JPH0834007B2 - Tracking error signal generator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tracking error signal generator,
In particular, the present invention relates to a tracking error signal generation device that detects a tracking error of information detection light by a so-called phase difference method in a device that records or reproduces information on an optical recording medium.

BACKGROUND ART In an apparatus for recording or reproducing information on an optical recording disc, a so-called tracking error signal indicating a separation state of a pickup information detection light spot and a recording track in a direction orthogonal to the recording track (disc radius) is generated. A generating device is provided, an example of which is shown in FIG.

In FIG. 4, reference numeral 1 denotes a four-division type light receiving element, and the light having passed through the recording surface of the spot light for information detection of the pickup is irradiated on the light receiving surface of the four division type light receiving element 1. The four-division type light receiving element 1 is composed of four elements 1a to 1d arranged adjacent to each other so as to form four light receiving regions divided by two straight lines α and β which are orthogonal to each other. The outputs of the elements 1a and 1c, which are arranged symmetrically with respect to the intersection of the straight lines α and β, are supplied to the adder 4 via the buffer amplifiers 2 and 3, respectively. The outputs of the elements 1b and 1d are supplied to the adder 7 via the buffer amplifiers 5 and 6, respectively.

The addition outputs of the adders 4 and 7 are waveform-shaped by the waveform shaping circuits 8 and 9 including a comparator and the like, and then supplied to the phase difference detection circuit 10. In the phase difference detection circuit 10, the output p of the waveform shaping circuit 8 is a D-type flip-flop.
12 clock input terminals and a D-type flip-flop 14 reset input terminal. At the same time, the output p of the waveform shaping circuit 8 is supplied to the inverter 15. The inverted signal p- of the output p is output from the inverter 15 and supplied to the clock input terminal of the D-type flip-flop 11 and the reset input terminal of the D-type flip-flop 13.

The output r of the waveform shaping circuit 9 is the D-type flip-flop 11
And a clock input terminal of the D-type flip-flop 13. At the same time, the output r of the waveform shaping circuit 9 is supplied to the inverter 16. The inverted signal r- of the output r is output from the inverter 16 and the reset input terminal of the D-type flip-flop 12 and D
It is supplied to the clock input terminal of the flip-flop 14.

A power supply voltage is applied to the D input terminal and the set input terminal of the D-type flip-flops 11-14. The Q outputs q ₁ and q ₂ of the D-type flip-flops 11 and 12 are supplied to the negative side input terminal of the differential amplifier 18 via an OR (logical sum) gate 17. Also, the Q output of the D-type flip-flops 13 and 14
q ₃ and q ₄ are supplied to the positive side input terminal of the differential amplifier 18 via the OR gate 19. The output of this differential amplifier 18 is LP
It is output as a tracking error signal e via an F (low pass filter) 20.

In the above-described configuration, in the four-division type light receiving element 1, the center of the light spot formed on the light receiving surface by the light from the recording surface coincides with the intersection of the straight lines α and β, and the straight line α is the information detecting light spot. It is assumed that the pattern of the intensity distribution of the light from the recording surface is arranged in parallel with the moving direction in accordance with the movement following the recording track. At this time, when the information detecting light spot is moving following the recording track, the pattern of the light intensity distribution in the light spot formed on the light receiving surface of the light receiving element 1 changes from, for example, the elements 1a to 1b. Although it moves in the direction (downward in the figure), the pattern of this light intensity distribution is symmetrical with respect to the straight line α. Then, the phase difference between the waveform shaped output p and r "0", D-type flip-flop 11 to 14 is kept in the reset state Q output q ₁ to q ₄ will remain low. As a result, the negative phase input x and the positive phase input y of the differential amplifier 18
There is no level difference between them, the output of the differential amplifier 18 becomes the ground level, and the level of the tracking error signal e output from the LPF 20 becomes equal to the ground level.

Next, the information detection light spot is displaced in the inner circumferential direction,
The pattern of the light intensity distribution in the light spot formed on the light receiving surface of the four-division type light receiving element 1 is, for example, from the element 1d.
The case of displacement in the direction toward 1a (left in the figure) will be described with reference to FIG. 5 (A) is a waveform diagram of the waveform shaping output p, FIG. 5 (B) is a waveform diagram of the inverted output p-, FIG. 5 (C) is a waveform diagram of the waveform shaping output r, and FIG. ) Is a waveform diagram of the inverted output r-, (E) is the Q output
q ₁ waveform diagram, (F) waveform diagram of Q output q ₂ , (G) waveform diagram of Q output q ₃ , (H) diagram of Q output q ₄
2 (I) is a waveform diagram of the negative phase input x of the differential amplifier 18, and FIG. 6 (J) is a waveform diagram of the positive phase input y of the differential amplifier 18.

When the pattern of light intensity distribution is displaced in the direction from element 1d to 1a, waveform shaping output p and inverted output
The phase of p- leads the phases of the waveform shaping output r and the inverted output r- by an angle corresponding to the displacement amount of the information detection light spot. Then, the D flip-flops 11 and 12 are in the set state for the time corresponding to the angle, and the Q outputs q ₁ and q ₂ are at the high level for the time corresponding to the angle. Also, D
Type flip-flops 13 and 14 remain in the reset state and the Q outputs q ₃ and q ₄ remain low. As a result, only the negative-phase input x of the negative-phase input x and the positive-phase input y of the differential amplifier 18 becomes high level over the time corresponding to the displacement amount of the information detection light spot. Therefore, the differential amplifier 18
Outputs a negative polarity pulse having a pulse width corresponding to the displacement amount of the information detecting light spot, the level of the tracking error signal e output from the LPF 20 becomes negative, and its absolute value is equal to that of the information detecting light spot. The value depends on the amount of displacement.

Next, the information detection light spot is displaced in the outer peripheral direction,
The pattern of the light intensity distribution in the light spot formed on the light receiving surface of the four-division type light receiving element 1 is, for example, from the element 1a.
A case of displacement in the direction toward 1d (right side in the figure) will be described with reference to FIG. FIGS. 6 (A) to 6 (J) show waveforms of the same signals as the signals shown in FIGS. 5 (A) to 5 (J), respectively.

When the pattern of light intensity distribution is displaced in the direction from element 1a to element 1d, waveform shaping output p and inverted output
The phase of p- lags behind the phases of the waveform shaping output r and the inverted output r- by an angle corresponding to the displacement amount of the information detection light spot.
Then, the D-type flip-flops 13 and 14 are in the set state only for the time corresponding to the angle, and the Q outputs q ₃ and q ₄
Becomes high level for the time corresponding to the angle. Also,
The D-type flip-flops 11 and 12 remain in the reset state, and the Q outputs q ₁ and q ₂ remain at the low level. As a result, only the positive phase input y of the negative phase input x and the positive phase input y of the differential amplifier 18 becomes high level over a time period corresponding to the displacement amount of the information detection light spot. Therefore, the differential amplifier
A positive polarity pulse having a pulse width corresponding to the displacement amount of the information detecting light spot is output from 18 and the level of the tracking error signal e output from the LPF 20 becomes positive, and its absolute value is an absolute value of the information detecting light spot. The value depends on the displacement amount of.

In the conventional tracking error signal generating device as described above, when only the objective lens in the pickup device in which the four-division type light receiving element 1 is stored for performing tracking control is displaced, the light receiving surface of the four-division type light receiving element 1 The position of the light spot formed on the
It moves from the position shown by as shown by the broken line v or w. Then, the pattern of the light intensity distribution in the light spot formed on the light receiving surface of the four-division type light receiving element 1 is a straight line α due to the deviation of the position of the information detecting light spot on the recording surface of the recording medium from the recording track. As in the case of being asymmetrical with respect to, the amount of incident light on the elements 1a to 1d becomes unbalanced. Therefore, for example, when the position of the light spot formed on the light receiving surface of the four-division type light receiving element 1 exists at the position shown by the broken line v in FIG. 7, the respective outputs of the elements 1a to 1d are respectively shown in FIG. Amplitudes of the outputs of the elements 1a to 1d become unbalanced as shown in FIGS. As a result, the phase difference between the diagonal sum components output from the adder circuits 4 and 7 does not accurately correspond to the distance between the information detection light spot and the recording track, and an offset occurs in the tracking error signal. was there.

More specifically, as shown in FIG. 7 of the present application, the photodetection signals (hereinafter, 1ch, 2ch) of the respective divided areas 1a, 1b, 1c, 1d of the light spot imaged on the detector 1 divided into four parts. , 3ch, 4ch) each contain phase information corresponding to the radial deviation between the pit string of the disc and the light beam. Therefore, the basic phase difference method is to generate diagonal sum signals (1ch + 3ch) and (2ch + 4ch) and differentially detect the polarity and magnitude of the phase difference between the diagonal sum signals. When an ideal disc is targeted, such as when the disc is completely flat (no skew) or the track eccentricity is zero, the light spot is distributed in the center of the detector, so the diagonal sum signal (1ch + 3ch ), (2ch + 4ch) simple addition can generate a correct error signal. However, in reality, because of disk skew and lens offset, the light spot is imaged at a position displaced from the center. In this case, the amplitude information of each channel is added to the phase information of the diagonal sum signal, and it becomes impossible to obtain a correct tracking error signal.

For example, assuming that 1ch and 3ch are x ₁ and x ₂ as a simple model, it can be written as x ₁ = acos (ωt + α) (1) x ₂ = bcos (ωt + β) (2). The diagonal sum signal x is X = rcos (ωt + γ) (3). However, r ² = a + b + 2abcos (α−β) (4) γ = tan ⁻¹ {(asinα + bsinβ) / (acosα + bcos
β)} ... (5)

Focusing on the equation (5), when the light spot is located at the center of the detector, a = b, and the phase information γ is
It depends only on the phase terms α and β. However, when the light spot deviates from the center of the detector, a ≠ b and the phase information γ
Also includes the amplitude information a and b, and the amplitude, that is, the disk skew includes the target value shift (offset) corresponding to the lens offset. The same applies to 2ch and 4ch.

Due to the occurrence of this offset, the track jump movement operation of the information detection point is performed, and when the total sum of the outputs of the elements 1a to 1d changes as shown in FIG. When the position of the formed light spot exists at the position shown by the solid line u in FIG. 7, the tracking error signal as shown by the solid line u ′ in FIG. When the position of the light spot formed on the light receiving surface of the light receiving element 1 moves to the positions indicated by broken lines v and w in FIG. 7, a broken line v ′ in FIG. 9 (B).
And w'changes the level of the tracking error signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tracking error signal generation device capable of generating a tracking error signal without offset.

The tracking error signal generation device of the present invention is the intensity of the reflected beam obtained from the recording medium by an optical system that irradiates the recording surface of the recording medium with a light beam to form a light spot for information reading or information writing. A tracking error signal generation device for detecting a tracking error by a phase difference method, the device including a light receiving element divided into four light receiving areas by two straight lines that intersect each other at a predetermined intersection near the center of distribution. Corresponding to the waveform processing means for making the amplitude of each photodetection signal by the photodetection region constant, and each photodetection signal by one photodetection region pair arranged at symmetrical positions with respect to the intersection of the four photodetection regions. Is arranged at a position symmetrical with respect to the intersection of the first light receiving unit and the first light receiving unit for adding the outputs of the waveform processing unit. Second adding the output of said waveform processing means corresponding to each light detection signal by the other light receiving area pairs that
And the phase difference detecting means for generating a signal corresponding to the phase difference between the addition outputs of the first and second adding means as a tracking error signal.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.

In FIG. 1, the four-division type light receiving element 1 and the buffer amplifiers 2, 3, 5, and 6 are connected in the same manner as in the device of FIG. However, in this example, the buffer amplifier 2,
The outputs of 3, 5, and 6 are supplied to limiters 21, 22, 23, and 24 as waveform processing means, respectively. Limiter 21 or
24 has a configuration in which the portion where the instantaneous level of the input signal is V ₁ or more and the portion where V _{2 is} V ₂ or less are clipped to limit the amplitude. The outputs of the limiters 21 and 22 are supplied to the adder 4. The output of the adder 4 is LPF (low pass filter) 2
It is supplied to the waveform shaping circuit 8 via 5 to be waveform-shaped and then supplied to the phase difference detection circuit 10. The outputs of the limiters 23 and 24 are supplied to the adder 7. The output of the adder 7 is supplied to the waveform shaping circuit 9 via the LPF 26 for waveform shaping, and then is supplied to the phase difference detection circuit 10.

In the above configuration, when signals as shown in FIGS. 2 (A) and 2 (B) are output as the outputs g and h of the buffer amplifiers 2 and 3, the limiters 21 and 22 make the instantaneous level V ₁ or more. By clipping the portion and the portion of V _{2 and} below, signals close to rectangular waves are obtained as the outputs i and j of the limiters 21 and 22 as shown in FIGS. When the outputs i and j of the limiters 21 and 22 are added and combined by the adder 4, an addition output k as shown in FIG. 2 (E) is obtained. This addition output k is a signal containing high-order harmonics because the outputs i and j are signals close to rectangular waves. The higher-order component of the addition output k is removed by the LPF 25, and the output m of the LPF 25 becomes a signal having a clear waveform at the zero cross point as shown in FIG.
Is supplied to. A waveform shaping output p consisting of a rectangular wave is output from the waveform shaping circuit 8 as shown in FIG. At the same time, a waveform shaping output r composed of a rectangular wave is formed in the same manner as the waveform shaping output p.
Is output from the waveform shaping circuit 9 and supplied to the phase difference detection circuit 10.

The phase difference between these waveform shaping outputs p and r becomes "0" when the information detecting light spot moves following the recording track, as in the apparatus of FIG. Then, the D-type flip-flops 11 to 14 in the phase difference detection circuit 10 remain in the reset state, and the Q outputs q _{1 to} q ₄ remain at the low level. As a result, no level difference occurs between the negative-phase input x and the positive-phase input y of the differential amplifier 18, the output of the differential amplifier 18 becomes the ground level, and the level of the tracking error signal e output from the LPF 20 is grounded. Will be equal to the level.

Next, the information detection light spot is displaced in the inner circumferential direction,
The pattern of the light intensity distribution in the light spot formed on the light receiving surface of the four-division type light receiving element 1 is, for example, from the element 1d.
When it is displaced in the direction toward 1a (left in the figure),
Similar to the apparatus of FIG. 4, the phases of the waveform shaping output p and the inverted output p- advance from the phases of the waveform shaping output r and the inverted output r- by an angle corresponding to the displacement amount of the information detecting light spot. Then, the D-type flip-flop in the phase difference detection circuit 10
11 and 12 are set for the time corresponding to the angle, and the D-type flip-flops 13 and 14 remain in the reset state. As a result, only the negative-phase input x of the negative-phase input x and the positive-phase input y of the differential amplifier 18 becomes high level over the time corresponding to the displacement amount of the information detection light spot, and the differential amplifier 18 outputs the information. A negative pulse having a pulse width corresponding to the displacement amount of the detection light spot is output, the level of the tracking error signal e becomes negative, and its absolute value is a value corresponding to the displacement amount of the information detection light spot. Become.

Next, the information detection light spot is displaced in the outer peripheral direction,
The pattern of the light intensity distribution in the light spot formed on the light receiving surface of the four-division type light receiving element 1 is, for example, from the element 1a.
If it is displaced in the direction toward 1d (right in the figure),
Similar to the apparatus of FIG. 4, the phases of the waveform shaping output p and the inverted output p- are delayed from the phases of the waveform shaping output r and the inverted output r- by an angle corresponding to the displacement amount of the information detection light spot. Then, the D-type flip-flops 13 and 14 in the phase difference detection circuit 10 are in the set state for the time corresponding to the angle, and the D-type flip-flops 11 and 12 are in the reset state. As a result, the negative phase input x of the differential amplifier 18
And only the positive phase input y of the positive phase inputs y becomes high level over a time period corresponding to the displacement amount of the information detection light spot,
The differential amplifier 18 outputs a positive polarity pulse having a pulse width corresponding to the displacement amount of the information detection light spot, the tracking error signal e becomes positive in level, and its absolute value is the displacement of the information detection light spot. The value depends on the quantity.

In the above operation, even if the positions of the light spots formed on the light receiving surface of the four-division type light receiving element 1 are displaced and the amplitudes of the outputs of the elements 1a to 1d become unbalanced, the outputs of the elements 1a to 1d are output. If the amplitude of the limiter 21 to 24 is such that the amplitude limiting action of the limiters 21 to 24 works,
The amplitude of the output of 24 does not change and becomes constant. Also, the two elements 1a arranged symmetrically with respect to the straight line β
Since the phase difference between the outputs of the two limiters 21 and 23, 22 and 24 corresponding to the outputs of 1 and 1b, 1c and 1d does not change depending on the position of the light spot formed on the light receiving surface, the addition circuit 4 and A phase difference does not occur between the outputs of 7 and an offset is prevented from occurring in the tracking error signal e.

FIG. 3 is a block diagram showing another embodiment of the present invention, which is a four-division type light receiving element 1, buffer amplifiers 2, 3, 5, 6, adder circuits 4, 7, LPFs 25, 26, waveform shaping circuit 8 , 9 and the phase difference detection circuit 10 are connected in the same manner as in the device of FIG. However, in this example, the outputs of the buffer amplifiers 2, 3, 5, 6 are the comparators 27, 28, 2 as the waveform processing means.
It has been supplied to 9,30. The comparators 27 to 30 compare the instantaneous level of each output of the buffer amplifiers 2, 3, 5, and 6 with the reference voltage Vr, and the instantaneous level of each output of the buffer amplifiers 2, 3, 5, 6 is equal to or higher than the reference voltage Vr. Is configured to output a high level signal. These comparators 27 and 28
Are output to the adder circuit 4. Further, the respective outputs of the comparators 29 and 30 are supplied to the adding circuit 7.

Also in the above configuration, the position of the light spot formed on the light receiving surface of the four-division type light receiving element 1 is displaced and the element 1a
Even if the amplitudes of the outputs of 1 to 1d become unbalanced, if the amplitudes of the outputs of the elements 1a to 1d are large enough that the instantaneous level of the inputs of the comparators 27 to 30 exceeds the reference voltage Vr, The amplitudes of the outputs of 27 to 30 are kept constant, which prevents the tracking error signal e from being offset.

EFFECTS OF THE INVENTION As described in detail above, the tracking error signal generator according to the present invention performs waveform processing to make the amplitudes of the output signals of the four elements of the four-division type light receiving element constant, and then
The tracking error signal is a signal corresponding to the phase difference between the two signals obtained by adding the respective waveform processing outputs corresponding to the outputs of the two pairs of elements that are symmetrical with respect to the intersection of the two straight lines divided into one element. Since the output amplitudes of the four elements are constant even if the position of the light spot formed on the light receiving surface of the four-division type light receiving element is displaced, the two elements are divided into four elements. It is possible to prevent an offset from occurring in the tracking error signal because the phase difference between the two signals obtained by adding the waveform processing outputs corresponding to the outputs of the two pairs of elements that are symmetric with respect to the intersection of the straight lines does not change. You will be able to do it.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of each part of FIG. 1, and FIG. 3 is a block diagram showing another embodiment of the present invention. FIG. 4 is a block diagram showing a conventional tracking error signal generator, and FIG.
4 is a waveform diagram showing the operation of each part of the apparatus of FIG. 4, FIG. 6 is a waveform diagram showing the operation of each part of FIG. 4, and FIG. FIG. 8 is a diagram showing the positions of the light spots formed, and FIG. 8 is a waveform diagram showing the outputs of the elements 1a to 1d when the positions of the light spots formed on the light receiving surface of the four-division type light receiving element 1 move. FIG. 9 is a diagram showing the relationship between the position of the light spot formed on the light receiving surface of the four-division type light receiving element 1 and the waveform of the tracking error signal. Explanation of main part code 1 …… 4-division type photo detector 4,7 …… Adding circuit 10 …… Phase difference detecting circuit 21,22,23,24 …… Limiter 27,28,29,30 …… Comparator

Claims (3)

[Claims] 1. An optical system for irradiating a recording surface of a recording medium with a light beam to form a light spot for reading information or writing information, and the reflection beams obtained from the recording medium are close to each other in the vicinity of the center of their intensity distribution. A tracking error signal generation device for detecting a tracking error by a phase difference method, the tracking error signal generation device including a light receiving element divided into four light receiving areas by two straight lines intersecting at a predetermined intersection, Waveform processing means for making the amplitudes of the detection signals constant, and the waveform processing means corresponding to each light detection signal by one light receiving area pair arranged symmetrically with respect to the intersection of the four light receiving areas. Of each of the four light receiving areas and the other pair of light receiving areas arranged symmetrically with respect to the intersection of the four light receiving areas. Second adding means for adding the outputs of the waveform processing means corresponding to the output signal; and the first adding means.
And a phase difference detecting means for generating, as a tracking error signal, a signal corresponding to the phase difference between the respective addition outputs of the second adding means, the tracking error signal generating device. 2. The tracking error signal generating device according to claim 1, wherein the waveform processing means comprises a limiter for limiting the amplitude of the photodetection signal for each of the light receiving regions. 3. The waveform processing means comprises a comparison circuit which outputs a signal of a predetermined level when the instantaneous level of the photodetection signal exceeds a reference level for each of the light receiving regions. A tracking error signal generator according to the first section.