JPH0364949B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a signal processing circuit in a recorded information reading device, and more particularly to a signal processing circuit that processes a read signal read from a digital audio disk or the like.

Background Art In digital audio disks and the like, audio signals are digitized using a modulation method such as PCM (Pulse Code Modulation), converted into pulse train signals, and recorded. This pulse train signal is, for example, EFM (Eight to Fourteen
Modulation method makes the signal suitable for recording.

A circuit shown in FIG. 1 is conventionally known as a circuit for signal processing of an EFM signal (read signal) read from a digital audio disk. In the figure, read from disk
The EFM signal becomes the comparison input of comparator 1.
Comparator 1 is for converting the EFM signal to TTL level. The output signal of the comparator 1 is supplied to another signal processing circuit (not shown) at the next stage via the switch circuit 2, and is also supplied to the LPF
(Low pass filter) 3 is also supplied. LPF3
extracts the reduced component of the output signal of comparator 1 and uses it as a reference input to comparator 1. Comparator 1 and LPF 3 level-slice the signal waveform read from the disk and perform EFM modulation of NRZI (Non Return To Zero).
A waveform shaping means is configured to return the signal to an Inverted) signal.

The EFM signal read from the disk is also supplied to a detection circuit 4 that detects missing portions of recorded information on the disk based on the amplitude of the signal. As the detection circuit 4, for example, one having a configuration comprising means for envelope-detecting the EFM signal and means for generating a detection output when the output level of the means is smaller than a predetermined reference level can be used. The detection output of this detection circuit 4 is supplied to the switch circuit 2,
The switch circuit 2, which is normally on (closed), is turned off (open).

In such a configuration, since no information is recorded on the mirror surface of the disk or between recording tracks during a search, the EFM signal disappears.
Therefore, the detection circuit 4 generates a detection output, turns off the switch circuit 2, and prohibits passage of the output signal of the comparator 1. In other words, EFM
This prevents the noise component of the signal from causing the reference voltage of the comparator 1 to swing, causing an erroneous EFM signal to be sent to the next stage signal processing circuit, thereby preventing the circuit from malfunctioning.

Conventional circuits configured in this way work effectively during searches, but during normal play (playback mode), if the disc gets dirty, problems may occur depending on the type of dirt. This may occur. For example, if the disc is smeared with fingerprints, the smeared area will
Since the amplitude of the EFM signal becomes smaller, the detection circuit 4
determines this dirty portion as a missing portion of recorded information and generates a detection output. In this case, the period T during which the amplitude of the EFM signal decreases corresponding to the range of the fingerprint is quite long and far exceeds the error correction length of the digital audio disk. In the case of dirt caused by fingerprints, EFM is applied to that area as well.
Since the signal component remains, normal sound can be reproduced even if the EFM signal is passed through as is, but in the conventional circuit, this part is also judged as a missing part of the recorded information and the EFM signal is completely transmitted during period T. Since the structure was designed to block out the sound, it had the disadvantage that the sound could not be corrected and turned into noise.

SUMMARY OF THE INVENTION The present invention has been made to eliminate the drawbacks of the conventional devices as described above, and provides a recorded information reading device that can sufficiently cope with a decrease in the amplitude of the EFM signal caused by dirt such as fingerprints on the disk. The purpose of the present invention is to provide a signal processing circuit for use in a computer.

The signal processing circuit in the recorded information reading device according to the present invention is configured to prohibit control of the switch means by the detection output obtained by detecting the missing portion of the recorded information on the disk based on the amplitude of the read signal in the reproduction mode. ing.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals. In the figure, there is a connection between the switch circuit 2 and the detection circuit 4, which is normally on (closed) and turned off (open) in response to a control signal indicating that the recorded information reading device is in play (reproduction mode). A switch circuit 5 is provided that prohibits control of the switch circuit 2 by the detection output of the detection circuit 4.
Other than that, the configuration is the same as that shown in FIG. As the switch circuit 5, for example, an analog switch can be used.

In this configuration, the switch circuit 5 is in an on state in states other than play, such as searching, starting, and stopping the recorded information reading device, and performs the same operation as the conventional circuit shown in FIG. During play (which may include pauses), the switch circuit 5 is turned off in response to a control signal indicating that the play is in progress, and the switch circuit 2 is prohibited from being controlled by the detection output of the detection circuit 4. Even if the amplitude of the EFM signal decreases due to dirt on the disk due to fingerprints or the like, the EFM signal is allowed to pass through the switch circuit 2 as is.

Here, factors that cause the amplitude of the EFM signal to decrease during play include scratches on the disc protective surface (acrylic surface), scratches on the disc signal surface, stains on the disc protective surface due to fingerprints, air bubbles on the disc protective surface, etc. Among these, except for the above, the time for the amplitude of the EFM signal to decrease is usually short, so
This hardly disturbs the reference level of the comparator 1, and its influence can be eliminated by lowering the band of the LPF 3. Additionally, the erroneous EFM signal caused by this will be supplied to other signal processing circuits in the next stage, but since the time width is sufficiently short, it is possible to reliably correct the error as in the case of conventional circuits. be. In the above case, the EFM signal component remains in the fingerprint area, and by passing the EFM signal as is,
Data can be read normally and normal sounds can be reproduced.

In this way, by appropriately selecting the control of the switch circuit 2 based on the detection output of the detection circuit 4 using the switch circuit 5 according to the operation mode of the recorded information reading device, the control of the switch circuit 2 can be controlled in all modes such as search, startup, and play. A stable state can be achieved.

In the above embodiment, only error correction on a disk with dirt such as fingerprints was explained, but if the EFM signal in the area of the scratch disappears, the spindle servo will naturally be disturbed, which will further worsen the condition. During a play, the EFM signal is passed through as is, and during a search or the like, the detection output of the detection circuit 4, that is, the switch circuit 5 is controlled by a control signal that activates a servo switch, for example.

Further, in the above embodiment, the switch circuit 5 has an analog switch configuration, but as shown in FIG. 4, it may be replaced with a transistor Q that grounds the output line of the detection circuit 4 in response to a control signal.

Effects of the Invention As explained above, according to the signal processing circuit according to the present invention, during play, the switching means is activated by the detection output obtained by detecting the missing portion of recorded information on the disc based on the amplitude of the EFM signal. Since it is configured to prohibit control, it can sufficiently cope with a decrease in the amplitude of the EFM signal due to dirt such as fingerprints on the disk, and a stable state can be obtained in all modes. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a waveform diagram of an EFM signal in a portion of the disk contaminated with fingerprints, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. Switch circuit 5 in
FIG. 2 is a circuit diagram showing a specific configuration. Description of main parts, 1... Comparator, 2, 5
...Switch circuit, 4...Detection circuit.

Claims (1)

[Claims] 1. Waveform shaping means for shaping the waveform of a read signal from a recording disk on which predetermined information has been subjected to a predetermined digital modulation process and pulsed and recorded; and a waveform shaping means for shaping the waveform of a read signal from a recording disk on which predetermined information has been subjected to predetermined digital modulation processing and pulsed recording; and based on the amplitude of the read signal, a missing portion of the recorded information on the recording disk A signal processing circuit in a recorded information reading device, comprising a detection means for detecting the waveform shaping means, and a switch means for passing the output signal of the waveform shaping means except when a detection output of the detection means is generated. A signal processing circuit in a recorded information reading device, characterized in that the signal processing circuit includes prohibition means for prohibiting control of the switch means by the output of the detection means in a reproduction mode.