JPH03100928A - Focus error signal detecting method - Google Patents

Abstract

PURPOSE:To reduce cross talk by taking out a signal, for which a value obtained from a track error signal is subtracted from a focus error signal, as the focus error signal. CONSTITUTION:Reflected light from an optical disk is made incident on a 4-divided photodetector 10. The outputs of photodetectors 10A-10D are respective ly inputted to current/voltage converters 11A-11D. Output voltages A and B are added through resistors R1 and R2, inverted and amplified by an operational amplifier 12. The, by adjusting gain G with a feedback resistor R5, the voltage of -G(A+B) is outputted. Samely, the voltage of -(C+D) is outputted from output voltages C and D by an operational amplifier 13. A focus error signal FFS of G(A+B)-(C+D) is taken out from these output voltages by an opera tional amplifier 14. On the other hand, a track error signal TES of (C-D) is taken out from the voltages C and D by an operational amplifier 15. From the signal, the signal of K¦C-D¦ is taken out through an operational amplifier 19 and the FES signal of G(A+B)-(C+D)-K¦C-D¦ is taken out from these signals through an operational amplifier 20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for detecting a focus error signal, and in particular detects a focus error signal by detecting the spot size of light reflected from an optical disk using a split photodetector. The present invention relates to a focus error signal detection method.

Postscript type or! In an optical disk device that records and reproduces information on and from a replaceable optical disk, a light spot is focused by an objective lens to form a light spot on the optical disk. At this time, it is necessary to stably detect the focus 1 color signal even if the light spot crosses the entire surface of the optical disk.

(Prior art) Conventionally, the spot size number detection method (
SSD method) is used. This SSD method is shown in Figure 4 (A
) As shown in (), light from an optical disk passes through an objective lens (none of which is shown), enters a plano-convex lens 1, is further condensed by this plano-convex lens 1, and enters a three-split photodetector 2 (or 3). do.

3-split light detection! As shown in FIGS. 4(B) to 4(D), li2 has three divided light receiving elements 2A, 2 divided into 3 parts v1 in a cloth shape.
It is composed of B and 2C. The 3-split photodetector 3 is also composed of 3 split light-receiving elements F3A to 3C as shown in FIGS. 4(E) to 4(G). They are located closer to the plano-convex lens 1, and only these two are provided in the optical disk device.That is, for convenience, two three-part photodetectors 2.3 are shown at the same time.

When the optical disk, which is a recording medium, moves away from the objective lens with reference to the focal position of the objective lens, the 3-separation photodetector 2
．． The area of the light spot on the light receiving surface of No. 3 becomes large as shown in Fig. 4 (B) and (E), and when it approaches, the area becomes large as shown in Fig. 4 (D) and (G).
), the light-receiving area becomes small, and when the light is exactly at the focal position, it becomes as shown in (C) and (F) of the same figure.

In the SSD method, a focus error signal is detected by utilizing the fact that the area of the light spot on the light receiving surface of the 3-split photodetector 2 or 3 changes depending on the relative distance between the optical disk and the objective lens. do.

For example, the divided light receiving element 2A of the three-divided photodetector 2.

Assuming that the values of the output signals 2B and 2C are represented by A, B, and C, a focus error signal is obtained based on the arithmetic expressions (A+C)- and B. Alternatively, if the values of the output signals of the 30-split photodetector 3A, 3B, and 3C are represented by A, B, and C, the gain ratio G is used to increase the focus sensitivity. There is also a method of obtaining a focus error signal based on the arithmetic expression A+C)-8.

The above (A+C)-8 can be regarded as a special case where the latter G is "1".

(1lli to be solved by the invention) By the way, some optical discs have a guide groove called a pre-group formed in advance at the manufacturing stage, and a pushbutton 1 that generates a track error signal from a pattern of reflected light from this pre-group is used. The pull method has been known for some time.

However, for optical discs with this pre-group, the reflected light pattern changes when the light spot crosses the pre-group, such as during seek, which affects the focus error signal and causes the focus error signal to fluctuate (this There is a problem called crosstalk.

The present invention has been made in view of the above points, and an object of the present invention is to provide a focus error signal detection method that can reduce crosstalk.

(Means for Solving the Problems) The present invention comprises a divided photodetector for detecting the spot size of reflected light from an optical disk, which is composed of four divided light receiving elements, and two of the divided photodetectors. The value obtained from the track error signal generated based on the output signal of the split light receiving element is
A value corresponding to the sum of the output signals of the other two divided light receiving elements of the divided photodetector and the difference between the output signals of the two divided light receiving elements is reduced and extracted as a detection focus error signal. It is structured as follows.

(Operation) The present invention focuses on the fact that the crosstalk of the focus error signal is related to the track error signal.In other words, the zero stalk is as shown by ■ in FIG.
When the light spot is at the position where it should originally be (track position 0), it is a pyro, but as it deviates from this track position O, the opening speed increases, and reaches its maximum when the light spot deviates by ±1/2 track.

On the other hand, as shown by ■ in Fig. 3, the track error signal is zero when the optical spot is at track position 0, but from this track position 110, it increases in polarity according to the direction of deviation and increases according to the amount of deviation. , the absolute value is maximum when the deviation is ±1/4 track, decreases as the deviation amount increases, and becomes zero when the deviation is ±1/2 track. Therefore, the absolute value of the track error signal changes within the ±1/41/4 track range in the same way as the crosstalk.

Therefore, in the present invention, a value obtained from a track error signal (for example, an absolute value) is subtracted from a focus error signal obtained by a conventional calculation formula, and a signal is extracted as a detected focus error signal. In this focus error signal, crosstalk is greatly reduced at least within the ±174 track range.

〔Example〕

FIG. 1 shows a circuit diagram of an embodiment to which the method of the present invention is applied. In the same figure, 10 is a split photodetector, which is emitted from a light source,
The optical disc (
A light beam irradiated onto a disk (not shown) is reflected by this optical disk, and the reflected light passes through an objective lens and a focusing lens (corresponding to the plano-convex lens 1 in FIG. 4), respectively, and enters the optical disk.

Therefore, the area of the light spot on the light receiving surface of the split photodetector 10 depends on the relative distance between the optical disk and the objective lens, as shown in FIGS. It changes accordingly.

In FIG. 1, the divided photodetector 10 includes divided light receiving elements 10A and 10 at both ends of the divided light receiving elements divided into three in the horizontal direction.
The center divided light receiving element excluding B is further divided into two in the vertical direction in the same figure to form divided light receiving elements 10G and 10D, making a total of 4 divided light receiving elements.
It consists of divided light receiving elements 10A to IOD. The divided light-receiving elements 10A to 100 perform photoelectric conversion, and convert a current corresponding to the light intensity of the light incident on each light-receiving surface into a current-voltage converter 11.
Output to A to 11D.

1! - Voltages A and B taken out from the voltage converters 11A and 11B are added via resistors R+ and Rz, and then supplied to the inverting input terminal of the operational amplifier 12, where they are inverted and amplified with a predetermined gain. This gain #1IIG is operational amplifier 1
It can be varied by adjusting the feedback resistor Rs of No. 2. As a result, the operational amplifier 12 outputs 10 (A
A voltage represented by +8> is taken out.

On the other hand, voltages C and D taken out from the current-voltage converters 11C and 11D are amplified via resistors Rs and R4, and then supplied to the inverting input terminal of the fraud amplifier 13, where they are inverted and amplified. The gain at this time is determined by the feedback resistor R6 of the essential amplifier 13 and the above-mentioned resistors R3 and R4. -Here, a voltage represented by -(C+D) is taken out from the operational amplifier 13.

Each signal taken out from the operational amplifiers 12 and 13 is connected to the resistors Ry, Rs, Rs, R interpolation and operational amplifier 1, respectively.
A signal with a value represented by G (A+8) - (C+D) is extracted from the operational amplifier 14. In other words, this signal is calculated by the conventional arithmetic formula based on the focus error. signal (FES).

Moreover, the voltages C and D are resistors R71lRI2°RI3
．． The signal is supplied to a differential circuit section consisting of an RM and an arithmetic amplifier 15, where it is differentially amplified, and a signal represented by (CD) is taken out from the arithmetic amplifier 15 to an output terminal 16. The output signal to this output terminal 16 is the difference between the output signals of the central two divided light receiving elements 10G and 1°D, and is used as a track error signal (rEs).

The above track error signal is generated by a circuit section consisting of resistors R+s, R+s, an operational amplifier 17, and a diode O+, and a resistor R
Iy * RIe * a'j is supplied to the sieve amplifier 18 and the circuit section consisting of the diode D2, and after being half-wave rectified in each circuit section, the resistor RI9. It is added via RN and supplied to the inverting input terminal of operational amplifier 19. Here, the directions of the diodes D1 and D2 are opposite, and the rectified wave signals of the negative and positive recycle periods of the track error signal are taken out from the diodes D+ and D2. Therefore, at the inverting input terminal of the operational amplifier 19, -1C-D
An absolute value signal denoted by I is input.

The operational amplifier 19 has a feedback resistor R21 as a variable resistor, and inverts and amplifies the input signal at its inverting input terminal I with a gain determined by the resistor Rss "-R2+. Therefore, the output of the operational amplifier 19 The signal is K I C-D
Represented by I. Here, K corresponds to the above gain and can be adjusted by the resistor R21.

The operational amplifier 20 serves as a feedback resistor R25, and the above K I
The absolute value of the track error signal represented by C-D I is supplied to the inverting input terminal via the resistor R22, and the conventional focus error signal represented by G (A+8)-(C+D) mentioned above is supplied to the inverting input terminal via the resistor R22. After being resistor-divided by R23 and R24, the signals are supplied to the non-inverting input terminal, and these two human input signals are differentially amplified. Therefore, from the operational amplifier 20 to the output terminal 21, FES-G (A+8)-(C+D)-K.
IC-DI (1
) is extracted, and this signal is output as a focus error signal.

FIG. 2 shows a comparison between the zero stalk of the focus error signal of this embodiment and the crosstalk of the conventional focus error signal. In the figure, ■ is the focus error of this embodiment, - signal crosstalk, and G in the above equation 0) is 4.19
, shows the crosstalk when K is 0.056. In addition, ■ is the crosstalk of the conventional focus error signal, and G in the calculation formula of G (A + 8) - (C + D) is
．． 19 shows crosstalk.

As can be seen from Fig. 2, the crosstalk (■) of this embodiment is smaller than the conventional crosstalk (■), and is particularly true by ±174 tracks centered on the position @ (track position [0)] where the light spot should originally be. The 0-stoke reduction effect is large within the range of .

Also, when exceeding ±1/4 track, the absolute value of the track error signal is no longer proportional to the crosstalk as explained with the third FA, but the track error signal is :)1/4 except during seek. Crosstalk rarely exceeds 4 tracks (and even when it exceeds ±174 tracks, as shown in FIG. 2, crosstalk is reduced to some extent in this embodiment compared to the conventional method).

Note that the present invention is not limited to the above-mentioned embodiments, and for example, the value to be subtracted from the conventional focus error signal may be any value obtained from the track error signal, and may not be an absolute value. For example, ( Even if the quadratic equation (CD) is subtracted, if the coefficients are appropriately determined, the same or greater crosstalk reduction effect can be obtained. Therefore, the shape of the 4-split photodetector is not limited to this embodiment, and a shape divided into tenths and others can be used.

(Effects of the Invention) As described above, according to the present invention, it is possible to significantly reduce crosstalk in a focus error signal within a range of at least ±174 tracks around track position 10,
It has features such as being able to reduce crosstalk even when exceeding ±174 tracks, and enabling focus servo to be performed more stably than before, especially during seek.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment to which the method of the present invention is applied, Fig. 2 is a diagram showing a comparison between this embodiment and the conventional zero-stoke control, and Fig. 3 is the relationship between crosstalk and track error signal 7. FIG. 4 is an explanatory diagram of focus error signal detection using the SSD method. In the figure, 10 is a divided photodetector, 10A to 10D are divided light receiving elements, 11A to 110 are current-voltage converters, and 21 is a focus error signal output terminal.

Claims (1)

[Claims] A focus system that detects the spot size of reflected light from an optical disk using a divided photodetector (10), calculates the output signal of the divided photodetector (10), and obtains a focus and an error signal. In the error signal detection method, the divided photodetector (10) is divided into four divided light receiving elements (10
A to 10D), and two divided light receiving elements (10C) of the divided photodetector (10).
, 10D) is added to the sum of the output signals of the other two divided photodetectors (10A, 10B) of the divided photodetector (10). The corresponding value and the two divided light receiving elements (10C, 10
A focus error signal detection method characterized by subtracting the value of the difference from the output signal of D) and extracting it as a detected focus error signal.