JPH0711867B2 - Tracking error signal generator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tracking error signal generation device, and more particularly to a tracking error signal generation device in an apparatus for recording or reproducing 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. 5, 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 detecting information of the pickup irradiates 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. Elements symmetrically arranged about the intersection of straight lines α and β
The outputs of 1a and 1c are the buffer amplifiers 2 and 3, respectively.
Is supplied to the adder 4 via. Also, the element
The outputs of 1b and 1d are the buffer amplifiers 5 and 6, respectively.
Is supplied to the adder 7 via.

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 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. An 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 supplied to the reset input terminal of the D-type flip-flop 11 and the reset 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. An inverted signal r- of the output r is output from the inverter 16 and supplied to the reset input terminal of the D-type flip-flop 12 and the clock input terminal of the D-type 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 q _{3 of} the D-type flip-flops 13 and 14
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 LPF.
It is output as a tracking error signal e via a (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 detection light spot moves 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 is, for example, an element.
Although it moves in the direction from 1b to 1a (upward 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 split type light receiving element 1 is, for example, elements 1a to 1d.
The case of displacement in the direction toward (to the right in the figure) will be described with reference to FIG. FIG. 6 (A) is a waveform diagram of the waveform shaping output p, FIG. 6 (B) is a waveform diagram of the inverted output p−, and FIG. 6 (C) is a waveform diagram of the waveform shaping output r. ) Is a waveform diagram of the inverted output r−, FIG. 7E is a waveform diagram of Q output q ₁ , FIG. 6F is a waveform diagram of Q output q ₂ , and FIG. _{3 is} a waveform diagram of FIG. ₃ , (H), a waveform diagram of Q output q ₄ , FIG. (I) is a waveform diagram of the negative phase input x of the differential amplifier 18, and FIG. 3 is a waveform diagram of the positive phase input y of FIG.

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 p
The − phase advances 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 11 and 12 are in the set state only for the time corresponding to the angle, and the Q outputs q ₁ and q ₂
Becomes high level for the time corresponding to the angle. Also,
The D-type flip-flops 13 and 14 remain in the reset state, and the Q outputs q ₃ and q ₄ remain at the low level. 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
A negative 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 negative, and the absolute value of the tracking error signal e is an information detecting light spot. The value depends on the displacement amount of.

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 split type light receiving element 1 is, for example, elements 1d to 1a.
The case of displacement in the direction toward the left side (left side in the figure) will be described with reference to FIG. FIGS. 7 (A) to 7 (J) show waveforms of the same signals as the signals shown in FIGS. 6 (A) to 6 (J), respectively.

When the pattern of light intensity distribution is displaced in the direction from element 1d to 1a, waveform shaping output p and inverted output p
The phase of − is 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 are in the set state for the time corresponding to the angle, and the Q outputs q ₃ and q ₄ are at the high level for the time corresponding to the angle. Further, 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 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 positive polarity pulse having a pulse width corresponding to the displacement amount of the information detection light spot, the level of the tracking error signal e output from the LPF 20 becomes positive, and its absolute value Is a value corresponding to the displacement amount of the information detection light spot.

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 at the position moves from the position indicated by the solid line u in FIG. 8 to 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 with respect to the 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 asymmetry, the amounts of light incident on the elements 1a to 1d become 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. 8, 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.

Due to the occurrence of this offset, the track jumping movement operation of the information detection point is performed and the total output of the elements 1a to 1d changes as shown in FIG. 10 (A). When the position of the formed light spot exists at the position shown by the solid line u in FIG. 8, 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 shown by broken lines v and w in FIG. 8, tracking error as shown by broken lines v ′ and w ′ in FIG. 10 (B). The signal level changes.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a tracking error signal generator capable of generating a tracking error signal without offset.

The tracking error signal generating device according to the present invention uses two signals obtained by exclusive ORing the outputs of two pairs of elements that are symmetrical with respect to the intersection of two straight lines that divide the four-division type light receiving element into four elements. A signal corresponding to the phase difference between the two is generated as a tracking error signal.

EXAMPLES Examples of the present invention will be described below in detail with reference to FIGS. 1 to 4.

In FIG. 1, a four-division type light receiving element 1, a buffer amplifier 2,
3,5,6 are connected in the same way as the device of FIG. However, in this example, the outputs of the buffer amplifiers 2, 3, 5, and 6 are waveform-shaped by the waveform-shaping circuits 21, 22, 23, and 24, respectively. The waveform shaping circuits 21 to 24 are, for example, comparators that compare the instantaneous level of each output of the buffer amplifiers 2, 3, 5, and 6 with a reference level and generate a signal according to the comparison result. The outputs g and h of the waveform shaping circuits 21 and 22 are supplied to the exclusive OR circuit 25. The outputs i and j of the waveform shaping circuits 23 and 24 are supplied to the exclusive OR circuit 26. These exclusive OR circuits 25 and
The outputs s and t of 26 are supplied to the phase difference detection circuit 27. In the phase difference detection circuit 27, the output s of the exclusive OR circuit 25 is supplied to the clock input terminal of the D flip-flop 28 and the inverter 29. The reaction signal s- of the output s is output from the inverter 29 and supplied to the reset input terminal of the D-type flip-flop 30. The output t of the exclusive OR circuit 26 is supplied to the clock input terminal of the D-type flip-flop 30 and the inverter 31. The inverted signal t- of the output t is output from the inverter 31 and supplied to the reset input terminal of the D-type flip-flop 28.

A power supply voltage is applied to the D input terminals and set input terminals of the D-type flip-flops 28 and 30. The Q output q ₅ of the D flip-flop 28 is supplied to the positive side input terminal of the differential amplifier 32.

The Q output q ₆ of the D flip-flop 30 is supplied to the negative side input terminal of the differential amplifier 32. This differential amplifier
The output of 32 is output as the tracking error signal e via the LPF 33.

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 directly coincides with the intersection of 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 detection light spot moves 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 is, for example, an element.
Although it moves in the direction from 1b to 1a (upward in the figure), the pattern of this light intensity distribution is symmetrical with respect to the straight line α. The operation of each unit in this case will be described with reference to FIG. 2 (A) is a waveform diagram of the waveform shaping output g, FIG. 2 (B) is a waveform diagram of the waveform shaping output i, FIG. 2 (C) is a waveform diagram of the waveform shaping output h, and FIG. ) Is the waveform shaping output j
The waveform diagram of FIG. 3E shows the output s of the exclusive OR circuit 25.
(F) is a waveform diagram of the inverted output s−, (G) is a waveform diagram of the output t of the exclusive OR circuit 26, and (H) is an inverted output t−. (I) is a waveform diagram of Q output q ₅ , (J) is a waveform diagram of Q output q ₆ , and (K) is a waveform of output k of the differential amplifier 32. Figure, Figure (L)
[Fig. 3] is a waveform diagram of a tracking error signal e.

As shown in FIGS. 2 (A) to 2 (D), waveform shaping output
The phase difference between g and j and between h and i is “0”. Then, the phase difference between the outputs s and t of the exclusive OR circuits 25 and 26 becomes "0", and the D flip-flops 28 and 30 remain in the reset state. As a result, the Q outputs q ₅ and q ₆ remain at the low level, and the output of the differential amplifier 32 becomes the ground level.
The level of the tracking error signal e output from the circuit 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 split type light receiving element 1 is, for example, elements 1d to 1a.
The case of displacement in the direction toward (to the left in the figure) will be described with reference to FIG. FIGS. 3 (A) to 3 (L) show the same signal waveforms as those shown in FIGS. 2 (A) to 2 (L).

When the pattern of the light intensity distribution is displaced in the direction from the element 1d to the element 1a, the respective phases of the waveform shaping outputs i and j are determined from the respective phases of the waveform shaping outputs h and g according to the displacement amount of the information detecting light spot. Delayed by the angle. Then, the phase of the output s of the exclusive OR circuit 25 becomes the exclusive OR circuit 26.
From the phase of the output t of the angle t according to the amount of displacement of the light spot for information detection, and D over the time corresponding to the angle.
The flip-flop 28 is set and the Q output q ₅ becomes high level. Further, the D-type flip-flop 30 remains in the reset state and the Q output q ₆ remains at the low level. As a result, the differential amplifier 32 outputs a positive polarity pulse having a pulse width corresponding to the displacement amount of the information detection light spot, the level of the tracking error signal e output from the LPF 33 becomes positive, and its absolute value Is a value corresponding to the displacement amount of the information detection light spot.

Next, the information detection light spot is displaced in the outer peripheral direction,
A case where the pattern of the light intensity distribution in the light spot formed on the light receiving surface of the split type light receiving element is displaced, for example, in the direction from the elements 1a to 1d (right side in the figure) will be described with reference to FIG. To do. FIGS. 4 (A) to 4 (J) show the same signal waveforms as those shown in FIGS. 3 (A) to 3 (J), respectively.

When the pattern of the light intensity distribution is displaced in the direction from the element 1a to the element 1d, the respective phases of the waveform shaping outputs i and j are determined from the respective phases of the waveform shaping outputs h and g according to the displacement amount of the information detection light spot. Advance only the angle. Then, the phase of the output s of the exclusive OR circuit 25 is delayed from the phase of the output t of the exclusive OR circuit 26 by an angle corresponding to the displacement amount of the information detection light spot, and the phase corresponds to the angle. The D-type flip-flop 30 is set and the Q output q ₆ becomes high level. Further, the D-type flip-flop 28 remains in the reset state and the Q output q ₅ remains at the low level. As a result, the differential amplifier 32 outputs a negative polarity pulse having a pulse width corresponding to the amount of displacement of the information detection light spot, the level of the tracking error signal e output from the LPF 33 becomes negative, and its absolute value Is a value corresponding to the displacement amount of the information detection light spot.

In the above configuration, the position of the light spot formed on the light receiving surface of the four-division type light receiving element is displaced and the elements 1a to
Even if the amplitudes of the outputs of 1d become unbalanced, the buffer amplifiers 2, 3, which are inputting the outputs of the elements 1a to 1d,
If the amplitude of the output of the elements 1a to 1d is large enough that the peak level of each output of 5 and 6 exceeds the reference voltage of the comparator forming the waveform shaping circuits 21 to 24, the waveform shaping circuits 21 to 24 The amplitudes of the waveform shaping outputs g to j that are output do not change and are constant. In addition, the two elements 1a, 1b and 1c arranged symmetrically with respect to the straight line β
And between the two waveform shaping outputs g and h corresponding to the output of 1d and
Since the phase difference between i and j does not change depending on the position of the light spot formed on the light receiving surface, there is no phase difference between the outputs of the exclusive OR circuits 25 and 26, and the tracking error signal e is offset. Are prevented from occurring.

Further, the waveform shaping outputs g and i, h and j corresponding to the respective outputs of the elements 1a and 1c, 1b and 1d arranged symmetrically with respect to the intersection of the straight lines α and β are exclusive OR circuits.
Since it is supplied to 25 and 26, the output of the elements 1a and 1c, 1b and 1d is at the same timing as the state transition points of the outputs of the exclusive OR circuits 25 and 26, that is, the rising edge and the falling edge. The transition point appears. For this reason,
The outputs of the exclusive OR circuits 25 and 26 are signals having a frequency almost twice that of the waveform shaping outputs p and r in the conventional device shown in FIG. Since the outputs of the exclusive OR circuits 25 and 26 are supplied to the phase difference detection circuit 27, the exclusive logical OR circuits 25 and 26 are operated by the two D-type flip-flops 28 and 30 at substantially the same cycle as the conventional device shown in FIG. A pulse indicating the phase between the outputs of the summing circuits 25 and 26 is obtained, and the configuration is simple as compared with the conventional device.

In the above embodiment, the outputs of the elements 1a to 1d are supplied to the exclusive OR circuits 25 and 26 via the waveform shaping circuits 21 to 24, respectively. , 26 and the reference level of the comparator forming the waveform shaping circuits 21 to 24, the waveform shaping circuits 21 to 24 are removed and each output of the elements 1a to 1d is linearly exclusive. OR circuits 25 and 26
Can also be supplied to.

EFFECTS OF THE INVENTION As described in detail above, the tracking error signal generator according to the present invention is the exclusive OR of the outputs of two pairs of elements which are symmetrical with respect to the intersection of two straight lines which divide the four-division type light receiving element into four elements. Since a signal corresponding to the phase difference between the two signals obtained by the above is generated as a tracking error signal, the position of the light spot formed on the light receiving surface of the four-division type light receiving element changes. Even if the amplitudes of the outputs of the four elements of the four-division type light receiving element become unbalanced, as long as the phase information of the four elements, that is, the edge information does not fluctuate, the position between the two signals obtained by exclusive OR is obtained. The phase difference does not change, and the occurrence of offset of the tracking error signal can be prevented.
Further, since the tracking error signal is generated based on the edge information even if the laser power fluctuates, it is possible to prevent the fluctuation of the gain of the tracking servo loop.

In addition, the number of D-type flip-flops can be reduced as compared with the conventional device to simplify the circuit structure, and at the same time, since an adder circuit is not required, it can be easily made into a digital circuit.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of each part of the apparatus of FIG. 1, and FIG.
FIG. 4 is a waveform diagram showing the operation of each part of the apparatus of FIG. 1 when the position of the information detecting light spot is displaced in the inner peripheral direction, and FIG. 4 is the position of the information detecting light spot being displaced in the outer peripheral direction. 1 is a waveform diagram showing the operation of each part of the apparatus of FIG. 1, FIG. 5 is a block diagram showing a conventional tracking error signal generator, and FIG. 6 is an operation of each part of the apparatus of FIG. Waveform diagram, FIG. 7 is a waveform diagram showing the operation of each part of the device of FIG. 5, FIG. 8 is a diagram showing the position of the light spot formed on the light receiving surface of the four-division type light receiving element 1, FIG. 9 is a waveform diagram showing the outputs of the elements 1a to 1d when the position of the light spot formed on the light receiving surface of the four-division type light receiving element 1 moves,
FIG. 10 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. Description of main part symbols 1 …… 4-division type photo detector 21,22,23,24 …… Wave shaping circuit 25,26 …… Exclusive OR circuit 27 …… Phase difference detection circuit

Claims (1)

[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 or writing information, and intersects with each other at a point in the vicinity of the center of intensity distribution of a reflected beam obtained from an optical system. A light receiving element composed of four light receiving regions divided by two straight lines, and two pairs of light receiving regions arranged at symmetrical positions with respect to an intersection of the two straight lines of the four light receiving regions. A tracking error signal generation device comprising: an exclusive OR means for taking an exclusive OR, and a signal according to a phase difference between outputs of the exclusive OR means is generated as a tracking error signal.