Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Control of information signal processing channel
Reexamination Certificate
1999-09-08
2002-03-26
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Control of information signal processing channel
C369S053150
Reexamination Certificate
active
06363042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical disk drives, and more particularly, to an optical disk drive provided with means for preventing an inner reference clock signal from being disturbed due to a partial missing of a read reproduction signal caused by a defect on a disk medium.
2. Description of the Related Art
In optical disk drives for reproducing information recorded on a disk medium such as a DVD-ROM, in general, to extract data from a bit reproduction (RF) signal (clock signal mixed with data) read from the disk medium, an inner reference clock signal generated inside the optical disk drives is synchronized in phase and in frequency with the RF signal and the data is extracted with the use of a window signal formed from the inner reference clock signal.
In this case, such an optical disk drive is provided with a phase-locked loop (PLL) circuit having a voltage-controlled oscillator (VCO), a phase comparator, and a low-pass filter (LPF). In addition, a frequency comparator is also provided in order to speed up the synchronization of the PLL circuit to the RF signal and to adjust the inner reference clock signal so as to be always in the best condition. In this optical disk drive, when the frequency of a read RF signal varies, the frequency change is detected by the frequency comparator, a frequency error signal is sent to the PLL circuit, and the frequency of the inner reference clock signal is adjusted to the best condition. In this way, the synchronization of the inner reference clock signal with the RF signal is sped up and then data can be accurately extracted.
FIG. 3
is a block diagram showing an example structure of a main section of a known optical disk drive performing such an operation.
As shown in
FIG. 3
, this known optical disk drive is provided with a VCO
31
constituting a controllable free-running oscillator, a phase comparator
32
, an LPF
33
, a frequency comparator
34
, a data-latch circuit
35
, a window-signal generation section
36
, an RF-signal input terminal
37
, a data output terminal
38
, and an inner-reference-clock-signal output terminal
39
. In this case, the VCO
31
, the phase comparator
32
, and the LPF
33
form a PLL circuit
30
.
One input end of the VCO
31
is connected to the output end of the LPF
33
, the other input end is connected to the output end of the frequency comparator
34
, and the output end is connected to the input end of the window-signal generation section
36
and to the inner-reference-clock-signal output terminal
39
. One input end of the phase comparator
32
is connected to an RF-signal input terminal
37
, the other input end is connected to the output end of the VCO
31
, and the output end is connected to the input end of the LPF
33
. One input end of the frequency comparator
34
is connected to the RF-signal input terminal
37
and the other input end is connected to the output end of the VCO
31
. The latch end of the data-latch circuit
35
is connected to the output end of the window-signal generation signal
36
, the input end is connected to the RF-signal input terminal
37
, and the output end is connected to the data output terminal
38
.
The known optical disk drive having the above structure schematically operates in the following way.
The RF signal obtained by reading a disk medium is sent to the phase comparator
32
, the frequency comparator
34
, and the data-latch circuit
35
through the RF-signal input terminal
37
. The phase comparator
32
compares the inner reference clock signal generated by the VCO
31
with a clock signal included in the RF signal, generates a phase error signal indicating a phase difference therebetween, and sends it to the LPF
33
. The LPF
33
smoothes the phase error signal, converts it to a phase error voltage, and sends the voltage to the VCO
31
. The frequency comparator
34
compares in frequency the inner reference clock signal generated by the VCO
31
with the clock signal included in the RF signal, generates a frequency error signal indicating a frequency difference therebetween, and sends it to the VCO
31
.
In the VCO
31
, the phase of the inner reference clock signal is adjusted in response to the sent phase error voltage, and the frequency of the inner reference clock signal is adjusted so as to be a predetermined frequency in response to the sent frequency error signal. In this way, the inner reference clock signal output from the VCO
31
is adjusted so as to be synchronized in phase and in frequency with the clock signal included in the RF signal.
The inner reference clock signal output from the VCO
31
is sent to the inner-reference-clock-signal output terminal
39
, and is also converted to a window signal to be generated when data in the RF signal reaches, in the window-signal generation section
36
, and is sent to the data-latch circuit
35
. The data-latch circuit
35
reads the data when the window signal is sent, namely, when the data in the sent RF signal reaches, and sends the read data to the data output terminal
38
.
In the known optical disk drive, the PLL circuit
30
formed of the VCO
31
, the phase comparator
32
, and the LPF
33
synchronizes in phase the inner reference clock signal output from the VCO
31
with the clock signal included in the RF signal. In a closed control loop formed of the VCO
31
and the frequency comparator
34
, the frequency of the inner reference clock signal output from the VCO
31
is adjusted so as to promptly become equal to the frequency of the clock signal included in the RF signal.
When the known optical disk drive reads a disk medium having a defect described later, in other words, when the defective portion on the disk medium is read, such as a scrape and a scratch on the reading surface of the disk medium, a bit defect and a missing bit (interruption) on the bit recording surface of the disk medium, or a stain (black dot), such as that formed by a magic marker, which is stuck to the reading surface of the disk medium and does not reflect light, an RF signal having an inaccurate clock signal is output or an RF signal having no clock signal is output. Therefore, the frequency error signal output from the frequency comparator
34
becomes extremely large or extremely small, and the inner reference clock signal output from the VCO
31
has an inappropriate frequency largely deviated from the appropriate frequency. When the frequency of the inner reference clock signal output from the VCO
31
is largely deviated from the appropriate frequency, phase synchronization is not performed in the PLL
30
and the inner reference clock signal output from the VCO
31
becomes runaway.
Once the inner reference clock signal goes runaway, even when a normal RF signal having the clock signal arrives again when the defective portion on the disk medium has been read, it takes a long time for the inner reference clock signal output from the VCO
31
to have the appropriate frequency.
As described above, in the known optical disk drive, when a disk medium having a defect is read, the frequency of the inner reference clock signal output from the VCO
31
is temporarily deviated from the appropriate frequency greatly, and during that period, data in the RF signal cannot be read by the data-latch circuit
35
.
To solve this drawback, there has already been proposed a disk drive in which a missing portion of an RF signal is detected according to the envelope of the RF signal, and when the missing portion is detected, the frequency of the inner reference clock signal output from the VCO is maintained at the frequency used immediately before the missing portion is detected to prevent the frequency of the inner reference clock signal from being greatly deviated; and a disk drive, as disclosed by the Unexamined Patent Publication No. Hei-10-69734, in which the switching means is opened due to a missing detection signal obtained by detecting a missing portion of the RF signal to maintain the frequency of the inner reference clock signal output from the
Alps Electric Co. ,Ltd.
Hindi Nabil
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