JP3678509B2 - Focus servo circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focus servo circuit, and more particularly to a focus servo circuit used in a servo system of an optical disc player such as a compact disc (hereinafter simply referred to as CD) player or a mini disc player.
[0002]
[Prior art]
In such an optical disc player, for example, a CD player, the objective lens built in the optical pickup and the signal surface of the disc against vertical movement of the disc signal surface caused by disc warpage or vibration disturbance when the disc rotates. A focus servo circuit is indispensable in order to control the distance between the two to be constant.
[0003]
In such a focus servo circuit, an error voltage in the vertical movement direction (focus direction) with respect to the disk signal surface, that is, a focus error signal is generated, and the distance between the objective lens and the signal surface is made constant based on the focus error signal. Can keep.
[0004]
When generating such a focus error signal, the astigmatism method is widely adopted. According to this astigmatism method, the light obtained by each light receiving portion of the four-divided sensor is replaced with an electric signal, and a diagonal line is obtained. A focus error signal is generated by adding and subtracting the output of the light receiving unit located above.
[0005]
However, according to the focus servo circuit employing such an astigmatism method, if the sensitivity of each light receiving part of the four-divided sensor varies, or if there is an offset in the circuit system such as an adder, Even though the signal surface is on the focal plane of the optical system, an offset amount occurs in the focus error signal, and this focus error signal may not become zero.
[0006]
Therefore, in the conventional focus servo circuit, the focus bias voltage generated using a semi-fixed resistor is added to the focus error signal to cancel the offset of the focus error signal. Thus, the focus servo bias adjustment can be realized.
[0007]
However, in such a bias adjustment, it takes a lot of labor to perform the adjustment work manually in the production line, and this work requires skill.
[0008]
Even when bias adjustment is performed in this manner, when actually reproducing a disc, the refractive index varies depending on the thickness and material of the reproduction disc, and the resulting focus shift may occur. There was a situation where it was impossible to deal with it.
[0009]
Accordingly, a focus servo circuit disclosed in Japanese Patent Application Laid-Open No. 6-231477 has been developed to cope with such a situation.
[0010]
This focus servo circuit is based on an error signal generation circuit that generates a focus error signal, a jitter detection circuit that detects the jitter amount of an RF signal reproduced from a disk, and a jitter amount detected by the jitter detection circuit. Measures the bottom value, sets a threshold value obtained by adding a predetermined value to the bottom value, detects two corresponding bias values corresponding to the set threshold value, and optimizes based on these two corresponding bias values A focus bias voltage adjusting circuit for calculating a bias value, a focus bias voltage generating circuit for generating a focus bias voltage based on an optimum bias value calculated by the focus bias voltage adjusting circuit, and a focus of the focus bias voltage generating circuit Add the bias voltage and the focus error signal of the error signal generation circuit. And a servo circuit for performing a focus servo based on the signal.
[0011]
This focus servo circuit pays attention to the fact that the amount of jitter of the RF signal is minimized during just focus, and the amount of jitter corresponding to the focus bias error is converted into an EFM (Eight to Fourteen Modulation) signal (binarized signal). The time difference between the edge of the synchronized clock and the change point of the EFM signal is measured, and a focus bias voltage that minimizes this time difference is generated, and the bias adjustment is automatically performed.
[0012]
Now, focus bias automatic adjustment processing in the focus servo circuit will be described. FIG. 5 is a flowchart showing the processing operation of the focus bias voltage adjustment circuit in the conventional focus bias automatic adjustment processing.
[0013]
In FIG. 5 , the focus bias voltage adjustment circuit sets the focus bias value to “0”, detects jitter via the jitter detection circuit (step S201), and swings this bias value to “+” or “−”. While detecting the jitter, the jitter bottom value Z is measured (step S202). Note that FIG. 6 is a graph showing the relationship between convenience simplified jitter amount and the bias value, near the jitter bottom value Z as shown in FIG. 6 is the case of the flat.
[0014]
In this way, the jitter bottom value Z measured in step S202 is stored (step S203), and the threshold value X obtained by adding the predetermined value α to the jitter bottom value Z is set and stored (step S204).
[0015]
Now, the reason why the predetermined value α is added to the jitter bottom value Z in step S204 will be described. Showed graph convenience simplified in FIG. 6, originally, as can be seen from Figure 7, as shown in FIG. 6, not a pretty graphs form. This indicates that the variation in jitter amount increases depending on the state of the disk.
[0016]
Therefore, in the idea that it is normal to play a clean disc, it is more certain that the jitter bottom value Z is added to some extent, that is, the predetermined value α, and the midpoint value, for example, is used to ensure the optimum bias. It can be said that the value can be obtained.
[0017]
For this reason, when the threshold value X is set by adding the predetermined value α to the jitter bottom value Z in step S204, two corresponding bias values FA and FB corresponding to the set threshold value X are obtained by shifting the bias value. Is detected (step S205), and when these two corresponding bias values FA and FB are detected, the optimal processing is performed by performing an arithmetic process of “(FA + FB) / 2” based on these corresponding bias values FA and FB. A bias value is calculated (step S206), the calculated optimum bias value is set in the focus bias voltage generation circuit, that is, a focus bias is set (step S207), and the focus bias automatic adjustment process is terminated.
[0018]
The focus bias voltage generation circuit then generates a focus bias voltage based on the set optimum bias value, and cancels the offset of the focus error signal by this focus bias voltage.
[0019]
Therefore, according to the above conventional focus servo circuit, the bias adjustment work that has been performed manually by the skilled worker in the production line can be automatically performed, for example, every time a playback disk is inserted into the player. In addition, it is possible to realize optimum bias adjustment corresponding to each disk even if the thickness and material of the disk to be reproduced are different.
[0020]
[Problems to be solved by the invention]
According to the conventional focus servo circuit, when the bias is adjusted when the power is turned on, the measurement starts from “0 V” as the initial value of the jitter bottom value measurement. However, there is a variation in the characteristics of electric elements such as a photodetector. Therefore, since the jitter bottom value is biased to either the “+” side or the “−” side as shown in FIG. 8, when the jitter bottom value measurement is started from “0 V”, the jitter bottom value measurement is performed. In this case, there is a problem that it takes a long time and the adjustment time required for the bias adjustment becomes long. As described above, there is a problem that the automatic adjustment of the focus bias is not performed accurately within a short time.
[0021]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a focus servo circuit that can significantly reduce the adjustment time required for bias adjustment.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, a focus servo circuit according to claim 1 of the present invention comprises an error signal generating means for generating a focus error signal and a jitter amount which is an amount corresponding to the jitter of an RF signal reproduced from a disk. Jitter detection means for detecting the threshold value, and based on the jitter amount detected by the jitter detection means, the bottom value is measured, and a threshold value obtained by adding a predetermined value to the bottom value is set. Focus bias voltage adjusting means for detecting two corresponding bias values corresponding to the threshold value and calculating an optimum bias value based on the corresponding bias values, and based on the optimum bias value calculated by the focus bias voltage adjusting means Focus bias voltage generating means for generating a focus bias voltage and generating the focus bias voltage A focus servo circuit having a servo means for executing focus servo based on an addition signal of the focus bias voltage of the stage and the focus error signal of the error signal generation means, wherein the focus bias voltage adjustment means Optimal bias value storage means for storing the bias value as the previous optimal bias value, bottom value storage means for storing the previous bottom value as the previous bottom value, and the previous optimal bias value stored in the optimal bias value storage means If there is a threshold value setting means for setting the previous bottom value stored in the bottom value storage means as a measurement bottom value and adding the predetermined value to the measurement bottom value to set a threshold value.
[0023]
The schematic configuration of the error signal generation means, jitter detection means, focus bias voltage adjustment means, focus bias voltage generation means, and servo means is substantially the same as the focus servo circuit according to claim 1.
[0024]
The configuration of the focus bias voltage adjusting means in the focus servo circuit according to claim 1 is particularly characterized in that it has an optimum bias value storage means, a bottom value storage means and a threshold value setting means.
[0025]
The optimum bias value storage means stores the optimum bias value measured during the previous bias adjustment as the previous optimum bias value.
[0026]
The bottom value storage means stores the previous bottom value, that is, the bottom value related to the optimum bias value, as the previous bottom value.
[0027]
Therefore, according to the focus servo circuit of claim 1, if there is a previous optimum bias value in the optimum bias value storage means at the time of bias adjustment, the last bottom value related to the last optimum bias value from the bottom value storage means. Since reading the value and omitting the measurement of the current bottom value and making this previous bottom value the measurement bottom value, the adjustment time required for bias adjustment is further reduced by eliminating the time required for the current bottom value measurement. The whole can be greatly shortened.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which a focus servo circuit of the present invention is applied to a CD player will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a focus servo circuit in an embodiment according to the present invention.
[0029]
In FIG. 1, the focus servo circuit outputs an optical pickup 20 that optically reads the signal surface recorded on the signal surface of the disk 10 and outputs from the optical pickup 20 according to a known generation method such as an astigmatism method. An error signal generation circuit 30 that is an error signal generation means for generating a focus error signal based on the error signal, and a focus error signal generated by the error signal generation circuit 30 and a focus bias voltage, which will be described later, are added to obtain a focus error signal. And an adder 40 that cancels the DC offset of the signal, and a drive signal for controlling the focus actuator in the optical pickup 20 based on the output signal of the adder 40, and sends the drive signal to the optical pickup 20. From the drive circuit 50 serving as servo means and the optical pickup 20 A jitter detection circuit 60 that is a jitter detection unit that detects the jitter amount of the RF signal, and a focus bias voltage that is a focus bias voltage adjustment unit that calculates an optimum bias value based on the jitter amount detected by the jitter detection circuit 60 A focus bias voltage which is a focus bias voltage adjusting means for generating a focus bias voltage which is one input signal of the adder 40 based on the adjustment circuit 100 and a bias value calculated by the focus bias voltage adjustment circuit 100 And a generation circuit 70.
[0030]
The RF signal output from the optical pickup 20 is supplied to a PLL circuit (not shown), used to generate a PLL clock (PLCK) synchronized with the RF signal, and supplied to a digital signal processing system (not shown). Thus, signal processing such as EFM demodulation and error correction is performed on the basis of the PLL clock and is derived as an audio output.
[0031]
The jitter detection circuit 60 measures the jitter amount corresponding to the focus bias error as a time difference (phase difference) between the edge of the PLL clock and the changing point of the EFM signal, and this time difference is a predetermined time. This is equivalent to the number of counts when the measured value is equal to or greater than a certain value (for example, 60 nsec) within the reference time (for example, time for 8 frames; about 16 μsec per frame).
[0032]
The error signal generation circuit 30 is zero when the signal surface of the disk 10 is in the focal plane of the optical system based on the output of the focus servo system from the optical pickup 20 according to a known generation method such as an astigmatism method. A focus error signal is generated that becomes negative (or positive) when the signal surface approaches the objective lens and becomes positive (or negative) when the signal surface moves away from the objective lens.
[0033]
FIG. 2 is a block diagram showing a configuration of the focus bias voltage adjustment circuit 100 which is a main part of the focus servo circuit in the present embodiment.
[0034]
In FIG. 2, the focus bias voltage adjustment circuit 100 includes a bottom value measurement unit 101 that is a bottom value measurement unit that measures a jitter bottom value Z based on the jitter amount detected by the jitter detection circuit 60, and the bottom value measurement. A bottom value memory 102 which is a bottom value storage means for storing the jitter bottom value Z measured by the unit 101; and a predetermined value memory 103 for storing a predetermined value α to be added to the jitter bottom value Z to generate the threshold value X. A threshold value memory 104 that is a threshold value setting means for storing the threshold value X, a corresponding bias value detection unit 105 that detects two corresponding bias values FA and FB corresponding to the threshold value X, and a corresponding bias value detection unit 105 A corresponding bias value memory 106 for storing the corresponding bias values FA and FB detected in this manner, and these two corresponding bias values FA. An optimum bias value calculation unit 107 that calculates an optimum bias value based on the FB, an optimum bias value memory 108 that is an optimum bias value storage unit that stores the optimum bias value calculated by the optimum bias value calculation unit 107, and In-measurement jitter / bias value memory 109 for sequentially storing a bias value sequentially measured by the corresponding bias value detection unit 105 and a jitter amount corresponding to the bias value, and a current jitter detected by the jitter detection circuit 60 Jitter deterioration detecting unit 110 which is a jitter amount determining means for determining whether or not the deterioration of the image is detected, a predetermined situation detecting unit 112 which is a situation detecting means for detecting a predetermined situation described later, and the entire focus bias voltage adjusting circuit 100 And a control unit 111 that is a start-up means for controlling. The control unit 111 is connected to the jitter detection circuit 60 described above and a focus error detection circuit 80 for detecting a focus error such as a focus drop.
[0035]
The optimum bias value calculation unit 107 calculates the average value of the values obtained by adding the two corresponding bias values FA and FB detected by the corresponding bias value detection unit 105, that is, (FA + FB) / 2. The optimal bias value is calculated by the calculation process.
[0036]
The jitter deterioration detection unit 110 determines whether the current jitter amount detected by the jitter detection circuit 60 is larger than the previous jitter bottom value Z stored in the bottom value memory 102 by a predetermined value α. If it is determined that the current jitter amount is larger than the previous jitter bottom value Z by the predetermined value α, it is determined that the current jitter has deteriorated.
[0037]
The predetermined situation detected by the predetermined situation detection unit 112 is, for example, when the playback mode is changed from the stop mode using the same disk, or when the playback disk is replaced, the playback time of the disk using the same disk reaches a certain time When a certain time has elapsed since the disk was replaced, regardless of disk playback, when disk playback has been performed a predetermined number of times on the same disk, or when a mode other than the disk playback mode has been entered. It is equivalent. Note that modes other than the disc playback mode correspond to, for example, a tape mode and a radio mode. Each circuit described above can also be realized as a function of a microcomputer.
[0038]
Next, the operation of the focus servo circuit in the present embodiment will be described. FIG. 3 is a flowchart showing the processing operation of a microcomputer (not shown) on the CD player side in the normal disk reproduction process.
[0039]
In FIG. 3, the microcomputer determines whether or not the disc 10 has been inserted into the CD player (step S11). If the disc 10 has been inserted into the CD player, the disc rotation / focus servo / tracking servo is performed. The optical pickup 20 reads the signal of the disk 10 (step S13), executes a focus bias automatic adjustment process described later (step S14), and shifts to audio reproduction (step S15). It is determined whether or not the reproduction has ended (step S16). If this audio reproduction is completed, the normal disk reproduction process is terminated. The reading of the TOC information on the disk 10 is executed at an appropriate timing, for example, at the time of the processing operation in step S13 or step S14, or prior to the processing in step S15.
[0040]
If the disc 10 is not inserted into the CD player in step S11, the normal disc playback process is terminated. If the audio reproduction has not ended in step S16, the process proceeds to step S15.
[0041]
Next, the focus servo circuit in the present embodiment will be described. FIG. 4 is a flowchart showing the processing operation of the control unit 111 in the focus bias automatic adjustment processing.
[0042]
This automatic adjustment of focus bias corresponds to this previous optimum bias value by omitting the measurement of the current jitter bottom value Z if, for example, the previous optimum bias value is stored when bias adjustment is performed at power-on. The previous jitter bottom value Z is set as the current jitter bottom value Z, the corresponding bias values FA and FB are detected from the jitter bottom value Z by the processing operation as described above, and the optimum bias value is determined based on the corresponding bias values FA and FB. Is calculated.
[0043]
In FIG. 4, the control unit 111 determines whether or not the previous optimum bias value at the time of the previous bias adjustment is stored in the optimum bias value memory 108 (step S111). If there is no previous optimum bias value in the optimum bias value memory 108, the bottom value measuring unit 101 measures the jitter bottom value Z from the bias value of “0V” as the initial value as in the conventional case (step S112).
[0044]
When the bottom value measuring unit 101 measures the jitter bottom value Z, the measured jitter bottom value Z is stored in the bottom value memory 102 (step S113), and the jitter bottom value stored in the bottom value memory 102 is stored. The threshold value X is set by adding the predetermined value α stored in the predetermined value memory 103 to Z, the set threshold value X is stored in the threshold memory 104 (step S114), and the corresponding bias value detection unit At 105, detection of two corresponding bias values FA and FB corresponding to the set threshold value X is started (step S115).
[0045]
When the two corresponding bias values FA and FB are detected by the corresponding bias value detector 105, the two corresponding bias values FA and FB detected are stored in the corresponding bias value memory 106 (step S116). Based on the two corresponding bias values FA and FB stored in the bias value memory 106, the optimum bias value is calculated by executing the calculation process of (FA + FB) / 2 (step S117), and the calculated optimum bias is calculated. The value is stored in the optimum bias value memory 108 (step S118), and the optimum bias value stored in the optimum bias value memory 108 is set in the focus bias voltage generation circuit 70 as a focus bias (step S119). The focus bias automatic adjustment process is terminated.
[0046]
If there is a previous optimum bias value in the optimum bias value memory 108 in step S111, the previous jitter bottom value Z corresponding to this optimum bias value is stored in the bottom value memory 102 as it is (step S120), and in step S114. Transition.
[0047]
Therefore, according to the focus servo circuit in the present embodiment, for example, when the bias adjustment is performed when the power is turned on, the current jitter bottom value Z is measured if there is a previous optimum bias value in the optimum bias value memory 108. Since the jitter bottom value Z related to the previous optimum bias value is read from the bottom value memory 102 and the previous jitter bottom value Z is set as the measured jitter bottom value Z, the time required for the current jitter bottom value measurement is omitted. By omitting, the entire adjustment time required for bias adjustment can be significantly shortened compared to the focus servo circuit of the second embodiment.
[0048]
【The invention's effect】
According to the focus servo circuit of the present invention configured as described above, if there is a previous optimum bias value in the optimum bias value storage means at the time of bias adjustment, the last time related to the previous optimum bias value from the bottom value storage means. Since the bottom value is read and the current bottom value measurement is omitted and the previous bottom value is set as the measured bottom value, the adjustment required for bias adjustment is further reduced by eliminating the time required for the current bottom value measurement. The overall time can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a focus servo circuit in a CD player showing an embodiment of the present invention.
Similarly, FIG. 2 is a block diagram showing a schematic configuration inside a focus bias voltage adjustment circuit which is a main part of the focus servo circuit in the embodiment.
FIG. 3 is also a flowchart showing the processing operation of the microcomputer on the CD player side in normal disk playback processing.
FIG. 4 is also a flowchart showing the processing operation of the control unit in the focus bias automatic adjustment process.
FIG. 5 is a flowchart showing a processing operation of a control unit in a conventional focus bias automatic adjustment process.
FIG. 6 is a simplified graph showing a relationship between a jitter amount and a bias value in automatic focus bias adjustment.
FIG. 7 is an actual graph showing a relationship between a jitter amount and a bias value in automatic focus bias adjustment.
FIG. 8 is a practical graph showing a relationship between a jitter amount and a bias value in automatic focus bias adjustment.
[Explanation of symbols]
30 Error signal generation circuit (error signal generation means)
40 adder 50 drive circuit (servo means)
60 Jitter detection circuit (jitter detection means)
70 focus bias voltage generation circuit (focus bias voltage generation means)
100 focus bias voltage adjustment circuit (focus bias voltage adjustment means)
101 Bottom value measuring unit (bottom value measuring means)
102 Bottom value memory (bottom value storage means)
104 threshold memory (threshold setting means)
106 Corresponding bias value memory 107 Optimal bias value calculation unit 108 Optimal bias value memory (optimum bias value storage means)
110 Jitter deterioration detector (jitter amount determination means)
111 Control unit (starting start means)
112 Predetermined situation detector (situation detector)

Claims (2)

Error signal generating means for generating a focus error signal;
Jitter detecting means for detecting a jitter amount which is an amount corresponding to the jitter of the RF signal reproduced from the disc;
Based on the amount of jitter detected by the jitter detection means, the bottom value is measured, a threshold value obtained by adding a predetermined value to the bottom value is set, and two corresponding biases corresponding to the set threshold value are set. A focus bias voltage adjusting means for detecting a value and calculating an optimum bias value based on these corresponding bias values;
A focus bias voltage generating means for generating a focus bias voltage based on the optimum bias value calculated by the focus bias voltage adjusting means;
A focus servo circuit having servo means for executing focus servo based on a sum signal of the focus bias voltage of the focus bias voltage generating means and the focus error signal of the error signal generating means,
The focus bias voltage adjusting means includes
Optimal bias value storage means for storing the previous optimal bias value as the previous optimal bias value ;
And the bottom value storage means for storing previous bottom value as the previous bottom value,
If there is a previous optimum bias value stored in the optimum bias value storage means, the previous bottom value stored in the bottom value storage means is set as a measurement bottom value, and the predetermined value is added to the measurement bottom value to obtain a threshold value. And a threshold value setting means for setting the focus servo circuit. The time difference between the edge of the clock synchronized with the binarized signal in the RF signal and the change point of the binarized signal is measured, and it is detected that the time difference is greater than the reference time. 2. The focus servo circuit according to claim 1 , wherein the number of counts counted within a predetermined time is set as the jitter amount .

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