JPS61177683A - Signal processing circuit in record information reading device - Google Patents

Abstract

PURPOSE:To make it possible to deal with lowering of an EFM signal amplitude due to stain caused by fingerprint on a disk by inhibiting control of switching means due to detection output obtained by detecting the disk defect part based on the read signal amplitude during the reproduction mode. CONSTITUTION:A comparator 1 converts EFM signals into TTL level and supplies converted signals through a switch circuit 2 to the succeeding stage processing circuit while also supplying them to an LPF 3. It extracts low range component and inputs it to the comparator 1 as reference signals. The EFM signals are also supplied to a disk defect detecting circuit 4, and the output of which is inputted to the switch circuit 2 through a switch circuit 5 to turn the switch 2 on and off. The switch 5 is ON in the state other than the play state but it is turned OFF during play in accordance with control signals indicating that the device is in the play state so as to inhibit the control of the switch circuit 2 due to detection output of the detecting circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 disc or the like.

BACKGROUND TECHNOLOGY In digital audio discs, etc., the audio signal is PCM (Pulse Code ModulaN).
The pulse train signal is digitized and recorded using a modulation method such as E F M (E 1oht to F
The signal is suitable for recording using the teenager modulation method.

E read from this digital audio disc
FM signal (read signal) 9゛ As a circuit for signal processing,
Conventionally, the device shown in FIG. 1 has been known. In the figure, the EFM signal read from the disk becomes the comparison input of comparator 1. Comparator 1 converts the EFM signal to T
This is for converting to TL 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 (
It is also supplied to low pass filter) 3. The LPF 3 takes out the low frequency component of the output signal of the comparator 1 and uses it as a reference input to the comparator 1. This comparator 1 and LP
F3 level-slices the signal waveform read from the disk and EFM modulates the NRZ I (Non
Return To Zer.

A waveform shaping means for returning the signal to an Inverted ) signal is configured.

The EFM signal read from the disc is also supplied to a detection circuit 4 that detects missing portions of recorded information on the disc based on the amplitude of the signal. As the detection circuit 4, for example, one having a structure 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 (r
1A release) state.

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, and the detection circuit 4 generates a detection output to switch the switch circuit 2. The output signal of comparator 1 is set in the off state and the passage of the output signal of comparator 1 is prohibited. In other words, on the mirror surface of the disc or between recording tracks during a search,
This prevents the noise component of the EFM signal from swinging the reference voltage of the comparator 1 and sending an erroneous EFM signal 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 playback mode, if there is dirt on the disc, problems may occur depending on the type of dirt. There are cases.

For example, if the disc is smudged with fingerprints,
As shown in FIG. 2, since the amplitude of the EFM signal becomes small at the dirty portion, the detection circuit 4 generates a detection output that detects the dirty portion as a missing portion of recorded information. 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 disc.

In the case of dirt caused by fingerprints, the EFM signal component remains in that area, so normal sound can be reproduced even if the EFM signal is passed through as is.However, in conventional circuits, this area is also treated as a missing area of recorded information. Since the structure was such that the EFM signal was completely cut off during the period T, the sound could not be corrected and the sound would become ``no'', ``a'', and ``z''.

11 Moxibustion"L The present invention has been made in order to eliminate the drawbacks of the conventional ones as described above, and is a method for reading recorded information 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 is to provide a signal processing circuit in a device.

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

Example 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 the figure, parts equivalent to those in FIG. 1 are given the same reference numerals. In the figure, the connection between the switch circuit 2 and the detection circuit 4 is normally in an on (open) state, and the recording information reading device is in a playback state.
Off (open) in response to a control signal indicating that playback mode is in progress
A switch circuit 5 is provided which prohibits control of the switch circuit 2 by the detection output of the detection circuit 4 when the detection circuit 4 is in the state.
Other than that, the configuration is the same as that shown in FIG. 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. And while playing (can also include pauses)
In this case, the switch circuit 5 is turned off in response to a control signal indicating that play is in progress, and by prohibiting the control of the switch circuit 2 by the detection output of the detection circuit 4, the amplitude of the EFM signal is Even if the voltage decreases, the signal is allowed to pass through the switch circuit 2 as is.

Here, the factors that cause the amplitude of the EFM signal to decrease during play are: ■ Scratches on the disc protective surface (acrylic surface) ■ Scratches on the disc signal surface ■ Dirt due to fingerprints, etc. on the disc protective surface ■ Air bubbles, etc. on the disc protective surface mentioned. Among these, except for the above ■, usually EF
Since the time for the amplitude of the M signal to decrease is short, this will hardly disturb the reference level of the comparator 1, and its influence can be eliminated by lowering the band of the LPF 3. Also, the incorrect EFM caused by this
The signal will be supplied to another signal processing circuit in the next stage, but since the time width is sufficiently short, the error can be reliably corrected as in the case of the conventional circuit. EFM signal components remain in the fingerprint area, and EFM
By allowing the signal to pass through as is, the data can be read correctly and normal sound 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, stable operation can be achieved in all modes such as search, startup, and play. It is possible to obtain the state.

In addition, in the above embodiment, only error correction for a disk with stains such as fingerprints was explained, but in the case of a scratched area E.
If the FM signal disappears, the spindle servo will naturally be disturbed, which will further worsen the situation. Therefore, during play, the EFM signal is passed through as is, and during searches, for example, the detection circuit is controlled by a control signal that activates a servo switch. The detection output of No. 4 is controlled, that is, the switch circuit 5 is controlled.

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.

1.11 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 the control is configured to prohibit the control, it is possible to sufficiently cope with a decrease in the amplitude of the EFM signal due to dirt such as fingerprints on the disk.
A stable state can be obtained in all modes.

[Brief explanation of the drawing]

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, and Fig. 3
The figure is a block diagram showing one embodiment of the present invention, and FIG.
FIG. 2 is a circuit diagram showing a specific configuration of the switch circuit 5 in the figure. Explanation of symbols of main parts 1... Comparator 2.5... Switch circuit 4... Detection circuit

Claims (1)

[Claims] a 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; A signal processing circuit in a recorded information reading device, comprising a detection means for detecting, and a switch means for passing an 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 when the recorded information reading device is in a reproduction mode.