Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Control of information signal processing channel
Reexamination Certificate
2000-12-27
2004-10-19
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Control of information signal processing channel
C369S059210, C369S124050
Reexamination Certificate
active
06807134
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for recording/reproducing digital information by using an information carrier, and more particularly to a technique for detecting jitter or asymmetry in a reproduced signal obtained from the information carrier.
BACKGROUND OF THE INVENTION
A type of recording/reproduction apparatus which is capable of recording/reproducing digital information onto/from a removable recording medium is known in the prior art. An optical disk having a recording layer made of a phase change medium or a magneto-optical medium is widely used as the information carrier (or the recording medium).
For example, when digital information is recorded onto an optical disk having a phase change medium by using laser light, the optical disk is irradiated with laser light having a waveform as illustrated in FIG.
16
A. As a result, marks are formed on the optical disk as illustrated in
FIG. 16B
, each having a length associated with the length of the corresponding piece of the recorded digital data. The marks recorded on the optical disk are read out by using laser light, thus producing a continuous analog signal as a reproduced signal, as illustrated in FIG.
16
C. The reproduced analog signal is sliced at a predetermined level lv so as to be converted into a digital signal as illustrated in
FIG. 16D
, from which the original digital information is reproduced.
However, the shape of marks formed on the recording medium may vary due to the individual difference among different apparatuses or the individual difference among different recording media even if the digital information is recorded by using laser light of the same laser power and the same pulse waveform. A shift in the shape of a mark from the intended shape would result in a shift in the waveform of the reproduced analog signal and that of the converted digital signal from the intended waveforms, thereby degrading the quality of the reproduced signal. Thus, in the prior art, recording/reproduction apparatuses have a problem in that the quality of the reproduced signal from the recording medium may vary substantially for different apparatuses or recording media.
In order to prevent such degradation in reliability of the reproduced signal, the recording/reproduction apparatus performs a test recording operation or a calibration operation upon loading of the recording medium, for example. More specifically, the recording/reproduction apparatus records data having a known pattern in a predetermined area on the recording medium and reproduces the recorded data to measure the signal quality thereof. The recording/reproduction apparatus optimizes the characteristics of the reproduction system or the parameters relating to the recording operation (recording parameters) based on the measured signal quality.
The quality of a reproduced signal is determined based on, for example, the error rate and the jitter (fluctuations of the reproduced signal along the time axis). The recording/reproduction apparatus optimizes the characteristics of the reproduction system or the recording parameters so as to minimize the error rate and the jitter in the reproduced signal.
Particularly, in the case of a recording medium onto which information is recorded with heat by using laser light, or the like, heat interferences occur between adjacent recording patterns. As a result, the shape of a mark formed on the medium is likely to be different from the intended shape. When recording information onto such a recording medium, it is necessary to set the optimal recording parameters for the individual recording patterns.
The recording parameters include those varying in the direction of the time axis such as the recording pulse width and those varying in the direction of the reproduced signal amplitude such as the recording power as illustrated in FIG.
16
A. Jitter can be used to evaluate those parameters which vary in the direction of the time axis of the recording pulse, whereas asymmetry in the reproduced signal can be used to evaluate those parameters which vary in the amplitude direction. When the recording power is not appropriate, there occurs asymmetry in the reproduced signal.
The structure of a conventional optical disk recording/reproduction apparatus which calibrates the recording parameters by using jitter and asymmetry in a reproduced signal will now be described with reference to
FIG. 12
to FIG.
14
.
As illustrated in
FIG. 12
, reflected light from an optical disk
1
is converted by a photodiode, or the like, in a pickup portion of an optical head
2
into an electric signal, thus reproducing an analog signal which corresponds to digital information recorded on the optical disk
1
. The obtained reproduced signal is subjected to a waveform shaping operation by a waveform equalizer
3
. The waveform-shaped reproduced signal is sliced at a predetermined level Vc by a digitization circuit
4
which includes a comparator
15
(see FIG.
13
), etc. Thus, the reproduced signal is converted into a continuous digital or binary signal.
The digital signal output from the digitization circuit
4
is input to a PLL (Phase Locked Loop) circuit including a phase comparator
5
, an LPF (Low Pass Filter)
6
and a VCO (Voltage-Controlled Oscillator)
7
, and a reproduction clock signal is produced in the PLL circuit. In the phase comparator
5
, the input digital signal and a clock signal output from the VCO
7
are compared with each other, thus detecting a phase error therebetween. The detected phase error is averaged by the LPF
6
which includes a capacitor, and the like, so as to be converted into a voltage for driving the VCO
7
. Thus, by varying the driving voltage for the VCO
7
according to the value of the phase error, a feedback control is performed on the oscillation frequency of the VCO
7
so that the phase error output from the phase comparator
5
approaches zero. In this way, it is possible to produce a reproduction clock signal which is in synchronization with the digital signal.
Even when a PLL circuit is used so that a reproduction clock signal in synchronization with the digital signal is output from the VCO
7
, as described above, a phase error still occurs between the digital signal and the reproduction clock signal due to the length of the recorded mark differing from the ideal length. A jitter detection circuit
11
integrates absolute values of phase errors output from the phase comparator
5
for a predetermined period of time or for a predetermined number of zero-crossing points so as to calculate a jitter amount. The jitter amount is calculated for each of the individual recording patterns.
The calculated jitter amount is transferred to a recording parameter setting circuit
12
. The recording parameter setting circuit
12
determines whether a recording parameter such as the recording pulse width is appropriate based on the jitter amount which is input thereto. When it is determined that the recording parameter is not appropriate, a more appropriate recording parameter is estimated and output to a recording compensation circuit
9
.
The recording compensation circuit
9
converts a recording pattern obtained from a pattern generation circuit
8
into a pulse waveform by using the recording parameter output from the recording parameter setting circuit
12
. A laser driving circuit
10
records digital information onto the optical disk
1
according to the obtained pulse waveform. Then, the recorded digital information is reproduced again to determine a jitter amount as described above. The recording/reproduction apparatus continues to optimize the recording parameter until it is determined that the jitter amount is less than or equal to a predetermined level in the recording parameter setting circuit
12
.
Next, a case where the calibration operation is performed based on asymmetry in a reproduced signal will be described.
FIG. 13
illustrates the structure of a conventional asymmetry detection section.
FIG. 14
illustrates an example of a reproduced signal which has asymme
Konishi Shinichi
Miyashita Harumitsu
Nakajima Takeshi
Takahashi Toshihiko
Akin Gump Strauss Hauer & Fled, L.L.P.
Matsushita Electric - Industrial Co., Ltd.
Tran Thang V.
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