HK1020383B - Apparatus for reading or writing optical recording carriers and method for adjusting delay elements of such apparatus - Google Patents

Description

Apparatus for reading or writing optical recording media and method for adjusting a delay element of such an apparatus

The invention relates to a device for reading from and/or writing to optical recording media.

A device of this type is disclosed in US 4,497,048. In this known device, a photodetector is provided which is divided into four regions. The tracking information is obtained by combining the signals from the two areas one at a time to form a sum signal, and the phase difference between the first and second sum signals is determined, so that it is not necessary to obtain the amplitude of the reproduction signal. The effect of such a device is satisfactory when the information carrier layer of the optical recording medium to be read out has a precise and constant geometry. In particular, it is required that the grooves, so-called pits, in the information carrier layer for information storage have a fixed depth with respect to the wavelength of the light used for the read-out operation.

A disadvantage of this known device is that only slight variations in the pit geometry can be tolerated, whereas large deviations can lead to errors in the formation of the tracking information. As a result, a high error rate may be generated during reading of the optical recording medium or, in extreme cases, the reading operation may not be performed at all.

It is an object of the invention to improve such a known device in such a way that no problems arise in use even if the pits of the optical recording medium have different depths or different geometries.

According to the invention, this object is achieved in that a delay element is assigned to at least one region of the photodetector. This has the advantage that the areas of the photo detectors can be adjusted in time relative to each other. Since the interference pattern received by the photodetector is caused by pits arranged on the optical recording medium and may vary with the geometry of the optical disc and the geometry of the tracks (depth of pits, etc.), the type of optical disc, manufacturing tolerances, and the lifetime of the laser scanner, the time relationship between the detector signals also varies. The time adjustment that can be made according to the invention between the detection signals relative to each other allows compensation for such variations. In which case the time adjustment can be performed with a single delay element allocated for one area of the photodetector. However, if one delay element is allocated to a plurality of or each of the regions, the adjustment effect is better. Maximum flexibility is obtained if one delay element is assigned to each region. If only one area has no delay elements assigned to it, all areas provided with delay elements can be adjusted to that area without delay elements. It is also possible to combine the regions into groups, assign a delay element to each group, and adjust between groups. If a zone is made up of a plurality of separate zones, a delay element may be assigned to each such separate zone.

The delay element may be set externally, for example during the manufacture of the device or during maintenance of the device.

The invention provides a control device for setting the delay time of a delay element. This has the advantage that the delay elements can be adjusted at any time. For example, it may be adjusted at specific time intervals after each insertion of a new optical recording medium, for example during a brief interruption in the playback or writing operation of the optical recording medium, or at differently well-defined intervals. One possibility of adjustment is to set a fixed delay time that is adapted to the type of optical recording medium. In this case, the type of recording medium is defined by the depth or geometry of the pits, the track width, or similar characteristics. What may be mentioned here is the well-known audio CD or a new optical recording medium with a high recording density, the so-called DVD. It is also possible to change the delay time in a "heuristic" with respect to the initial setting and to keep the new value when the tracking state improves. If the tracking state gradually deteriorates, the delay time is reset to the previous set value.

The invention also provides a phase detection device for detecting the phase angle of the signal emitted by the region of the photodetector. This has the advantage that the adjustment can be performed in an optimal manner, since an accurate phase angle can be determined and thus the delay time of the delay element can be set accurately.

A further improvement of the present invention is to provide a circuit arrangement for combining the signals output by the respective zones to the phase angle detector. This has the advantage that the phase angle of each signal can be calculated with one phase angle detector, to which the signals of each region of the photo detector are supplied in turn by means of the circuit arrangement. Such a circuit arrangement, for example a multiplexer, can advantageously be installed in the apparatus, so that the phase angle can be determined from within. On the other hand, the phase angle can be determined from the outside, since in this case no unnecessarily high outlay is required.

The circuit arrangement is preferably switched by a control device, such as a microcontroller. According to the invention, the switching can be effected by triggering the clock in a defined time period or in a different manner.

An advantageous improvement of the invention is that the phase angle detector is the phase angle detector of the device itself. This has the advantage that no additional components are required and that in any case those functional groups which the device has can be optimally utilized.

In a further development of the invention, a microcontroller can be used to control the circuit arrangement and the setting of the delay time of the delay elements. This has the advantage that the control can be performed in an inexpensive integrated manner with one component and can be flexibly adapted to changing boundary conditions. A logic circuit may be used instead of the microcontroller.

An advantageous improvement of the invention is that a low-pass filter is provided at the output of the phase detector. This has the advantage that an average Direct Current (DC) signal can be emitted in this way, so that the delay time can be set automatically even if the light beam used for scanning the optical recording medium does not follow a track. In this case, the light pulse impinging on the detector does not necessarily have to emanate from one data track; they may be equivalent to the signals generated when randomly crossing a data track. In this way it is possible to set the delay time quickly before starting the actual playback or recording operation. Since the phase detector does not need to perform tracking during this period in any case, it is not necessary to switch between the tracking function and the phase adjustment of the delay element.

The adjustment of the settable delay elements of the inventive device can be performed according to the inventive method. According to the invention, a method for adjusting delay elements that can be set in a device for reading from and/or writing to optical recording media is provided, wherein delay elements are assigned to specific regions of a photodetector of the device, wherein, in a first method step, the phase angles of the signals emitted by the respective regions are compared in order to determine the last signal in chronological order, wherein, in a second method step, the delay times of the delay elements are changed until the phases of all the signals coincide with the last signal in chronological order, and wherein these changed delay times are determined as the optimum setting values for the device. This has the advantage that the phase differences caused by the component properties can be compensated in a simple and inexpensive manner. After the method has been performed, the device can obtain the most suitable set value, which can be maintained until readjustment is needed or desired, as required. The method can be used not only in the process of optimally setting the device, but also for adjustment during operation of the device. The latter case may be done manually during maintenance or automatically at regular intervals.

Those delay elements which can be set to a minimum delay time before the first method step of the method of the invention is performed. This has the advantage that the delay element of the region with the chronologically last signal does not need to be changed and the largest possible margin can be provided for the other delay elements.

The method according to the invention can also be advantageously used when the track is not actually tracked. In this case, the light pulses falling on the detector originate from randomly crossing tracks. However, this is not important if the method of the invention is used to set the delay time, since, in the case of a rotating recording medium, the track adjustment circuit is still open, the chronological order of the signals of the individual detector elements is virtually identical to that in the case of a closed adjustment circuit. Thus, even before closing the track adjust circuit, an optimal adjustment of the delay time can still be performed using the method of the present invention, and it is considerably facilitated to close the track adjust circuit in sequence to some extent, since no error signal needs to be used at this time.

According to one embodiment of the method, the signal phases of the regions a and B are first compared in a first method step, and if the phase of a leads the phase of B, the signal phases of the regions B and C are compared, otherwise the signal phases of the regions a and C are compared; if the phases of B and A lead C, respectively, the phase angles of C and D are compared with one another, otherwise the phases of B and A are compared with the phase of D, respectively, the last signal in the chronological order is determined at the end of these comparisons, and the other signals are then set to the phase angle of the last signal in said chronological order by changing the delay time of the delay element in accordance with the second method step. Its advantage is especially easy implementation. The device according to the invention can be used as a playback or recording device for optical recording media, such as CDs, CD-ROMs, CD-Is, CD-Rs, DVDs, DVD-ROMs, DVD-Rs, etc.

The various features of the invention may also be combined with each other as appropriate. Further advantages of the apparatus and method of the present invention will be apparent from the description that follows.

In the drawings:

FIG. 1 is a schematic view of an apparatus according to the present invention;

figure 2 shows a flow chart of a method pertaining to the present invention.

Fig. 1 schematically shows an apparatus according to the invention. A light beam generated by a light source 1 is irradiated onto an optical recording medium 4 through a half mirror 2 and an objective lens 3, reflected on the medium, and transmitted to the mirror 2 through the objective lens 3, refracted from the mirror to a detector 5. The detector 5 in the figure is represented both laterally (left side) and in a plane rotated by 90 ° (right side). This representation shows that the detector 5 is composed of four regions a, B, C and D.

The optical recording medium 4 is rotated by a motor M. On the optical recording medium 4 there are indentations, i.e. pits, arranged in spiral tracks. The objective lens 3 functions to focus the light beam onto the optical recording medium 4. For this purpose, a drive 6 can be used to adjust the distance from the objective lens to the optical recording medium 4. For tracking the track, which cannot be said to be the case, the drive 6 can move the objective lens 3 in a radial direction relative to the optical recording medium 4 for tracking purposes. For this purpose the tracking signal TS needs to be supplied to the driver 6.

The output signals of the regions a, B, C and D are supplied to delay elements 7, 8, 9 and 10, respectively. The delay times of the delay elements 7, 8, 9 and 10 are τ, respectively_A，τ_B，τ_CAnd τ_DTheir set values can be changed. This results in delayed signals a ', B', C 'and D' at the outputs of the delay elements 7, 8, 9 and 10, respectively. The signal is supplied to a circuit arrangementAnd 11, the two outputs 12 and 13 of which are supplied to a phase detector 14.

The signals a 'and C' are also supplied to a first adder 15, the output signal of which is supplied to the circuit arrangement 11. The signals B 'and D' are correspondingly supplied to the second adder 16, whose output signal is likewise supplied to the circuit arrangement 11. The output signals of the first adder 15 and the second adder 16 are also supplied to a third adder 17, the output signal of which represents the information signal HF. Further processing of the signal HF is not described in detail herein, since it is performed in a manner known to those skilled in the art.

The high frequency components of the signal present at the output 12 are supplied via a capacitor 18 to a converter 19. The analog input signal is converted by a converter 19 into a square wave signal having two possible states. Such a square-wave signal corresponds substantially to the information that "light is irradiated on the respective areas of the photodetector" or that "no light is irradiated on these areas", that is to say substantially to the analog input signal. This type of converter is also referred to as a "data slicer". Corresponding measures are also taken for the signal present at the output 13, which is passed through the capacitor 18 'and the converter 19'. The digitized signals from the converters 19, 19' are supplied to a phase comparator 20. If the phase angles of these input signals are the same, the output signal of the phase comparator is 0; if there is a phase shift, the output signal of the phase comparator 20 deviates from 0 in the positive or negative direction, the more the deviation, the larger the instantaneous phase shift of the input signal. The output signal of the phase comparator 20 is filtered by a low-pass filter 21, which in the present exemplary embodiment has a cut-off frequency of about 50kHz, and then is amplified by an amplifier 22 and output as a track error signal TE.

The signal TE is filtered by a further low-pass filter 23, the cut-off frequency of which is very low, in the exemplary embodiment about 10Hz, and the signal is then supplied to a microcontroller 24 as control means. The microcontroller 24 controls the circuit arrangement 11 via a line 25 and controls the delay elements 7 to 10 via a line 26. In the exemplary embodiment, line 25 is a three-bit data line, and line 26 is designed as a serial data line for transmitting a control signal having the required resolution for each delay element 7, 8, 9 and 10.

In the exemplary embodiment, circuit arrangement 11 is implemented as a multiplexer, which connects two by seven inputs to two outputs. To perform tracking, two input terminals a + C and B + D, each shown at the bottom in the figure, are connected to the output terminals 12 and 13, respectively.

Deviations of the light beam used for reading the optical recording medium 4 from the track center cause an asymmetric distribution of the diffraction pattern falling on the detector 5, which results in different phase angles of the signals a + C and B + D. The greater the degree to which the output signal TE deviates from 0, the greater the deviation of the beam from the track center and, consequently, the greater the shift in the phase angle of the signals a + C and B + D from each other. On the basis of which an adjuster (not shown) determines the desired tracking value and supplies it as signal TE to the driver 6.

The function of the delay elements 7 to 10 is to allow the signals emitted by the areas a, B, C and D to be adjusted in time with respect to one another. In this case, it is preferable to adjust from the detector signal which is chronologically leading to the last signal in the chronological order, with the relative phase shift between each other finally becoming 0 °. This results in a best quality signal source for the track error signal TE with minimal noise. This method for determining the track error signal TE is called the "differential phase detection" method (DPD). Since the delays to each other occurring in the respective areas a to D of the detector are determined by the depth of the tracks and the geometry of the optical recording medium and the linear scanning speed, which delays may be different for different types of optical recording media 4, the delay elements 7 to 10 are readjusted each time the optical recording medium is changed. The order of the detector signals occurring from regions a to D is also determined by this inexpensive phase detector 14 on the basis of the existing phase detector 14 which generates the track error signal TE from the sum signals a + C and B + D by the DPD method and automatically adjusts the delay elements.

The chronological order of the detector signals of the regions a to D with respect to one another is determined in such a way that: the signals a, B, C and D are compared with each other, from which the phase angles between them are determined. In order to be able to reliably determine the last occurring signal in chronological order, six combinations are required. These combinations are A and B, A and C, A and D, B and C, B and D and C and D. Depending on the position of the switch, the multiplexer of the circuit arrangement 11 can switch all said comparison combinations to the input of the phase detector 14. The average dc voltage component in the output signal of the phase detector 14 can be determined by means of an additional low-pass filter 23, which can also be implemented in the microcontroller 24, for example as an FIR filter. First all delay elements 7 to 10 are set to the smallest possible delay, i.e. τ_A＝τ_B＝τ_C＝τ_D0. If two input signals with different phase angles are supplied to the phase detector 14 and the average dc voltage component is measured at its output, a voltage deviating from 0 is generated, the positive and negative of which are determined by the phase angle. The phase angle decision can be made using a software comparator whose comparison level is 0 volts. The speed with which such interrogation is performed is fast, since the original purpose is simply to determine the chronological order of the detector signals of the areas a to D by alternating interrogation. There is no need to wait for the determination of the low-pass filter 23 at all. Only trends (greater or less than 0) need be identified here. After the last signal in the chronological sequence has been determined by means of software or a state machine in an appropriate form of alternative interrogation, the actual adjustment of the delay elements 7 to 10 is carried out in the microcontroller 24 of the present embodiment.

This adjustment process is as follows: since the last signal in time order has been determined, three consecutive steps can be used to move the other three leading signals to the last signal in time order. The criterion for successful motion is still the average of the outputs of the phase detector 14A direct voltage component. The chronologically leading signals are compared one after the other with the chronologically last signal and the delay time τ of each leading signal is increased until the average dc voltage component at the output of the phase detector 14 reaches the value zero. This operation is performed by microcontroller 24 comparing the voltage value to a software comparator at 0 volts. In this case, the microcontroller 24 can be used to adjust the delay times τ of the delay elements 7 to 10 continuously or in small steps_A，τ_B，τ_CAnd τ_D. After having shifted all signals such that their relative phase angles coincide with each other, the track error signal TE can be obtained from the sum of the signals a '+ C' and B '+ D'. The automatic adjustment method according to the invention has the advantage that the influence of the detector signals on the time relationship depending on the geometry of the optical disc and the geometry of the tracks, the type of optical disc, the manufacturing tolerances of the laser scanner, i.e. the optical device (1 to 5), and also on the linear velocity, i.e. the velocity of the optical recording medium at the current position of the light beam can be compensated.

In addition, with only a slight increase in the outlay (delay elements 7 to 10, circuit arrangement 11, and low-pass filter 23), it is possible to determine the temporal relationship between the detector signals of the regions a to D with a logic circuit or microcontroller 24 as shown in the figure and to shift the temporal relationship between the signals with the delay elements 7 to 10.

Fig. 2 shows a flow chart of a method for automatically adjusting the delay elements 7 to 10 that can be set. First all the delay times tau_A，τ_B，τ_CAnd τ_DIs set to zero. The phase angles of signals a and B are compared with each other in sequence. In this case the multiplexer is in the switching position shown. If signal a leads signal B, the left branch is taken, otherwise the right branch is taken. The lagging signals B and a are then in each case compared with the signal C. Viewed from the top of the circuit arrangement 11, this corresponds to the fourth and the second, respectivelyAnd switching the position. The signal determined to be lagging in the second comparison step is then compared with the signal D.

After this third comparison, it can be seen which signal is the last in time. In three successive steps, the delay times τ of the delay elements of the other respective signals are set_i. At the far left of fig. 2, the situation is shown where the signal D lags the most. First, τ is adjusted_AUntil the signals A' and D are in phase, and then τ is adjusted accordingly_BFollowed by_C. To the right in this case, the situation is shown where the signal C lags the most. In this case, the number τ is adjusted accordingly_A，τ_BAnd τ_D. To the right in this case, the situation is shown where the signal B lags the most, and to the rightmost side, the situation is shown where the signal a lags the most. After setting other three delay times tau_IAfter that, the switching position of the multiplexer of the circuit arrangement 11 is placed in the lowermost switching position shown in the figure. Thus, the summed signals a + C and B + D are supplied to the phase detector 14 to generate the track error signal TE. This completes the setting operation of the delay elements 7 to 10.

Claims (10)

1. An apparatus for reading from or writing to an optical recording medium (4), comprising:

a detector (5) having four regions (A, B, C, D) on which the light beam from the optical recording medium (4) impinges, at least two delay elements (7, 8, 9, 10) assigned to at least two of the four regions (A, B, C, D), and

a phase detector (14) for generating a track error signal (TE), which has at each input the sum signal of two of the regions (A, B, C, D) of the photodetector (5) and at the output of which a track error signal (TE) is available,

the method is characterized in that:

at least for one of the delay elements (7, 8, 9, 10), the delay time (τ) of at least one other delay element (7, 8, 9, 10) may be independent_A，τ_B，τ_C，τ_D) To set the delay time (tau) thereof_A，τ_B，τ_C，τ_D) And an

A control device (24) for controlling the delay time setting of the delay elements (7, 8, 9, 10) is connected to the respective delay element (7, 8, 9, 10).

2. A device according to claim 1, characterized in that a phase detection means for detecting the phase angle of the signal emitted by the area (a, B, C, D) of the photodetector (5) is connected to the respective area (a, B, C, D).

3. A device as claimed in claim 1, characterized by a circuit arrangement (11) for supplying variable combinations of its input signals to its outputs, the outputs of the regions (a, B, C, D) of the photodetector (5) being connected to the inputs of the circuit arrangement (11), and the outputs of the circuit arrangement (11) being connected to the inputs of said phase detector (14).

4. A device according to claim 3, characterized in that said phase detector (14) is a phase angle detector.

5. An apparatus according to claim 4, characterized in that said control means (24) is a microcontroller for receiving inputs from said phase detector (14) and providing control signals to said circuit means (11) and to said at least two delay elements (7, 8, 9, 10), controlling the circuit means (11) and controlling the settings of the delay elements (7, 8, 9, 10).

6. An apparatus according to claim 5, characterized in that a low-pass filter (23) is arranged between the output of the phase detector (14) and an input of said microcontroller.

7. Method for adjusting delay elements (7, 8, 9, 10) that can be set in a device for reading from and/or writing to optical recording media, the delay elements being assigned to specific regions (A, B, C, D) of a photodetector (5) of the device, the phase angles of the signals emitted by the respective regions (A, B, C, D) being compared in a first method step in order to determine the last occurring signal in chronological order, and the delay times (τ) of the delay elements (7, 8, 9, 10) being changed in a second method step_A，τ_B，τ_C，τ_D) Until the phase of all signals coincides with the last signal in time sequence, and these changes are delayed by a time (τ)_A，τ_B，τ_C，τ_D) Is determined as the best setting for the device.

8. A method as claimed in claim 7, characterized in that the delay elements (7, 8, 9, 10) which can be set are set to their respective minimum delay times (τ) before the first method step_i＝0)。

9. Method according to claim 7, characterized in that the signal phases of the regions A and B are first compared in a first method step, the signal phases of the regions B and C being compared if the phase of A leads the phase of B, and the signal phases of the regions A and C being compared otherwise; if the phases of B and A lead C, respectively, the phase angles of C and D are compared with one another, otherwise the phases of B and A are compared with the phase of D, the last signal in the chronological sequence is determined when the comparisons are ended, and the delay times (τ) of the delay elements (7, 8, 9, 10) are then varied by a second method step_A，τ_B，τ_C，τ_D) The other signals are set at the phase angle of the last signal in said time sequence.

10. A device according to claim 1, characterized in that the delay elements (7, 8, 9, 10) are assigned to at least three of the four regions.