Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal gain processing
Utility Patent
1998-03-20
2001-01-02
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal gain processing
C369S124140, C369S124080
Utility Patent
active
06169716
ABSTRACT:
The present invention relates to a device for reading from and/or writing to optical recording media which has a data slicer for generating a digital output signal from an analogue input signal.
A device of this type is disclosed for example in “The art of digital audio”, J. Watkinson, Focal Press, ISBN 0-240-51270-7, in particular page 464. In this known device, the data slicer comprises a comparator, to one of whose inputs the analogue input signal is applied, to whose other input a comparison signal is applied and whose output signal is the digital output signal. The comparison signal is generated from the digital output signal by a comparison signal generating unit. For this purpose, the said output signal is fed to an integrator having a relatively long time constant. If the analogue input signal has, on average, a 50% distribution between positive and negative regions, that is to say the high and the low phases of the digital output signal are likewise represented equally often on average over time, then the comparison signal remains essentially constant. If, on the other hand, the analogue input signal has a shift in the positive or negative direction, a so-called DC voltage offset component, then the ratio of the high to the low components of the digital output signal deviates from 50%. The integrator increases or reduces the comparison signal until a corresponding 50% value is reached again. This known device may be regarded as having the disadvantage that relatively long desired deviations from a 50% distribution, that is to say a relatively long so-called maximum run length, likewise lead to a change in the comparison signal. This means that only a specific maximum duration of the high and of the low phases is possible if reliable and error-free functioning of the data slicer is to be achieved. Lengthening of this maximum period of time must be accompanied by an increased time constant of the integrator, in order not to provoke an excessively fast change in the comparison signal. The consequence of this is that the comparison signal is changed only relatively slowly, as a result of which- actual interference, for example a DC voltage offset, caused for example by the reflectivity of the recording medium being changed on account of soiling, can no longer be followed rapidly enough by the data slicer. This would lead to errors in the digital output signal.
An object of the present invention is to develop a device wherein as far as possible optimum functioning of the data slicer is ensured at any time, independently of the maximum run length in the analogue input signal.
According to the invention, this object is achieved by means of the features noted below. According to the invention, the comparison signal is changed as a function of a temporal shift between the digital output signal and the clock signal. To that end, it is preferred to compare specific edges of the respective signals. This has the advantage that the value of the comparison signal is changed not as a direct function of the digital output signal but as a function of the comparison between digital output signal and clock signal. The two signals should have a constant shift with respect to one another when there is no DC voltage offset on the analogue input signal. In other words, edges of the analogue output signal should occur simultaneously with edges of the clock signal or with a constant shift with respect thereto, the analogue output signal generally having a much lower number of edges than the clock signal. Consequently, a device according to the invention enables greater run lengths in the analogue input signal without this having adverse effects on the digital output signal. Consequently, it is advantageously possible to use the device according to the invention also to read from and/or write to novel optical recording media which operate for example according to the DVD standard, that is to say which have greater run lengths of the channel data in comparison with previous recording media. In this case, the pulse generating device can compare for example the rising and falling edges of the digital output signal with one type of edges of the clock signal, that is to say rising or falling edges, in which case the time between the edge of the output signal and that of the clock signal should be the same both for rising and for falling edge of the output signal. In this case, it is ensured that the output signal is free from a DC voltage offset.
The pulse generating device preferably has controllable switching elements which connect the output thereof to a first or a second reference voltage for the duration of a difference between digital output signal and clock signal. In this case, the reference voltages are advantageously the positive and negative supply voltages, but any other suitable reference voltages can likewise be employed in a device according to the invention. This has the advantage that the comparison signal is changed only when the time durations of the difference between the phases of clock signal and output signal are not identical. In general, however, this time duration is significantly shorter than the positive or negative components or run lengths of the digital output signal, with the result that only a slight variation occurs particularly with long run lengths.
The pulse generating device is preferably designed as a phase comparison device, which carries out a phase comparison between analogue output signal and clock signal, similarly to the above-described comparison effected as a function of the edges, as a function of the analogue output signal. This has the advantage that even in the event of edges of the respective signals which optionally deviate to a great extent from the ideal shape, a phase comparison of these signals is nevertheless possible in a specific interval. Such an interval begins, for example, at a zero crossing of the analogue output signal and ends at the next positive zero crossing of the clock signal. Other, optionally longer, suitably selected intervals are also possible according to the invention.
According to the invention, the pulse generating device has a data output unit, which generates a synchronized data signal from the digital output signal and the clock signal. This has the advantage that relative shifts of the edges of the digital output signal in comparison with the clock signal are compensated for, which shifts may be caused for example by slight fluctuations, for example in the comparison signal. An even more uniform data signal is generated in this way.
The invention furthermore provides for the data signal and the digital output signal to be compared with one another. This has the advantage that the data signal, which likewise contains the clock information of the clock signal, can be used for comparison and, consequently, the data output unit is used doubly. Furthermore, a particularly low circuitry outlay for phase comparison can be attained in this way.
The comparison signal generating unit preferably has an integrator. This has the advantage that the input signal of the comparison signal generating unit is integrated and, consequently, relatively small fluctuations are averaged out. Nevertheless, a DC voltage offset possibly present in the input signal leads to a change in the comparison signal which lasts until the DC voltage offset has been compensated for.
The invention provides a switching device by means of which the digital output signal can be applied to the input of the comparison signal generating unit. This has the advantage of enabling a changeover from the pulse generating device to the output signal in the case of a signal of the pulse generating device which is unsuitable or affected by interference. Such an unsuitable signal may be present for example in the absence of a clock signal or in the event of a clock signal affected by severe interference. However, it is completely within the scope of the invention to perform such a changeover in the case of other circumstances being present, too, for example in dependence
Deutsche Thomson-Brandt GmbH
Hindi Nabil
Kiel Paul P.
Tripoli Joseph S.
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