JPH03160645A - Signal processing circuit for magneto-optical recording device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording device, and more particularly to an F5 processing circuit for reproducing recorded information.

[Conventional technology]

So-called magneto-optical recording records information based on the direction of magnetization of a magnetic film. The coercive force HC required to reverse the magnetization of the magnetic film decreases as the temperature rises. By utilizing this principle, a laser beam is focused on a magnetic film to perform magnetization reversal and record news. The direction of magnetization is determined by the direction of the externally applied magnetic field, and the direction of external magnetic elevation is reversed when information is erased and recorded.

To reproduce the news recorded on the magnetic film, a laser beam having a lower intensity than the laser beam used for recording is used. When a single straight laser beam is directed anti-J1-1 onto the magnetic film, the plane of polarization of the reflected laser beam rotates depending on the direction of magnetization on the surface of the magnetic film. This is called the magnetic Kerr effect and is due to the interaction between light and magnetism. The plane of polarization of the linearly polarized laser beam reflected by the magnetic film is rotated by θk clockwise or counterclockwise depending on the direction of magnetization. θk is called Kerr rotation or angle, and is generally very small, less than 1 degree. Recorded information is reproduced by electrically detecting changes in force and rotation angle.

FIG. 5 shows the configuration of a conventional magneto-optical recording device.

The magneto-optical recording device includes a laser light source 1 for emitting a laser beam, a collimator lens 2 for converting the laser beam into a parallel beam, a linear fan plate 3 for converting the parallel laser beam into a straight line, and a straight line beam. It includes an objective lens 5 for focusing the emitted laser beam onto a magneto-optical recording medium 4 on which news is recorded. However, the linear polarizing plate 3 is blank even when it is not particularly necessary, so n and '7 can be omitted. Furthermore, there is a beam splitter 6 for taking out the laser beam reflected from the magneto-optical storage medium 4, and an X. a converging lens 7 of b, a polarizing beam splitter 8 for splitting the anti-elbow laser beam into two according to its linear polarization axis, and a polarizing beam splitter 8 placed at the convergence position of the split laser beam to receive and detect each split component. It includes a pair of light receiving elements 9 and IO.

To reproduce the fI1# information recorded on the magneto-optical recording medium 4, the recording medium 4 is irradiated with a laser beam emitted from the laser light source 1, and the Kerr rotation angle of the reflected laser beam is detected by η■. Let's do it. The reflected laser beam is split by the polarizing beam splitter 8, and the intensity of the split light components is relatively different depending on the Kerr rotation angle.

Therefore, it is possible to electrically process the output signal components of the pair of light receiving elements 9 and 10 to determine the difference, and to reproduce information from the polarity.

[Problem that the invention seeks to solve]

As described above, magneto-optical recording devices use changes in the Kerr rotation angle to reproduce information, but the amount of change is about 1 degree, which is extremely small. Therefore, the amplitude feminization of the output signal components of the pair of light receiving elements is also very small.

In order to detect the feminization of the Kerr rotation angle, the difference between the output signal components of a pair of light receiving elements is taken. Therefore, if the balance or balance of the output signal components of the pair of light-receiving elements is disrupted, it becomes difficult to accurately detect changes in the rotation angle of the car, resulting in a car with a deteriorated S/N ratio in information reproduction. The balance between the pair of light receiving elements is unavoidably caused by unevenness and roughness of the reflection of the magneto-optical recording medium, distortion of the track group, etc. Therefore, in the conventional magneto-optical recording device, the mechanical balance between the pair of light receiving elements is 5l! Although II adjustment was carried out, it was difficult to maintain perfect balance due to eclipse over time and shaking of the magnetic recording medium.

[Means for resolving problems]

In view of the above-mentioned problems of the prior art, it is an object of the present invention to automatically balance the output signal component levels of a pair of light-receiving elements without performing mechanical balance adjustment. Another purpose is to maintain an optimal balance by constantly following changes over time and periodic surface wobbling that occurs during rotation of the magneto-optical recording medium.

In order to achieve the above purpose, a laser beam is irradiated onto a magneto-optical recording medium on which information is recorded, the reflected light is split and received by a pair of light receiving elements, and a corresponding pair of output signals are generated by photoelectric conversion. Improvements have been made to signal processing circuits for reproducing information by processing the components.

That is, the improved signal processing circuit includes a subtraction circuit for reproducing the first information by performing subtraction processing on a pair of signal components and outputting a difference signal, and a subtraction circuit for reproducing the first information by performing addition processing on a pair of signal components and outputting a difference signal. an adder circuit for reproducing the second information by outputting the signal; a control circuit for processing the difference signal and the sum signal and outputting a control signal according to the relative phase relationship; and a control circuit for outputting a control signal according to the relative phase relationship; and an adjustment path 1''h that performs relative adjustment of the amplitude level of the signal and maintains a balance between the signal power of the pair to be processed in the calculation circuit.

Preferably, the subtraction circuit reproduces the actual news, ie, data, recorded magneto-optically in each sector of the magneto-optical recording medium, the addition circuit reads identification information, ie, address, etc. of each sector, and the control circuit preferably During the reading period of the identification information, the difference signal and the sum signal are processed and control number 13 is sequentially output for each sector.

More preferably, the control circuit includes a multiplication circuit that performs multiplication processing of the difference signal and the sum signal, and outputs a control signal according to the phase relationship between the difference signal and the sum signal.

[For production]

According to the present invention, the relative adjustment of the amplitude level of the signal component of the first daughter is automatically performed by circuit means, and the reduction 'r5
I! ! It functions to maintain the balance of a pair of signal components to be processed in the I path in a feedback manner.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a signal processing circuit according to the present invention. The signal processing circuit is connected to a pair of light receiving elements 9 and 10 built into the magneto-optical recording device shown in FIG. Photodetector T9 and lO are divided into two anti-Jl
, l laser beam components, each outputs an AC signal component whose amplitude decreases in accordance with the optical intensity tabulation of the laser beam component. Signal processing P4 according to the present invention! The circuit includes a subtraction circuit 11 that performs a subtraction process on a pair of signal components and outputs a difference signal D, and a subtraction circuit 11 that reproduces the first information by a subtraction circuit 11 that performs a subtraction process on a pair of signal components and outputs a sum signal S! It has an adder circuit 12 for reproducing the second information. Further, a filter/amplifier 13 for waveform shaping and amplification of the difference signal D is connected to the downstream stage of the adder circuit 11, and a filter/amplifier 14 is similarly connected to the downstream stage of the adder circuit 12. A control circuit for processing the difference signal D and sum signal S and outputting a control signal C according to the relative phase relationship is connected between the subtraction circuit 1l and the addition circuit 12. The control circuit includes a multiplication circuit 15 that multiplies the difference signal and the sum signal, a gate circuit 1B that passes the multiplied product signal M in accordance with the gate signal G, and an integration process of the passed product signal M. and an integrating circuit l7 for outputting a control signal C. Furthermore, the signal processing circuit includes an adjustment circuit 1'h that performs relative adjustment of the amplitude levels of the pair of signal components according to the control signal C and maintains a balance between the pair of signal components to be processed in the subtraction circuit 1l. ing. The adjustment circuit 18 includes a gain adjustment circuit connected between one of the light receiving elements IO and one of the manual terminals of the subtraction circuit 11 to adjust the gain of one signal component.

Next, the operation of the signal processing circuit shown in FIG. 1 will be explained with reference to FIGS. 2 and 3. In this embodiment, a case will be described in which information recorded on a magneto-optical disk on which a spiral track is formed is reproduced. However, it goes without saying that the present invention is applicable not only to magneto-optical disks but also to all kinds of magneto-optical recording media #j. The spiral track is divided into a plurality of sectors, and each sector is made up of an address area for recording identification information such as an address, and a data area for recording substantive information such as data.

In the address area, information is recorded in the form of an embossed bit string, and in the data area, information is recorded magneto-optically as described above.

When reproducing information, a laser beam is irradiated along a spiral track, and in a certain sector, at timing TI, information written in the address area is reproduced, and at subsequent timing T2, the information written in the data area is reproduced. It is designed to play back information. At timing TI, the intensity of the reflected laser beam changes depending on the reflectance of the embossed pit row, and the pair of light receiving elements 9 and 1O output AC signal components accordingly.

Therefore, as shown in the figure, at timing TI, the adder circuit 12 outputs the sum (.?) of the change in amplitude according to the arrangement of the embossed pit rows by 4, and at timing T2, the embossed bit rows are no longer U/I:L. Therefore, a flat sum signal S is output.

On the other hand, in the data area, information is recorded magneto-optically. Therefore, at timing T2, the Kerr rotation angle of the opposite laser beam shifts, and the intensity of the light split and received by the pair of light receiving elements 9 and 10 shifts relative to each other. On the other hand, at timing Tl, there is no variation in the Kerr rotation angle, so the intensities of the light split and received by the light receiving cables T9 and IO are essentially equal.

Therefore, the subtraction circuit 1l outputs the difference signal D whose amplitude hardly changes at timing T1, and outputs the difference signal D whose amplitude hardly changes at timing T2.
, outputs a difference signal D whose amplitude changes in an alternating current manner according to a change in the relative amount of light received by the pair of light receiving cables 9 and 10.

However, if the levels of the pair of signal components input to the subtraction circuit I1 are not balanced, a difference signal D containing some fluctuation components is output even at the timing Tl as shown in the figure. The phase or polarity of this fluctuation component indicates the amount of unbalance between the input terminals in the subtraction circuit it, and the ZJI that processes the difference signal D at timing T1 provides a sum for monitoring the amount of unbalance. For this purpose, a multiplication circuit 15, a gate circuit 16, and an integration circuit 17 are connected between the subtraction circuit if and the addition circuit 12.

The operation of the multiplication circuit 15 will be explained with reference to FIG.

If the human power level is tilted toward the positive side between both the positive and negative terminals of the subtraction port 1l, the difference signal D+ is output at a certain moment of timing TI, for example, as shown in the figure. The difference signal D0 has a positive peak in the first half and a negative peak in the second half. Conversely, when the human power level in the four-way subtraction l1 leans toward the negative side, the difference signal D- is output. The difference signal D1 has a negative peak high in the first half and a positive peak high in the second half.

That is, the difference signals D0 and D- have redundant phases or polarities depending on the direction of input level imbalance.

On the other hand, the adder circuit 12 outputs a sum signal S0 or S- according to the polarization of the input signal components, regardless of the balance between its two input terminals.

The sum signals S0 and S1 have a positive peak in the first half and a negative peak in the second half, and are in phase with each other. As a result, when the human power level of the subtraction circuit 1l is tilted to the positive side, the difference signal D+ and Washin +38+ are the same tj, and conversely, when the input level of the subtraction circuit 1l is tilted to the negative side, the difference signal Signal D1 and sum signal S-
are inversely related to each other.

The multiplier p circuit 15 performs multiplication processing on the difference signal and the sum signal and outputs a product signal M. As is clear from FIG. 3, if the human power level of the subtraction circuit 11 is on the positive side,
It outputs a product signal M+ that has two positive peaks H, and conversely, when the human power level of the subtraction circuit H leans toward the negative side, the negative peak 2
A product signal M-, which multiplies two by six, is output. The multiplication circuit 15 continuously performs such multiplication processing and outputs a product signal M. The gate circuit 16 responds to the gate signal G and allows the product signal M to pass through for a period of timing T1. In this manner, the amount of unbalance at the human power level of the subtraction circuit 11 is monitored only at timing T1. The product signal M passing through the gate path l6 is integrated by an integrating circuit l7 and outputted as a control signal C. Control 8 signal C is subtraction circuit 1! It is used as a phase correction signal for the servo system, and is automatically balanced by feeding it back to the gain adjustment circuit l8. Perform I adjustment. That is, the gain is 1!1.21 The adjustment circuit 18 adjusts the gain of the signal component output from one of the light receiving elements 10, and adjusts the amplitude level of the signal component sent to the positive input terminal of the subtraction circuit 11. It operates to maintain the balance of the 11 input levels.

Finally, FIG. 4 shows a specific circuit structure of the multiplication circuit 15.

This multiplication circuit is called a balanced mixer circuit. The balanced mixer circuit consists of a pair of transistors l9
and 20 and accepts the difference signals D and 6. One transistor l9 has a pair of transistors 2l and 22.
are connected to accept sum signals S and S, respectively. Further, another pair of transistors 23 and 24 are connected to transistor 20, and similarly receive sum signals S and S. These four transistors 21 to 24 perform multiplication processing of the sum signal and the difference signal, with transistor 21 outputting product signal M and transistor 22 outputting product signal M.

The balanced mixer circuit described above is only an example of a multiplication circuit, and it goes without saying that other types of multiplication circuits may be used. Further, the circuit that processes the difference signal and the sum signal to find the relative phase relationship is not limited to a multiplication circuit, but may generally be any circuit that can detect the phase difference between the two signals.

〔Effect of the invention〕

As described above, according to the present invention, the relative adjustment of the vibration levels of a pair of signal components is performed in accordance with the control signal to maintain the balance between the pair of signal components to be processed in the subtraction circuit. The balance between the positive and negative terminals of the circuit is always automatically maintained by servo control, enabling stable information reproducing operation of the magneto-optical recording device and significantly improving the S/N ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a signal processing circuit of a magneto-optical recording device according to the present invention, FIG. 2 is a timing chart for explaining the operation of the signal processing circuit shown in FIG. 1, and FIG. 1. FIG. 4 is a circuit diagram showing an emitter example of the multiplication circuit shown in FIG. 1, and FIG. 5 is a general example of a magneto-optical recording device. FIG. 9... Light receiving element 10... Light receiving element l1
...Subtraction circuit l2...Addition circuit l5.
...Multiplication circuit 16...Gate M path l7.
...Integrator circuit l8...gain 2 Seikawa Michiru
Applicant Co Pal Co., Ltd. Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A laser beam is irradiated onto a magneto-optical recording medium on which information is recorded, the reflected light is split and received by a pair of light receiving elements, and a pair of corresponding signal components generated by photoelectric conversion are detected. A signal processing circuit that reproduces information by processing, a subtraction circuit that reproduces the first information by performing subtraction processing of a pair of signal components and outputting a difference signal, and an addition of the pair of signal components. an adding circuit for reproducing the second information by processing and outputting a sum signal; a control circuit for processing the difference signal and the sum signal and outputting a control signal according to the relative phase relationship; and an adjustment circuit for relatively adjusting the amplitude levels of the pair of signal components in accordance with the above, and maintaining the balance of the pair of signal components to be processed in the subtraction circuit. 2. The subtraction circuit reproduces the substantive information recorded magneto-optically in each sector of the magneto-optical recording medium, the adder circuit reads the identification information of each sector, and the control circuit reads the identification information during the reading period of the identification information. 2. The signal processing circuit according to claim 1, wherein the signal processing circuit processes a difference signal and a sum signal and outputs a control signal. 3. The signal processing circuit according to claim 1, wherein the control circuit includes a multiplication circuit that performs multiplication processing of a difference signal and a sum signal. 4. The signal processing circuit according to claim 1, wherein the adjustment circuit comprises a gain adjustment circuit connected between one of the pair of light receiving elements and the subtraction circuit to adjust the gain of one signal component.