JPS6159605A - Information recording and reproducing device - Google Patents

Abstract

PURPOSE:To reproduce easily an accurate information signal when a recording medium is replaced, by controlling a bias magnetic field on a basis of a signal which detects the duty cycle of a reproduced signal. CONSTITUTION:A modulator 2 modulates a laser beam when information is recorded on a disc 9; and when the bias is adjusted, the modulator 2 modulates the laser beam so that the duty cycle is 50% to prevent the distortion of the reproduced signal. When information is recorded on the disc 9 at 50% duty cycle, the pit shape on the disc 9 is changed by the intensity of the bias magnetic field. An output proportional to the intensity of the magnetic field is obtained in a comparator 6 by this change, and this output is used to set automatically a proper bias magnetic field intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an information recording/reproducing device, and particularly to a recording bias υ control device.

[Prior art]

Magneto-optical recording uses a disc made of glass or other disc-shaped material sputtered with magnetic material as a recording medium. A perpendicular magnetic field is applied to this recording medium to magnetize the magnetic material in a certain direction. By irradiating the disk with a laser beam modulated by the information signal to be transmitted, the temperature of the magnetic material in the irradiated area is raised to above the magnetic transition temperature (Curie temperature), and the magnetization of the irradiated area is reversed, thereby transmitting information. Information signals are recorded on a disk, and during reproduction, the magnetic Kerr effect, Faraday effect, etc. are used to reproduce the information signals recorded on the disk using a laser beam.

In magneto-optical recording, the sensitivity of the magnetic material that becomes the recording medium,
The size of the recorded bit differs depending on the power of the laser beam and the strength of the perpendicular magnetic field.

Therefore, when the magnetic field and laser power are constant, if there is a sensitivity difference in the disk-shaped recording medium during disk replacement, the pit size will not be appropriate, and the signal duty cycle will change as the level of the reproduced signal decreases. Then, MFM (Modified Frequency)
Accurate demodulation of signals modulated by a modulation method such as +5 adulation is impossible.

In addition, the size of the pits changes between the outer and inner peripheries of the disk, and the pit size also changes depending on the energy density of the laser beam. change or bias (
(Bias) by changing the magnetic field, but if there is a difference in sensitivity between disk-shaped recording media, accurate correction is impossible.

A method of changing the beam power has also been considered as a means of changing the size of the pit.

When using a semiconductor laser to increase beam power, there are many problems in terms of drive method and absolute power.

〔the purpose〕

An object of the present invention is to eliminate the drawbacks of the conventional example described in Section 11u and to realize an information recording and reproducing apparatus that can accurately reproduce information with a relatively simple configuration.

〔Example〕

FIG. 1 is a block diagram of one embodiment of the present invention, in which 1 is an optical pickup for recording and reproducing signals on a magneto-optical disk (recording medium) 9, and 2 is a modulation system that modulates a laser beam with an information signal during recording. Prefix 1?3 reproduces error signals and information signals for focusing and tracking during recording and playback. 4 is a servo circuit for applying servo to the pickup L based on the focus error and tracking error signals from the preamplifier 3; 5 is a controller for moving the optical pickup 1 in the diametrical direction of the disk; Preamplifier 3
a comparator for binarizing the information signal from 7
is a low-pass filter connected to the output of comparator 6, and 8 is a signal from low-pass filter 7 via controller 5 and pickup 1 on disk 9.
This is a bias control circuit that controls the bias magnetic field applied to the disk 9 depending on the position of the disk 9.

The operation of the embodiment configured as above will be explained below.

In FIG. 1, the modulator 2 modulates the laser beam when recording information on the disk 9.
When adjusting the bias yA, the laser beam is modulated so that the duty cycle is 50% so that the reproduced signal is not distorted. When recording is performed on the disk 9 with a duty cycle of 50%, the shape of the pits on the disk changes as shown in FIGS. 2(a), (b) and (C) depending on the strength of the bias magnetic field.

FIG. 2(a) shows a case where the bias magnetic field is weak, the pit shape A1 is small, and the signal output waveform of the signal preamplifier 3 becomes like A2 in the figure, and the signal is converted into a z-value by the comparator 6. The resulting signal looks like A3 (7) in the figure, and by passing it through the low-pass filter 7, the direct current (
By detecting the pc) component, it is possible to detect the minus (negative) DC component.

When the strength of the bias magnetic field is appropriate, as shown in FIG. 2(b), the recording pit shape on the disk becomes Bl, the duty cycle of the reproduction signal becomes 50%, and the output of the low-pass filter 7 The 1α flow of is almost 0.

The size of the pit at this time is 1.2 to 1-3 p, m. In the figure, B2 indicates the output of the amplifier 3, and B3 indicates the output of the comparator 6.

If the bias magnetic field is even stronger, the second V! As shown in J(c), the recording pit shape becomes C1.

The output of the low-pass filter 7 detects the positive DC4 component. In the figure, 02 indicates the output of the amplifier 3, and C3 indicates the output of the comparator 6.

Note that since the size of the recording pit changes depending on the strength of the magnetic field, the output of the comparator 7 is approximately proportional to the strength of the magnetic field. Utilizing this fact, the appropriate bias magnetic field strength is automatically set. Flowcharts of this operation are shown in FIGS. 3 and 4 and will be explained in detail.

As shown in FIG. 3, first, in St, the pickup 1 is moved to the outermost circumference of the disc 9 (recordable in that system), and the process proceeds to S2, where a subroutine is executed. That is, as shown in FIG. 4, first, the bias is set to a preset standard value in Sll, and in S12 a signal modulated by the modulator 2 is recorded on the disk so that the duty cycle is 50%. Next, in step 513, the signal just recorded is reproduced, and in step S14, the DC component of the binarized signal at that time is detected by the low-pass filter 7, and the value is sent to the bias control circuit 8, and the DC component of the binarized signal of the reproduced signal is detected. Determine whether the DC component is within the allowable value (-〇), above it, or below, and if the DC level is greater than the allowable range, proceed to 515, and if it is less than the allowable range, proceed to 31B, When the value is within the permissible range, that is, approximately O, the process returns to the main routine. In S15, the bias amount Δ to be changed is set to - (minus) and Sl? Then, in 318, the bias measure Δ to be changed is set to + (plus), and the process proceeds to 517. In S17, the bias amount Δ is changed to the previous bias value.
A signal modulated with a duty cycle of 50% is recorded on the disk by a bias value in which . Therefore, the process returns to S14 and the DC component applied to the reproduced signal is detected again, and the above process is repeated.
The detection DC level in S14 is within the permissible range (#O
), the process returns to 53 of the main routine, where the bias value is input to the first bias control circuit 8 (not shown).
It is stored in the memory 8-1.

Next, in step 54, the pickup is advanced to the center of the disk, and the process proceeds to step S5, which proceeds to the aforementioned subroutine and performs the same thing as above, and in step S6, the final bias value is set to the second
It is stored in the memory 8-2.

Furthermore, in step 57, the pickup is sent to the innermost circumference of the disk, and the process proceeds to step S8, which proceeds to the aforementioned subroutine and performs the same thing as described above, and in step S9, the final bias value is set to the third
It is stored in the memory 8-3.

Then, at 510, the outer circumference, the center, and the inner circumference are
Using the bias value at the point as a reference, the bias control circuit 8 calculates the slope of the bias value between the values at the outer periphery and the center, determines the bias value suitable for that location (position) at each position, and The bias is changed to the determined bias value at each position in between. The same process can be performed between the central and outer stations, or a bias value at an arbitrary position can be determined by calculating a curve (straight line) passing through the three points using a known calculation method.

In this way, by determining the appropriate bias at three points on the disk, and applying the bias estimated from the determined appropriateness/heias at the three points in the middle of each point, an appropriate bias magnetic field can be applied over the entire disk in a relatively short period of time. You can get it at

The above operation is automatically started after the sensor etc. detects that the disk is mounted, and the servo circuit 4 detects 2ft where the focus servo is applied.

In the above embodiment, the recording bias was measured at three points, but it is also possible to further increase this number.

Although the duty cycle is detected using a low-pass filter, the same effect can be obtained by detecting it using a device that detects the pulse width of the z-valued signal using a clock.

〔effect〕

As described above, according to the present invention, it is possible to easily and accurately reproduce information signals even when the recording medium is replaced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. Figure ff52 is an explanatory diagram of pits on the disc and reproduction signals. 3 and 4 are processing flowcharts of one embodiment of the present invention. 1...Optical pickup. 2...Modulator, 3...Preamplifier, 4...Servo circuit. 5... Controller, 6... Comparator, 7... Low pass filter, 8... Bias control circuit, 9... Disk.

Claims (1)

[Claims] Means for detecting a duty cycle of a reproduced signal; means for changing the strength of a bias magnetic field during information recording; and controlling the bias magnetic field based on the signal detected by the detection means. An information recording/reproducing device comprising: means.