JPS6122442A - Automatic gain controller of optical disc device - Google Patents

Abstract

PURPOSE:To improve the tracking of an optical beam which changes focus servo at recording and after recording of information by obtaining automatically a constant servo error signal detecting gain even when fluctuation of reflectance of a medium is generated after recording of information. CONSTITUTION:An attenuator 3 consists of a resistor 31 and an FET30 and an attenuator 5 is constituted similarly. A servo error signal 8 is connected to a drain of the FET30 via the resistor 31 and outputted to a signal line 11. Since the source of the FET30 is grounded. The attenuator is constituted by a drain- source resistance of the FET30 decided by the level of a gain control signal 10 connected to the gate of the FET30 and the resistor 31, and the level of the servo error signal 8 is controlled by the gain control signal 10. The level of a sum signal 9 is controlled in the attenuator 5 similarly, both the characteristics are made well coincident and a servo error signal having always a prescribed gain is detected.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an optical information recording and reproducing apparatus that uses optical means to record information on a recording medium or to reproduce information that has already been recorded. In particular, it relates to a tracking and focus position control device for said device.

(Prior art and its problems) A laser beam is used as a light source, and this laser beam is modulated with a pulsed signal from an external information source to record binary information on a recording medium on a disk, or to record information that has already been recorded. In optical information recording and reproducing equipment that reads out information, in order to accurately record or reproduce information, focus control is used to control the condenser lens so that the surface of the recording medium is always at the focal point of the condenser lens. The focal position in the optical axis direction is controlled, and the track position control of the original spot of the laser beam with respect to the information track during information recording or reproduction is usually performed by setting the optimal width for the optical spot on the recording medium. At this time, when recording information, the power of the laser beam is increased by about 10 times that of reading, and the information is thermally recorded on the surface of the recording medium. When the laser source power is increased in this way, the reflected light also becomes larger, and the servo error signal detected based on this reflected light also becomes larger. As a result, the servo system causes oscillation and information is recorded accurately. Moreover, the light spot goes out of control and jumps to a data track other than the desired data track.

Further, after information is recorded, the reflectance decreases depending on the type of recording medium, and in this case, contrary to the above, the reflected light decreases and the servo error signal also decreases. As a result, the loop gain of the servo system decreases, the followability to the data track deteriorates, and information reading after information recording is not performed accurately.

In this way, the servo error signal and detection gain change significantly due to changes in the power of the laser beam and changes in the reflectance of the recording medium, resulting in poor data trunk followability or poor followability of the light spot on the disk surface, resulting in information recording and reproduction. reliability will be greatly reduced.

(Object of the Invention) The object of the present invention is to provide an automatic gain control device that eliminates the above-mentioned drawbacks and can always provide a constant servo error detection gain even when changes in the power of the laser beam and changes in the reflectance of the recording medium occur. There is a particular thing.

(Structure of the Invention) According to the present invention, there is provided a two-split optical sensor for receiving reflected light from a disk surface and generating a servo error signal;
a first operational amplifier that outputs a servo error signal that is the difference between two outputs of the split optical sensor; and a first attenuator that receives the servo error signal and changes the gain for the servo error signal in accordance with a gain control signal. a second operational amplifier that outputs a sum signal that is the sum of the two outputs of the two-split optical sensor; and a second attenuator to which the sum signal is connected and whose gain changes according to the gain control signal. , a third operational amplifier that receives the output of the second attenuator, calculates the difference from the reference signal, and outputs the gain control signal, and responds to the change in light amount received by the two-split optical sensor. The detection gain of the servo error signal, which is the output of the first attenuator, is controlled to be constant by controlling the gain control signal so that the output of the second attenuator becomes equal to the reference signal. An automatic gain control device is obtained.

(Example) Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the present invention. 15 of each of the two-split optical sensor 1
．． The difference between the signals detected from 16 is calculated by the operational amplifier 2, and the signal is sent to the signal line 8 as a servo error signal.
is output to signal line 1 as a gain-controlled servo error signal via attenuator 3 whose gain is controlled by gain control signal 10.
1 is output. On the other hand, the sum of the two signals detected by the two-split optical sensor 1 is calculated by the operational amplifier 4, and the sum is outputted to the signal line 9 as a sum signal. sum signal 9
is input to the differential amplifier 6 via the attenuator 5, the difference with the reference signal 7 is calculated, and as a result, the gain control signal 10 is output from the differential amplifier 6 and input to the attenuators 3 and 5. , each gain is controlled. That is, if the gain-controlled sum signal 12 is larger than the reference signal 7, the attenuator 3
A gain control signal that lowers the gains of attenuators 3 and 5 is output, and conversely, if the sum signal 12 is smaller than the reference signal 7, a gain control signal that increases the gains of attenuators 3 and 50 is output, and finally the sum signal 12
The gains of the attenuators 5 and 3 are controlled by the gain control signal 10 so that the magnitude of the reference signal 7 and the reference signal 7 are equal to each other. At this time, attenuators 5 and 3
If the gain change characteristics for each gain control signal are made equal, attenuators 5 and 3 will have the same gain for the gain control signal .

By doing this, the gains of attenuators 5 and 3 are controlled so that the sum signal 12 is always equal in magnitude to the reference signal 7 even when there is a large change in reflected light power, which is typical when recording information, and servo errors are reduced. The magnitude of the signal 8 is also controlled by the attenuator 3, and a servo error signal having a constant detection gain is always output to the signal line 11.

FIG. 2 is a circuit diagram showing in detail the attenuator 3 and attenuator 5 of FIG. 1. Attenuator 3 is resistor 31. The attenuator 5 also includes a resistor 51 and an FET 50, similar to the attenuator 3. Servo error signal 8 is sent to FF1 via resistor 31.
It is connected to the drain of T50 and output to the signal line 11 at the same time. At this time Fl'
:Since the source of T2O is grounded, an attenuator is formed by the resistance between the drain and source of FET 50 and the resistor 31, which is determined by the level of the gain control signal IO connected to the gate of FET 50, and the gain control signal IO prevents servo errors. The magnitude of signal 8 is controlled. On the other hand, attenuator 5 also has attenuator 3.
Since the configuration is similar to that of the sum signal 9, the magnitude of the sum signal 9 is controlled by the gain control signal. At this time, I
By using the composite type i ET formed on the same substrate as the ET50'i, the characteristics of the two can be matched well, and as explained in Figure 1, the power fluctuations of the reflected light can be It is also possible to detect a servo error signal that always has a constant gain.

(Effects of the Invention) As explained above, according to the present invention, the power of reflected light changes more than 10 times as much when recording information as compared to when reading information, and furthermore, the medium after information recording, 3- Even if 6g reflection source fluctuation occurs due to reflectance fluctuation, a constant servo error signal detection gain can be automatically obtained, and tracking servo and focus servo can be stably applied during and after recording information. This makes it possible to greatly improve the followability of the original beam on the disk surface and the data tracks.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing a first embodiment of the present invention, and Fig. 2 is a block diagram showing a first embodiment of the present invention.
The figure shows the attenuators 3 and 5 of FIG. 1 in detail. In the figure, 1...-2 division source sensors, 2.4...
...Arithmetic gain 3.5...Attenuator,
6... differential amplifier, 7... reference signal, respectively.

Claims (1)

[Claims] Optical means is used to control the tracking position of a light spot on a concentric or spiral data track provided on a recording medium to record information on the recording medium or to record information already recorded on the recording medium. In an optical disk device that performs reading, a two-split optical sensor receives reflected light from the disk surface and generates a servo error signal, and a second optical sensor outputs a servo error signal that is the difference between the two outputs of the two-split optical sensor. a first attenuator that receives the servo error signal and whose gain for the servo error signal is changed by a gain control signal; and a sum signal that is the sum of two outputs of the two-split optical sensor. calculating the difference between a second operational amplifier to output, a second attenuator to which the sum signal is connected and whose gain changes according to the gain control signal, and a reference signal receiving the output of the second attenuator; and a third operational amplifier that outputs the gain control signal, and responds to changes in the amount of light received by the two-split optical sensor.
The detection gain of the servo error signal, which is the output of the first attenuator, is controlled to be constant by controlling the gain control signal so that the output of the second attenuator is equal to the reference signal. automatic gain control device for optical disk devices.