that generates a hold signal, a second peak hold circuit 423 that generates a secondary peak hold signal from the primary peak hold signal, and inputs of the primary peak hold signal and the secondary peak hold signal And a comparator circuit 424 for generating a defect detection signal. Reference numeral 425 denotes a filter circuit provided for removing a pit component in the digital RF signal, and reference numeral 426 denotes a gain adjustment circuit for a secondary peak hold signal.
JP 2000-90467 A

  However, in the servo control circuit described above, since there is a time lag in the defect detection signal output from the defect detection signal generation circuit, the timing at which the signal input to the servo control voltage output circuit is switched from the servo control signal to the hold signal. However, a delay of a predetermined time from the timing at which the output signal of the pickup fluctuates, and a fluctuation component is also incorporated into the hold signal itself output from the hold signal generation circuit. This makes it difficult to input a normal servo control voltage.

  Specifically, referring to FIG. 8, when a scratch or dust is present on the disk, the servo error signal generated from the output signal of the pickup has a large fluctuation as shown in FIG.

  At this time, as shown in FIG. 8B, the primary peak hold signal has a level drop due to the level drop of the pickup output signal. On the other hand, since the secondary peak hold signal holds the normal value of the primary peak hold signal, by using the primary peak hold signal and the secondary peak hold signal, the comparator circuit detects the defect shown in FIG. A signal is being output.

  Here, the threshold level is set in advance in the comparator circuit, and the defect detection signal becomes “High” when the primary peak hold signal falls below the threshold level. A time lag t ′ is a time from when the level of the peak hold signal starts to decrease to when it falls below the threshold level.

  During this time lag t ', since the servo error signal has already fluctuated, the hold signal generation circuit holds the constant value of the servo error signal based on the defect detection signal and generates the hold signal. In this case, the fluctuation component is also taken into the hold signal.

  Therefore, it is possible to reduce the fluctuation component captured in the hold signal by shortening the time lag t ′ by increasing the threshold level. However, there is a possibility that the servo hold state occurs and the operation stability is hindered.

  Therefore, in the servo control method of the present invention, a servo error signal and a defect detection signal are generated from the output signal of the pickup, and a servo control signal and a hold signal are generated from the servo error signal, and a servo is generated based on the defect detection signal. In the servo control method of switching the control signal to the hold signal by switching to either the control signal or the hold signal, when the servo control signal is switched to the hold signal, the hold signal is generated from the servo error signal before the switching timing. It was decided to generate.

  The servo control circuit according to the present invention generates a servo control signal, a hold signal, and a defect detection signal from the output signal of the pickup, and switches to either the servo control signal or the hold signal based on the defect detection signal. In the servo control circuit that performs servo control of the pickup, a delay circuit is provided on the input side of the hold signal generation circuit for generating the hold signal. Further, the defect detection signal generation circuit for generating the defect detection signal is characterized in that a switching timing delay circuit for delaying the timing for switching from the hold signal to the servo control signal based on the defect detection signal is provided. .

  In the optical disk apparatus having the servo control circuit of the present invention, the servo control signal, the hold signal, and the defect detection signal are generated from the output signal of the pickup, and any of the servo control signal and the hold signal is generated based on the defect detection signal. In an optical disc apparatus having a servo control circuit that performs servo control of the pickup by switching to either one, a delay circuit is provided on the input side of the hold signal generation circuit for generating a hold signal.

  According to the first aspect of the present invention, the servo error signal and the defect detection signal are generated from the output signal of the pickup, the servo control signal and the hold signal are generated from the servo error signal, and the servo is generated based on the defect detection signal. In the servo control method in which the servo control of the pickup is performed by switching to one of the control signal and the hold signal, when the servo control signal is switched to the hold signal, the hold signal from the servo error signal before the switching timing Therefore, the generated hold signal does not capture the fluctuation component generated in the servo error signal during the time lag of the defect detection signal, and stably holds the servo of the pickup. A hold signal that can be generated can be generated.

  According to the second aspect of the present invention, the servo control signal, the hold signal, and the defect detection signal are generated from the output signal of the pickup, and the servo control signal and the hold signal are switched based on the defect detection signal. In the servo control circuit for performing servo control of the pickup, a delay circuit is provided on the input side of the hold signal generation circuit for generating the hold signal, so that the generated hold signal is similar to the invention according to claim 1. Can generate a hold signal that can stably hold the servo of the pickup without incorporating a fluctuation component generated in the servo error signal during the time lag of the defect detection signal.

  According to the invention described in claim 3, the defect detection signal generation circuit for generating the defect detection signal is provided with the switching timing delay circuit for delaying the timing for switching from the hold signal to the servo control signal based on the defect detection signal. When the servo control of the pickup by the servo control signal is switched to the servo control by the hold signal, the servo control signal generation circuit restarts generating the servo control signal based on the appropriate state variable. Servo control signals can be output, and servo control can be stably performed immediately after returning from the hold state.

  According to the fourth aspect of the present invention, the servo control signal, the hold signal, and the defect detection signal are generated from the output signal of the pickup, and the servo control signal and the hold signal are switched based on the defect detection signal. In the optical disk apparatus having the servo control circuit for performing the servo control of the pickup, a delay circuit is provided on the input side of the hold signal generation circuit for generating the hold signal. The hold signal does not incorporate the fluctuation component generated in the servo error signal during the time lag of the defect detection signal, and can generate a hold signal that can stably hold the servo of the pickup. it can. Therefore, the operational stability of the optical disc apparatus can be improved.

  In the servo control method, servo control circuit, and optical disc apparatus having the servo control circuit of the present invention, either one of the servo control signal generated from the output signal and the hold signal based on the defect detection signal generated from the output signal of the pickup Is selected and servo control of the pickup is performed. In particular, when the servo control signal is switched to the hold signal, the hold signal is generated from the servo error signal before the switching timing. .

  That is, the hold signal is generated using the servo error signal before the time lag period of the defect detection signal.

  Therefore, the hold signal generated in this way does not include the fluctuation component generated in the servo error signal during the time lag of the defect detection signal, and the pickup servo can be stably held. A hold signal can be generated.

  In order to generate a hold signal using a servo error signal before the time lag period that the defect detection signal has, the servo control circuit has an input side of the hold signal generation circuit for generating the hold signal. A delay circuit is provided, and in the delay circuit, the servo error signal input to the hold signal generation circuit is output after being delayed by a time longer than the time lag period of the defect detection signal.

  Therefore, a signal delayed by a predetermined time can be input to the hold signal generation circuit very easily, and the hold signal can be generated smoothly.

  The servo control signal generation circuit that generates the servo control signal is connected to a state variable storage circuit that stores the state variable of the servo control signal generation circuit. When the servo control signal is switched to the hold signal, the servo control signal is generated. The signal generation circuit is configured to use a predetermined state variable from among the state variables stored in the state variable storage circuit.

  Therefore, when the servo control of the pickup by the servo control signal is switched to the servo control by the hold signal, the servo control signal generation circuit restarts the generation of the servo control signal based on the appropriate state variable. Servo control signals can be output, and servo control can be stably performed immediately after returning from the hold state.

  In particular, the state variable used when resuming the generation of the servo control signal is a state variable that is a predetermined time before the timing of switching the hold signal from the servo control signal based on the defect detection signal, and this predetermined time is the time lag period of the defect detection signal. By using a state variable that can generate a stable servo control signal by preventing the fluctuation component of the pickup output signal from being taken into the state variable used by the servo control signal generation circuit can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating the configuration of the servo control circuit 4 of the present embodiment. In the present embodiment, the servo control circuit 4 is a tracking servo control circuit that controls the reading point of the pickup 1 to the track center of the disk 2 for convenience of explanation. However, the servo control circuit is not limited to the one that performs tracking servo control, and can be applied to a servo control circuit having another servo hold function such as focus servo control.

  A part of the RF signal read from the disk 2 by the pickup 1 and input to the reproduction circuit 3 is input to the servo control circuit 4.

  The servo control circuit 4 includes an error signal generation circuit 41 that generates a servo error signal from an RF signal that is an output signal of the pickup 1, a defect detection signal generation circuit 42 that generates a defect detection signal from the RF signal, and a servo error signal. A servo control signal generation circuit 43 that generates a servo control signal based on the signal, and a hold signal generation circuit 44 that generates a hold signal that holds a constant value obtained from the servo error signal whose waveform is adjusted in the servo control signal generation circuit 43; The servo control voltage output circuit 45 outputs a servo control voltage based on a servo control signal or a hold signal. In FIG. 1, reference numeral 46 denotes a changeover switch that switches a signal input to the servo control voltage output circuit 45 between the servo control signal and the hold signal based on the defect detection signal output from the defect detection signal generation circuit 42.

  The error signal generation circuit 41 is provided with an A / D converter so as to output a servo error signal composed of a digital signal.

  In this embodiment, the hold signal generation circuit 44 is input with the servo error signal whose waveform is adjusted by the servo control signal generation circuit 43, and the hold signal generation circuit 44 is not provided with a circuit for waveform adjustment. However, the hold signal generation circuit 44 may be provided with a waveform adjustment circuit, and the servo error signal output from the error signal generation circuit 41 may be directly input to the hold signal generation circuit 44.

  An input delay circuit 47 is provided on the input side of the hold signal generation circuit 44, and a servo error signal delayed by a predetermined time by the input delay circuit 47 is input to the hold signal generation circuit 44. The delay time by the input delay circuit 47 is T. This delay time T is set to be longer than the time lag t of the defect detection signal generated in the defect detection signal generation circuit 42 described later.

  Furthermore, in the present embodiment, the servo control signal generation circuit 43 is connected to a state variable storage circuit 48 that stores a state variable representing the state of the servo control signal generation circuit 43. When the signal input to the servo control voltage output circuit 45 is switched from the servo control signal to the hold signal based on the defect detection signal, it is stored in the state variable storage circuit 48 as the state variable of the servo control signal generation circuit 43. A predetermined state variable is used from among the state variables.

  Here, as the predetermined state variable, a default value that is known to enable generation of an appropriate servo control signal may be used, or a predetermined value may be determined based on the timing at which the hold signal is switched from the servo control signal based on the defect detection signal. You may use a state variable that is only one hour ahead. For convenience of explanation, the predetermined time is the same as the delay time T described above. However, the predetermined time is not necessarily the same as the delay time T, but is longer than the time lag t included in the defect detection signal generated by the defect detection signal generation circuit 42.

  As shown in FIG. 2, the defect detection signal generation circuit 42 includes an A / D converter circuit 51 that converts an analog RF signal that is an output signal of the pickup 1 into a digital RF signal, and a primary peak hold signal of the digital RF signal. A first peak hold circuit 52 to be generated, a second peak hold circuit 53 that generates a secondary peak hold signal from the primary peak hold signal, and a defect detection signal based on the input of the primary peak hold signal and the secondary peak hold signal Comparator circuit 54, and the defect detection signal output from comparator circuit 54 determines the timing for switching the input to servo control voltage output circuit 45 from the hold signal to the servo control signal for a predetermined time. It comprises a switching timing delay circuit 55 for delaying. Here, the trailing edge delay time by the switching timing delay circuit 55 is T ′. 56 is a filter circuit provided for removing pit components in the digital RF signal, and 57 is a gain adjustment circuit for the secondary peak hold signal.

  By configuring the defect detection signal generation circuit 42 in this way, as shown in FIG. 3, the presence of scratches or dust on the disk 2 causes the servo error signal generated from the output signal of the pickup 1 to When a large fluctuation occurs as shown in a), the defect detection signal generation circuit 42 has a level corresponding to a drop in the level of the output signal of the pickup 1 in the primary peak hold signal as shown in FIG. When the reduction occurs, a defect detection signal as shown in FIG. 3C can be generated and output.

  In the defect detection signal, there is a time lag t that is a time from when the level of the primary peak hold signal starts to decrease to a level lower than the threshold level as in the conventional case.

  Conventionally, a time lag also exists in the trailing edge portion of the defect detection signal for a time substantially equal to the time lag t. However, the switching timing delay circuit 55 sets the trailing edge to a delay time T ′ longer than the time lag t. By delaying, when the signal input to the servo control voltage output circuit 45 is switched from the hold signal to the servo control signal based on the defect detection signal, the servo control signal is generated based on the normal servo error signal. By being generated by the circuit 43, the servo control can be stably performed immediately after the return from the hold state.

  Finally, the operations of the input delay circuit 47 and the state variable storage circuit 48 will be described in detail.

  First, in the present embodiment, the servo control signal generation circuit 43 stores the first circuit element 43a storing the first state variable m1 (n) and the second state variable m2 (n) as shown in FIG. The loop filter includes a second circuit element 43b, a third circuit element 43c that stores a third state variable m3 (n), and a first addition circuit 43d.

  The hold signal generation circuit 44 is a low-pass filter that includes a fourth circuit element 44a that stores the fourth state variable m4 (n) and a second addition circuit 44b.

Here, for convenience of explanation, explanation will be made using discrete time by Z conversion. In particular, the time in the control circuit is expressed in discrete time based on the servo error signal.

  If a defect detection signal is generated between time TE (n) and time TE (n + 3) as shown in FIG. 5A, the abnormal state period E is the time as shown in FIG. 5B. From TE (n-1) to time TE (n + 2).

  FIG. 5C shows the transition of the first state variable m1 (n) in the first circuit element 43a, and FIG. 5D shows the second state variable m2 (n) in the second circuit element 43b. FIG. 5 (e) shows the transition of the third state variable m3 (n) in the third circuit element 43c.

  FIG. 5 (f) shows the transition of the first state variable m 1 (n) stored in the state variable storage circuit 48, and FIG. 5 (g) shows the second state variable m 2 stored in the state variable storage circuit 48. FIG. 5 (h) shows the transition of the third state variable m3 (n) stored in the state variable storage circuit 48. FIG.

  In the present embodiment, as shown in FIG. 5, the state variable storage circuit 48 includes a state variable m1 (n) that is a predetermined time before the first circuit element 43a, the second circuit element 43b, and the third circuit element 43c. ), m2 (n), and m3 (n) are stored. Here, the predetermined time is the same as the delay time T described above.

  Then, as shown in FIG. 5, when the signal input to the servo control voltage output circuit 45 is switched from the servo control signal to the hold signal at time TE (n) based on the defect detection signal, the servo control signal generation circuit The state variables stored in the state variable storage circuit 48 at that time are input to the 43 circuit elements 43a, 43b, and 43c.

  The predetermined time T is set to be longer than the time lag t included in the defect detection signal generated in the defect detection signal generation circuit 42, so that the state variable m1 () input to each circuit element 43a, 43b, 43c It is possible to prevent the fluctuation component due to the fluctuation of the servo error signal from being included in n-3), m2 (n-3), and m3 (n-3).

  Therefore, when the servo control based on the servo control signal is resumed from the hold of the pickup 1 based on the hold signal, the servo control signal generation circuit 43 resumes the generation of the servo control signal based on an appropriate state variable. A normal servo control signal can be output promptly, and servo control can be stably performed immediately after returning from the hold state.

  If a state variable that can generate a normal servo control signal is known in advance, the state variable may be input.

  Further, as another embodiment, the state variable storage circuit 48 includes state variables m1 (n) and m2 (n) at the time of the first circuit element 43a, the second circuit element 43b, and the third circuit element 43c. , m3 (n), and when the signal input to the servo control voltage output circuit 45 is switched from the servo control signal to the hold signal at time TE (n), each of the servo control signal generation circuit 43 The state variables stored in the state variable storage circuit 48 that are stored in the state variable storage circuit 48 may be read and input to the circuit elements 43a, 43b, and 43c.

  When the signal input to the servo control voltage output circuit 45 is switched from the servo control signal to the hold signal at time TE (n), the state variable storage circuit 48 stores the state variables of the circuit elements 43a, 43b, and 43c. And the state variable stored at time TE (n) is retained. Then, after the abnormal state period E has elapsed, the state variable storage circuit 48 resumes the storage of the state variables.

  FIG. 5 (j) shows the transition of the fourth state variable m 4 (n) in the fourth circuit element 44 a of the hold signal generation circuit 44. Since the servo error signal delayed by the delay time T longer than the time lag t by the input delay circuit 47 is input to the hold signal generation circuit 44, the servo control voltage output circuit is based on the defect detection signal. When the signal to be input to 45 is switched from the servo control signal to the hold signal, the hold signal generation circuit 44 can input a servo error signal with no fluctuations. Can be generated. Therefore, it is possible to generate a hold signal that can hold the pickup servo stably.

It is a block diagram of a servo control circuit according to the present invention. It is a block diagram of a defect detection signal generation circuit. It is explanatory drawing of the defect detection signal produced | generated by the defect detection signal generation circuit. It is explanatory drawing of the servo control signal generation circuit in a servo control circuit, and a hold signal generation circuit. It is operation | movement explanatory drawing of a state variable memory circuit and a hold signal generation circuit. It is a block diagram of a conventional servo control circuit. It is a block diagram of a conventional defect detection signal generation circuit. It is explanatory drawing of the defect detection signal produced | generated by the conventional defect detection signal generation circuit.

Explanation of symbols

1 pickup 2 disc 3 playback circuit 4 servo control circuit
41 Error signal generation circuit
42 Defect detection signal generation circuit
43 Servo control signal generation circuit
44 Hold signal generation circuit
45 Servo control voltage output circuit
46 selector switch
47 Input delay circuit
48 State variable memory circuit
51 A / D converter circuit
52 First peak hold circuit
53 Second peak hold circuit
54 Comparator circuit
55 Switching timing delay circuit
56 Filter circuit
57 Gain adjustment circuit

Claims (4)

A servo error signal and a defect detection signal are generated from the output signal of the pickup, a servo control signal and a hold signal are generated from the servo error signal, and the servo control signal and the hold signal are generated based on the defect detection signal. In the servo control method for performing servo control of the pickup by switching to either one,
A servo control method, wherein when the servo control signal is switched to the hold signal, the hold signal is generated from the servo error signal before the switching timing. A servo control signal, a hold signal, and a defect detection signal are generated from an output signal of the pickup, and servo control of the pickup is performed by switching to either the servo control signal or the hold signal based on the defect detection signal. In the servo control circuit,
A servo control circuit, wherein a delay circuit is provided on an input side of a hold signal generation circuit for generating the hold signal.   The defect detection signal generation circuit for generating the defect detection signal is provided with a switching timing delay circuit for delaying a timing for switching from the hold signal to the servo control signal based on the defect detection signal. 2. The servo control circuit according to 2. A servo control signal, a hold signal, and a defect detection signal are generated from an output signal of the pickup, and servo control of the pickup is performed by switching to either the servo control signal or the hold signal based on the defect detection signal. In an optical disc apparatus having a servo control circuit,
An optical disc apparatus comprising a delay circuit provided on an input side of a hold signal generation circuit for generating the hold signal.

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