JPH04248137A - Formation of tracking error signal - Google Patents

Abstract

PURPOSE:To form the tracking error signal without being affected with variation of the optical characteristics the disk, when the tracking error signal of a sample servo type optical disk generates. CONSTITUTION:In the arithmetic circuitry 3, by using the reproducing output waveform of a wobble pit and the reproducing output waveform of a clock pit, the amplitude A is calculated. In the arithmetic circuitry 4, by using the reproducing output waveform of a wobble pit, the offset value C is calculated. In the arithmetic circuitry 5, a phase phi is sought and the tracking control is conducted by driving the phase phi into zero.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error signal generation method suitable for use in tracking control of, for example, a sample servo type optical disk.

0002

[Prior art] In a sample servo type optical disk,
Each track is divided into multiple sectors, and each sector is further divided into multiple segments. A servo area is provided for each of these segments. In this servo area, two wobble pits are arranged with the same amount of offset in directions facing each other with respect to the track center, and a clock pit is arranged above the track center. In the conventional sample servo type optical disc recording/reproducing apparatus, a tracking error signal is generated from the difference signal between the reproduction signal levels of two wobble pits in this servo area.

That is, in a conventional sample servo type optical disc recording/reproducing apparatus, reproduction signals of two wobble pits are supplied to a comparator. A tracking error signal is generated from the output of the comparator. The output of this comparator is fed to an actuator that controls the beam in the radial direction of the disk. The actuator is then driven so that the comparison output from the comparator becomes zero. Tracking is thereby controlled so that the beam is located at the track center.

0004

[Problems to be Solved by the Invention] However, in the conventional tracking error signal generation method of generating a tracking error signal from the difference signal between the reproduced signal levels of two wobble pits, There is a problem in that variations in the optical characteristics of the disk cause variations in the strength of tracking control.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for generating a tracking error signal that allows tracking control to be performed without being affected by variations in optical characteristics of a disk.

[0006]

[Means for Solving the Problems] In the present invention, servo areas are provided at predetermined intervals, and a pair of wobble pits are arranged in the servo areas at positions offset by the same amount in the direction opposite to the track center. In a method for generating a tracking error signal when performing tracking control on a disc in which a clock pit is arranged at the track center, the reproduction output of a pair of wobble pits and the reproduction output of a clock pit are used to generate a tracking error signal in an output signal. This is a tracking error signal generation method in which an optical characteristic element is calculated and a tracking error signal is generated by removing the optical characteristic element.

[0007]

[Operation] Obtains the amplitude A and DC offset C that depend on the optical elements of the disc, removes the components that depend on these optical elements, and generates a tracking error signal, without being affected by variations in the optical characteristics of the disc. Enable tracking control.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. An embodiment of the present invention allows tracking control to be performed without being affected by variations in the optical characteristics of the disc. First, the principle of an embodiment of the present invention will be explained.

As shown in FIG. 2, wobble pits PaL1 and PbL1, PaL2 and PbL are formed in the servo areas of continuous tracks L1, L2, L3, . . . on the optical disc.
2, PaL3, PbL3, . . . are provided, and clock pits PcL1, PcL2, PcL3, . . . are provided, respectively. Wobble pit PaL1 and PbL1, PaL2 and PbL2, PaL3 and Pb
It is assumed that the L3s are arranged at positions that are offset from each other in the direction opposite to each other by a distance corresponding to 1/4 of the distance between the tracks from the track center.

When the pickup is moved in the radial direction,
Wobble pits PaL1, PaL2, PaL3, ..., clock pits PcL1, PcL2, PcL3, ..., wobble pits Pb of consecutive tracks L1, L2, L3, ...
Reproduction RF signals Ra, Rc, and Rb as shown in FIGS. 3A to 3C are obtained from L1, PbL2, PbL3, . . . , respectively.

Successive tracks L1 and L2 shown in FIG. 3A
, L3, ... wobble pits PaL1, PaL2, Pa
The reproduced RF signal waveform Ra of L3,... is Ra=Asin
φa +C (1) A: Amplitude C: Can be expressed as DC offset.

[0012] Wobble pits PaL1, PaL2, Pa
L3,... and clock pit PcL1, PcL2, PcL
3,... are separated by 1/4 of the distance between the tracks (2π/4=π/2), so the clock pit PcL1 of the consecutive tracks L1, L2, L3,... shown in FIG. 3B
, PcL2, PcL3, ... The reproduced RF signal waveform Rc is as follows: Rc = Asin (φC +π/2) + C = Acos
It can be expressed as φC +C (2).

Furthermore, the continuous track L1 shown in FIG. 3C
, L2, L3, ... wobble pits PbL1, PbL2
, PbL3,..., the reproduced RF signal waveform Rb is Rb=As
in (φb +π)+C = −A sin φb +C (3).

Conventionally, tracks L1, L2, L3, . . .
The reproduced RF signal waveform Ra (Fig. 3a) of the wobble pits PaL1, PaL2, PaL3, ... and the tracks L1, L
2. Wobble pits of L3, PbL1, PbL2, P
A tracking error signal Te is obtained from the difference signal between the reproduced RF signal waveform Rb (FIG. 3C) of bL3, .

That is, conventionally, the tracking error signal Te is calculated as Te=Ra−R from equations (1) and (3).
b = (A sin φa +C) - (-A sin φb +
C)=A sin φa + Asin φb. Here, if φa = φb = φc = φ, Te=2A sin φ (4).

Tracking error control of the conventional sample servo type optical disk recording/reproducing apparatus uses this tracking error signal Te (Te=2A sin φ
) is controlled so that it becomes 0. The tracking error signal Te of such a conventional sample servo type optical disk recording/reproducing apparatus depends on the amplitude A, as shown in equation (4). This amplitude A is determined by variations in the optical characteristics of the disc, such as the reflectance of the disc and the shape of pits. Therefore, in the conventional sample servo type tracking error signal generation method, the strength of tracking control pull-in varies due to variations in the optical characteristics of the disk, such as the reflectance and pit shape of the disk.

Therefore, in the present invention, this amplitude A factor is removed so that tracking control with stable pulling strength can be performed regardless of variations in the optical characteristics of the disk. This will be explained.

As mentioned above, the continuous tracks L1,
Wobble pits PaL1, PaL2, of L2, L3, ...
Reproduction RF signal waveform Ra of PaL3, ..., reproduction RF signal Rc of clock pits PcL1, PcL2, PcL3, ...
, wobble pits PbL1, PbL2, PbL3, . . . reproduced RF signal waveforms Rb can be expressed as shown in equations (1) to (3), respectively. Here, when formulas (1) to (3) are transformed, sin φa = (Ra-C)/A...(5
) cos φc = (Rc-C)/A...(6) si
n φb = (-Rb+C)/A (7). Here, if φa = φb = φc = φ, sin φ=(Ra-C)/A...(8) cos φ
=(Rc-C)/A...(9) sin φ=(-Rb
+C)/A...(10).

[0019] The DC offset C is expressed by equations (8) and (10).
According to the formula, (Ra-C)/A=(-Ra+C)/A, C=(Ra+Rb)/2...(11).

Furthermore, since sin 2 φ+cos φ2 =1 (13), the amplitude A can be obtained from equations (8) and (9) as follows. sin 2 φ+cos 2 φ = ((Ra-C)/A)2 + ((Rc-C)/A)2
=1 Therefore,

[Math 1]

Alternatively, from equations (9) and (10), sin
2 φ+cos 2 φ = ((-Rb-C)/A) 2 + ((Rc-C)/A)
2 = 1 Therefore,

[Math 2]

[0022] In this way, the wobble pits PaL1, P
Reproduction RF signal waveform Ra of aL2, PaL3, ..., reproduction RF of clock pit PcL1, PcL2, PcL3, ...
Signal Rc, wobble pit PbL1, PbL2, PbL
Using the reproduced RF signal waveform Rb of 3, . . . , the DC offset C and amplitude A are determined. Therefore, tracking control with stable pulling strength can be performed regardless of variations in the optical characteristics of the disk, such as the reflectance of the disk and the shape of pits. In other words, tracking control can be performed by driving the amplitude φ to zero.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, a reproduced RF signal from an optical disc (not shown) is supplied to an input terminal 1. This optical disc is provided with a servo area for each predetermined segment, and as shown in FIG.
Two wobble pits PaLn and PbLn and a clock pit PcLn are provided. Wobble Pit PaLn
and PbLn are arranged offset from each other by the same amount (equivalent to 1/4 of the distance between tracks) with respect to the track center. Clock pit PcLn is arranged on the track center.

The reproduced RF signal from input terminal 1 is supplied to registers 2A, 2B, and 2C, respectively. The register 2A takes in the playback signals of the wobble pits PaLn, PaLn+1..., and the register 2B takes in the playback signals of the wobble pits PaLn, PaLn+1...
, PcLn+1... are taken in, and the register 2
Reproduction signals of wobble pits PbLn, PbLn+1, . . . are taken into C.

From register 2A, wobble pit Pa
The reproduced RF signal waveform Ra of Ln, PaLn+1, . . . is output. This reproduced RF signal waveform Ra is supplied to the arithmetic circuit 3 and also to the arithmetic circuit 4. From register 2B,
The reproduced RF signal waveform Rc of the clock pits PcLn, PcLn+1, . . . is output. This reproduced RF signal waveform Rc is supplied to the arithmetic circuit 3 and also to the arithmetic circuit 5. From register 2C, wobble pits PbLn, P
The reproduced RF signal waveform Rb of bLn+1... is output. This reproduced signal waveform Rb is supplied to the arithmetic circuit 4.

The arithmetic circuit 3 calculates the amplitude A based on equation (13) or equation (14). The arithmetic circuit 3 is provided with a table for finding the solution to equation (13) or equation (14). The amplitude A determined by the arithmetic circuit 3 is supplied to the arithmetic circuit 5.

The arithmetic circuit 4 determines the DC offset C based on equation (11). The DC offset C determined by the arithmetic circuit 4 is supplied to the arithmetic circuit 5. The arithmetic circuit 5 determines the phase φ. The phase φ is obtained as (φ=cos −1(Rc−C)/A)). Tracking control is performed by controlling this phase φ to be 0.

The phase φ determined by the arithmetic circuit 5 is supplied to the register 6 as a tracking error signal T. The output of the register 6 is supplied to a two-axis device 9 via a phase compensation circuit 7 and an amplifier 8. A two-axis device 9 controls the optical system of the pickup. The two-axis device 9 is driven so that the phase φ determined by the arithmetic circuit 5 becomes 0. Tracking control is thereby performed.

In the above-mentioned embodiment, the phase φ is controlled to be zero, but the cos φ may be controlled to be zero.

[0030]

According to the present invention, the amplitude A and the DC offset C that depend on the optical elements of the disk are determined, and the tracking error signal is generated by removing the components that depend on the optical elements. Therefore, tracking control can be performed without being affected by variations in the optical characteristics of the disc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a schematic diagram used to explain one embodiment of the present invention.

FIG. 3 is a waveform diagram used to explain one embodiment of the present invention.

[Explanation of symbols]

1 Input terminal 3 Arithmetic circuit 4 Arithmetic circuit 5 Arithmetic circuit 9 2-axis device

Claims (1)

[Claims] 1. Servo areas are provided at predetermined intervals, and a pair of wobble pits are provided in the servo areas at positions offset by the same amount in a direction opposite to the track center, and a clock is provided at the track center. In a method for generating a tracking error signal when performing tracking control of a disk on which pits are arranged, an element of optical characteristics in an output signal is determined by using the playback output of the pair of wobble pits and the playback output of the clock pit. A method for generating a tracking error signal, in which a tracking error signal is generated by calculating and removing the above-mentioned optical characteristic elements.