JP2003099960A - Method and apparatus for evaluating jitter characteristics of optical pickup - Google Patents

Abstract

(57) [Problem] To measure and evaluate the defocus tolerance of an optical pickup at a lower cost than before and without adversely affecting tact. SOLUTION: A step of applying a focus bias voltage to a focus actuator and applying a disturbance voltage to the focus bias voltage, a step of changing the focus bias voltage while measuring a jitter amount, and the jitter amount becomes a minimum value. Determining the focus bias voltage value, capturing the amount of jitter within the range of the disturbance voltage at the determined focus bias voltage value into a computer, and centering on the captured focus bias voltage determined. Evaluating the jitter characteristic of the optical pickup from the amount of jitter within the range of the disturbance voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup jitter characteristic evaluation method and apparatus.

[0002]

2. Description of the Related Art For example, an apparatus shown in FIG.
It is disclosed in Japanese Patent Publication No. 7756. In FIG. 12, 1
Reference numeral 00 denotes an optical disk, which is mounted on the rotary shaft of a spindle motor (not shown) and both are located outside the optical pickup 101. Optical pickup 1
01 is a (laser) light emitting element 1d, a semi-transparent mirror 1c, an objective lens 1a, and an objective lens focus actuator 1
b, irradiating a focused laser beam on the optical disc 100. The optical pickup 101 further includes a light receiving element 1e.
A head amplifier 2 is also provided, which outputs a tracking error signal in addition to the information reproduction signal (RF) and the focus error signal (FE). As the information reproduction signal (RF), the information recorded on the optical disc 100 is converted into the objective lens 1a.
What is read by the laser beam through the light receiving element 1
It is converted into an electric signal by e or the like and outputted. The focus error signal (FE) is output as an electric signal with a constant value that corresponds to the distance between the focal position of the focused laser beam and the information recording surface of the optical disc 100. This focus error signal is used as a focus adjustment circuit (feedback means) 10
It is fed back to the focus actuator 1b of the optical pickup 101 via 3, and as a result, FE = 0 with the focal point due to the movement of the objective lens. The offset controller includes a shift signal generation circuit and a sample hold circuit. By adding this output to the focus adjustment circuit 103 at an appropriate correction timing as a response to a change in the focus with time, the focus control system is provided. An offset that changes sequentially (for example, changes linearly as −FE0 → 0 → + FE0) is added. If the offset amplitude is made sufficiently large, the laser beam focus moves so as to cross the information recording surface. The RF evaluation means 12 is an in-focus detection means, and detects that the focus is on the recording surface by the change in the amplitude or jitter of the RF signal at this time. The moment when the laser beam focus crosses the information recording surface is detected by the maximum amplitude or the minimum jitter of the RF signal, and the sample hold circuit holds the value of the shift signal at the time of focusing to correct the offset. Amount △ FE
Is added to the focus adjustment circuit 103. At this time, the focus of the focused laser beam is near the surface of the optical disc recording medium and is kept constant. However, this device evaluates the jitter characteristics of the optical pickup before it goes on the market and is a good product.
Nothing is said about determining defective products.

[0003]

In the evaluation of the characteristics of the conventional optical pickup, it is general to measure the jitter at the focus bias of 1 point where the focus is closest to the recording surface of the optical disk. Therefore, it is impossible to accurately evaluate the tolerance of defocus of jitter and the asymmetry of the characteristic curve. Further, by reading an appropriate focus bias such that a constant standardized jitter value can be obtained centering on the focus bias point of the in-focus point, at least three points or more are repeated in order to evaluate more comprehensive characteristics of the optical pickup. Jitter measurement is required at a static focus bias point (using a signal that is not a disturbance signal), which adds to the cost and costs of software and hardware additions and changes in measurement equipment. An object of the present invention is to reduce such cost increase.

[0004]

[Means for Solving the Problems] The above problems are caused by applying a focus bias voltage to the focus actuator,
Applying a disturbance voltage to the focus bias voltage,
Changing the focus bias voltage while measuring the jitter amount, determining the focus bias voltage value that minimizes the jitter amount, and the range of the disturbance voltage at the determined focus bias voltage value. The process of taking in the amount of jitter in the computer,
A method for evaluating a jitter characteristic of an optical pickup, the method comprising: evaluating a jitter characteristic of an optical pickup from a jitter amount within a range of the disturbance voltage centered on the determined focus bias voltage that has been captured. Or, a means for applying a focus bias voltage to the focus actuator, applying a disturbance voltage to the focus bias voltage, a meter for measuring a jitter amount, and a means for changing the focus bias voltage.
Determining the focus bias voltage value that minimizes the jitter amount, inputting a jitter amount within the range of the disturbance voltage at the determined focus bias voltage, and the captured determination. A jitter characteristic evaluation device for an optical pickup, which comprises means for evaluating the jitter characteristic of the optical pickup from the amount of jitter within the range of the disturbance voltage centered on the focus bias voltage, or a tracking actuator for tracking. Apply a bias voltage,
A step of applying a disturbance voltage to the tracking bias voltage; a step of changing the tracking bias voltage while measuring a jitter amount; a step of determining the tracking bias voltage value that minimizes the jitter amount; The optical pickup from the step of loading into the computer the amount of jitter within the range of the disturbance voltage at the tracking bias voltage, and the amount of jitter within the range of the disturbance voltage centered at the determined tracking bias voltage that has been captured. And a step of evaluating the jitter characteristic of the optical pickup, or a means for applying a tracking bias voltage to the tracking actuator, applying a disturbance voltage to the tracking bias voltage, and a jitter amount. With a meter to measure The means for changing the tracking bias voltage, the means for determining the tracking bias voltage value that minimizes the jitter amount, and the amount of jitter within the range of the disturbance voltage at the determined tracking bias voltage are input. A jitter of an optical pickup, comprising: a computer; and means for evaluating a jitter characteristic of the optical pickup from a jitter amount within a range of the disturbance voltage centered on the determined tracking bias voltage that has been fetched. And a characterization device.

With the above structure, the average jitter amplitude measured in the injection state of the focus drive disturbance is determined by the correlation curve discrimination between the two samples A and B described later.
The fact that the optical pickup has a large defocusing characteristic makes it possible to determine in a single measurement that the optical pickup has a desired defocus characteristic in the procedure shown in the flow chart of FIG. Therefore, it is not necessary to measure the defocus transformer of the optical pickup to be measured or the jitter at three or more focus bias points for evaluating the asymmetry, and a new circuit is added to the equipment (measurement circuit) side. Evaluations can be performed while minimizing the effects on tact such as software modification and increasing the number of jitter measurements. The means of FIG. 12 shows a conventional method.

[0006]

FIG. 1 shows an optical pickup and a security evaluation / measurement apparatus. The optical pickup 101 ′ to be measured includes an objective lens 1a, a focus actuator 1b, a focus actuator 1b, and a light emitting element 1.
d, a light receiving element 1e, a pickup internal circuit, a half mirror 1c, and the like. A measuring disk 100 and a measuring device (not shown) for measuring a read signal emitted to the outside of the optical pickup are connected to the outside of the optical pickup 101.

FIG. 1 shows a defocus tolerance evaluation circuit for an optical pickup 101 'according to an embodiment of the present invention.
A focus bias voltage supply circuit 20 is connected to b, and the output voltage is variable. Further, the disturbance applying circuit 22 is connected. This output is a sine wave 100H
It is 1V in peak to peak in Z. The output of the head amplifier 2 is supplied to a jitter meter 24 (for example, manufactured by Kikusui Electronics Co., Ltd.) (including an equalizer and a slicer), and this output is connected to a computer 26. In FIG. 1, the focus servo system and the reproduction system are not shown.

In the evaluation, first, the best point of jitter is detected. As shown in FIG. 2, an arbitrary focus bias voltage Va is applied from the focus bias voltage supply circuit 20 to the focus actuator 1b. At this time, a sine wave disturbance signal is also supplied from the disturbance applying circuit 22 at the same time. The jitter amount a is detected at one peak and the jitter amount b is detected at the other peak, and the average value of the sine wave scanning corresponding to the difference is read by the jitter meter 24. When the focus bias voltage is increased from Va, the output of the jitter meter 24 increases, so decrease it. When this output decreases and a = b as shown in FIG. 3, the amount of jitter becomes the minimum. The focus bias voltage is determined as Vb. Conventionally, the application of the disturbance signal is turned off here without measuring the jitter value, and without judging the tolerance width or asymmetry with respect to the defocus (FIG. 13). However, according to the present invention, the output c of the jitter meter is output to the computer 26 as shown in FIGS.
Supply to. The average value of the output c, for example, the computer 2
It is calculated in 6 and displayed on the display.
A level regarded as a non-defective item is stored in the computer 26 and compared with it. Therefore, the quality of the optical pickup is uniformly determined.

Although FIG. 5 shows a case where the output is defective, the output d of the jitter meter is greatly fluctuated, and this average value is larger than the non-defective product level stored in the computer.
Therefore, this optical pickup is determined to be defective.

In the above, the good product level stored in the computer is compared with the output of the jitter meter, and it is automatically judged as good or bad. However, the output waveforms c and d of the display of the computer 26 are observed. However, it may be determined as good or bad. Alternatively, such a determination method may be added.

Here, the definition of defocus will be described. Although the focus servo is turned off in the above, in the case of the focus servo, the area where the servo error signal can be detected depends on the detection method and the design of the optical system.
It is about ± 20 μm at most. Therefore, when the focus servo is applied, it is necessary to first cut the servo loop and then move the focus actuator up and down so that the focus actuator is within this range. At this time, if the focus error signal is within the correct range, an error signal in the form of "S" appears in the focus error signal as shown in FIG.
At the same time, collecting the total amount of light returning from the disc gives an intensity signal as shown in the figure. When the intensity signal has reached a certain level, the focus servo is completed by turning on the focus servo loop (turning the vertical movement of the actuator off) while seeing the zero cross of the focus error signal.

When the S-shaped curve of FIG. 6 is enlarged, it becomes as shown in FIG. When the S-shaped level is expressed as a peak-to-peak voltage, defocus (%) = focus bias point (V) / S-shaped level (V) × 100. 8 and 9 are actual measurement values showing the relationship between the defocus (%) and the jitter (%) of the DVD without causing any disturbance. However, in the case where FIG. 8 is a good product, the minimum value of the jitter is 7 to 8%. FIG. 9 shows a case where the product is defective because it has a large asymmetry. In the embodiment of the present invention,
The definition of asymmetry will be described with reference to FIG.
, Is the defocus for which the jitter is 14%, is the defocus for which the jitter is the minimum value, Tolerance width = − Asymmetry (%) = {(−) − (−)} / (−
) × 100. The allowable jitter is 14 depending on the product specifications.
% Can be changed, but if asymmetry (%) is set to a certain value, non-defective products and defective products can be equally determined.
FIG. 11 shows the asymmetry (%) and the Δ jitter defined as above, that is, (the amount of jitter when a disturbance is applied) −
(Jitter amount when no disturbance is applied) = measured data of the jitter variation amount is shown. When the asymmetry is large as shown in the figure, the Δ jitter is large. Therefore, by reading the jitter amount when the disturbance is applied with the focus bias voltage that gives the minimum jitter, and reading the jitter amount when the disturbance signal with the same defocus (%) or bias voltage is turned off. , The asymmetry of the jitter curve can be immediately determined from these differences. For example, 0.5% may be stored as Δjitter (%) in FIG. 11 in the computer 26, and if it is smaller than this, it may be determined as a good product, and if larger, it may be determined as a defective product.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made based on the technical idea of the present invention.

For example, in the above embodiment, the bias voltage is applied to the focus actuator, and the disturbance signal is added to this to measure the jitter. Similarly, the jitter is also disturbed in the tracking bias signal to the tracking actuator. It is also possible to determine whether the optical pickup is good or bad based on the jitter characteristic in the same manner as described above by adding and measuring. Of course, in the case of the focus actuator, the jitter curve changed substantially along the quadratic curve, but in the case of the tracking actuator, it did not change in this way. Therefore, the magnitude and shape of the disturbance signal also have the above-mentioned sine shape. Drastically changed from.

[0015]

As described above, conventionally, only the bias voltage which is the minimum point of the jitter value is obtained, and the focus bias voltage for defocus tolerance is changed in various steps after the disturbance signal is turned off. Since the amount of jitter at that time was measured, a heavy burden was placed on the equipment side.However, according to the present invention, the focus bias voltage is changed to obtain the jitter best point, and at the same time, the quality of the optical pickup is not good or bad. Since the non-defective product can be determined, the manufacturing cost can be reduced and the manufacturing tact can be significantly improved as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an optical pickup according to an embodiment of the present invention and a circuit for evaluating a jitter characteristic of the pickup.

FIG. 2 is a diagram showing an operation for obtaining the best point of jitter using the apparatus of FIG.

FIG. 3 is a chart showing a jitter curve at the best point.

FIG. 4 is a chart of a jitter curve of an optical pickup having a symmetrical jitter characteristic by the device.

FIG. 5 is a chart showing a jitter curve of an optical pickup having an asymmetrical jitter characteristic.

FIG. 6 is a schematic diagram provided for explaining a bias of a focus actuator.

FIG. 7 is an enlarged view of an S curve in FIG.

FIG. 8 is a diagram showing a non-defective jitter curve obtained by obtaining a jitter curve of an optical pickup without applying disturbance.

FIG. 9 is a diagram of a jitter curve of an optical pickup which has a narrow tolerance and is asymmetrical and is regarded as a defective product.

FIG. 10 is a chart illustrating the definition of asymmetry.

FIG. 11 is a chart showing the relationship between asymmetry and delta jitter.

FIG. 12 is a block diagram of a conventional optical pickup.

FIG. 13 is a flowchart showing conventional jitter measurement.

FIG. 14 is a flowchart showing jitter measurement according to the present invention.

[Explanation of symbols]

1b ... Focus actuator, 24 ... Jitter meter, 20 ... Focus bias voltage supply circuit, 22
…… Disturbance application circuit, 26 …… Computer.

Claims (16)

[Claims] 1. A step of applying a focus bias voltage to a focus actuator, applying a disturbance voltage to the focus bias voltage, a step of changing the focus bias voltage while measuring a jitter amount, and a jitter amount having a minimum value. The step of determining the focus bias voltage value, the step of loading a jitter amount within the range of the disturbance voltage at the determined focus bias voltage value into a computer, and the step of centering the determined focus bias voltage And a step of evaluating the jitter characteristic of the optical pickup from the amount of jitter within the range of the disturbance voltage. 2. A jitter characteristic evaluation method for an optical pickup according to claim 1, wherein the disturbance voltage is a sine wave voltage having a constant amplitude and frequency. 3. The jitter amount within the range of the disturbance voltage taken into the computer is evaluated from the symmetry of the jitter amount centered on the determined focus bias voltage. A method for evaluating jitter characteristics of the optical pickup described. 4. The jitter characteristic evaluation method for an optical pickup according to claim 2, wherein evaluation is performed by a difference between a jitter amount at one peak of the disturbance voltage and a jitter amount at the other peak of the disturbance voltage. 5. When the defocus (%) giving the minimum jitter (%) is, and the defocus (%) giving the predetermined jitter (%) is, and (>) and the tolerance width = −, Asymmetry (%) = {(-
)-(-)} / (-) × 100, and
The computer determines whether the value of jitter = (jitter when disturbance is applied at the determined focus bias voltage) − (jitter when disturbance is not applied at the determined focus bias voltage) is larger than a predetermined value. 3. The jitter characteristic evaluation method for an optical pickup according to claim 2, wherein the asymmetry is calculated by performing an internal calculation to determine a non-defective product or a defective product. 6. A means for applying a focus bias voltage to a focus actuator and applying a disturbance voltage to the focus bias voltage, a meter for measuring a jitter amount, a means for changing the focus bias voltage, and a jitter amount having a minimum value. Determining the focus bias voltage value, a computer for inputting a jitter amount within the range of the disturbance voltage at the determined focus bias voltage, and the determined focus bias voltage taken in as a center. And a means for evaluating the jitter characteristic of the optical pickup based on the amount of jitter within the range of the disturbance voltage. 7. The jitter characteristic evaluation device for an optical pickup according to claim 6, wherein the disturbance voltage is a sine wave voltage having a constant amplitude and frequency. 8. The jitter amount within the range of the disturbance voltage input to the computer is evaluated from the symmetry of the jitter amount centered on the determined focus bias voltage. The optical pickup jitter characteristic evaluation apparatus described in [1]. 9. The jitter characteristic evaluation device for an optical pickup according to claim 7, wherein evaluation is performed by a difference between a jitter amount at one peak of the disturbance voltage and a jitter amount at the other peak of the disturbance voltage. 10. When the defocus (%) that gives the minimum jitter (%) is and the defocus (%) that gives a predetermined jitter (%) is (>) and the tolerance width = −, Asymmetry (%) = {(
−) − (−)} / (−) × 100,
△ Jitter = (jitter when disturbance is applied at the determined focus bias voltage)-(jitter when no disturbance is applied at the determined focus bias voltage) is larger than a predetermined value 7. The jitter characteristic evaluation device for an optical pickup according to claim 6, wherein the asymmetry is detected by a computer to detect the asymmetry to determine a good product or a defective product. 11. A tracking bias voltage is applied to a tracking actuator, a disturbance voltage is applied to the tracking bias voltage, the tracking bias voltage is changed while measuring a jitter amount, and the jitter amount is a minimum value. The step of determining the tracking bias voltage value, the step of loading a jitter amount within the range of the disturbance voltage at the determined tracking bias voltage into a computer, and the step of determining the acquired tracking bias voltage as a center. And a step of evaluating the jitter characteristic of the optical pickup from the jitter amount within the range of the disturbance voltage. 12. The jitter amount within the range of the disturbance voltage taken into the computer is evaluated from the symmetry of the jitter amount centered on the determined tracking bias voltage. A method for evaluating jitter characteristics of the optical pickup described. 13. The jitter characteristic evaluation method according to claim 11, wherein the disturbance voltage is evaluated by a difference between a jitter amount at one peak of the disturbance voltage and a jitter amount at the other peak. 14. A tracking bias voltage is applied to a tracking actuator, a disturbance voltage is applied to the tracking bias voltage, a meter for measuring a jitter amount, a means for changing the tracking bias voltage, and a jitter amount having a minimum value. Means for determining the tracking bias voltage value, a computer for inputting the amount of jitter within the range of the disturbance voltage at the determined tracking bias voltage, and the acquired determined tracking bias voltage as a center. And a means for evaluating the jitter characteristic of the optical pickup based on the amount of jitter within the range of the disturbance voltage. 15. The jitter amount within the range of the disturbance voltage input to the computer is evaluated based on the symmetry of the jitter amount centered on the determined tracking bias voltage. The optical pickup jitter characteristic evaluation apparatus described in [1]. 16. The jitter characteristic evaluation device for an optical pickup according to claim 14, wherein the evaluation is performed by a difference between a jitter amount at one peak of the disturbance voltage and a jitter amount at the other peak of the disturbance voltage.