Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-12-02
2001-06-05
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S047170, C369S047550, C369S053370, C369S059110
Reexamination Certificate
active
06243339
ABSTRACT:
The invention relates to a method and an device for writing user information on an optical record carrier. Marks representing the user information are written in a radiation-sensitive recording layer of the record carrier by means of pulses series of radiation. A pulse series comprises one or more pulses. Before recording user information on a record carrier, a test pattern is written onto the record carrier. The read signal obtained from this pattern provides information for optimizing the recording process, in particular the form of the pulse series. The user information is subsequently written onto the record carrier with the optimized process.
European patent no. 0 669 611 discloses such a method and device for optimizing the write power of the pulse series. The known device writes a test pattern on the record carrier, the test pattern consisting of a series of sub-patterns, each sub-pattern being written with a different radiation power. Subsequently, the jitter of the read signal corresponding to each sub-pattern is measured. The recording power is set at the value where the jitter versus power curve shows a minimum jitter. The jitter of a data signal is a measure for the deviation between the position of falling and/or rising edges of the data signal and corresponding transitions of a clock signal, possibly recovered from the edges of the data signal. The deviation may be normalized on the duration of one period of the clock signal.
However, the known method does not always provide optimum recording conditions, in particular when record carriers and devices of different manufacturers are interchanged.
It is an object of the invention to provide a recording device and method with an improved adaptation of the recording conditions to the combination of a particular device and record carrier.
This object is achieved when the device according to the invention comprises recording means for writing a pattern of optically readable marks on the record carrier by irradiating the record carrier with pulse series of radiation, a mark being formed by one pulse series, a test signal generator for generating a test signal comprising a test pattern and supplying the test signal to an input of the recording means, reading means for reading marks on the record carrier and supplying a read signal, a jitter detector for measuring jitter of the read signal corresponding to the test pattern and supplying a leading-edge jitter signal and a trailing-edge jitter signal, control means for supplying a first control signal and a second control signal in dependence on the leading- and trailing-edge jitter signal respectively, the values of the control signals corresponding to an optimum quality of the read signal, processing means for converting input information to be recorded into an output signal supplied to the recording means, the output signal corresponding to pulse series of radiation and representing the input information, each pulse series having a leading part and a trailing part, an optimum value of a first parameter relating to the leading part being determined by the first control signal and/or an optimum value of a second parameter relating to the trailing part being determined by the second control signal.
It has turned out that the known device is not always able to find optimum recording conditions because it uses the total jitter, i.e. the combined jitter of both the leading and trailing edges of the read signal. When the leading- and trailing-edge jitter are determined separately, it is possible to improve further the recording conditions. Since the leading-edge jitter is a measure of the accuracy of the leading edge position of a written mark in the recording layer, the measured leading-edge jitter is preferably used to influence this position. The position of the leading edge of a mark may be influenced by varying a first parameter of the leading part of the pulse series used for writing the mark. Likewise, the trailing-edge jitter is a measure of the accuracy of the trailing edge position of a written mark, and the trailing-edge jitter is preferably used for optimizing a second parameter of the trailing part of the pulse series. The recording conditions are said to be optimum if the number of errors in the recovery of the information recorded under these conditions is minimal.
In general information is represented on the record carrier by a set of different marks. If, for instance, the information is coded according to the so-called EFM, the set will comprise marks having lengths of 3, 4, . . . 11 times a unit length and possibly a synchronization mark of 14 unit lengths. An mark having a length of n times the unit length is called an nT mark. A single mark out of the set of different marks is written by a pulse series of a corresponding set of different pulse series. The length of a pulse series increases with increasing length of the mark to be written. In the optimization method according to the invention the leading part of at least one pulse series of the set of pulse series is optimized; likewise, the trailing part of at least one pulse series of the set is optimized. Both the leading and trailing part of a pulse series may be optimized according to the invention.
Preferably, the leading part of short pulse series is optimized, whereas the trailing part of long pulse series is optimized. The leading part and trailing part of pulse series of intermediate length may be optimized. The caesura between short and long pulses should be closer to the shortest than to the longest pulse series, because the relative change in length of written marks of increasing length is larger for shorter marks than for longer marks. The caesura for the EFM-coded information is preferably at the T4 or T5 pulse series. The separate optimization of pulse series of different lengths provides a very suitable method to improve the recording conditions.
The first or second parameter to be optimized may be the radiation power of the leading or trailing part of the pulse series, respectively. A pulse series may comprise one or more radiation pulses. When a pulse series has two or more pulses, the first or second parameter may be the pulse widths of a pulse in the leading or trailing part of the pulse series, respectively. Alternatively, the first or second parameter may be a time duration between two pulses in the leading or trailing part of a pulse series. A combination of different parameters for the leading and trailing part is also possible, e.g. the radiation power of the leading part and a pulse width of the trailing part. In a preferred embodiment of the device the first parameter is the power of the leading part and the second parameter is the power of a trailing pulse of a pulse series.
The device according to the invention preferably sets the power of the pulse series at an optimum value in dependence on a measured amplitude or total jitter of the read signal corresponding to a recorded test pattern. The power applies to those parts of the pulse series where the power is not affected by the first or second parameter. The measured amplitude may be converted to a modulation or a so-called asymmetry of the read signal in order to set the power.
The parameter to be optimized first in the method according to the invention should be the parameter which most strongly affects the other parameters. A preferred order for determining the optimum recording conditions is to write first a test pattern with varying values of the first parameter, e.g. the power of only the leading part of pulse series. The optimum value of the first parameter is determined from this pattern by measuring the leading-edge jitter of the read signal and determining the value of the first parameter corresponding to the minimum jitter. A second test pattern is recorded using the optimum power and the optimum value of the first parameter and varying the value of a second parameter, e.g. the power of the trailing pulse of a pulse series. The optimum value of the second parameter is determined from the trailing-edge jitter of the re
Duchateau Johan P. W. B.
Horikx Jeroen J. L.
Spruit Johannes H. M.
Blek Michael E.
Huber Paul W.
U.S. Philips Corporation
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