JP2789189B2 - Optical head control signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial application >> The present invention relates to an optical information reading apparatus for reading out information recorded on a VD, a CD or the like by using a light beam, or writing information on a disk or the like using a light beam. The present invention relates to flaw detection correction of an optical information writing device. << Summary of the Invention >> The difference output of each light-receiving element on the same side divided by a straight line perpendicular to the track direction of the four-divided light-receiving element, which has information on the degree and state of entry and exit of the uneven pit on the disk, The signals are input to two comparators which output the signals in comparison with two reference voltages. These two comparators
In the ON / OFF state, the difference output of the diagonal sum of the four-division light-receiving element is taken out and a tracking error signal is generated. Is turned off, and no tracking error occurs. On the other hand, a hold circuit that holds the tracking error signal and the focusing error signal for a certain period of time is provided, and both converters are turned off.
In the state, the tracking error generation circuit adds the output from the tracking error hold circuit,
Furthermore, shut off the focusing error generation circuit,
Select the hold circuit output of the focusing error. As a result, the flaw detection is performed using the signal used in the tracking error generation circuit and the output of the simple hold circuit is switched without using a special circuit such as flaw detection based on the decrease in the amplitude of the RF signal. , A very simple configuration and a low cost. In addition, since the switching of the gain of the tracking servo or the tracking servo is not performed after the detection of the flaw, a very large effect can be obtained even in a place where there is much disturbance due to vibration. << Prior Art >> Conventionally, an optical information reading apparatus using a heterodyne method as a tracking shift detection method has been known. FIG. 2 is a schematic diagram of an optical information reading apparatus using the above-described method. The light emitted from the semiconductor laser 1 is reflected by the beam splitter 2 in the direction of the disk 5, is converted into parallel light by the collimator lens 3, and passes through the objective lens 4.
Light is collected on the disk 5. This light is reflected by an information track having an uneven pit shape, passes through the objective lens 4, the collimator lens 3, and the beam splitter 2 in a direction orthogonal to the incident light beam, and enters the light receiving element 6.
In the light receiving element 6, the reflected light from the disk 5 is detected, and the change is extracted as a signal. In addition, for focusing control or tracking control, a control signal for driving the objective lens 4 constituting the optical reading device to perform position control is formed. FIG. 3 shows a principle for explaining the heterodyne method (Patent Publication No. 56-30610) of the above-mentioned tracking control, and FIG. 4 shows a block diagram of a circuit for implementing the method. The reading light of the disk 5 has a diffraction pattern as shown in FIG. 3 on the light receiving element 6 due to the positional relationship between the light and dark pattern of the light diffracted by the pits and the spot of the laser light. FIG. 3A shows the positional relationship of the beam with respect to the pit P,
Figure b shows the pattern of the upper beam and the diffracted light. Note that the hatched portions indicate portions with a small amount of light.
From (1), (2), and (3), it can be seen that when the pit enters and exits the beam, the symmetry of the pattern of the diffracted light is reversed in the right and left cases. Therefore, at a certain timing when the pit enters and exits the beam, this symmetry is changed to D1, D2,
If it can be determined from the outputs from the light receiving elements D3 and D4, it can be used as a tracking control signal. FIG. 4 shows an embodiment based on the above-described principle based on (Publication Publication No. 57-74837). D1 of the four-segment light receiving element 6
To the adder circuit 10 the output of D3, also the output of D2 and D4 is input to the addition circuit 9, both sum output and input to the subtraction circuit 12 to obtain the difference signals S ₁ between the output. On the other hand, the outputs of D1 and D4 are added to the addition circuit 8
To, and the output of D2 and D3 input to the adder circuit 7 receives the two addition output to the addition output 11 to obtain a sum signal S ₂ of the two outputs. Signals S ₁ has as shown in FIG. 3, with respect to the spot, so the output signal corresponding to the symmetry of the collapse of the diffracted light when pits entering or leaving, including tracking error information, and the signal S ₂
Is a reproduction information signal. The output of the adder circuit 11 is
Is supplied to the falling pulse 14 falling and rising pulse generator 13, it generates the respective signals S ₃ and S _4. On the other hand, the output of the subtracting circuit 12 is supplied to the sampling hold circuits 15 and 16 is sampled by the respective pulse signals S ₃ and S _4, and holds this value is supplied to the subtraction circuit 17 to obtain a tracking error signal I have. FIG. 5 is a diagram showing the signal output of each of the main parts generated by the above circuit configuration. From the state where the pit is almost completely entered from the left with respect to the spot,
This shows the state of each signal output while the pit moves to the right and starts to exit from the right. Signals S _1, a signal including a tracking error information. Signal S ₂ is reproduced signal output. signal
S ₃ is rising pulse signal based on the zero-cross point of the signal S _2. Signal S ₄ is falling pulse signal to the zero-cross point of the signal S ₂ as a reference. Signal S ₆ shows that the polarity changes from negative to positive as the pit moves from left to right with respect to the beam,
Alternatively, the output is inverted from positive to negative, and is an output corresponding to the track shift amount, that is, a signal corresponding to the tracking error signal. << Problems to be Solved by the Invention >> However, in the conventional heterodyne method, since the tracking error generation circuit is configured using a pulse generation circuit and a sample hold circuit, the circuit configuration becomes complicated and costly. Disadvantage. In addition, when the surface of the disk is scratched, a false signal rides on the tracking error, and the tracking servo becomes unstable or a tracking jump occurs. For example, if there is a black dot scratch on the disk surface,
As shown in FIG. 6, the shielding of the light beam by the flaw always causes a point-symmetric shadow in the beam. This is because there is a flaw of about 700 μm and the beam (beam diameter 70
When the light beam erodes (0 to 800 μm), the portion where the incident light beam is blocked naturally becomes a shadow, but the light beam reflected by the disk is also blocked by the scratch. Therefore, a point-symmetric shadow is generated on the four-divided light receiving element. FIG. 7 shows the effect of such a flaw on each signal. Assuming that the pit is on the track, the right half of the beam is blocked by a flaw. Time t ₁ earlier, scratches in the absence come in the beam, at this time, signals S ₁ is zero, signal S ₂ is subjected to modulation determined by the reflectivity of the disk and bit depth, tracking The error signal is also zero. However, when the beam by the time t ₁ after wound begins to be gradually eroded, but the shadows of point symmetry begins to occur because,
Signals S ₁ which the modulated component has thought of pits is generated flaw signal. On the other hand, the signal S ₂ is an amount corresponding to eroded by shadow modulation by pits drops. However, the phase relationship of the signal S ₁ and the signal S ₂ is not almost disturbed is that by scratches. Therefore the signal S ₂
When the sample hold at zero-crossing, scratches, by the time t ₂ which are incident symmetrically in the right half of the beam, the tracking error signal is almost generate a negative pseudo signal. Time t ₂
Later, as the wound gradually protrude from the beam, the signal having the polarity of the status and reverse are produced to the signal S _1, the tracking error signal is generated the most positive of the pseudo signal. Therefore, in the method of obtaining the pattern change of the intensity distribution of the diffracted light from the difference signal of the diagonal sum of the four-divided light receiving elements and generating the tracking error signal, in any method, the tracking error signal includes Suspected signals due to wounds always appear. As a result, the tracking servo becomes unstable, causing a tracking jump. In particular, when the flaw blocks half of the beam with respect to the track direction, this tendency was remarkable. Also in the focus servo, a method of generating a focus error signal from a difference signal of the diagonal sum of the four-divided light receiving elements as in the astigmatism method has the same effect as the above phenomenon. Inside, a signal appears due to the wound. For this reason, the focus actuator is shaken, and a focus shift occurs in a wider range than the size of the flaw due to a transient phenomenon. As a result, the beam becomes larger, crosstalk with the adjacent track and crosstalk with the next signal occur, the distribution of the diffracted light becomes abnormal, the diagonal difference signal also becomes abnormal, and the tracking error signal becomes a suspect signal. Become. Therefore, the present invention solves such a conventional disadvantage by obtaining a tracking error signal at a low cost and equivalent to that of the heterodyne method, and achieving high-precision and stable tracking without generating a false signal due to a scratch. It is intended to easily obtain an error signal and a focusing error signal. << Means for Solving the Problems >> In order to solve the above-mentioned problems, the present invention provides a reading light which is made incident on a disk by an optical reading device and modulated by the disk, in effect in a track direction and a track direction. And first and second addition circuits for receiving output signals of at least four light receiving elements divided in a direction perpendicular to the direction and adding output signals of the respective light receiving elements in opposite diagonal directions, and a straight line perpendicular to the track direction. A third and a fourth addition circuit for adding the output signals of the respective light receiving elements on the same side, a fifth subtraction circuit for generating a difference signal between the output signals of the first and second addition circuits, A sixth circuit that generates a signal whose polarity is inverted with respect to the difference signal, and a difference signal between output signals of the third and fourth addition circuits,
At least two reference voltages are set to create substantially three states, and in either of the two states, one of the output of the fifth circuit and the output of the sixth circuit is selectively output. A seventh circuit for cutting off the output of the fifth circuit and the output of the sixth circuit, a low-pass filter circuit, an eighth hold circuit for holding a signal passed through the low-pass filter circuit for a certain period, and the low-pass filter The output that has passed through the circuit and the output of the eighth hold circuit
A ninth circuit for synthesizing the output made conductive in one of the two states. The output signal passing through the ninth circuit is used as a tracking error signal, and the focusing error signal obtained from the light receiving element is used in the two states. A tenth circuit for outputting, an eleventh hold circuit for holding the focusing error signal for a certain period of time, an output through the tenth circuit, and an output of the eleventh hold circuit in the remaining one state. It comprises a twelfth circuit for synthesizing an output that is sometimes made conductive, and the output signal passed through the twelfth circuit is used as a new focusing error signal. << Operation >> As described above, when a circuit is configured and an error signal is obtained, information relating to the degree and state relating to pit entry / exit is digitized, so that only information relating to pit entry / exit is provided.
Therefore, signals other than the pit tracking deviation information are not mixed into the tracking error signal. In the seventh circuit, if an appropriate slice level is set and the level of the information signal relating to the entry and exit of pits is restricted, a tracking error signal may be generated depending on the presence or absence of a flaw.
The tracking error signal is output while holding the tracking error signal while the tracking error signal is extinguished. If there is no tracking error signal, the signal becomes a normal tracking error signal. Therefore, mixing of a pseudo signal into the tracking error signal becomes a fluctuation within the residual error range, and is substantially completely eliminated.
Also, since a signal for generating a tracking error signal is used for the focusing error signal, flaw detection and correction can be performed completely in synchronization with the tracking error signal. Similarly, mixing of the pseudo signal in the focusing error signal is only a fluctuation within the residual error range, and is substantially completely eliminated. Therefore, it is possible to completely avoid the instability of the tracking servo, to eliminate the occurrence of a tracking jump, and to carry out highly accurate and stable tracking control and focusing control. << Example >> Hereinafter, an example of the present invention will be described with reference to the drawings.
As shown in Fig. 3, when pits enter and exit the beam,
The symmetry of the pattern of the diffracted light is broken on the left and right of the track, and when the pit depth is about 1/5 of the wavelength of the light used, such as CD or VD, A difference in the intensity distribution of the diffracted light occurs. By taking out the difference in the intensity distribution as a signal, it is possible to determine whether the pit enters or exits the beam. Therefore, if it is possible to determine from the above signal that the symmetry has been lost when the pit enters and exits the beam, it can be used as a tracking error signal. FIG. 1 is an example of a block diagram of a circuit for implementing the present invention based on the above principle. Reference numeral 6 denotes a four-division light receiving element, which has a track direction X and a radial direction
And four light receiving elements D1, D2, D3, and D4. 7C outputs alternately two states among the three states and the output S ₁₂ of the fifth subtraction circuit 25 and the output S ₁₃ of the sixth circuit 26, a fifth subtraction circuit when the remaining one state 25 outputs S ₁₂
When the seventh circuit to shut off the output S ₁₃ of the sixth circuit 26, in this embodiment the comparator (27, 28) inverter (33, 34)
And gate switches (29, 30). 9C is an output S ₂₁ of the hold circuit 36 of the eighth, the out by conduct current when the remaining one state, and its output, in the ninth circuit for synthesizing the output S ₁₉ passed through the low-pass filter 35 In this embodiment, an AND circuit 38 and a gate switch 39 are provided. 10C outputs a focusing error signal obtained from the light receiving element in two out of three states.
Here, the circuit comprises gate switches (31, 32). 12C outputs the output of the eleventh hold circuit 37 to the remaining 1
And output when it is in one of the states.
It is a twelfth circuit for combining the output having passed through the circuit 10C of FIG. The outputs of D1 and D2 of the quadrant light receiving element 6 are added to the adder circuit 20,
Further, the output of D3 and D4 inputted to the adding circuit 21, both the added output is input to the subtraction circuit 24 to obtain a difference signal S ₁₁ of both outputs. Signal S
₁₁ contains information about entering and exiting the pit. on the other hand,
The D1 and the addition circuit 22 the output of D3, also the output of D2 and D4 inputted to the adder circuit 23, both the added output is input to the subtraction circuit 25 to obtain a difference signal S ₁₂ of both outputs. Also, the outputs of D1 and D3, and D
The output of the 2 and D4, As to the polarity opposite to the signal S _12, and input to the subtraction circuit 26 to obtain a difference signal S _13. Although the signals S ₁₂ and S ₁₃ are signals of opposite polarities, as shown in FIG. 3, they are output signals corresponding to the broken symmetry of the diffracted light when the pit enters and exits the spot. Both signals include tracking error information. The output S ₁₁ of the subtracting circuit 24, two different reference voltages Vref1 and Vref2 and the respective comparison is input to the comparator 27, 28 outputs, to obtain the respective signals S _14, S _15.
The signal S ₁₄ and S _15, to obtain an inverted signal S ₁₆ and S ₁₇ is input to each inverter 33 and 34. FIG. 8 shows the relationship between these signals. Using the reference voltages Vref1 and Vref2 as reference voltages, respectively,
When the output signal S ₁₁ than the reference voltage is large, the signal S
_14, S ₁₅ becomes a high level, the signal S _16, S ₁₇ becomes low level. Further, when the output signal S ₁₁ is lower than the reference voltage, the signal S _14, S ₁₅ becomes a low level, the signal
S ₁₆ and S ₁₇ are at a high level. Accordingly, the signal S ₁₅ is, V
High level only when the voltage is higher than ref2, and the signal S
₁₆ becomes high level only when the voltage is lower than Vref1. On the other hand, the output S ₂₀ of the AND circuit 38 of the signal S ₁₄ and S ₁₇ is, Vref
It goes high only when the output is between 1 and Vref2. Now,
Preferably provided a switching circuit 29, 30, 31, 32 to open the gate when a high level signal S ₁₅ and S _16. Switching circuit 2
9,30 are each opened and closed by the signal S ₁₆ and S _15. FIG. 9 is a diagram showing a signal of a circuit portion for generating a tracking error signal. This shows the state of each signal output from the state in which the pit enters the spot almost entirely from the left side to the state in which the pit moves to the right and starts to exit from the right side. Signal S _11, a signal including information indicating a degree state and about and out of the pit. The signals S ₁₂ and S ₁₃ are signals containing tracking error information and have opposite polarities. Therefore,
When the signal S ₁₅ is high, i.e., if the pit has entered the beam, the gate switch 29, the signal S ₁₂
The output of addition, when the signal S ₁₆ is high, i.e., when the pit starts out from the beam, the gate switch 30, it put out an output signal S _13, signal S ₁₈ is obtained, the low-pass filter 35 By passing the tracking error signal S
₁₉ is obtained. Further, when the signals S ₁₅ and S ₁₆ are both at the low level, the signal S ₂₀ is at the high level and no tracking error signal is generated. At this time, the addition of the output of the output of the tracking error signal S ₁₉ from the hold circuit 36 which holds a certain period, a smooth tracking error signal S
You get ₁₉ . Next, consider a case in which a black dot-like flaw as well as a pit enters the beam. If a flaw is present, the modulation level due to the pits is significantly reduced, as shown in FIG. The scratch causes a point-symmetric shadow on the four-divided light receiving element. FIG. 10 shows the effect of such a shadow on each signal. Assuming that the pit is on the track, the beam shows a state in which the right half is blocked by a flaw. After time t _1, the beam begins to be gradually eroded by scratches, because although the shadow of point symmetry begins to occur, the flaws of the signal, the signal S ₁₂ which the modulated component is superimposed on the pit is generated. At the same time, the signal S ₁₂ opposite polarity of the signal S ₁₃ is also generated. On the other hand, the signal S ₁₁ is by an amount which is eroded by the shadow, modulation by pits drops. Accordingly, by appropriately setting the reference voltages Vref1 and Vref2, to obtain a signal S ₁₅ and S _16. The signal S _16, and outputs the switching input of the signal S ₁₅ and S _16, the signal _20, since extracting an output of the hold circuit 36, the tracking error signal is influenced by some wounds are but scars Is an average tracking error signal, and can be made sufficiently smaller than the normal amplitude of the tracking signal. Therefore, the generation of the pseudo signal due to the scratch has a degree of fluctuation within the residual error range, and does not affect the tracking servo. Further, with respect to the focusing error signal, the signal S ₁₅ and S _16, respectively gate switch
Open and close 32,31. The output is held by a hold circuit 37,
Preferably provided a gate switch 40 which opens and closes by a signal S _20. Therefore, when the influence of the flaw starts to appear, an average focusing error signal is obtained, and the average focusing error signal amplitude can be made sufficiently smaller than the normal amplitude of the focusing error signal.
Therefore, the generation of the pseudo signal due to the flaw is in the order of fluctuation within the residual error range in synchronization with the tracking error signal, and does not affect the focusing servo. << Effects of the Invention >> As described above, according to the present invention, the tracking error generation circuit does not require a complicated circuit configuration such as a pulse generation circuit and a sample-and-hold circuit, and includes a subtraction circuit, a comparator, a gate switch, and the like. Thus, a tracking error signal equivalent to that of the heterodyne method can be obtained, so that the cost is very low. In addition, since the information on the state and the degree related to the entry and exit of the pits in the beam becomes a signal of only the state related to the entry and exit of the pits by the comparator,
Signal components other than pit tracking deviation information are not mixed. In addition, the presence or absence of a flaw can be detected from information on the degree to which a pit enters or exits the beam. Therefore, if the level of the two reference voltages is properly set, and if a flaw exists, the output held in front is added. The pseudo signal caused by the scratches on the tracking servo can be kept within the residual error range, and can be made to have substantially no influence. In addition, a focusing error signal has the same effect as the above, and at the same time, a flaw is detected using the output of a comparator used for generating a tracking error signal, so that a special circuit needs to be provided. Without
In addition, since the flaw detection can be performed at a timing synchronized with the flaw detection for the tracking error signal, the accuracy is improved. Therefore, it is possible to completely avoid track jump, instability of tracking servo, and instability of focusing servo due to scratches. Also, since the flaw correction is not performed by switching the gain, there is no need to limit the servo band, and the behavior with respect to disturbance can be performed in the same manner as in the normal servo state. It can withstand use in many places, and can implement high-precision tracking servo and focusing servo.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a circuit according to the present invention. FIG. 2 is a schematic diagram showing an example of an optical system of an optical reader. FIG. FIG. 4 shows a pattern of the diffracted light on the divided light receiving element. FIG. 4 is a block diagram of a circuit based on the conventional heterodyne method. FIG. 5 is a waveform diagram of signal outputs of main parts according to the conventional heterodyne method. FIG. 7 showing a light / dark pattern on a divided light receiving element FIG. 7 Waveform diagram of signal output of main parts according to the conventional heterodyne method when there is a flaw FIG. 8 Partial circuit for generating timing of tracking method according to the present invention FIG. 9 is a waveform diagram of main signal outputs of various parts of the tracking system according to the present invention. FIG. 10 is a waveform diagram of main signal outputs of main parts of the tracking system according to the present invention when there is a flaw. ; Half Body laser 2; Beam splitter 3; Collimator lens 4; Objective lens 5; Disk 6; Quadrant light receiving element 7, 8, 9, 10, 11, 20, 21, 22, 23; Addition circuits 12, 17, 24, 25 , 26; subtraction circuit 13; rising pulse generation circuit 14; falling pulse generation circuit 15, 16; sample and hold circuits 27, 28; comparators 29, 30, 31, 39, 40; gate switches 33, 34; inverter 35; low-pass Filters 36 and 37; Hold circuit 38; AND circuit

Claims (1)

(57) [Claims] Incident on the disc by an optical reader,
First, the read light modulated by the disk is received by at least four light receiving elements divided into a track direction and a direction perpendicular to the track direction, and output signals of the respective light receiving elements in the opposite diagonal directions are added. A second adding circuit, third and fourth adding circuits for adding output signals of respective light receiving elements on the same side divided by a straight line perpendicular to the track direction, and the first and second adding circuits A fifth subtraction circuit that generates a difference signal between the output signals of the third and fourth addition circuits, a sixth circuit that generates a signal whose polarity is inverted with respect to the difference signal, and an output signal of the third and fourth addition circuits. The output of the fifth subtraction circuit is output in a first state in which the difference signal is lower than the first reference voltage, and the output of the sixth subtractor is output in a second state higher than the second reference voltage higher than the first reference voltage. And outputs of the third and fourth addition circuits. A seventh state in which the output of the fifth subtraction circuit and the output of the sixth circuit are cut off in a third state where the difference signal of the signal is higher than the first reference voltage and lower than the second reference voltage. A circuit, an output of the seventh circuit is input to a low-pass filter circuit, an eighth hold circuit for holding a signal passed through the low-pass filter circuit for a certain period, and an output of the eighth hold circuit to the third circuit. In the state, the output is combined with the output of the low-pass filter circuit to output a tracking error signal. A ninth circuit, and a tenth circuit for outputting a focusing error signal obtained from the light receiving element in the first state or the second state.
And an eleventh circuit for holding the focusing error signal for a certain period of time.
And a twelfth circuit that outputs the output of the eleventh hold circuit in a conductive state in the third state, combines the output with the output of the tenth circuit, and outputs a focusing error signal. An optical head control generation circuit characterized by the following.