WO2004102560A1

WO2004102560A1 - Optical disc drive, and method of measuring the nominal linear speed v1x of an optical disc

Info

Publication number: WO2004102560A1
Application number: PCT/IB2004/050662
Authority: WO
Inventors: Tony P. Van Endert; Jacob J. Romein
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-05-19
Filing date: 2004-05-12
Publication date: 2004-11-25
Also published as: TW200506833A

Abstract

A method is described for measuring the nominal linear speed (V ix) of an optical disc (2) in a disc drive (1). A frequency of an optical read signal (SR) component is measured, and the result is used in calculating the nominal linear speed. In an embodiment, the channel bit frequency (fcB) in the optical read signal is measured, and the nominal linear speed is calculated as:VIx = 27tR-fDIsc ' fcB,Ix/fc&dollar; wherein: R is the radius of the measuring position; fDlsc is the disc rotation frequency; fcB,lx is the prescribed channel bit frequency at nominal linear speed. In another embodiment, the wobble frequency (fw) in the optical read signal is measured, and the nominal linear speed is calculated as: VIx = 2itR•fDlsc - fw,lx/fw wherein: R is the radius of the measuring position; fDlsc is the disc rotation frequency; fw,lx is the prescribed wobble frequency at nominal linear speed.

Description

Optical disc drive, and method of measuring the nominal linear speed Vιχ of an optical disc

FIELD OF THE INVENTION

The present invention relates in general to the art of optical storage discs. More particularly, the present invention relates to a disc drive apparatus for writing/reading information into/from an optical storage disc; hereinafter, such a disc drive apparatus will also be indicated as "optical disc drive".

BACKGROUND OF THE INVENTION

As is commonly known, an optical storage disc comprises at least one track, either in the form of a continuous spiral or in the form of multiple concentric circles, of storage space where information may be stored in the form of a data pattern. Optical discs may be of the read-only type, where information is recorded during manufacture, which information can only be read by a user. The optical storage disc may also be of a writable type, where information may be stored by a user. For reading/writing information from/into the storage space of the optical storage disc, an optical disc drive comprises, on the one hand, rotating means for receiving and rotating an optical disc, and on the other hand optical means for generating an optical beam, typically a laser beam, and for scanning the storage track with said laser beam. Since the technology of optical discs in general, the way in which information can be stored in an optical disc, and the way in which optical data can be read from an optical disc are commonly known, it is not necessary here to describe this technology in more detail.

Optical discs and disc drives have been developed according to different standards or formats, such as, for example, the CD standard, DVD standard, etc. In these standards, several important parameters are defined. One such important parameter is the nominal linear speed with which the laser beam should scan the track; this nominal linear speed will be indicated hereinafter as Vιχ. The optical disc standards set certain limits for the nominal linear speed V) . For instance, in the case of CD, the allowed range for V_{I X CD} is between 1.2 and 1.4 m/s. In the case High Capacity CD Recordable Disc Systems (up to 100 minutes), the allowed range for VI_X]CD-H_C is between 1.13 and 1.2 m/s. In the case of DVD Single Layer, the allowed range for V_{I XIDVD}-_SL is between 3.46 and 3.52 m/s. In the case of DVD Dual Layer, the allowed range for V_{IX DVD}-_D is between 3.81 and 3.87 m/s. Thus, in practice, when a disc drive receives different discs, the nominal linear speeds Vιχ of these discs may vary appreciably.

However, the actual value of V_)X of the current disc being handled by the disc drive is an important parameter which is used by the disc drive in many calculations. This value is used, for example, to calculate a preset for the wobble PLL and for the data (HF) PLL, to calculate a set point for the disc drive motor, etc.

Therefore, it is important that the disc drive knows quite accurately the actual value of Vιχ of the current disc. Consequently, there is a need for a method of measuring the nominal linear speed Vιχ of an optical disc in a disc drive.

In a method known in practice, the track pitch is measured, which is correlated to the nominal linear speed Vιχ. It is necessary in such a method to make at least one jump from one radius to another, preferably from an inner radius to an outer radius. Making such a large jump may be difficult at high rotational speeds, especially on blank discs. Furthermore, in the case of a jump from a written area to a non-written area, the drive may have problems such that a recovering procedure is necessary. All these factors lead to a relatively long measuring time, which may be of the order of 0.5 s in a best case scenario, but which may easily be more than one second.

SUMMARY OF THE INVENTION

In general, the present inventions aims to provide a new method of measuring the nominal linear speed Vιχ of an optical disc in a disc drive.

More particularly, the present inventions aims to provide a measuring method capable of providing a sufficiently accurate measuring result within a measuring time substantially shorter than 0.5 s, preferably even shorter than 0.05 s.

According to an important aspect of the present invention, the nominal linear speed Vιχ of an optical disc is derived from a track parameter relating to a unit of track length.

In a first specific embodiment, the nominal linear speed Vιχ of an optical disc is derived from the channel bit frequency.

In a second specific embodiment, the nominal linear speed Vιχ of an optical disc is derived from the wobble frequency.

It is possible in principle to measure the above-mentioned parameters at one specific location on one specific track; however, it is preferred that multiple measurements are taken and averaged. In a preferred embodiment, measurements are averaged over one track revolution, leading to a measurement time of 0.025 s at a disc speed of 40 Hz.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects, features, and advantages of the present invention will be further explained by the following description with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:

Fig. 1 schematically shows relevant parts of an optical disc drive; Figs. 2A and 2B are graphs illustrating constant linear velocity operation and constant angular velocity operation;

Fig. 3 is a block diagram illustrating a calculation of the nominal linear speed Vιχ of an optical disc on the basis of a measurement of the channel bit frequency;

Fig. 4 is a block diagram illustrating a calculation of the nominal linear speed Vιχ of an optical disc on the basis of a measurement of the wobble frequency.

DESCRIPTION OF THE INVENTION

Fig. 1 schematically shows relevant parts of an optical disc drive 1 capable of handling an optical disc 2. The disc 2 is rotated by a disc motor 4. An optical system 10 is arranged for generating a laser beam 1 1 for scanning tracks (not shown) of the rotating optical disc 2 and for generating an electrical output signal S_R. A control circuit 20 has an input 21 receiving the electrical output signal S_R from the optical system 10 and has an output 22 for providing a control signal S_CM to control the motor 4. The control circuit 20 may control the motor speed on the basis of a tacho regulation, as is known per se.

The disc 2 has a nominal linear speed Vιχ which is specified in a standard. At any moment during operation, the actual linear track speed, indicated as V_L, can be expressed as

V_L = V_1X - Nχ (1) wherein x is a overspeed factor.

Figs. 2A and 2B are graphs illustrating constant linear velocity (CLV) operation and constant angular velocity (CAV) operation. In both graphs, the horizontal axis represents the location on the disc, i.e. the distance R from the rotational centre (radius), while the vertical axis represents the linear track speed V_L (Fig. 2A) and the disc rotation frequency foisc (Fig. 2B), respectively. Horizontal line 31 in Fig. 2A and curve 32 in Fig. 2B represent constant linear velocity (CLV) operation: the control circuit 20 controls the disc rotation frequency foisc as a function of the radius R such that the linear track speed V_L always has the same value that is independent of radius R. It is clear that in the CLV mode the disc rotation frequency f_Dιsc is lower at the outer disc radius than at the inner disc radius. Sloping line 33 in Fig. 2A and horizontal line 34 in Fig. 2B represent constant angular velocity (CAV) operation: the control circuit 20 controls the disc rotation frequency foisc to a fixed value independent of radius R. It is clear that in the CAV mode the linear track speed V_L is higher at the outer disc radius than at the inner disc radius.

The relationship between the disc rotation frequency foisc and the linear track speed V can be expressed as V_L = 2πR-f_Dιsc (2)

Combining expressions (1) and (2) yields foisc = (V,_x ^• Nx) / (2πR) (3)

When a track contains data written in it, this track contains a pattern of pits representing data bits, these pits having a certain length (as measured along the track) indicated as channel bit length CBL. When the track is read, the data are provided at a channel bit frequency fee in accordance with the following formula: f_CB = V_L / CBL (4)

The channel bit length CBL defines a certain track length unit, which should meet any requirements set in the standard. In the case of CD and DVD, the channel bit frequency fee at nominal linear speed Vιχ is fixed, according to fee_{, l} x = V i x / CBL = constant (5) thus fixing the channel bit length CBL. More particularly, f_CB,ιx(CD) = 4.3218 MHz, and f_CB;ιx(DVD) = 26.15625 MHz.

When the disc is played at an overspeed factor N_x, the actual channel bit frequency fee can be expressed as

The above applies to a CD-ROM or DVD-ROM disc, but also to the written parts of a CD-R, CD-RW, DVD-R, DVD-RW, etc. disc.

In the case of a writable disc (R;RW), the track has a wobble pattern having a certain wobble length WL. This wobble length or wobble period defines a certain track length unit, which should meet requirements of the standard. When the track is read, a wobble signal is provided having a wobble frequency fw in accordance with the following formula: fw = V_L / WL (7)

As was explained above with respect to the channel bit length, the wobble frequency fw at nominal linear speed Vιχ is fixed, according to f_W) l x = V i x / WL = constant (8) thus fixing the wobble length WL. More particularly, f_w,ιχ(CD) = 22.050 kHz. For DVD+ discs, f_w,ιx(DVD+) - 817 kHz. For DVD- discs, f_w,ιx(DVD-) = 140.6 kHz. When the disc is played at an overspeed factor Nx, the actual wobble frequency fw can be expressed as

The above applies to both the written and unwritten parts of a CD-R, CD-RW, DVD-R, DVD-RW, etc. disc. When a new disc is inserted into the disc drive 1, the control circuit 20 needs to establish the type of disc 2. Therefore, a start-up procedure is initiated, in which some tests are performed, as will be clear to those skilled in the art. At the end of this start-up procedure, the control circuit 20 knows whether the disc 2 is CD-type or DVD-type (or another type). This means that the control circuit 20 knows fcβ.ix and, in the case of a writable disc, fw.ix; these parameters are stored, for example, in a memory 23 associated with the control circuit 20.

Now, as part of the start-up procedure, or as an additional procedure after a standard start-up procedure, the control circuit 20 in accordance with the present invention will determine the nominal linear speed Vιχ on the basis of a frequency of a read signal (SR) component which is associated with a parameter relating to a unit of track length.

In a first specific embodiment, the said frequency is the channel bit frequency which is associated with the channel bit length CBL. In this embodiment, the control circuit 20 controls the optical system 10 to be located at a certain position R, and the control circuit 20 controls the motor 4 to rotate the disc 2 at a predetermined disc rotation frequency foisc, for example 40 Hz. In the case of a CD-ROM or DVD-ROM, said position R may be any position, for example a predefined position. In the case of an R-type disc or RW-type disc, said position R should be a position where the disc 2 contains data.

The control circuit 20 receives the data bits in signal S_R having a channel bit frequency fee- As will be clear to those skilled in the art, a data input section of the control circuit 20 contains a PLL circuit 41 which can provide the channel bit frequency fee, provided this PLL circuit 41 is operating in a locked condition. From the start-up procedure, indicated as block 40 in Fig. 3, the control circuit 20 has the nominal channel bit frequency fcB.ix available. Using formula (6) above, the control circuit 20 calculates the overspeed factor Nx as Nx = fee / fcB.ix , as indicated by divider block 42 in Fig. 3.

From said position R as set by the control circuit 20, indicated at block 43, and from said predetermined disc rotation frequency foisc as set by the control circuit 20, indicated at block 44, the control circuit 20 calculates the linear track speed V_L in accordance with formula (2) above, as indicated by multiplication block 45 in Fig. 3. Now the control circuit 20 is capable of calculating the nominal linear speed

Vιχ in accordance with formula (1) above, as indicated by divider block 46 in Fig. 3.

The nominal linear speed Vιχ thus calculated is used by the control circuit 20 for several calculations and operational settings, for example for calculating a setpoint for motor 4. In a second specific embodiment, the said frequency is the wobble frequency which is associated with the wobble length. In this embodiment, suitable in the case of an R-type disc or RW-type disc, the control circuit 20 controls the optical system 10 to be located at a certain position R, and the control circuit 20 controls the motor 4 to rotate the disc 2 at a predetermined disc rotation frequency foisc, for example 40 Hz. Said position R may be any position, for example a predefined position.

The control circuit 20 receives the wobble information in signal S_R, having a wobble frequency fw- As will be clear to those skilled in the art, a wobble input section of the control circuit 20 contains a PLL circuit 51 which can provide the wobble frequency fw, provided this PLL circuit 51 is operating in a locked condition. From the start-up procedure, indicated as block 50 in Fig. 4, the control circuit 20 has the nominal wobble frequency fw,ιx available. Using formula (9) above, the control circuit 20 calculates the overspeed factor Nx as Nx = fw / fw,ιx , as indicated by divider block 52 in Fig. 4.

From said position R as set by the control circuit 20, indicated at block 53, and from said predetermined disc rotation frequency foisc as set by the control circuit 20, indicated at block 54, the control circuit 20 calculates the linear track speed V_L in accordance with formula (2) above, as indicated by multiplication block 55 in Fig. 4.

Now the control circuit 20 is capable of calculating the nominal linear speed Vιχ in accordance with formula (1) above, as indicated by divider block 56 in Fig. 4. The nominal linear speed Vιχ thus calculated is used by the control circuit 20 for several calculations and operational settings, for example for calculating a setpoint for motor 4.

It is noted that it is not necessary for the control circuit 20 to calculate the nominal linear speed Vιχ in a sequence of steps. All in all, the overall result of said steps is that the nominal linear speed Vιχ is calculated in accordance with formulas (10) or (1 1), as applicable:

Vιχ = 2πR-f_Dιsc ^• fcB,ιχ/fcB (10)

V_lx = 2πR-f_Dlsc - fw_;ιχ/f_w (1 1) Thus, it is possible that the nominal linear speed Vιχ is calculated in one step, on the basis of four values R, foisc, fcβ.ix, and f_CB; or R, foisc, fw,ιx, and f_w.

As will be clear from the above explanation, the nominal linear speed Vιχ is calculated on the basis of four parameters. Two of these parameters, R and foisc, are constants which are "known" to the control circuit 20 because the control circuit 20 itself sets these values. A third parameter, fcβ.ix or fw_,ιx, is a constant which is prescribed by a standard, and it will be "known" to the control circuit 20 after a successful identification of disc type in a start-up procedure. Only one further parameter is required, fee or fw, and this parameter is measured in the data channel or in the wobble channel, as applicable, from an optical read signal S_R. It is noted that the measuring time required for obtaining a measurement value for said frequency (fee or fw, respectively) to be measured is much shorter than the time required for completing one disc revolution. Preferably, such a measurement is repeated a number of times during one complete disc revolution, and a value

(^<fc_B ^> or <fw>) averaged over the set of measurement results is calculated. Similarly, the actual disc rotation frequency values foisc are taken in conjunction with each of said measurements, and a value <foιsc^> averaged over the set of measurements is calculated. In that case, a more accurate calculation of the nominal linear speed Vιχ is achieved in accordance with formula (10a) or (1 la):

Vιχ = 2πR-<f_Dιsc> ^• fcB,ιχ/<f_CB> (10a)

V,_x = 2πR-<f_Dιsc> ^• fw,ιχ/<fw> (11 a)

1 ^N The operation <X> is defined here as < X > = — ~∑X i)

wherein X(i) indicates the individual measurement results, and N indicates the number of measurements. It is noted that, in the case of a writable (R or RW) disc, it is possible to measure the nominal linear speed Vιχ on the basis of the channel bit frequency as well as on the basis of the wobble frequency. The two results may be compared. If they differ too much, an error situation may be decided. If they differ only slightly, the average of the two measurements can be taken as the measurement result.

It is further noted that the position R may have any value in principle. However, it is preferred that the position R is chosen close to the inner radius in order to increase the chance that data is read in the case of a writable (R or RW) disc.

It will be clear to those skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that various variations and modifications are possible within the protective scope of the invention as defined in the appended claims.

For example, the measurement of the nominal linear speed was described above in the context of a start-up procedure. However, it is possible that the control circuit repeats the measurement at a later stage, for example at regular intervals, to check whether the disc is still in accordance with the standard, or to obtain an improved value of the nominal linear speed, for example in cases where the disc properties are not constant over the entire disc surface. Such a repeat measurement may be done while playing continues.

Furthermore, although the invention has been explained with reference to CD and DVD, the present invention is also applicable to other standards, such as, for example, Blue-Ray Disc.

The present invention was explained above with reference to block diagrams which illustrate functional blocks of the control circuit according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such a functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such a functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, etc.

Claims

CLAIMS:

1. Method of measuring the nominal linear speed (Vιχ) of an optical disc (2) in a disc drive (1) on the basis of measuring a frequency of a signal component of an optical read signal (S_R).

2. Method according to claim 1, wherein said signal component is associated with a parameter related to a track length unit.

3. Method according to claim 2, wherein the nominal linear speed (Vιχ) is calculated from a channel bit frequency (fee).

4. Method according to claim 3, wherein the nominal linear speed (Vιχ) is calculated in accordance with the following formula:

Vιχ = 2πR-foιsc ' fcB,ιχ/fcB wherein: R is the radius of the measuring position; foisc is the disc rotation frequency; fc_B.ix is the prescribed channel bit frequency at nominal linear speed; fee is the measured channel bit frequency.

5. Method according to claim 2, wherein the nominal linear speed (Vιχ) is calculated from a wobble frequency (fw).

6. Method according to claim 5, wherein the nominal linear speed (Vιχ) is calculated in accordance with the following formula:

Vιχ = 2πR-foιsc ' fw,ιχ/fw wherein: R is the radius of the measuring position; foisc is the disc rotation frequency; fw.ix is the prescribed wobble frequency at nominal linear speed; fw is the measured wobble frequency.

7. Method of measuring the nominal linear speed (Vιχ) of an optical disc (2) in a disc drive (1), comprising the steps of:

- determining the type (CD; DVD; etc) of the disc (2); determining the prescribed channel bit frequency fcβ.ix at nominal linear speed of discs of this type; rotating the disc (2) at a certain disc rotation frequency foisc;

- obtaining an optical read signal (S_R) from a track at a radius R;

- measuring the channel bit frequency fee in this optical read signal (SR);

- calculating the nominal linear speed (V_)X) in accordance with the following formula: Vιχ = 2πR-foιsc ' fcB,ιχ/fcB

8. Method of measuring the nominal linear speed (Vιχ) of an optical disc (2) in a disc drive (1), comprising the steps of: determining the type (CD; DVD; etc) of the disc (2); - determining the prescribed wobble frequency fw_,ιx at nominal linear speed of discs of this type; rotating the disc (2) at a certain disc rotation frequency foisc;

- obtaining an optical read signal (S_R) from a track at a radius R; measuring the wobble frequency fw in this optical read signal (S_R); - calculating the nominal linear speed (Vιχ) in accordance with the following formula:

Vιχ = 2πR-foιsc " fw,ιχ/fw

9. Method according to any of the preceding claims, wherein the said frequency (fee; fw) is measured multiple times during one revolution of the disc (2), and wherein the nominal linear speed (Vιχ) is calculated on the basis of an average value (<fcB^>; <fw>) of the measurement results.

10. Optical disc drive (1), comprising a control circuit (20) designed to perform a measurement in accordance with any of the previous claims.