MXPA99000332A - Apparatus for reading or writing optist registrar carriers - Google Patents

Abstract

The present invention relates to a device for reading from or writing to optical recording media, which uses the "Differential Phase Detection Method" for tracing. This method has deficiencies if the optical recorders that are to be used have different pit depths. The object of the present invention is to propose a device of this type that can also be used with the aforementioned optical recording means 4. The object is achieved by virtue of the fact that delay elements 7, 8, 9, 19 are arranged between the photodetector 5 and the phase detector 14. The device according to the invention is used as a player or recorder for media optical recorders such as, for example, CD, CD-ROM, CD-I, CD-R, DVD, DVD-ROM, DVD-R, e

Description

APPARATUS FOR READING OR WRITING OPTICAL RECORDING CARRIERS The present invention relates to a device for reading from and / or writing to optical recording media according to the preamble of Claim 1. A device of this type is disclosed in US 4,497,048. In this known device, there is provision of a photodetector that is divided into four areas. Tracking information is obtained by combining the signals of two areas in each case to form a summation signal and by determining a phase difference between the first and second summation signal such that it is not necessary to obtain the amplitude of the reproduced signal. This device works satisfactorily when the optical recording medium to be read has a well defined and constant geometry of the information carrier layer. In particular, it is necessary that the depressions in the information carrier layer that serves to store information, the so-called pits, have a constant depth in relation to the wavelength of the light used for operation d? read.

What is disadvantageous with the known device is the fact that only slight variations in the geometry of the pits are tolerated, and that major deviations lead to errors in the formation of the tracking information. The result of this is that high error figures occur during the reading of the optical recording medium, or, in the extreme case, such reading becomes completely impossible.

The object of the present invention is to improve the known device to the extent that it can be used without any of the problems even if the optical recording means have a different depth of pit or pit geometry. According to the invention, this is achieved by virtue of the fact that a delay element is assigned to at least one of the areas of the photodetector. This has the advantage that the areas of the photodetector can be temporarily adjusted in relation to one another. Since the photodetector receives an interference pattern that is caused by the pits arranged in the optical recording medium and can vary depending on the disk geometry and the trace geometry (pit depth, etc.), on the disk type and In manufacturing tolerances and also in the aging of the laser scanner, the temporal relationship between the detector signals also varies. The temporal adjustment of the detector signals in relation to one another which is possible according to the invention allows variations of this type to be compensated. The temporal adjustment can in this case be carried out by means of a single delay element assigned to an area of the photodetector. However, a better fit is significantly possible if a delay element is assigned to a plurality, or to each of the areas. Maximum flexibility is possible if a delay element is assigned to each of the areas. If a delay element is assigned to all but one of the areas, then all the areas provided with a delay element can be adjusted to that area without a delay element. It is also possible to combine the areas into groups, to assign a delay element to each group and to adjust the groups in relation 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 elements can be regulated externally, for example during the production of the device or when a service is given to the device. The invention provides the presence of control means to regulate the delay time of the delay element or elements. This has the advantage that the delay elements can be adjusted at any time. For example, the adjustment can be made after each insertion of a new optical recording medium, at specific time intervals, for example during brief interruptions in the reproduction or writing operation of an optical recording medium, or at intervals that are suitably defined in a different manner. One possibility of adjustment consists of establishing fixed delay times that are matched to the type of optical recording medium. The type of recording medium is in this case defined by pit depth or pit geometry, trail width or similar characteristic properties. What is involved here are the well-known audio CD media or the new optical recording media that have a high recording density (called DVD). It is also possible to vary the delay times in a type of "trial and error method" with respect to the initial settings and to retain the new value when the tracking behavior becomes better. If the tracking behavior becomes worse, the delay times are restored to the previous regulation. Provision has also been made to provide a means of phase detection to detect the phase angle of the signals emitted by the photodetector areas. This has the advantage that the adjustment is possible in an optimum manner since the exact angle of the phase is determined and, consequently, the delay times of the delay elements can be regulated exactly. A further refinement of the invention provides provision of a circuit arrangement for applying a combination of the output signals of the areas to a phase angle detector. This has the advantage that the phase angles of the individual signals are evaluated by a single phase angle detector in which the signals from the individual areas of the photodetector are successively passed to the phase angle detector via the circuit array. The circuit arrangement, for example a multiplexer, is advantageously installed in the device, with the result that the phase angle can be determined internally. Alternatively, this is advantageous for an external determination of the phase angle since in this case no unnecessary high margin is required to make contact. The circuit arrangement is advantageously connected by a control means, for example a microcontroller. According to the invention, it is also possible for the connection to be carried out according to a specific time cycle or in a different way by a clock with trigger. An advantageous development of the invention consists in the fact that the phase detector of the angle is the phase detector of the device. This has the advantage that an additional component is not necessary, and that the functional groups of the device that are present in any case are optimally used. In a development of the invention, provision has been made to use a microcontroller which controls both the circuit arrangement and the regulation of the delay time of the delay elements. This has the advantage that the control is carried out by means of a component that can be integrated in a cost-effective manner and can be flexibly adapted to changes in the boundary conditions. A logic circuit can also be advantageously used instead of a microcontroller.

An advantageous development of the invention consists in arranging a low pass filter at the output of the phase detector. This has the advantage that an average DC signal is emitted in this way, consequently allowing the automatic regulation of the delay time even if the light beam scanning the optical recording medium is not following a trace. The pulses of light incident on the detector do not have to originate from a data trail in this case; they can equally well be the signals that occur during the random crossing of the trails. In this way, a quick regulation of the delay times is possible before the current reproduction or when the registration operation begins. Since the phase detector is not required in any case for tracking during this time, a change between the tracking functions and the phase adjustment of the delay elements is also unnecessary. The adjustment of the delay elements of the device according to the invention which are possible to be regulated is advantageously achieved according to the method described in Claim 8. This has the advantage that the phase differences caused by the properties of the component they are compensated in a simple and affordable way. After the method has been carried out, the device is provided with optimally adapted regulations which are retained until, if appropriate, a necessary or desirable renewed adjustment. Not only can the method described during production be used for the purpose of optimum regulation of the device, it may also be employed for the purpose of adjustment during the operation of said device. The latter case can be carried out either manually, for example during the service, or automatically, for example at specific time intervals. Provision has been made for regulation of those delay elements that can be regulated at a minimum delay time prior to the first step of the method according to the invention. This has the advantage that the delay elements of the area with the chronologically last signal need not be altered, and that the maximum possible range is available for those other delay elements. The method according to the invention can also advantageously be employed if a trace is not actually being followed. In this case, the pulsations of the light striking the detector give randomly crossed traces. However, this is not important for the regulation of the delay times by the method according to the invention, since the chronological sequence of the signals of the individual detector elements in the case of a rotary recording medium but with the circuit The still open tracking regulator is virtually identical to the case of a closed regulator circuit. Optimal adjustment of delay times can be carried out by means of the method according to the invention even before the closing of the tracking regulating circuit, and this is something that significantly facilitates the subsequent closure of the tracking regulator circuit since they are not required wrong signals for this purpose. Claim 10 describes an embodiment of the method according to the invention which has the advantage of being particularly simple to execute. The device according to the invention is used as a player or recording device for an optical recording medium such as, for example, CD, CD-ROM, CD-I, CD-R, DVD, DVD-ROM, DVD-R, etc. The features cited in the individual claims can also be advantageously employed in combination with one another. Additional advantages of the device according to the invention and of the method according to the invention can be inferred from the following description. In the figures: Fig. 1 shows a diagrammatic illustration of a device according to the invention, Fig. 2 shows a flow diagram related to the method according to the invention. Fig. 1 diagrammatically illustrates the device according to the invention. A light source 1 generates a beam of light that passes through a semitransparent mirror 2 and a lens 3 lens to fall on the optical recording medium 4, from where it is reflected and passes through the objective of the lens 3 to the mirror 2, from where it is diverted towards the detector 5. The detector 5 is illustrated both in side view (on the left) and in a plan view rotated 90 ° (on the right). This illustration reveals that the detector 5 consists of four areas A, B, C and D. The optical recording medium 4 is forced to rotate by means of a motor M. Depressions, called pits, are arranged in a spiral trace on the recording medium 4. The objective of the lens 3 serves to focus the beam of light on the optical recording medium 4. For this purpose, its distance from the optical recording medium 4 can be adjusted by means of an impeller 6. To follow the trace, that is to say for the purpose of tracing, the objective of the lens 3 can be displaced by the impeller 6 in the radial direction with respect to the optical recording means 4. A tracking signal TS is applied to the impeller 6 for this purpose. The output signals of the areas A, B, C and D are fed to the delay elements 7, 8, 9 and , respectively. The delay elements 7, 8, 9 and 10 have delay times tA, tB, Xc, and tD, respectively, which can be regulated variably. The delay signals A ', B', C and D 'are then present at the output of the delay elements 7, 8, 9 and 10, respectively. Said signals are fed to a circuit arrangement 11 whose two outputs 12 and 13 are fed to a phase detector 14. The signals A 'and C are additionally fed to a first add circuit 15, whose output signal is fed to the array circuit 11. The signals B 'and D' are correspondingly fed to a second adder circuit 16, whose output signal is similarly supplied to the circuit arrangement 11. Additionally, the output signals of the first addiver circuit 15 and the second addor circuit 16 are supplied to a third adder circuit 17, whose output signal represents the information signal HF. The further processing of the HF signal is not described here in greater detail since this is carried out in a manner known to a person skilled in the art. The high frequency component of the signal present at the output 12 is fed via a capacitor 18 to a converter 19. This converter 19 converts the analog input signal to a square wave signal having two possible states. This square wave signal essentially corresponds to the information "light is striking the corresponding areas of the photodetector" or "light is not incident on these areas", this to say corresponds essentially to the analog input signal. Converters of this type are also referred to as "data slicers". The same applies correspondingly to the signal present in the output 13, whose signal passes through the capacitor 18 'and the converter 19'. The digitized signal emitted by the converters 19, 19 'is fed to a phase comparator 20. If the phase angle of these input signals is identical, then the output signal of the phase comparator is 0; if a phase change is present, then the output signal of the phase comparator 20 deviates from 0 in the positive or negative direction, specifically to a greater degree, the greater is the temporal phase change of the input signals. The output signal of the phase comparator 20 is filtered by means of a low pass filter 21, the cutoff frequency which is about 50 kHz in the embodiment of the example, and, having been amplified by means of an amplifier 22, is an erroneous TE trace signal output. The TE signal is filtered in an additional low pass filter 23, whose cut-off frequency is significantly lower, approximately 10 Hz in the embodiment of the example, and is fed to a microcontroller 24 which serves as control means. The microcontroller 24 controls both the circuit array 11 via a line 25 and the delay elements 7 through 10 via a line 26. In the embodiment of the example, line 25 is a "tri-bit" data line (three-bit ), while line 26 is designated as a line of serial data that transmits a control signal having the resolution required for each delay element 7, 8, 9 and 10.

In the embodiment of the example, the circuit arrangement 11 is realized as a multiplexer that connects seven times seven inputs to two outputs. For the purpose of tracking, the inputs A + C and B + D each illustrated in the lower part of the drawing are connected to outputs 12 and 13, respectively. A deviation of the light beam, which is read by the optical recording medium 4, from the center of the trace causes the diffraction pattern incident on the detector 5 to assume an asymmetric distribution, as a result of which the signals A + C and B + D They differ according to their phase angles. The output signal TE deviates from 0 to a greater degree, the greater the deviation of the light beam from the center of the trace and consequently the change in the phase angles of the signals A + C and B + D in relation to at each other. A controller (not illustrated here) determines a desired tracking value therefrom, which is sent as the signal TS to the impeller 6. The delay elements 7 to 10 are provided so as to allow the signals emitted by the areas A, B, C and D to be temporarily adjusted in relation to one another. In this case, it is favorable to chronologically adjust the conductive signals of the detector to the respective chronologically last signal, with the result that the relative phase change with respect to one another is 0 °. The best signal source quality with the minimum noise is then obtained for the tracking error signal TE. The cited method for determining the tracking signal error TE is called the method (DPD) "Differential Phase Detection". Since the delays that occur to the individual areas A to D of the detector in relation to one another depend on the depth of trace and the geometry of the optical recording medium as well as the linear scanning speed, which may vary for different Types of optical recording media 4 The delay elements 7 to 10 are adjusted again each time the optical recording medium is changed. Starting from the existing phase detector 14 to generate the trace error signal TE by means of the DPD method from the summing signals A + C and B + D, the phase detector 14 is similarly used, with small margin to determine the order of the detector signals that appear from areas A to D and to automatically adjust the delay elements. The chronological order of the detector signals from areas A to D in relation to one another is determined as follows: signals A, B, C and D are compared with each other in order to be able to hit their phase angles with respect to one another. Six combinations are necessary to be able reliably to guess the signal that appears last in chronological order. The combinations are A and B, A and C, A and D, B and C, B and D and also C and D. The multiplexer of the circuit arrangement 11 allows all the comparisons of the mentioned combinations to be connected to the inputs of the phase detector 14, depending on the position of the switch. The average DC voltage component of the output signal from the phase detector 14 can be determined with the aid of an additional low pass filter 23, which for example can also be realized in the microcontroller 24, for example as an FIR filter . All delay elements 7 to 10 are first regulated to the smallest possible delay, that is tA = tB = tc = tD = 0. If two input signals having a different phase angle are then passed to the phase detector 14 and the average DC voltage component and the consequent output is measured, a voltage deviation from zero is produced which is positive or negative depending on the phase angle. The decision concerning the phase angle can be made, for example, by means of a comparator program, the comparison level of which is 0 volts. Since it is initially attempted to determine only the chronological order of detector signals from areas A to D by an alternate interrogation, interrogation can be performed very quickly. It is not necessary to wait for the settlement of the low pass filter 23. It is only necessary to identify the trend (greater than or less than 0). After the chronologically last signal has been determined by means of an alternate interrogation in an appropriate way, by program or by a state machine, in the microcontroller 24 in the embodiment of the example, the actual adjustment of the delay elements 7 to 10 is carried out. This adjustment proceeds as follows: since the chronologically last signal has already been determined, it is easily possible, in three successive steps, to change the other three, conductive signals to the chronologically last signal. The criterion for satisfactory change is once the average DC voltage component at the output of the phase detector 14. The conductive signals are chronologically compared one after the other with the chronologically last signal and the delay time t of the respective signal conductive is increased until the average DC voltage component at the output of the phase detector 14 reaches the value zero. This operation is carried out with the help of the microcontroller 24, being compared the values of voltage with a comparator program to 0 volts. The delay times X, XB / XC and XD of the delay elements 7 to 10 can in this case be adjusted continuously or in small steps by the microcontroller 24. When all the signals have been changed in such a way that their relative angles of phase coincide, the trace error signal TE is obtained from the sums of the signals A '+ C and B' + D '. The automatic adjustment method according to the invention has the advantage of compensation for influences in the temporal relationship between the signals of the detector, which depends on the disk geometry and the trace geometry, the disk type, the manufacturing tolerances of the laser scanner, this is of the optical device (1 to 5), and also of the linear speed, that is the speed of the optical recording medium at the site where the light beam is generally located.

In addition, it is possible, with a small additional margin (delay elements 7 to 10, circuit arrangement 11 and low pass filter), with the inclusion of a logic circuit or, as illustrated, a microcontroller 24, to determine the temporal relationship between the detector signals of the areas A to D and changing the temporal relationship between the mentioned signals by means of delay elements 7 to 10.

Fig. 2 shows a flow diagram of the method for automatically adjusting the delay elements 7 to 10 that are in aptitude to be regulated. After the start, all the delay elements xA, XB C and XD are set to zero. The phase angles of signals A and B are subsequently compared with each other. The multiplexer is in this case in the switch position shown. If signal A conducts signal B, then the left branch is taken, otherwise the right branch is taken. In each case, the lagged signal B and A, respectively, is then compared to the signal C. This corresponds to the fourth and the second switch position, respectively, of the circuit arrangement 11 from above. The signal that is determined to be a lag in this second comparison step is subsequently compared to the signal D. After this third comparison, it is evident which signal is the most lagged in time. In three successive steps, the delay times Xi of the delay elements of other respective signals are regulated. In the far left part in Fig. 2 this is illustrated for the case where the signal D is the most lagged. xA is the first of all adjusted until the signals A 'and D are in phase, then xB and, subsequently to it, xc are correspondingly adjusted. To the right of this, the case where the signal C is the most lagging is illustrated. In this case, xA, xB, and D are adjusted accordingly. To the right of this, the case is illustrated where the signal B is the most lagging and, far to the right, the case where the signal A is the most lagging. After three other respective time delays Xi have been regulated, the multiplexer of the circuit arrangement 11 is set to its interrupt position which is illustrated as the lowest interruption position in the display. Consequently, the summing signals A + C and B + D are fed to the phase detector 14 to generate the trace error signal TEA. The regulating operation of the delay elements 7 and 10 is thus concluded.

Claims (11)

1. A device for reading from or writing to optical recording media, having a detector, which has four areas and on which a beam of light comes from the optical recording medium, delay elements, which are apt to be adjusted and be assigned to two. of the four areas and a phase detector, to whose inputs the summation signals of in each case two of the areas of the photodetector are present and to which output a trace error signal can be taken, characterized in that at least one of the elements Delay can be regulated independently of the others.

2. A device according to claim 1, characterized in that a control means for regulating the delay element or elements is present.

3. A device according to Claim 1, characterized in that a phase detection means for detecting the phase angles of the signals emitted by the areas of the photodetector is present.

4. A device according to Claim 1, characterized in that a circuit arrangement for applying a variable combination of the output signals from the areas of the photodetector to a phase angle detector is present.

5. A device according to Claim 4, characterized in that the phase angle detector is the phase detector of the device.

6. A device according to Claim 5, characterized in that a microcontroller is present, which controls the circuit arrangement and the regulation of the delay elements.

7. A device according to Claim 5, characterized in that a low pass filter; it is arranged at the output of the phase detector.

8. A method for adjusting delay elements, which are apt to be regulated, of a device for reading from and / or writing on optical recording media, whose delay elements are assigned to specific areas of the photodetector of the device, in a first step of the method the phase angle of the signals emitted by the individual areas are compared, and in a second step of the method the delay times of the delay elements are altered until the phases of all the signals coincide with the chronologically last signal, and these altered delay times are retained as optimized regulated values of the device.

9. A method according to Claim 8 in which the delay elements that are able to be regulated are regulated at a minimum delay time equal to zero prior to the first step of the method.

10. A method according to Claim 8 in which the phases of the signals of the areas A and B are first of all compared in the first step of the method and, if the phase of A leads to that of B, the phases of the signals of areas B and C are compared, otherwise those of A and C are compared; if the phase of B and A, respectively, leads to that of C, then the phase angles of C and D are compared with each other, otherwise the phase of B and A, respectively, is compared with that of D, the chronologically last signal is evident at the end of these comparisons, the other signals are then adjusted to the phase angle of said chronologically last signal by altering the delay time of the delay elements according to the second step of the method.

11. A device according to Claim 1, characterized in that a delay element is assigned to at least three of the four areas.