KR100477475B1 - Apparatus for reading or writing optical recording carriers - Google Patents

Abstract

The present invention relates to an apparatus for reading or recording on an optical recording medium using a differential phase detection method for tracking. The method illustrates the disadvantages when optical recording media 4 of different pit depths are used. The object of the present invention is to design an apparatus of this type which can also be used for the optical recording medium 4. This object is achieved by means of a delay element 7, 8, 9, 10 being arranged between the photodetector 5 and the phase detector 14. The apparatus according to the present invention is used as a reproducing or recording apparatus for optical recording media such as CD, CD-ROM, CD-I, CD-R, DVD, DVD-ROM, DVD-R and the like.

Description

Apparatus and method for adjusting delay elements for reading or recording on an optical recording medium {APPARATUS FOR READING OR WRITING OPTICAL RECORDING CARRIERS}

The present invention relates to an apparatus for reading from and / or writing to an optical recording medium according to the preamble of claim 1.

Devices of this type are disclosed in US Pat. No. 4,497,048. This known apparatus is provided with a photodetector divided into four regions. The tracking information is obtained by combining the signals from the two regions to form a summation signal in each case so that there is no need to obtain the amplitude of the reproduced signal and the phase difference between the first and second summation signals. is obtained by checking the difference). The apparatus satisfactorily functions when the optical recording medium to be read has a clear and constant form of the information carrying layer. In particular, the depression, so-called pit, in the information carrier layer, which serves for information storage, needs to have a constant depth with respect to the wavelength of the light used for the reading operation.

The disadvantages of the known apparatus are that only slight variations in the pit shape are allowed, and that larger deviations lead to errors in the formation of the tracking information. As a result, a high rate of error occurs during reading of the optical recording medium, or in extreme cases, such reading becomes completely impossible.

1 is a schematic diagram of an apparatus according to the invention.

2 is a flow diagram relating to a method according to the invention.

It is an object of the present invention to improve the known apparatus so that it can be used without causing any problem even for optical recording media having different pit depths or other pit shapes.

According to the invention, this is achieved due to the fact that a delay element is assigned to at least one of the regions of the photodetector. This has the advantage that the areas of the photodetectors can be temporarily adjusted relative to each other. Photodetectors are caused by pits arranged on an optical recording medium and may vary depending on the shape of the disc and the shape of the track (pit depth, etc.), the type and manufacturing tolerances of the disc and the aging phenomena of the laser scanner. As the interference pattern is received, the temporal correlation between the detector signals also changes. According to the invention, this type of change is compensated for by the temporal adjustment of the detector signal with respect to each other where possible. In this case the temporal adjustment can be performed by a single delay element assigned to the area of the photodetector. However, considerably improved adjustments are possible if delay elements are assigned to multiple regions or each region. If delay elements are assigned to each area, the greatest flexibility is possible. If a delay element is assigned to all areas except one area, then all areas to which the delay element is provided can be adjusted for that area without a delay element. It is also possible to combine the regions into groups, assign delay elements to each group, and adjust the groups relative to each other. If an area consists of a plurality of individual areas, then a delay element can be assigned to each of these individual areas.

The delay element may be set externally, for example, during the fabrication of the device or when the service service of the device is being performed.

The present invention provides for the presence of a control element for setting the delay element or the delay time of the elements. This has the advantage that the delay element can be adjusted at any time. For example, adjustment may be made during each interruption of the reproduction or recording operation of the optical recording medium, at particular time intervals, or at other appropriately defined intervals, for example, after each insertion of a new optical recording medium. One adjustable possibility lies in setting a fixed delay time that matches the type of optical recording medium. The type of recording medium is in this case limited by the pit depth or pit shape, the width of the track or similar characteristic properties. Accompanying this is a known audio CD or a new optical recording medium (so-called DVD) having a high recording density. It is likewise possible to change the delay time with a type of "trial and error" relative to the initial setting and retain the new value when the tracking behaviour becomes better. If the tracking response gets worse, the delay time is reset to the previous setting.

Furthermore, phase detection means for detecting the phase angle of the signal emitted in the region of the photodetector are provided. This has the advantage that the adjustment is possible in an optimal way since the exact phase angle is determined, and consequently the delay time of the delay element can be set accurately.

Another improvement of the present invention is that a circuit arrangement is provided for applying a combined signal of the output signal of the region to the phase angle detector. This has the advantage that the phase angle of the individual signals is evaluated by a single phase angle detector in which the signals of the individual regions of the photodetector are continuously transmitted through the circuit arrangement. A circuit arrangement, for example a multiplexer, is preferably installed in the apparatus, so that the phase angle can be determined internally. Alternatively, this is advantageous for the external determination of the phase angle since an unnecessarily high contact-making expense is not necessary in this case.

The circuit arrangement is advantageously switched to a control means, for example a microcontroller. According to the invention, the switching is likewise possible in accordance with a particular timing cycle or clock that is otherwise triggered.

An advantageous improvement of the present invention lies in the fact that the phase angle detector is the phase detector of the device. This has the advantage that no additional component is needed and in some cases the functional group of the device present is optimally used.

In an improvement of the invention, it is prepared to use a microcontroller which controls both the setting of the delay time of the circuit arrangement and the delay element. This has the advantage that the control is carried out by a component that can be integrated in a cost-saving manner and flexibly adapted to the altered boundary conditions. Logic circuits can also be advantageously used in place of microcontrollers.

An advantageous improvement of the present invention is the arrangement of the low pass filter at the output of the phase detector. This has the advantage that the averaged DC signal is emitted in a manner that allows automatic setting of the delay time, even if the light beam scanning the optical recording medium does not follow the track. The light pulses that strike the detector need not be derived from the data track in this case; The light pulse is equally a signal that occurs during random traversal of the track. In this way, a rapid setting of the delay time is possible before the actual playback or recording operation takes place. Since a phase detector is not required in some cases to track during this time, a changeover between the function of tracking delay element and the function of phase adjustment is also unnecessary.

The adjustment of the delay element of the apparatus, which can be set according to the invention, is advantageously carried out according to the method described in claim 8. This has the advantage that the phase difference caused by the component properties is compensated in a simple and cost-saving manner. After the method has been carried out, the apparatus is provided with the optimally adapted setting values retained, as appropriate, until an updated adjustment is required or required. The described method can be used not only during fabrication for optimal setting of the device, but also for adjustment during operation of the device. The latter case can be implemented manually, for example during service work, or automatically, for example at specific time intervals.

In the method according to the invention it is prepared for setting this delay element which can be set to the minimum delay time before the first method step. This has the advantage that the delay component of the region having the last signal chronologically does not need to be changed, and that the maximum possible margin is available for the margin of the other delay components.

The method according to the invention can also be used advantageously when not actually following the track. In this case, the light pulses arriving at the detector are from randomly traversed tracks. However, this is not important for setting the delay time in the method according to the invention, because the chronological order of the signals of the individual detector elements in the case of rotating recording media with the track adjustment circuit still open. This is because is substantially the same as the order in the case of a closed adjustment circuit. Therefore, the optimum adjustment of the delay time can be performed by the method according to the invention, even before closing the track adjustment circuit, and this is after the track adjustment circuit since the wrong signal does not have to be used for this purpose. There is a side which makes the closing of the material considerably easier.

Claim 10 describes an embodiment of the method according to the invention which has advantages that are particularly simple to implement. The apparatus according to the present invention is used as a reproduction or recording apparatus for optical recording media such as, for example, CD, CD-ROM, CD-I, CD-R, DVD, DVD-ROM, DVD-R, and the like.

The features described in the individual claims can also be conveniently used in combination with one another. Another advantage of the device according to the invention and of the method according to the invention can be deduced from the following detailed description.

1 schematically shows a device according to the invention. A light beam is generated by the light source 1 so that the light beam passes through the translucent mirror 2 and the objective lens 3 to reach the optical recording medium 4, and reflects the light beam from the optical recording medium to the objective. It passes through the lens 3 to reach the mirror 2, from which the light beam is deflected onto the detector 5. The detector 5 is shown both in side view (shown on the left) and in plan view (shown on the right) rotated by 90 °. This example shows that the detector 5 consists of four regions A, B, C, and D. FIG.

The optical recording medium 4 is rotated due to the motor M. As shown in FIG. So-called pit depressions are arranged in a spiral track on the optical recording medium 4. The objective lens 3 serves to focus the light beam on the optical recording medium 4. For this purpose, the distance from the optical recording medium 4 can be adjusted by the drive 6. In order to follow the track, that is to say tracking, the objective lens 3 can be moved in the radial direction with respect to the optical recording medium 4 due to the drive 6. The tracking signal TS is applied to the drive 6 for this purpose.

Output signals in regions A, B, C, and D are supplied to delay elements 7, 8, 9, and 10, respectively. Delay elements 7, 8, 9, and 10 have delay times τ _A , τ _B , τ _C , and τ _D , which can be set variably, respectively. Delayed signals A ', B', C ', and D' then appear at the outputs of delay elements 7, 8, 9, and 10, respectively. The signal is supplied to the circuit arrangement 11, and the two outputs 12 and 13 of the circuit arrangement are supplied to the phase detector 14.

The signals A 'and C' are additionally supplied to the first adder 15, and the output signals thereof are supplied to the circuit device 11. The signals B 'and D' are also correspondingly supplied to the second adder 16, and the output signals thereof are similarly supplied to the circuit device 11 as well. Moreover, the output signals of the first adder 15 and the second adder 16 are supplied to the third adder 17, and the output signal of the third adder represents the information signal HF. Further processing of the signal HF is not described here in further detail because it is performed in a manner known to those skilled in the art.

The high frequency component of the signal present at the output 12 is supplied to the converter 19 via a capacitor 18. The converter 19 converts the analog input signal into a square-wave signal having two possible states. This square wave signal essentially corresponds to information saying "light is reaching the corresponding area of the photodetector" or "light is not reaching this area", that is to say essentially an analog input signal. Corresponds. This type of converter is also referred to as "data slicers". The same applies to the signal present at the output 13, which passes through the capacitor 18 ′ and the converter 19 ′. The digitized signal emitted from the transducers 19, 19 'is fed to the phase comparator 20. If the phase angles of these input signals are the same, then the output signal of the phase comparator is zero, and if there is a phase shift, then the output signal of phase comparator 20 is positive from zero. Direction or negative direction, specifically, the larger the phase shift in time of the input signal, the larger the deviation. The output signal of the phase comparator 20 is filtered by the low pass filter 21, whose cutoff frequency of the filter is about 50 kHz in an exemplary embodiment, and after being amplified by the amplifier 22, the track error signal TE Is output as.

The signal TE is filtered in another low pass filter 23, whose cutoff frequency is about 10 Hz, which is considerably lower in the exemplary embodiment, and is supplied to the microcontroller 24 serving as a control means. The microcontroller 24 controls both the circuit arrangement 11 via line 25 and the delay elements 7 to 10 via line 26. In an exemplary embodiment, line 25 is a three bit data line while line 26 transmits a control signal with the resolution required for each delay element 7, 8, 9, and 10. Is designed as a serial data line.

In an exemplary embodiment, the circuit arrangement 11 is realized as a multiplexer which connects twice the input of seven inputs to two outputs. For tracking purposes, the inputs A + C and B + D shown below in the figures, respectively, are connected to outputs 12 and 13, respectively.

The deviation of the light beam from the track center, which reads the optical recording medium 4, causes the diffraction grating reaching the detector 5 to exhibit an asymmetric distribution, and as a result the signals A + C and B + D ) Is different in terms of its phase angle. The greater the deviation of the light beam from the track center and hence the phase angles of the signals A + C and B + D with respect to each other, the greater the deviation from zero. A regulator (not shown here) determines from this the desired tracking value, which is sent to the drive 6 as a signal TS.

Delay elements 7 to 10 are provided so that the signals emitted in regions A, B, C and D can be adjusted in time with respect to each other. In this case, it is preferable to adjust the detector signal leading in chronological order to the last signal in each chronological order, so that the relative phase shift with respect to each other becomes 0 °. This gives the best signal source quality with minimal noise for the track error signal TE. This method, cited for determining the track error signal (TE), is called the "Differential Phase Detection" (DPD) method. Since the delays that occur in the individual areas A to D of the detector relative to each other depend on the track width and shape of the optical recording medium as well as the linear scanning speed which may vary for different types of optical recording medium 4. The delay elements 7 to 10 are newly adjusted each time the optical recording medium is changed. Starting with the existing phase detector 14 for generating a track error signal TE using the DPD method from the addition signals A + C and B + D, this phase detector 14 is in the areas A to D. In order to determine the order of the detector signals appearing from) and to automatically adjust the delay factor, it is likewise used without any extra expense.

The chronological order of the detector signals of the regions A to D with respect to each other is determined as follows: The signals A, B, C, and D are compared with each other to be able to identify their phase angles with respect to each other. . Six combinations are needed to reliably identify the last signal that appears in chronological order. The combination is A and B, A and C, A and D, B and C, B and D, and C and D. The multiplexer of the circuit arrangement 11 allows all of the above comparison combinations to be switched to the input of the phase detector 14 in accordance with the switch position. The average DC voltage component of the output signal of the phase detector 14 can be determined with the aid of an additional low pass filter 23, which is also realized in the microcontroller 24 as, for example, an FIR filter. Can be. All delay elements 7 to 10 are first set to the smallest possible delay time, ie τ _A = τ _B = τ _C = τ _D = 0. If two input signals with different phase angles are then passed to the phase detector 14 and the average DC voltage component is measured at the output of the detector, the voltage deviating from zero is generated positively or negatively depending on the phase angle. Decisions relating to the phase angle can be made, for example, by a software comparator whose comparison level is zero volts. Since the software comparator was initially intended to determine only the chronological order of the detector signals of regions A through D by alternative interrogation, the query can be executed very quickly. There is no need to wait for settling by the low pass filter 23. You only need to check the trend (greater than zero or less than zero). Delay elements 7 to 10 should only be determined after the last signal has been determined, in chronological order, as a software or state machine, by means of said alternative question in a suitable form in the microcontroller 24 in the exemplary embodiment. Actual adjustments are made.

This adjustment process proceeds as follows: Since the last signal in chronological order has already been determined, it is easily possible to shift the other three leading signals to the last signal in chronological order in three successive steps. Do. The criterion for successful movement is once again the average DC voltage component at the output of phase detector 14. The preceding signals in chronological order are compared one by one with the last signal in chronological order and the delay time [tau] of each preceding signal is increased until the average DC voltage component at the output of phase detector 14 reaches a zero value. This operation is performed with the help of microcontroller 24, whose voltage value is compared with a software comparator at zero volts. The delay times τ _A , τ _B , τ _C , and τ _{D of the} delay elements 7 to 10 can in this case be adjusted continuously or in a small number of steps by the microcontroller 24. When all the signals have been shifted in such a way that their relative phase angles coincide, the track error signal TE is obtained from the sum of the signals A '+ C' and B '+ D'. The automatic adjustment method according to the invention has the advantage of compensating for the influence on the temporal correlation between the detector signals, which correlates with the shape of the disc and the shape of the track, the type of the disc, the laser scanner or optical device ( Manufacturing tolerances of 1 to 5), and the linear speed, that is, the speed of the optical recording medium where the current light beam is located.

Furthermore, determining the temporal correlation between detector signals in areas A through D and shifting the temporal correlation between the signals by delay elements 7-10 are additional expense. Without the expense (delay elements 7 to 10, circuit arrangement 11 and low pass filter 23) it is possible to insert a logic circuit or microcontroller 24 as shown.

2 is a flow chart illustrating a method for automatically adjusting the delay elements 7 to 10 that can be set. After the start, all delay times τ _A , τ _B , τ _C , and τ _D are set to zero. The phase angles of the signals A and B are then compared with each other. The multiplexer is in the switch position shown in this case. If signal A precedes signal B, then it is selected as the left branch, otherwise it is selected as the right branch. In each case, lagging signals B and A are then compared with signal C, respectively. This corresponds to the fourth switch position and the second switch position, respectively, from above the circuit arrangement 11. The signal determined to lag in this second comparison step is then compared with signal D.

After this third comparison, it becomes clear which signal is the most lagging in time. In three successive steps, the delay time tau _i of the delay component of each other signal is set. The leftmost in Fig. 2 is shown for the case where the signal D is the most backward. τ _A is adjusted first until signals A and D are in phase, then τ _B is adjusted, followed by τ _C correspondingly. On the right side of this, the case where the signal C is lagging behind is shown. In this case, τ _A , τ _B , and τ _D are adjusted accordingly. On the right hand side, the case where the signal B is lagging behind is shown, and on the far right side, the case where the signal A is lagging behind is shown. Only after each of the other three delay times τ _I is set, the multiplexer of the circuit arrangement 11 is set to the switch position, which is shown as the lowest switch position in the figure. As a result, the addition signals A + C and B + D are supplied to the phase detector 14 to generate the track error signal TE. The setting operation of the delay elements 7 to 10 hereby ends.

An advantageous improvement of the present invention is the arrangement of the low pass filter at the output of the phase detector. This has the advantage that the averaged DC signal is emitted in a manner that allows automatic setting of the delay time, even if the light beam scanning the optical recording medium does not follow the track. The light pulse that strikes the detector does not need to originate from the data track in this case; The light pulse is equally a signal that occurs during random traversal of the track. In this way, a rapid setting of the delay time is possible before the actual playback or recording operation takes place. Since the phase detector is not required for tracking during this time in some cases, a change is also unnecessary between the function of tracking the delay element and the function of phase adjustment.

Claims (11)

Apparatus for reading from or recording to the optical recording medium 4, comprising: a detector having four regions A, B, C, D, in which a light beam incident from the optical recording medium 4 arrives (5), delay elements (7, 8, 9, 10) that can be set and assigned to two of the four areas (A, B, C, D), and at the input of the photodetector (5) In each of the areas A, B, C, and D, a summation signal of two areas is present and at its output is provided with a phase detector 14 in which a track error signal TE is collected and transmitted. In the apparatus for reading from or recording to the optical recording medium (4), Apparatus for reading from or writing to an optical recording medium (4), characterized in that at least one of the delay elements (7,8,9,10) can be set independently of other delay elements. The medium according to claim 1, characterized in that there are control means 24 for setting the delay element or elements 7, 8, 9, 10. Device for recording. The optical recording medium according to claim 1, wherein there is a phase detecting means for detecting a phase angle of the signal emitted from the regions A, B, C, and D of the photodetector 5. (4) A device for reading from or writing to the medium. 2. A circuit arrangement (11) according to claim 1, wherein there is a circuit arrangement (11) for applying a variable combination of the output signals of the regions (A, B, C, D) of the photodetector (5) to a phase angle detector. A device for reading from or recording on an optical recording medium (4). 5. Device according to claim 4, characterized in that the phase angle detector is the phase detector (14) of the device. 6. The optical recording medium (4) according to claim 5, characterized in that there is a microcontroller (24) which controls the setting of the circuit arrangement (11) and the delay elements (7, 8, 9, 10). Apparatus for reading or writing to the medium. 6. Device according to claim 5, characterized in that a low pass filter (23) is arranged at said output of said phase detector (14). A method for adjusting the delay elements 7, 8, 9, 10 of an apparatus for reading and writing from an optical recording medium or for reading or writing on the medium, the delay elements may be set and the A delay element adjustment method, which is assigned to specific areas A, B, C, D of the photodetector 5 of the device, The first method step compares the phase angles of the signals emitted in the individual regions A, B, C, D, and the second method step the delay times τ of the delay elements 7, 8, 9, 10. _A , τ _B , τ _C , τ _D ) are changed until the phase of all the signals coincide with the phase of the last signal in chronological order, and these modified delay times (τ _A , τ _B , τ _C , τ _D ) are Delay element adjustment method, which is retained at the optimized setting of the device. 9. A method according to claim 8, wherein the delay element (7, 8, 9, 10) that can be set is set to a minimum delay time (τ _i = 0) before the first method step. 9. The phase of the signal of the areas (B and C) according to claim 8, wherein the phases of the signals of the areas (A and B) are first compared in the first method step, and if the phase of A is ahead of the phase of B. The phases are compared, otherwise the signal phases of A and C are compared, and if the phases of B and A respectively precede the phases of C, then the phase angles of C and D are compared with each other, otherwise B and A The phases of are compared with the phases of B respectively, the chronological order of the last signal being evident at the end of these comparisons, wherein the other signal is in accordance with the second method step of the delay elements 7, 8, 9, 10. Delay phase (τ _A , τ _B , τ _C , τ _D ) by setting the phase angle of the last signal in the chronological order. Apparatus according to claim 1, characterized in that the delay elements (7, 8, 9, 10) are assigned to at least three of said four areas. .