JPH03154270A - Noise reduction device - Google Patents

Abstract

PURPOSE:To improve the error rate performance of the system by providing a means compressing noise within a prescribed level range in the vicinity of zero cross in a reproduction signal in an information reproducing device. CONSTITUTION:A noise compression circuit 20 and an amplifier 21 are added to a conventional information reproduction device. The circuit 20 sets a noise compression window in the vicinity of zero cross with respect to an output signal of an LPF 11 to compress noise. The width of the window is set so that a voltage V2 is adjusted by a variable resistor VR1 thereby adjusting an idle current flowing through a series connection path comprising a resistor R2, diodes D2, D1 and a resistor R1 through the use of a voltage V1 depending on resistors R5, R6 in a way of sufficiently exceeding a slice level Vs in a level comparator 13. Thus, the production of noise in the reproduction signal is suppressed and the error rate performance of the system is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information reproducing device such as an optical disk device,
The present invention relates to a noise reduction device that reduces the probability of occurrence of extra pulses and improves error rate performance.

[Prior Art] As a conventional magneto-optical disk device, one having the configuration shown in FIG. 8 is known.

This magneto-optical disk device includes a magnet 2 that applies a magnetic field to an optical disk 1, a spindle motor 3 that rotates the optical disk 1, an optical pickup 4 that reads information from the optical disk 1, and an in-phase amplifier 5 and a differential amplifier that amplify reproduced signals. 6, a changeover switch (switching 5W) 7 for selecting these amplifiers 5.6, a changeover timing section 8 for controlling this changeover switch 7, and an SM signal detection section 9 for detecting a sector mark signal. . optical disc 1
The playback signal from the is divided into a preformat signal and a data signal as described below,
By the operation, the signal amplified by the in-phase amplifier 5 is selected as the preformat signal, and the signal amplified by the differential amplifier 6 is selected as the data signal.

Furthermore, this magneto-optical disk device further includes a differential amount 10 for differentiating the amplified signal from the changeover switch 7, and a low-pass filter 1 for cutting high-frequency noise components of this differential signal.
1, a zero cross comparator 12 that takes the zero cross of this filter output signal, a level comparator 13 that detects the level of the filter output signal, and a delay element 1 that sequentially delays the output signal of this level comparator 13.
4.15 and an OR circuit 1 that takes the logical sum of these delayed signals.
6, this OR output and the zero cross comparator 12
A NAND circuit 17 which calculates the AND with the zero-cross signal of , and outputs the inverter signal; It has a delay element 19 that is reset after a certain period of time.

FIG. 9 is a timing chart showing signal waveforms of each part in the above configuration.

This magneto-optical disk device converts the amount of reflected light from the optical disk l into an analog electrical signal as shown in the figure (■), and converts this analog signal into a digital Z signal by the waveform shaping process shown in the figures (■ to ■) with the above configuration. Convert to digitized signal.

[Problems to be Solved by the Invention] However, in the conventional example described above, the slice level of the level comparator 13 for converting the analog playback signal into a digital binary signal is set to a predetermined fixed potential Vs. When a level signal equal to or higher than the slice level VS is input, the level comparator 13 operates to output a Z-valued digital signal without distinguishing between the original signal and noise.

Therefore, for example, as shown in (■) in FIG. 10, an extra pulse may be generated depending on the state of the logic level in the undefined region (■ in FIG. 10) of the output signal of the zero-cross comparator 12.

Magneto-optical disks, like so-called compact disks, have a preformat signal section that is detected by the intensity of the amount of light reflected from the disk, and a card that rotates the plane of polarization of the amount of light reflected from the disk depending on the direction of magnetization of the magnetic film of the disk. The signal of the data signal part is very weak compared to the signal of the preformat part, and generally has a poor S/N ratio.

However, on the other hand, since the playback circuit has a common block that converts the analog playback signal into a digital binary signal, the data signal processing section (described above) is used to align the weak data signal with the level of the preformat signal. It must be amplified by a differential amplifier 6) to a level that has a sufficient margin with respect to the threshold level VS of the level comparator 13.

However, in this case, it is desired to increase the signal level as much as possible by amplification and maintain sufficient stability with respect to the level comparator 13, but when the signal level is amplified, the level of the noise component also increases with the same degree of amplification. Therefore, in general, in the case of a magneto-optical disk device with a weak data signal with a poor S/N ratio, the probability of occurrence of the above-mentioned extra pulse becomes significant, and the error rate worsens.

Furthermore, when attempting high-density recording on an optical disk, there are limitations due to the size of the beam diameter determined by the reproduction laser beam in the optical pickup and the optical head. Code amount interference occurs, and the level of the reproduced signal is lower than that of a portion without interference.

Therefore, in order to achieve high-density recording, especially in a magneto-optical disk device, it is necessary to avoid an increase in the noise level due to the processing of the above-mentioned weak signals with a poor S/N ratio, and a decrease in the signal level due to code amount interference. Due to both factors, the slice level of the level comparator cannot be uniquely determined, making it difficult to obtain an optimal slice level.

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise reduction device that can suppress the probability of noise occurrence in a reproduced signal, reduce the occurrence of extra pulses, and improve the error rate performance of the system.

[Means for Solving the Problems] The present invention is characterized in that an information reproducing apparatus is provided with means for compressing noise within a predetermined level range in the vicinity of zero crossing in a reproduced signal.

[Function] In the present invention, since a means for compressing noise within a predetermined level range near the zero crossing in the reproduced signal is provided, low level noise components near the zero crossing can be removed, reducing the probability of occurrence of extra pulses. , it is possible to improve the error rate performance of the system.

[Example] FIG. 1 is a block diagram showing one embodiment of the present invention.

The reproducing device according to this embodiment has a noise compression circuit 20 and an amplifier 21 newly added to the configuration of the conventional example shown in FIG. 8, and the other configurations are the same as the conventional example. Therefore, the same reference numerals are given and the explanation is omitted. Note that, in FIG. 1, the configuration before the low-pass filter 11 is omitted.

The noise compression circuit 20 sets a noise compression window of a predetermined width in the vicinity of the zero crossing for the output signal of the low-pass filter 11, and compresses noise that falls within the width of this window.

Further, the amplifier 21 is for restoring the signal level lowered by the noise compression circuit 20.

FIG. 2 is a timing chart showing the signal conversion processing process in the above configuration.

In this embodiment, compared to the conventional process shown in FIG. 9 above, [stock] and
As shown in the figure, by cutting the window range set in the noise compression circuit 20, noise in this range is removed. The width of the window is determined by the level comparator 13.
The slice level VS is set to sufficiently exceed the slice level VS. Therefore, for example, if there is a noise component higher than the slice level Vs in the region @ in Figure 1, the probability of it becoming an extra pulse is high in the past, but in this embodiment, the noise component within the window width is It will not be detected due to noise compression. As shown by @ in Figure 1, noise exceeding the window width cannot be removed and becomes extra pulses, but the number of extra pulses is significantly smaller than when no noise compression processing is performed.

FIG. 3 is a circuit diagram showing a specific configuration of the noise compression circuit 20. As shown in FIG.

The noise compression window width described above is
By adjusting the voltage v2, from the voltage v1 determined by the resistors R5 and R6, the resistor R2 diodes D2, DI
, and can be set arbitrarily by adjusting the idle current flowing through the series connection path of the resistors R1.

FIGS. 4A and 4B are schematic diagrams showing the relationship between idle current and noise compression window width.

As shown in the figure, the smaller the idle current, the larger the noise compression window width can be.

Also, the signal path starts from the emitter of transistor Q+ and passes through capacitor CO to diode D1 and capacitor C.
1, the path is transmitted from the base of transistor Q2 through the emitter to the next stage amplifier 21, and the path from the emitter of transistor Q1 to the capacitor Co
There are two routes for transmitting the signal: passing through the series connection of the diode D2 and the capacitor C2, and passing from the base to the emitter of the transistor Q2 to the next stage amplifier 21.

FIG. 5 is a schematic diagram showing the relationship between the resistors R1 to R4 and the idle current, and FIG. 6 is a circuit diagram schematically showing the path of the idle current.

The voltage v3 is set according to the following relationship, v, , v2
The relationship between Ml)V3>V2 and fX is as follows.

V3 = R3Vl / (R3+Ra)
+R4V2 / (R3+R4) Also, resistors R1 to R4 become the input impedance of the signal source when viewed from the emitter of transistor Q1, so R
If the combined resistance of 1-R4 is set to be small, the contrast between the signal component compressed by the front-stage noise window width and the signal component not compressed can be set to be larger.

FIG. 7 is a schematic diagram illustrating a signal waveform in comparison with a conventional waveform when a defective area of a noise-limited disk is reproduced by a magneto-optical drive device actually equipped with the device of this embodiment.

When this embodiment is applied as shown in FIG. 7(B), low-level noise components are compressed by noise compression, and the slice of the level comparator 13 is compared to the conventional case shown in FIG. 7(A). The probability of occurrence of noise exceeding the level can be reduced.

As described above, according to the present embodiment, before the processing by the level comparator 13, the noise compression circuit 20 compresses the noise within the noise window width, and the signal level is restored to the level before passing through the noise compression circuit 20. By setting the noise window width to be equal to or higher than the slice level of the level comparator 13, the probability of occurrence of noise exceeding the slice level of the level comparator 13 is suppressed, and the probability of occurrence of extra pulses is reduced. It is possible to improve the error rate performance of the system.

[Effects of the Invention] As explained above, according to the present invention, since a means for compressing noise within a predetermined level range in the vicinity of the zero cross in the reproduced signal is provided, the following effects can be obtained. .

(1) The probability of extra pulse occurrence is reduced and error rate performance is improved. This is particularly effective in magneto-optical disk drives where the SZN ratio of the reproduced signal is poor.

(2) Significant performance improvement is possible with a small number of parts and increased cost.

(3) It is the removal of low-level noise components and does not violate the band limit by filters, etc., so the signal quality does not deteriorate. Especially in magneto-optical disk devices, the ratio of defective sectors in the disk can be reduced. .

(4) It is versatile because the range of noise compression can be set arbitrarily.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a timing chart showing the signal processing process in the same embodiment. FIG. 3 is a circuit diagram showing a specific configuration of the noise compression circuit in the same embodiment. FIGS. 4(A) and 4(B) are schematic diagrams showing the relationship between the idle current and the noise compression window width in the same embodiment. FIG. 5 is a schematic diagram showing the relationship between resistance and idle current in the same embodiment. FIG. 6 is a circuit diagram schematically showing the path of the idle current in the same embodiment. FIGS. 7(A) and 7(B) are schematic diagrams illustrating signal waveforms when an optical disk is actually reproduced by a magneto-optical drive device equipped with the device of the embodiment, in comparison with conventional waveforms. FIG. 8 is a block diagram showing a conventional example of a magneto-optical disk reproducing apparatus. FIG. 9 is a timing chart showing the signal processing process in the conventional example. FIG. 10 is a timing chart showing a case where an actual noise signal is included in the signal processing process shown in FIG. 1... Optical disc, ? ... Magnet, 3... Spindle motor, 4... Optical pickup, 5... Common mode amplifier, 6... Differential amplifier, 7... Switching SW, 8... Switching timing section, 9 ... SM signal detection section, 10 ... Differentiator, 11 ... Low pass filter, 12 ... Zero cross comparator, 13 ... Level comparator. 14.15.19...Delay element, 16...OR circuit. 17.-N A N 0 circuit, 18...D flip flow rough. 20... Noise compression circuit, ・21... Amplifier.

Claims (2)

[Claims] (1) A noise reduction device for an information reproducing device, characterized in that it is provided with means for compressing noise within a predetermined level range in the vicinity of zero crossings in a reproduced signal. (2) In claim (1), the information reproducing device has a reproducing circuit that detects the peak position of the reproduced signal by a detection means using a differentiating circuit, and in this reproducing circuit, the peak position of the reproduced signal is detected based on a predetermined slice level. 2
A noise reduction device characterized in that the above noise compression means is provided at the input stage of a level comparator that generates a valued digital signal.