JPH0415532B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical information recording and reproducing device that uses optical means to record information on a recording medium or to reproduce information that has already been recorded. , and more particularly 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 panel signal from an external information source to record binary information on a recording medium on a disk, or to record information on a recording medium that has already been recorded. In an optical information recording/reproducing device 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 of the laser beam is controlled, and the track position control of the optical spot of the laser beam with respect to the information track during information recording or reproduction is usually performed by determining the optimum width and width of the optical spot on the recording medium. A guide groove with the optimum depth for the wavelength of the laser beam used is provided, and the track position is controlled so that the beam spot follows the guide groove.

At this time, when recording information, the power of the laser beam is increased about 10 times that of reading, and the information is thermally recorded on the surface of the recording medium. When the laser light 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 the information is not accurate. The data is not recorded, and furthermore, the optical spot goes out of control and flies 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.

As described above, changes in the power of the laser beam and changes in the reflectance of the recording medium cause large changes in the servo error signal and detection gain, resulting in poor data track followability or poor followability of the optical spot on the disk surface, resulting in information loss. The reliability of recording and reproduction is 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, a two-split optical sensor receives reflected light from a disk surface and generates a servo error signal, and a servo error signal that is the difference between the two outputs of the two-split optical sensor is generated. the sum of two outputs of a first operational amplifier that outputs, 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 the two-split optical sensor; a second operational amplifier that outputs a sum signal, a second attenuator to which the sum signal is connected and whose gain changes according to the gain control signal, and a second attenuator that receives the output of the second attenuator and receives a reference a third operational amplifier that calculates the difference between the gain control signal and the gain control signal; By controlling the gain control signal to be equal to , an automatic gain control device is obtained in which the detection gain of the servo error signal, which is the output of the first attenuator, is controlled to be constant.

(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. The difference between the signals detected from the respective elements 15 and 16 of the two-split optical sensor 1 is calculated by the operational amplifier 2, and the result is output to the signal line 8 as a servo error signal, and the result is outputted to the signal line 8 by the gain control signal 10. Through the attenuator 3 whose gain is controlled by
It is output to the signal line 11 as a gain-controlled servo error signal. 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 attenuator 5
The gain control signal 10 is outputted from the differential amplifier 6, inputted to the attenuators 3 and 5, and the difference with the reference signal 7 is calculated. Gain is controlled. That is, when the gain-controlled sum signal 12 is larger than the reference signal 7, a gain control signal that lowers the gain of the attenuators 3 and 5 is output, and conversely, when the sum signal 12 is smaller than the reference signal 7, A gain control signal that increases the gain of attenuators 3 and 5 is output, and finally the sum signal 12
Attenuator 5 is controlled by gain control signal 10 so that
and a gain of 3 is controlled. At this time, if the gain change characteristics of the attenuators 5 and 3 with respect to the gain control signal are made equal, the attenuators 5 and 3 will have the same gain with respect to the gain control signal 10. By doing this, the gains of the 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. The magnitude of the servo error 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 the attenuators 3 and 5 of FIG. 1 in detail. The attenuator 3 is composed of a resistor 31 and a FET 30.
Attenuator 5 also has a resistor 5 similar to attenuator 3.
1 and FET50. The servo error signal 8 is connected to the drain of the FET 50 via the resistor 31 and is output to the signal line 11 at the same time. At this time, the source of FET50 is grounded, so it is determined by the level of gain control signal 10 connected to the gate of FET50.
Drain-source resistance of FET50 and resistance 31
constitutes an attenuator, and the magnitude of the servo error signal 8 is controlled by the gain control signal 10. On the other hand, since the attenuator 5 has the same configuration as the attenuator 3, the magnitude of the sum signal 9 is controlled by the gain control signal. At this time, by using a composite type FET formed on the same substrate as the FET 50, it is possible to match the characteristics of the two well, and as explained in FIG. It is 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 the reflectance of the medium changes after recording information. It is possible to automatically obtain a constant servo error signal detection gain even when reflected light fluctuations occur due to The followability of the light beam on the surface and on the data track can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing details of attenuators 3 and 5 of FIG. 1. In the figure, 1... 2-split optical sensor, 2, 4...
...Arithmetic amplifier, 3, 5...Attenuator, 6...
Differential amplifier, 7 . . . indicates a reference signal, respectively.

Claims (1)

[Claims] 1 Using optical means 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 that has already been recorded on the recording medium. In an optical disk device that performs readout, a two-split optical sensor receives reflected light from the disk surface and generates a servo error signal, and outputs a servo error signal that is the difference between the two outputs of the two-split optical sensor. a first operational amplifier that receives the servo error signal and whose gain for the servo error signal is changed by a gain control signal; and a sum of two outputs of the two-split optical sensor. a second operational amplifier that outputs a certain sum signal, a second attenuator to which the sum signal is connected and whose gain changes according to the gain control signal, and a reference signal that receives the output of the second attenuator. a third circuit that calculates the difference between the two and outputs the gain control signal;
an operational amplifier, and a gain control signal is controlled so that the output of the second attenuator becomes equal to the reference signal in response to changes in the amount of light received by the two-split optical sensor, An automatic gain control device for an optical disk device, characterized in that the detection gain of the servo error signal, which is the output of the first attenuator, is controlled to be constant.