JPS6022746A - Automatic control circuit of servo gain - Google Patents

Abstract

PURPOSE:To obtain a stable driving output of an optical head in both reproduction and recording modes regardless of variation of the total reflected light quantity, by providing a changeover switch which switches the gains of both amplifiers with switch signals of recording and reproduction modes and a control means which stabilizes the outputs of both amplifiers approximately at the same level regardless of a recording or reproduction mode. CONSTITUTION:The servo gain is decided by amplifiers 2 and 3, and the gain of the amplifier 3 is decided from the equivalent drain-source resistance value of an FET4 as well as resistances R18 and R19. Then the gain of the amplifier is decided based on the mean value of laser power of a recording mode. Thus the servo gain is liable to have a shortage despite the gain setting of an amplifier 16 since the level of the laser power is low in a reproduction mode. In this respect, an analog switch 14 is controlled by a recording/reproduction gate to obtain the drive voltage approximately equal between recording and reproduction modes in order to compensate a track shift. For this purpose, the values of resistances R18 and R19 are properly selected. In such a way, the optimum servo gain is obtained.

Description

Detailed Description of the Invention μ) Technical Field of the Invention The present invention relates to a control circuit in an optical disk device or a magneto-optical disk device, and particularly relates to an automatic servo gain adjustment circuit for stabilizing track servo and focus servo. .

■) Prior art and problems Conventionally, in optical disk devices or magneto-optical disk devices, when recording information, there is a difference in the relative circumferential speed between the optical head and the disk at the inner or outer circumference of the disk, so the same recording is performed on the disk surface. To obtain these conditions, it is necessary to make the recording laser beam stronger toward the outer periphery. For this control, the track number information recorded in advance on the DINUK is restored.
7. The laser power is controlled by converting it.

On the other hand, servo threads such as track servo and focus servo that drive the optical head use reflected or transmitted light, so when the laser power changes, the servo drive signal also becomes ashes. Therefore, in order to obtain a stable servo drive signal, it is necessary to automatically change the servo gain so that an averaged servo drive signal can be obtained regardless of changes in laser power.

FIG. 1 shows a conventional servo gain control circuit.

In the figure, reference numeral 1 denotes a four-division photodetector known by the cylindrical lens method, which outputs a track deviation signal, a focus deviation signal, and three types of total reflection light 1i (No. 8 thread) from the L stage shown in the figure. The thread 2 of the shift signal is a differential amplifier, and 8 and 5 are amplifiers, respectively, which are connected to the La column and output the track servo drive aiIIItN to the output terminal 6.The thread 7 of the focus shift 1B is a differential amplifier. , 8
and LO are amplifiers, which are connected in series and output a focus support drive signal to the output terminal 11. The total reflection light beam has an inverting amplifier 12 and a filler 1B connected in series, and the output of the filter 13 has a negative polarity and is connected in parallel to each gate terminal G of field effect transistors (hereinafter abbreviated as FET) 4 and 9. , the source terminals S of FETs 4 and 9 are connected to ground, and the drain terminals of FETs 4 and 9 are connected to amplifiers 8 and 8, respectively.
The circuit configuration is connected to one input terminal of the

FIG. 2 is an example of a characteristic curve of the gate voltage "08 of the NET versus the equivalent drain/source resistance [Rns," which has a quadratic curve characteristic as shown.

Here, let P be the center point of the straight line area.

The operation of the servo gain control concave path shown in FIG. 1 will be briefly explained.

The output of the amplifier 12 is a total reflection light amount signal, and after noise components are filtered out and removed by a filter 18, the output is connected in parallel to each gate terminal G of FETs 4 and 9, and the level fluctuation of the total reflection light amount signal is the gate voltage (2). S is applied, and the equivalent drain/source resistance RDS corresponding to the gate voltage VGS of the characteristic curve of FIG. 2 changes. The resistance value of FET4 is RDs4. Resistor 1 of FET9 is RDS9 and amplifier 3
The resistance between one input terminal and the output terminal of the amplifier M8 is R3: The same resistance of the amplifier M8 is Ha.

The amplification gain is automatically controlled according to the change in the resistance IulRns of each FET. In other words, as the total reflected light quantity decreases, the gate voltage VGS decreases in proportion to this, and the resistance value RD8 also decreases.Conversely, the amplification gain increases, which can be used to average the servo drive signal output. I'm counting.

By the way, since the intensity ratio of the laser beam is large when recording information and when reproducing information, the output of the amount of total reflected light, that is, the output of the amplifier 12 is small when reproducing information, and the FET shown in FIG.
Since it is necessary to use a region with poor linearity of the characteristics, it is not possible to obtain sufficient amplification gain, and a stable servo circuit cannot be realized.

(C) @ Akira's Purpose This investigation was conducted by Kita-Ki. In view of the drawbacks of the conventional method, the servo gain was increased during playback, and the servo gain was changed in accordance with the output of the total reflected light amount of the optical head during recording, during playback and recording. An object of the present invention is to provide an automatic servo gain adjustment circuit that can obtain a stable drive output for an optical head regardless of changes in the amount of total reflected light.

(d) Structure of the invention and this object according to the invention
In a disk device that is equipped with amplifiers that amplify a rack deviation signal and a focus deviation signal, and adjusts servo gain to perform track servo and focus servo using the outputs of the respective amplifiers, a switching signal for recording and playback is provided. A switching switch is provided for switching the gain of the podium width device, and a control means is provided for stabilizing the output of the podium width device to approximately the same level regardless of whether the recording or reproduction is performed. This is accomplished by providing an automatic servo gain adjustment circuit.

(e) @Ming Example Embodiments of the present invention will be described in detail below with reference to the drawings.

In the plan view, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant explanation thereof will be omitted.

FIG. 8 shows an example of the configuration of an automatic servo gain adjustment circuit according to the present invention, and only shows changes from the conventional example shown in FIG.

In the figure, 14 and 15 are contact points 20.21 and 22, respectively.
．． 28, the analog switch has a terminal 1
It is driven by a disc recording/reproducing gate signal manually inputted by the controller 7. Reference numeral 16 denotes an amplifier to which the total reflection light quantity signal that has passed through the filter 13 is input, and its output is connected to the gate terminal G of the FET 4 via the contact 22 of the analog switch 15.

Also, the output of the filter 18 is branched and connected to the FET via contact 2B.
Connect to gate terminal G of 4. Source terminal S of FET4
The drain terminal is connected to one input terminal of the amplifier 3, and is also connected to the amplifier 3 via the grounding terminal 20 of the analog switch 14, the resistor R18, the contact 21, and the resistor R19.
A circuit groove is commonly connected to the output terminals of the two.

Next, the operation of the circuit shown in FIG. 8 will be explained. First, the contacts 20 and 22 of the analog switches 14 and 15 are set so that when the human input signal from the terminal [7] closes during playback, the contacts 21 and 23 open and perform the opposite action when the human input signal (words) is recorded. There is.

First, all of the outputs of the four-part photodetector 1 shown in FIG.
The resulting total reflected light intensity signal is amplified by the inverting amplifier 12 so that the output becomes negative polarity, but when the output is manually applied as the gate voltage of FET 4 through the filter 13 in the next stage, the Input game) The gain of the amplifier 12 is set so that the average pressure of the K pressure becomes 1iff (that is, point P), which is the long stroke of the linearity shown in FIG. 2, when recording information.

When reproducing information, the laser power is lowered, but the gain of the amplifier 16 is set so that the input gate voltage of the FET 4 at that time is about the same as the average case during recording.

When the input gate voltage of FET 4 is applied to the recording/reproducing gate terminal 17 in this state, during recording, the input gate voltage of FET 4 fluctuates within a range with good linearity around the two points of the characteristic curve in Figure 2 during recording. During reproduction, a gate voltage without much fluctuation can be obtained around the output determined by the functional limit of the amplifier 16 (operation P, gate voltage that can approach depression).

Next, set the servo gain. For example, when the track deviation signal from the photodetector l is amplified by the differential amplifier 2, this output represents the direction and magnitude of the track deviation, and the objective lens is connected via amplifiers 8 and 5 to correct the track deviation. It is connected to a coil that causes it to move. Here, the servo gain is set by amplifiers 2 and 3, and the gain of amplifier 3 is set by the equivalent drain/source resistance of FET 4.
Determined by S4 and resistors Rxs, Rf9, amplifier 3
It is expressed in the game.

Here, the amplifier I is set based on the average laser power during recording.
If a gain of 2 is set, the laser power is low during reproduction, so even if the gain setting of the amplifier 16 is f:
Servo gain tends to be insufficient. Therefore, the analog switch 14 is controlled by the recording/reproducing gate, and the track deviation is approximately the same during recording/reproducing.
The optimum servo gain can be set by selecting the resistors R1 and Rlg so as to obtain a drive IC pressure of 111.

Although the circuit of FIG. 3 has been explained for the track servo drive number 1 thread, it can be applied in the same way to the thread of the focus shift signal, and in the circuit of FIG. By replacing amplifiers 3 and 5 with 8 and 10, respectively, a stable focal servo drive signal can be obtained.

(f) More than the effects of the invention, the servo gain by Kizudaki has been revealed in detail! The 1IIIr:j1M rectifying circuit has a simple configuration and has the effect of easily obtaining a stable servo drive signal even if the output of the total reflection light amount recoils regardless of whether information is being recorded or reproduced.

[Brief explanation of drawings]

Figure 1 shows the conventional servo gain control circuit, Figure 2 i; jF
ET+7) Characteristic Curve of Gate Voltage vs. Equivalent Drain/Sone Resistance Value FIG. 8 shows an example of the configuration of the automatic gain adjustment circuit according to the present invention. In the figure, 1 is a quadrant photodetector, 2 and 7 are differential amplifiers,
8.5. '8, 10.16 is an amplifier, 4 and 9 are FETs,
12 is an inverting amplifier, 6 and 11 are output terminals, 14. ! =1
5 is an analog switch, 17 is a recording/reproduction gate input terminal, 20, 21, 22, 28 are analog switch contacts,
R18 and R1 represent resistance.

Claims (1)

[Claims] In a disk device that is equipped with an amplifier that amplifies the track signal No. 7148 from an optical head and a focus shift signal, and adjusts the servo gain to perform track servo and focus servo using the output of each amplifier, recording is performed. A changeover switch is provided for changing the gain of the amplifier according to a switching signal for time and reproduction, and a control means is provided for stabilizing the power of the Itl recording amplifier at approximately the same level regardless of the recording and reproduction time. An automatic servo gain adjustment circuit is provided.