JPH0589551A - Transversal filter - Google Patents

Abstract

PURPOSE:To provide a transversal filter correcting the asymmetrical shape of a reproduced signal asymmetrical in the direction of time axis. CONSTITUTION:A first tap 12 outputting a signal corresponding to a reproduced signal obtained from a recording medium, a second tap 13 setting forward a certain amount of time with respect to the output signal of the tap 12 and outputting a signal corresponding to the reproduced signal, a third tap 14 setting back a certain amount of time with respect to the output signal of the tap 12 and outputting a signal corresponding to the reproduced signal, amplifiers 15 and 16 provided at the taps 13 and 14 and an adder 19 adding the outputs of the respective taps 12 to 14 are provided. The amplifiers 15 and 16 provided at the taps 13 and 14 have different amplification factors from each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transversal filter for equalizing the waveform of a reproduction signal obtained from a recording medium, and more particularly to a transversal filter suitable for equalizing the waveform of a reproduction signal in a magneto-optical recording / reproducing apparatus. -Regarding the monkey filter.

[0002]

2. Description of the Related Art Conventionally, there has been known a magneto-optical recording / reproducing apparatus for writing information on a recording medium by modulating the direction of a magnetic field according to a recording signal and turning on a laser beam by DC.

In such a magneto-optical recording / reproducing apparatus, the detected reproduction signal waveform is distorted due to band limitation due to the spot diameter of laser light, aberration of the optical system and the like.

Therefore, in order to correct the reproduced signal having such distortion, a waveform equalizing circuit has been conventionally used. This waveform equalizing circuit has a characteristic of emphasizing the high frequency part of the reproduced signal, and an LC filter, operational amplifier, or the like can be used as long as it has such a characteristic. A transversal filter that adds a time delay Δτ to a reproduction signal as shown in Fig. 6 to create an echo of the reproduction signal, weights the echo signal with a certain weight (hereinafter referred to as gain), and adds / subtracts to / from the true reproduction signal is used. .. Further, as the conventional transversal filter, a filter having the same gain of the echo signal to be added / subtracted to the true reproduction signal (hereinafter, referred to as a symmetrical transversal filter) has been used.

[0005]

However, even if the symmetrical transversal filter is applied to the reproduction signal processing system of the magneto-optical recording / reproducing apparatus of the magnetic field modulation recording system,
There is a drawback that sufficient waveform equalization cannot be performed.

Recording pits on the optical disc, on which information is recorded by the magnetic field modulation recording method, have an arrow-blade shape in which the leading edge portion and the trailing edge portion of the pit have different shapes, as shown in FIG. 5 (a). The waveform of the reproduced signal obtained from the pit has an asymmetrical shape in which the waveforms at the leading edge and the trailing edge are different in the time axis direction, as shown in FIG. 5B.

If the waveform of the reproduction signal is asymmetric, in the case of the pit edge recording system in which information is provided at the front and rear edges of the recording pit, that is, in the case of pit length recording, the reproduction signal is recorded with respect to the front and rear edges of the recording pulse. Since the front and rear edges are shifted non-uniformly in the front and rear, the edge interval changes, which makes it difficult to accurately detect information.

The asymmetrical shape of the reproduced signal waveform cannot be corrected even if the waveform is equalized using a conventional transversal filter.

[0009]

The present invention has been made in view of the above problems, and sufficient waveform equalization is performed even when applied to a reproduction signal processing system of a magneto-optical recording / reproducing apparatus of a magnetic field modulation recording system. It is an object of the present invention to provide a transversal filter capable of doing so.

The above object is to provide a first signal for outputting a signal corresponding to the reproduced signal in a transversal filter for equalizing the waveform of the reproduced signal obtained from the recording medium.
Of the output signal of the first tap and the output signal of the first tap, the output signal of the second tap that outputs a signal corresponding to the reproduction signal and the output signal of the first tap are delayed for a predetermined time. A second tap for outputting a signal corresponding to the reproduction signal, an amplifier provided for the second and third taps, and an adder for adding outputs of the respective taps, The amplifiers provided in the third tap are achieved by making the gains different from each other. In a transversal filter that equalizes the waveform of a reproduction signal obtained from a recording medium, a first tap that outputs a signal corresponding to the reproduction signal and a constant time for the output signal of the first tap. A second tap that outputs a signal corresponding to the reproduction signal that has advanced, and a third tap that outputs a signal corresponding to the reproduction signal that is delayed by a certain time with respect to the output signal of the first tap. An amplifier provided in each of the second and third taps and an adder that adds outputs of the taps are provided, and the second tap and the third tap are provided.
Each of the amplifiers provided in the taps has gain adjustments that can be independently adjusted.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings.

FIG. 1 shows a magneto-optical recording / reproducing apparatus to which the transversal filter of the present invention is applied.

In FIG. 1, 1 is an optical disk which is an information recording medium, 2 is a spindle motor for rotating the optical disk 1 at a predetermined number of revolutions, and 3 is information on the optical disk 1 using laser light. Is an optical head for recording or reading the information recorded on the optical disk 1. Reference numeral 4 denotes a head amplifier that amplifies a signal from an optical sensor incorporated in the optical head 3, 10 reduces intersymbol interference of a reproduction signal from the head amplifier, and the waveform of the reproduction signal is a target waveform in the time axis direction. A transversal filter (hereinafter referred to as an asymmetrical transversal filter) which is a waveform equalizing circuit for achieving the above. 6 is a binarization circuit for converting the analog signal waveform of the output signal of the transversal filter into a digital signal of "1" and "0", 7 is a CPU, 8 is a recording signal,
A flying magnetic head for switching the polarity of the magnetic field applied to the optical disk 1, and 9 is a magnetic head driver for supplying a current according to a recording signal to a coil wound around the core of the floating magnetic head.

Next, an embodiment of the transversal filter of the present invention is shown in FIG. 2 and the operation principle thereof will be described.

Shown here is a 3-tap transformer.
It is a monkey filter. In FIG. 3, reference numeral 11 is an input end of the reproduction signal, 12 is a center tap for outputting a signal in the same state as the reproduction signal input from the input end 11 (a signal having the same waveform and amplitude), and 13 is the center. A first reproduction signal obtained by advancing the tap output signal for a predetermined time.
Left tap that outputs the signal processed with the gain of 14
Is a second delay of the reproduction signal delayed from the output signal of the center tap for a certain period of time, which is different from the first gain.
Light tap that outputs the signal processed with the gain of 15
Is an amplifier having the first gain provided in the left tap, 16 is an amplifier having the second gain provided in the right tap, and 17 delays a reproduction signal between the center tap 12 and the left tap 13. Delay circuit,
Reference numeral 18 is a delay circuit for delaying the reproduction signal between the center tap 12 and the write tap 14, 19 is an adder, 2
0 is an output terminal. The gains of the amplifiers 15 and 16 are 0 or more and 1.0 or less and are negative gains.

First, by using a delay line, the input reproduction signal is recorded for the time (shortest interval recording) of 1/2 (Δτ = 1/2 × 1 / fmax) of the reciprocal of the maximum recording frequency (fmax) of the recording signal. The recording pit detection time interval when the pit is played back). (For example, 2T for a 1-7 random signal, 3T for a 2-7 random signal; T is the channel rate of the recording code). The setting of this delay time is most effective when a transversal filter is applied to the waveform of the reproduction signal when reproducing the pits recorded on the magneto-optical disk based on the recording code of the modulation method having a random time length. It is the time interval to leave.

The left tap and right tap amplifiers on both sides with respect to the center tap are provided with different independent gains, and the signal is added to the center tap signal by the adder 19. And this adder 19
The output signal is output from the output end 20, and the waveform equalization ends. The gains of the left-tap and right-tap amplifiers can be adjusted independently of each other. The gain takes into consideration the amount of jitter after waveform equalization (the amount of deviation of the edge of the reproduction signal from the recording pulse on the time axis). Set to the optimum value.

Next, FIG. 3 (a) shows the result of showing the relationship between the gain of the taps on both sides (left and right) and the jitter after waveform equalization with respect to the center tap of the 3-tap asymmetrical transversal filter by contour lines. Here, the horizontal axis shows the gain of the left tap and the vertical axis shows the gain of the right tap, and the gain of each tap is changed from -0.6 to 0.6. Here, the smaller the jitter, the more appropriate the transversal filter. The mark * is the lowest point on the contour line and the lowest jitter.

From this, the smallest jitter was obtained when the gain of the center tap was 1.0, the gain of the left tap was -0.200, and the gain of the right tap was -0.125.

From this, it is understood that the asymmetrical transversal filter is most suitable for the waveform equalizing circuit of the reproduced signal in the magneto-optical recording / reproducing apparatus of the magnetic field modulation recording system. Further, the asymmetry of the recording pits is clear from the fact that the recording pits are tear-shaped even in the optical modulation recording system, and the asymmetric transversal filter is effective also in the optical modulation recording system.

Although the present invention has been described in the above embodiment using a 3-tap transversal filter, a configuration having more taps may be used.

In the above embodiment, the center tap is not provided with an amplifier, but an amplifier may be provided.

[0023]

As described above, in the asymmetrical transversal filter of the present invention, with respect to the asymmetrical waveform obtained by reproducing the arrow blade-shaped pits and the tear-shaped pits which are the recording pits peculiar to the magneto-optical recording, Not only can the conventional waveform interference be reduced, but it can also be corrected to a symmetrical reproduced waveform. As a result, both edges of the reproduced waveform can be accurately detected.

[Brief description of drawings]

FIG. 1 is a diagram showing a magneto-optical recording / reproducing device to which an asymmetric transversal filter of the present invention is applied.

FIG. 2 is a block diagram showing an embodiment of an asymmetric transversal filter of the present invention.

FIG. 3 is a diagram showing the relationship between left and right tap gains and jitter of the asymmetric transversal filter of the present invention.

FIG. 4 is a block diagram showing a conventional symmetrical transversal filter.

FIG. 5A is a diagram showing a shape of a recording pit formed by a magnetic field modulation recording method. 5B is a diagram showing a reproduced waveform obtained from the recording pit shown in FIG.

Claims (3)

[Claims] 1. A transversal filter for equalizing a waveform of a reproduction signal obtained from a recording medium, wherein a first tap and a first tap for outputting a signal corresponding to the reproduction signal.
Corresponding to the reproduction signal delayed by a predetermined time with respect to the output signals of the second tap and the first tap, which outputs a signal corresponding to the reproduction signal advanced by a predetermined time with respect to the output signal of the tap A third tap for outputting the signal, an amplifier provided for the second and third taps, and an adder for adding the outputs of the respective taps, and provided for the second tap and the third tap. The transversal filter is characterized in that the amplifiers have different gains from each other. 2. A transversal filter for equalizing a waveform of a reproduction signal obtained from a recording medium, wherein a first tap and a first tap for outputting a signal corresponding to the reproduction signal.
Corresponding to the reproduction signal delayed by a predetermined time with respect to the output signals of the second tap and the first tap, which outputs a signal corresponding to the reproduction signal advanced by a predetermined time with respect to the output signal of the tap A third tap for outputting the signal, an amplifier provided for the second and third taps, and an adder for adding the outputs of the respective taps, and provided for the second tap and the third tap. The transversal filter is characterized in that the respective amplifiers can adjust the gain independently. 3. The maximum recording frequency (fmax) of the information according to claim 1, wherein the fixed time is
Is set to 1/2 of the reciprocal of (Δτ = 1/2 × 1 / fmax).