JPH02187930A - Adjusting method for focus bias signal in optical disk reproducing device - Google Patents

Abstract

PURPOSE:To quantitatively and quickly adjust a focus bias signal to an optimum point by setting a bias signal of a focus circuit between prescribed first and second average values. CONSTITUTION:A clock whose synchronization is larger than that of a reproducing output RF by an optical pickup from an oscillating circuit 30 passing through a level converting circuit 31 is supplied to an adder 29 of a focus servo- circuit 12, and the left and the right minimum values, respectively of a convex curve to an optimum bias value of a waveform of the output RF are held in minimum value holding circuits 33, 34 through switches 36, 38 controlled by a clock passing through an inverter 32. When a variable resistance 14A of the circuit 12 is adjusted so that a difference of these holding values becomes '0' by a subtracting circuit 39, a bias is controlled to an optimum point of an average value of both the holding values. In the same way, an optimum point of an average value against the jitter quantity is determined, and focus bias point is brought to optimum control easily and quantitatively without executing a visual observation of a reproducing waveform from a middle point of both the optimum points.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a method for adding a predetermined focus bias signal to a focus error signal obtained from an optical pickup of an optical disk reproducing device so that the signal has a predetermined value. The present invention relates to a method for adjusting a predetermined focus bias signal of a focus servo circuit for moving the optical pickup up and down with respect to an optical disk.

[Summary of the invention]

The present invention provides a method for moving an optical pickup up and down with respect to an optical disc so that a signal obtained by adding a predetermined focus bias signal to a focus error signal obtained from an optical pick amplifier of an optical disc playback device becomes a predetermined value. In a method for adjusting a predetermined focus bias signal of a focus servo circuit, a periodically changing adjustment signal is superimposed on the focus bias signal to gradually change the average value of the focus bias signal, and the optical pickup The first average value is the average value of the focus bias signal when the level of the reproduced signal obtained from the above is constant, and the average value of the focus bias signal when the amount of jitter of the reproduced signal is constant. By determining the second average value and setting the focus bias signal between the first average value and the second average value, the adjustment of the focus bias signal to the optimal point can be performed quantitatively. This can be done efficiently and quickly.

[Conventional technology]

In an optical disc playback device, the distance d between the optical pickup and the optical disc is set so that the playback signal RF obtained from the optical pickup is always maintained in a good condition.
A focus servo circuit is used to always maintain a predetermined value.

Fig. 8 shows a so-called compact disc (CD) playback device, which is a type of optical disk playback device. In this Fig. 8, [1] is an optical disk, (2) is a spindle rotation motor, and (3) is an optical pickup. The reproduced signal RF output from the optical pickup (3) via the connection terminal (4) is converted into a binary signal by the waveform shaping circuit (5) and then sent to the digital signal processing circuit (6) and It is supplied to the spindle servo circuit (7).

In addition, the connection terminal (8) is connected to the optical pickup (3).
) The tracking error signal TE output through the tracking servo circuit (9) and the radial feed circuit (1
The focus error signal FE, which is supplied to the optical disc (1) and output via the connection terminal (11), is supplied to the focus servo circuit (12), and its optical pickup (3) Positioning is performed by a servo mechanism in the r direction and the d direction.

In the focus servo circuit (12), the connection terminal (
11) The focus error signal FE supplied from the adder circuit (13) is supplied to one input terminal of the adder circuit (13), and the other input terminal of the adder circuit (13) is connected to the movable contact of the variable resistor (14A). It is connected.

Also, since the resistor of the variable resistor (14A) is connected between the high-side power supply (14B) and the low-side power supply (14C), the variable resistor (14A>
A focus bias signal FB, which is an arbitrary voltage between the voltage of the high power supply (14B) and the voltage of the low power supply (14C), is generated at the movable contact of the switch, and this variable focus bias signal FB is applied to the adder circuit. This means that the signal is supplied to the other input terminal of (13).

Then, the adder circuit (13) supplies a correction signal FEB obtained by adding the focus bias signal FB to the focus error signal FE to the servo circuit (15). The optical pickup (3) is positioned in the d direction so that the angle is 0.

Various methods have been proposed for generating the focus error signal FE and tracking error signal TE.
An example of a method combining the astigmatism method and the three-beam method will be explained with reference to FIGS. 9 to 11. Track T of the optical disc (1) is
(N) is irradiated with the main beam spot (16) and the sub beam spots (17) and (18) (Figure 9).
, main beam (16)
A) The sub-beam sub-board is attached to the photodetectors A, B, C, and D.
The respective images (17) and (18) are created by the reflected light of (17) and (18).
A) and (18A) are formed on the light receiving elements E and F. The output signals 5A-3n of the light-receiving elements A-D are supplied to the adder (19), and the playback signal RF is output from the connection terminal (4).
At the same time, it is supplied to the adders (20), (21) and the differential amplifier (22), and a focus error signal FE is output from the connection terminal (11). In addition, the output signals S8 and Sp of the light receiving elements E and F are connected to the differential amplifier (2
3) and a tracking error signal TE is output from the connection terminal (8). Therefore, the following formula holds true.

RF= SA0Ss+Sc+So −・・・・
-(1)FE” (SA+SC) (SR1SD)
...”(2) TE=-5E-5F
(3) When the optical pickup (3) moves up and down in the d direction with respect to the optical disk (1), the image of the main beam spot (16) becomes (16B) as shown in FIG.
or (16C), the focus error signal FE becomes S as shown in FIG. 11B as a relation of d.
Changes in a curved manner.

However, the focus position d of d. The focus error signal FE does not necessarily become 0 even in
There is. Therefore, as shown in FIG. 8, the adder circuit (13)
The value of the focus error signal FE is "-△" using
The correction signal FE is obtained by adding the focus bias signal FB of
I got a B. Therefore, by setting this correction signal FEB to 0, the optical pickup (3)
The position in the d direction is the focus position d. is set to Furthermore, by gradually changing the value of the focus bias signal FB, the optical pickup (3)
This means that the position in the d direction of the optical pickup (3) can be gradually changed, and at the same time, it also means that the reproduced signal RF obtained from the optical pickup (3) can be variously changed to obtain the best waveform.

[Problem to be solved by the invention]

Conventionally, in order to adjust the focus bias signal FB of the focus servo circuit (12) to the optimum point when manufacturing the compact disc playback device shown in FIG.
The reproduced signal RF was extracted from the buffer circuit (24) from 4), and the extracted reproduced signal RF was manually inputted to the oscilloscope (25).The waveform of the reproduced signal RF (25a) )
The operator visually observes the level of the reproduced signal RF, and applies the focus bias signal FB to the location where the level of the reproduced signal RF is the highest and the amount of jitter, which is the variation 1 on the time axis of the reproduced signal RF, is considered to be the smallest. It was adjusted and fixed.

However, this method in which the operator visually observes and makes adjustments has the disadvantage that there is variation among the operators and lacks quantitative properties, and that it takes a long time to make the adjustments.

In view of the above, an object of the present invention is to make it possible to quantitatively and quickly adjust the focus bias signal of the focus servo circuit of an optical disk reproducing device to the optimum point.

[Means for Solving the Problems] A method for adjusting a focus bias signal in an optical disc reproducing apparatus according to the present invention, for example, as shown in FIGS. In a method of adjusting a predetermined focus bias signal FB of a focus servo circuit for moving an optical pickup up and down with respect to an optical disk so that the signal obtained by adding the predetermined focus bias signal FB becomes a predetermined value, the focus By superimposing a periodically changing adjustment signal fb on the bias signal FB and gradually changing the average value FB of the focus bias signal FB, the level RF Lm of the reproduced signal obtained from the optical pickup becomes constant. A first average value FB is an average value of the focus bias signal FB.

and a second average value FB, which is the average value of the focus bias signal FB when the jitter level RFJ of the reproduced signal is constant, and then calculate the first average value FBo and the second average value FBo. The focus bias signal FB is set between the average value FB and the average value FB.

[Effect]

According to the present invention, the level RFL of the reproduced signal obtained from the optical pickup generally changes in a convex and symmetrical manner with respect to the focus bias signal FB.
If the level RFL of the reproduced signal obtained by superimposing the periodically changing adjustment signal fb on the focus bias signal FB is constant, the focus bias signal FB The level RFL of the reproduced signal corresponding to the first average value FBo, which is the average value of , becomes maximum. Furthermore, since the amount of jitter RFJ of the reproduced signal obtained from an optical pickup generally changes in a concave and symmetrical manner with respect to the focus bias signal FB, the periodically changing adjustment signal fb is applied to the focus bias signal FB. If the jitter amount level RFJ of the reproduced signal obtained when superimposed is constant, the jitter amount RFJ of the reproduced signal corresponding to the second average value FB, which is the average value of the focus bias signal FB. is the minimum.

Therefore, the first average value FB and the second average value FB+
By setting the focus bias signal FB between the This means that the optimum point has been set quantitatively and quickly.

〔Example〕

Hereinafter, a method for adjusting a focus bias signal in an optical disc reproducing apparatus according to the present invention will be explained with reference to FIGS. 1 to 7. This example is a compact disc (CD)
The present invention is applied to a method for adjusting a focus bias signal of a focus servo circuit of a playback device, and the parts and corresponding signals in FIGS. 1 to 7 that correspond to FIGS. 8 to 11 are the same. Reference numerals are given and detailed explanation thereof will be omitted.

In this example, the criteria for quantitatively evaluating the quality of the reproduced signal RF obtained from the optical pickup of the compact disc playback device are: ■ the level of the reproduced signal RF, and ■ the amount of fluctuation of the reproduced signal RF on the time axis. Use quantity.

Among these, the level of the reproduced signal RF of (2) is defined as follows. That is, the magnitude of the reproduced signal RF changes depending on the presence or absence of pits on the recording surface of the optical disk, and the reproduced signal RF changes in a waveform as shown in Figure 1 as a fraction of time, so it can be observed with an oscilloscope, for example. As a result, a so-called eyebacoon is formed. In this example, the level of the reproduced signal RF is defined by the minimum value of the wave-like signal, and a signal corresponding to this level is referred to as an RF level signal RFL.

However, it is clear that the maximum value, average value, maximum amplitude (Peak to Peak Level), etc. of the reproduced signal RF may be used as the level of the reproduced signal FR.

Empirically, the value of the focus bias signal FB is gradually increased from the smallest value to F Bo+ -F BO2-F BO-F B
When changing from O3 to F B, the reproduced signal R
The signal waveform of F is approximately the curve (26c) - curve (2) in FIG.
6b) → curve (26a) → curve (2'6b) → curve (26c). in this case,
RF level signal RFL indicating the level of the reproduced signal RF
The value is approximately RF Lc-RF Lb-RF La-RF
The focus bias signal FB changes to Lb-RF Lc.

It is maximum when . Therefore, this RF level signal RFL has a substantially symmetrical convex shape with respect to the focus bias signal FB, as shown in FIG. 3, with the value FBo as the center.

Further, the sick amount of the reproduced signal RF in (2) is defined as follows. That is, the ideal reproduction signal RF is waveform-shaped and
The converted signal looks like the curve (27a) in FIG. 2A, and the period of the binary signal in this case is a predetermined fundamental period T. It is an integer multiple of Then, the value of the focus bias signal FB in this case is FB.

shall be. Next, when the value of this focus bias signal FB decreases to FBz (FBz<FB,), the signal obtained by binarizing the reproduced signal RF becomes, for example, a curve (27b) shown in FIG. The point of rise is △T+,
ΔT2. ...and it starts to shift. Furthermore, the value of the focus bias signal FB increases to FB, □(F
When BI2 > FBI), the binarized signal of the reproduced signal RF is, for example, the curve (27C) shown in Figure 2C.
The rising time is ΔTs and ΔT.

...and it starts to shift. Such a deviation from the ideal state at the time of rise is jitter as a fluctuation on the time axis of the reproduced signal RF.

Therefore, the sick amount of the reproduced signal RF is the high-level "1" signal that exists between the rising point of the binarized signal and the rising point of the ideal state (shaded areas in FIG. 2 B and C). ) is integrated for a predetermined period of time.
This signal RFJ can be expressed as FJ, and this signal RFJ is called an RF jitter signal. The value of this RF jitter signal RFJ is minimum when the value of focus bias signal FB is FB, so the curve obtained by plotting this RF jitter signal RFJ against focus bias signal FB shows the value as shown in Fig. 3. It is substantially symmetrical and concave with FB as the center.

In this example, the value of the focus bias signal FB is
The value FBo when the RF level signal RFL is the maximum and the value FB when the RF jitter signal RFJ is the minimum,
FB, which is an intermediate value between FB and FB. Therefore, f:
BM=(F Bo+F B,)/2 holds true. With this setting, the level of the reproduced signal RF is approximately maximum and the amount of jitter of the reproduced signal RF on the time axis is approximately minimum, so there is an advantage that the state of the reproduced signal RF is the best.

However, in practical terms, the value of the focus bias signal FB is F Bob FB, 9 FBI
.--It may be determined so that (4) is satisfied.

In this example, in order to obtain the value FBO of the focus bias signal FB when the level of the above-mentioned reproduced signal RF becomes the minimum and the value FB+ of the focus bias signal FB when the jitter amount of the reproduced signal RF becomes the minimum, As shown in FIGS. 4 and 5, a rectangular wave signal fb with a period τ0 is superimposed on the focus bias signal FB so that the average value FB of the focus bias signal FB is gradually changed.

In this case, the corresponding RF level signal RFL becomes a rectangular wave signal as shown by signal RF Lx in FIG. 4A. Then, the average value FB of the focus bias signal FB is FB
, , the signal RF
The level of L books is approximately constant. In other words, the signal R
The focus bias signal F when the level of F Lx is approximately constant, that is, the amplitude of the signal RFL is the minimum.
The average value FB of B is FB. Similarly, the corresponding R
Since the F jitter signal RFJ is a rectangular wave signal as shown by the signal RFJ in Fig. 5, the focus bias is set so that the level of this signal RFJ zero is approximately constant, that is, the amplitude of the signal RFJ* is minimized. When the average value FB of the signal FB is set, the average value FB is FB.

Next, an example of a focus bias adjustment device for a compact disc playback device for carrying out the above adjustment method will be described with reference to FIG. 6. In this example, the focus servo circuit (12 ) for separately supplying a square wave signal fb from the outside.
28) and an adder circuit (29). This addition circuit (
29) is connected to its connection terminal (28), the output signal of the adder circuit (13) is supplied to the other input terminal of this adder circuit (29), and the output signal of the adder circuit (29) is The signal is supplied to the servo circuit (15). in this case,
The output signal of the adder circuit (29) becomes a correction signal FEB expressed by the following formula using the focus error signal FE, focus bias signal FB, and signal fb, where FEB=
FE+FB+ fb (5) The servo circuit (15) receives the correction signal F expressed by this equation (5).
The optical pickup (3) is positioned up and down in the d direction so that EB becomes O.

Further, in FIG. 6, (30) indicates an oscillation circuit, and this oscillation circuit (30) has a period τ. The clock signal CLK is supplied to the level conversion circuit (31) and the inverter (32), and the level conversion circuit (31) receives the clock signal CLK.
A rectangular wave signal fb that fluctuates with a period τ0 and a predetermined amplitude centered around the 0 level is generated from LK, and this rectangular wave signal fb
is supplied to the connection terminal (28) of the focus servo circuit (12) of the compact disc playback device to be tested. The inverter (32) generates a signal CLK which is an inversion of the clock signal CLK.

The connection terminal (4) and buffer circuit (2) are connected to the optical pickup (3) of the compact disc playback device to be inspected.
4) is supplied to each input terminal of the minimum value hold circuits (33) and (34). The minimum value hold circuit (33) is composed of, for example, a diode whose anode side is connected to the input terminal and a buffer circuit with high input impedance, and a hold capacitor (35) is connected to the cathode side of the diode via a switch circuit (36). At the same time, the switch circuit (36) becomes conductive (sample state) when the clock signal CLK is at high level "1" and outputs the clock signal C.
When LK is at low level "0", it is in the release state (hold state). Also, the minimum value hold circuit (34
), a switch circuit (38) and a hold capacitor (37) are similarly attached externally, and the switch circuit (38) is connected externally to the switch circuit (38).
) is made conductive when the inverted clock signal CLK is at a high level "1" and becomes open when the inverted clock signal CLK is at a low level "0".

The minimum value signals RFL and RF L2 held by the minimum value hold circuits (33) and (34) are respectively supplied to one and the other input terminals of the subtracter (39), and the subtracter (39) The signal RFL expressed by the formula is supplied to an RF level maker (40) consisting of a voltage meter.

RF L * books = RFLI-RFL, ・
...(6) Also, the reproduced signal RF taken in via the buffer circuit (24) is sent to the RF jitter measurement circuit (4).
1).

In principle, this RF jitter measuring circuit (41) binarizes the reproduced signal RF and then generates a high level "1" signal between the ideal rising point and the actual rising point (see Fig. 2B). and C corresponds to the shaded portion.)-125142. This RF jitter measurement circuit (41)
The period τ generated by RF jitter signals RFJ are supplied to respective input terminals of sample/hold circuits (42) and (43).

A hold capacitor (44) is externally connected to the sample/hold circuit (42), and a switch circuit (45) is connected between the input terminal and the hold capacitor (44). ) is the clock signal C
When the clock signal CLK is at a high level "1", it is in a conductive state (sample state), and when the clock signal CLK is at a low level "0", it is in a released state (hold state). Similarly, a hold capacitor (46) and a switch circuit (47) are externally connected to the sample/hold circuit (43).
The switch circuit (47) is made conductive when the inverted clock signal CLK is at a high level "1" and becomes open when the inverted clock signal CLK is at a low level "0". In addition, those sample/hold times ii: @(
42) and (43>), a maximum value hold circuit or a minimum value hold circuit may be used.The RF jitter signals RFJ and RFJ2 held by these sample/hold circuits (42) and (43), respectively are supplied to one and the other input terminals of a subtracter (48), respectively, and the subtracter (48) supplies a signal RFJ expressed by the following equation to an RF jitter meter (49>) consisting of a voltage meter.

RFJ main book = RF J2-RF J,
(7) The operation of the example shown in FIG. 6 will be explained with reference to FIG. 7. The period r of the clock signal CLK (A in FIG. 7) generated by the oscillation circuit (30). is the reproduced signal RF
The basic period To is set to be sufficiently larger than the basic period To. In this case, the focus bias signal FB of the focus servo circuit (12) has a substantially period τ via the connection terminal (28) and the addition circuit (29). Since the rectangular wave signal fb is superimposed, the waveform of the reproduced signal RF is 2 as shown in FIG.
The period τ for the two curves (50a) and (5011)
At 0, it seems like they alternate. Then, the minimum value hold circuit (33) operates for a period T, , T, . . . of the reproduced signal RF.
. . , the minimum value signal RFL held by the minimum value hold circuit (33) becomes as shown in FIG. 7C. Also, periods T, , T3. During the sample period of ..., the hold capacitor (
35), a minute current can freely flow into it from the input terminal of the minimum value hold circuit (33).

Moreover, the minimum value hold circuit (34)
Period T2. Since it operates to hold each minimum value in T,..., the minimum value hold circuit (
The minimum value signal RFL2 held at 34) is as shown in Fig. 7. The minimum value hold circuit (34) also allows a minute current to freely flow into its hold capacitor (37) during the sampling period. In this case, the subtractor (39
) and whose value is displayed on the RF level make (40) becomes a substantially DC signal as shown in Figure 7, but this signal RFLs tree is the signal shown in Figures A and B. Corresponds to the amplitude of RF Lx.

Therefore, if the value of the focus bias signal FB when the level of the reproduced signal RF is minimum is FBo, in this example, the variable resistor (14A) is adjusted to reduce the signal RFL0 displayed on the RF level meter (40). By setting the value of zero to 0, the state shown in FIG. 4B is realized, and the value of the focus bias signal FB at that time becomes FB as it is. The value FBo of the focus bias signal FB at this time is the focus servo circuit (1
It can be read from the check terminal (not shown) provided at 2>.

Next, to explain the procedure for reading FB, which is the value of the focus bias signal FB when the amount of jitter on the time axis of the reproduced signal RF is minimum in the example of FIG. 6, the focus servo circuit (12) Via the connection terminal (28) and the adder circuit (29), the focus bias signal RF is supplied with substantially the period τ. Corresponding to the fact that the periodically changing signal fb is superimposed on the signal fb, the RF jitter signal RFJ* generated by the RF jitter measurement circuit (41) also has a period τ. It changes periodically. Then, in the sample/hold circuits (42) and (43), for example, the minimum value RFJ and the maximum value RFJ of the RF jitter signal RFJ, respectively.
2 is retained, so RF
Signal RFJ whose value is displayed on the jitter meter (49)
s corresponds to the amplitude of RF jitter signals RFJ generated by the RF jitter measurement circuit (41).

Therefore, by adjusting the variable resistor (14A) and setting the actual value of the signal RFJ displayed on the RF jitter meter (49) to 0, the average value FB of the focus bias signal FB can be adjusted as shown in FIG. This means that a state consistent with FB, has been realized, and the value of the focus bias signal FB at that time becomes FB, as it is. This value FB can also be read from a check terminal (not shown) provided in the focus servo circuit (12).

Finally, the variable resistor (
14^) By adjusting the value of the focus bias signal FB to a value FB that is intermediate between the value FB obtained by the above method and the value FB+, the focus bias signal of the compact disc playback device to be tested can be adjusted. The setting of the FB to the optimum point is completed. Thereafter, the connection terminal (28) of the focus servo circuit (12) is connected to, for example, a ground terminal of the compact disc playback device to be tested. As described above, according to the example in FIG. 6, the focus servo circuit (12) of the compact disc playback device to be inspected includes the connection terminal (28) for superimposing the periodic signal fb on the focus bias signal FB, and the addition circuit (29). ) is provided, and when the periodic signal fb is added, the reproduced signal R
RF level meter ( 40) and an RF jitter meter (49) for direct reading. Therefore, the value FB of the focus bias signal FB when the indicated value of the RF level meter (40) becomes 0 with the periodic signal fb added.

Simply read the value FB of the focus bias signal FB when the indicated value of the RF jitter meter (49) becomes 0, and set the value of the focus bias signal FB to be between the value FBo and the value FB. Therefore, there is an advantage that the focus bias signal FB can be adjusted quantitatively and quickly.

In the above embodiment, the focus servo circuit (12
), the rectangular signal f is added to the focus bias signal FB.
This rectangular wave signal fb
Instead of Q, for example, a signal that changes sinusoidally around the 0 level may be superimposed. Additionally, an optical pickup (
The focus error signal FE outputted from 3) may be generated by, for example, the critical angle method or the Foucault method.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various configurations may be adopted without departing from the gist of the present invention.

〔Effect of the invention〕

The present invention superimposes a periodically changing adjustment signal on a focus bias signal, and obtains a first average value, which is the average value of the focus bias signal when the level of the reproduced signal obtained from the optical pickup is constant. , and a second average value which is the average value of the focus bias signal when the level of jitter amount of the reproduced signal becomes -start, and a value between the first average value and the second average value is calculated. Since the focus bias signal is set, there is an advantage that the focus bias signal can be adjusted to the optimum point quantitatively and quickly.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in the level of the reproduced signal RF according to an embodiment of the present invention, FIG. 2 is a diagram showing changes in the jitter amount of the reproduced signal RF, and FIG. 3 is a diagram showing changes in the amount of jitter of the reproduced signal RF according to an embodiment of the present invention. Diagrams showing the optimum point of the focus bias signal FB, FIGS. 4 and 5
The figure shows the focus bias signal FB as FBo and F, respectively.
6 is a diagram showing the configuration of a focus bias adjustment device according to an embodiment of the present invention, and FIG. 7 is a signal waveform diagram of each part showing the operation of the example shown in FIG. 6. , FIG. 8 is a block diagram showing the main parts of the compact disc reproducing apparatus, and FIGS. 9 to 11 are diagrams for explaining the example in FIG. 8, respectively. (1) is an optical disc, (3) is an optical pickup, (
12) is a focus servo circuit, (30) is an oscillation circuit,
(32) is an inverter, (39) is a subtracter, (40) is an RF level meter, (41) is an RF jitter measurement circuit, (
48) is a subtracter, and (49) is an RF thick meter. Substitute Hide Hitomatsu Kuma Mori Regeneration I Tomigoshaku F Chika Diagram 2

Claims (1)

[Claims] To move the optical pickup up and down with respect to the optical disk so that a signal obtained by adding a predetermined focus bias signal to a focus error signal obtained from an optical pickup of an optical disk reproducing device becomes a predetermined value. In the method for adjusting the predetermined focus bias signal of the focus servo circuit, the average value of the focus bias signal is gradually changed by superimposing a periodically changing adjustment signal on the focus bias signal, and a first average value that is the average value of the focus bias signal when the level of the obtained reproduced signal is constant; and an average value of the focus bias signal when the level of jitter of the reproduced signal is constant. Adjustment of a focus bias signal in an optical disc playback device, characterized in that the focus bias signal is set between the first average value and the second average value. Method.