JPS6052936A - Generating circuit of tracking error signal for disk record - Google Patents

Abstract

PURPOSE:To produce an accurate error signal by producing a tracking error signal from the signal given from a photodetecting area set in parallel to the tangent direction of a pit train and detecting and subtracting an offset voltage component from a level difference obtained in a total reflection mode. CONSTITUTION:The reflected light having a change by the presence or absence of a pit on a disk is received by a photodetector 18. Voltage signals Pa and Pb delivered from photodetecting areas PDa and PDb of the detector 18 are supplied to a tracking error signal producing circuit 24 as well as to an offset voltage detecting circuit 25. The circuit 24 supplies signals Pa and Pb to a subtractor 243 via PHF241a and 241b and absolute value circuit 242a and 242b. The circuit 25 supplies signals Pa and Pb to a substractor 252 via peak holding circuits 251a and 251b. Then output of the subtractor 243 is supplied to a subtractor 26 together with the output of the subtractor 252 obtained via a variable gain device 253. Then an accurate tracking error signal can be supplied to a tracking control circuit 20 from a subtractor 26.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a CD (optical compact disc), for example.
This relates to a disc record playback device suitable for DAD (digital audio disc) using the Kick-up tracking sensor, which eliminates the offset voltage that occurs in the push-pull tracking error signal due to the accuracy of the pickup. The present invention relates to a device that can be applied satisfactorily.

[Technical background of the invention]

Recently, in the field of audio equipment, a digital recording and reproducing method using PCI/I (mother code modulation) technology is being adopted in order to achieve high fidelity reproduction as much as possible. In other words, this is what is called digital audio, and the principle is to make the audio characteristics independent of the characteristics of the recording medium and far superior to those using conventional analog recording and playback methods. This is because it has been established.

In this case, a system that uses a disk as a recording medium is called a DAD system, and optical, electrostatic, and mechanical recording and reproducing methods have been proposed. Even when this method is adopted, the playback device that embodies it is still required to be able to satisfy various advanced control functions and performance that are not found in conventional devices.

In other words, if we take the CD system as an example,
A transparent resin disk with a diameter of 12 (W:) and a thickness of 1.2 [Nm] is equipped with bits (PCM) that correspond to digital (PCM) data.
A disk coated with a thin metal film that forms unevenness with different reflectance is processed using the CLV (Constant Linear Velocity) method.
It is rotated at a variable rotational speed of 00 to 200 [r, p, m], and is rotated from the inner circumferential side to the outer circumferential side using an optical pickup containing a semiconductor laser and a photoelectric conversion element.
J This is a near-tracking method for playback,
The disc has a track pitch of 1.6 μm, and a program area (25 to 5 seconds (mm) radius) that contains a huge amount of information that can be played in stereo for about an hour on one side.
The index data etc. are recorded in the lead-in area (radius 23 to 25 [:祁]
This can be easily seen from the fact that it is included in

What is especially important in the above-mentioned CD system disc record playback device is that in order to clearly read out the digitized data recorded on the disc, the light beam irradiated from the pickup is directed from the bit string of the disc. Tracking error control (tracking sensor?) is applied to accurately trace the bit string without shifting or causing any tracking errors.

Figure 1 shows the conventional tracking sensor. It shows the means. That is, the reference numeral 1 in the figure is a disk, and a bit string is recorded on one side of the disk. A pickup 12 is provided below the disk 11 in the figure, and the pickup 12 is movable in the radial direction of the disk 11 by a pickup feed motor (not shown). The pickup 12 also includes an objective lens 13 and a moving coil 15 for moving the objective lens 13 in the tracking direction (radial direction of the disk 110) 14 in cooperation with a magnet (not shown). Half 4 body laser 16. These include a beam splitter 17, a photo disk 18, and the like. The objective lens 13 is irradiated with a light beam emitted from the semiconductor laser 16 via a beam splitter 17. Therefore, the light beam is focused (spot) on the signal recording surface of the disk 1 by the objective lens 13, and is reflected depending on the presence or absence of bits on the disk 11. This reflected light travels backward through the objective lens 13, is reflected at right angles by the beam splitter 17, and is received by the photodetector 18.

Here, the photodetector 18 is of the so-called 2-pollution U type, in which light-receiving areas PDa and PDb made of photodiodes and the like are arranged line-symmetrically. Note that the arrow A-A in the figure corresponds to the tangential direction of the bit string, and the photodetector 18 has the light receiving areas PDa and PDb arranged with the dividing line t aligned with this arrow A-A. These light-receiving areas PD, L, and PDb output voltage signals Pa and Pb whose level changes depending on the presence or absence of a bit by receiving the reflected light, respectively, and these voltage signals Pa and Pb are not shown in the figure. The data is supplied to a data demodulation circuit and a focus servo circuit to undergo well-known processing, and is also supplied to each input terminal (G), ←) of a differential amplifier 19 that constitutes a tracking error signal generation circuit. There is.

This differential amplifier 19 receives the voltage signals PL, P.

It generates and outputs a signal of the difference voltage between. That is,
This differential amplifier 19 detects the difference in the amount of light received in each of the light receiving areas PDa and PDb of the photodetector 18, thereby detecting a shift in the forward and reverse directions of the spot of the light beam with respect to the bit string of the disk 11 (tracking error). be able to. The differential amplifier 19 outputs the differential voltage signal as a tracking error signal. The method of detecting a tracking error signal using a photodetector divided into two parts in the direction of movement of the spot is generally referred to as the dash-pull method. shall be.

That is, this tracking error signal PP indicates that the spot of the light beam is in the pit row P, as shown in FIG.
When the spot is correctly positioned above, it becomes a signal of O [■] level, and is output as positive and negative voltage signals corresponding to the positional deviation of the spot in the forward and reverse directions with respect to the bit string.

This tracking error signal PP is supplied to the moving coil 15 via a tracking control circuit 20 consisting of a phase compensation circuit, an amplifier circuit, etc., so that the spot is always correctly positioned on the bit string P. The objective lens 13 is controlled and a tracking sensor is applied thereto.

The tracking servo during disk playback has been explained above, but in this type of disk record playback device, for example, an arbitrary data portion can be quickly selected (searched) from among the dezotalized data recorded on the disk 11. In order to
The so-called S4 that moves at high speed in the radial direction of 1? It has a track skipping control means for performing track jumping of the cut. Hereinafter, this track skipping control means will be explained with reference to an example thereof shown in FIG.

That is, in FIG. 1, the reference numeral 21 in the figure is a system controller, and this system controller 221 is constituted by, for example, a microcomputer, and keys (not shown) operate the system record playback device according to operation commands from a computer or the like. This is to comprehensively control each operation and various display systems. And now, for the above keyboard, the third
When a track skipping operation command (this includes target address information indicating a portion of the disk 11 where target data to be selected is recorded) is issued at time tl in the figure, the system controller 21 first At the same time, a switching signal as shown in FIG. ) generates a track skipping signal as shown in

Here, the system controller 21 moves the t2 pickup 12 toward the outside of the disk 11 based on the target address information input into the keyboard and the current address information obtained from the bit string currently being reproduced by the pickup 12. In addition to calculating movement direction information indicating whether to move the pickup 12 toward the inner circumference or toward the inner circumference, information about the distance to which the pickup 12 should be moved is calculated. The moving direction information and distance information are then supplied to the track jumping signal generation circuit 22 as the track jumping command signal.

Then, based on the above-mentioned movement direction information signal, the pull-over skip signal generation circuit 22 has a positive polarity when moving the male pickup 12 toward the outer circumference of the disk 11, and has a negative polarity when moving it toward the inner circumference. In the case of FIG. 3(b), a voltage signal having positive polarity) is output. This voltage signal is sent to the tracking control circuit 2 as a track skipping signal.
0.

In this tracking control circuit 20, in response to a switching signal from the system controller 21, the tracking error signal PP is cut off to turn off the tracking search, and the track jumping signal generation circuit 22
The moving coil 15 is outputted with a track skipping signal that is supplied to the moving coil 15. Therefore, the objective lens 13 is moved toward the outer periphery of the disk 11, and the pickup feed motor is moved toward the pickup J.
2 is rotated to move it toward the outer circumference of the disk 11, and the big ringer 7° 12 is moved at high speed in the direction of the target pit row, so that the spot can jump over the track.

In this way, when the pickup 12 is moved at high speed in the direction of the outer circumference of the disk 1, the spot crosses a plurality of pit rows, thereby increasing the tracking error signal p.
p is output as a continuous alternating current waveform as shown in FIG. 3(c). However, since the tracking error signal PP, which has an AC waveform, is cut off within the tracking control circuit 2o as described above, it is not supplied to the moving coil 15, that is, the tracking error signal PP is not supplied to the moving coil 15. It is not offered to Then, the tracking error signal PP is supplied to a counter circuit 23, and the 〇[v] level crossing points at the time of the inclination are counted. In other words, to count the O(V)v hell cross points of the tracking error signal PP is to count the number of pit rows that the spot crosses without making any corrections, and this was explained earlier. So the track pitch is 1.6
Since it is [μm], it ultimately represents the distance that the big diameter f12 has moved over the disk 1.

Then, the big error fl obtained by the counter circuit 23, ? The moving distance of the system controller 221 is
If the calculated distance information matches the distance information at time t3 in FIG. 3, the system controller 21 stops generating the track jumping command signal. As a result, the track skipping signal generation circuit 22 stops generating the track skipping signal (to the 0 level), so that the picker f12 is forced to stop its movement. At the same time, the system controller 21 also stops generating the switching signal, returns the tracking control circuit 2o to a state corresponding to the reproducing operation, outputs the tracking error signal PP supplied thereto, and outputs the tracking error signal PP. This allows the above-mentioned tracking server to be performed based on the pp.

Here, as shown in FIG. 3(b), the track skipping signal is inverted to negative polarity at time t2, which is approximately the middle of the period from time t1 to time t3. This is done by accelerating the pickup 12 in the direction of the outer circumference of the disk 11 between times t1 and t2, and applying braking to the acceleration force between times t2 and t3 to reach the target position (corresponding to time t3). This is so that the pickup 12 can be stopped stably. Then, at the time t2 at which the polarity of this track skipping signal should be reacted, the system controller 21 calculates that the Big Ala 7°12 has reached approximately the distance of its total movement (corresponding to time t1 to t3). , is determined by being supplied to the track skipping signal generation circuit 22 as the track skipping command signal.

[Problems with background technology]

By the way, although the tracking error signal generating means using the push-pull method described above has the advantage of being able to have a simple circuit configuration, it also has the following drawbacks.

That is, the tracking error signal PP is generated depending on the relative positional relationship when the objective lens 13 is moved in the radial direction of the disk 11 with respect to the pit row on the disk 11. Beam Snorrita 1
Correct values cannot be obtained unless all of the light receiving sections, such as 7 and 18, move as one. For this reason, in the conventional push-pull type tracking error signal generation means, the light receiving section is integrated, and when the reflected light from the disk 11 enters the light receiving section correctly, the spot of the light beam is Voltage signals p, , p output from each light receiving area PDa, PDb of the photodetector 18 in a state where the photodetector 18 is correctly positioned above.
b must be made equal so that no error occurs in the tracking error signal pp.

Therefore, high precision is required in manufacturing the pickup, making the pickup extremely expensive.

Furthermore, even if the pickup is manufactured with high precision, if the disk is mounted at an angle to the pickup, the reflected light will shift from the center of the light receiving area, making it impossible to obtain a correct tracking error signal. .

For this reason, high precision is required for the disk mounting machine groove, which is economically disadvantageous. Furthermore, even if the above method is used, it cannot cope with distortion of the disc itself, and if this is significant, playback becomes impossible.

For the above-mentioned reasons, even though the spot is correctly positioned on the pit row, the reflected light at that time is unbalancedly irradiated onto each of the light receiving areas PDa, PD of the 7-detector 18. , a DC offset voltage appears in the tracking error signal PP, and a peak level difference occurs between the positive voltage region and the negative voltage region with respect to the 0 [V) level of the tracking error signal PP, and control of the pit row in the forward and reverse directions is performed. There will be a difference in range.

DC for tracking error signal PP as described above
The appearance of offset voltage also occurs when the pickup 12 is moved at high speed in the radial direction of the disk 11 because the objective lens I3 is biased in the forward or reverse direction during this high speed movement. Although such an offset voltage is at a small level during playback, it is generated at a large level during high-speed movement of Big Up No. 2, so as shown in FIG. One control area for drawing spots into the column will be much larger than the other control area.

Therefore, when the track jumping operation ends at time t3 shown in FIG. 3 and the tracking servo is turned on, the spot is pulled toward the pit row P, but its acceleration energy pulls it in the opposite direction. Therefore, it cannot be absorbed completely in the control area t4 to t5 for the target pit line P, and ends up entering the control area of the pit line Q adjacent to the target pit line P. Then this pit row. Similarly, one control region t6 to t7 is larger than the other control region t7 to t8, so there is a pit row. As a result, the spot ends up jumping over pit rows one after another, and the pickup 12 is stopped at one surface a short distance from the target pit row P. This makes it difficult to perform accurate track skipping operations.

[Purpose of the invention]

This invention was made in order to improve the above-mentioned problems, and even if a push-pull method is adopted, an accurate tracking error signal can be obtained, and the tracking servo can be stably and reliably controlled immediately upon completion of the spot track jumping operation. This increases the tolerance for disc inclination, deflection, and distortion, and also increases the tolerance for the accuracy of the pickup and disc mounting mechanism, making it economically advantageous. It is an object of the present invention to provide an extremely good tracking error signal generation circuit for a disc record playback device that can perform the following steps.

[Summary of the invention]

That is, the tracking error signal generation circuit of the disc record playback device according to the present invention irradiates a light beam onto a disc on which digitized data obtained by encoding an information signal is recorded as a bit string, and detects the pits of the bit string. The digitized data is read by receiving the reflected light that has been changed depending on the presence or absence of the bit string by a light receiving section arranged in first and second light receiving areas arranged in a tangential direction of the bit string and converting it into an electrical signal. In the disc record playback device, a tracking error signal is generated corresponding to a shift in the forward and reverse directions of the light beam with respect to the bit string based on first and second signals output from the first and second light receiving areas. a first means, detecting a level when the reflected light is totally reflected from the first and second signals respectively, and generating a voltage signal corresponding to the level difference, so that the reflected light reaches the light receiving section; a second means for detecting an offset voltage component of the tracking error signal caused by deviation from the center; and subtracting the voltage signal obtained by the second means from the tracking error signal obtained by the first means. The present invention is characterized in that it includes a third means for generating a tracking error signal that substantially cancels out the offset voltage.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 4 to 15.

First, the principle of this invention will be described. That is, the push-pull type tracking error signal, each light receiving area PDa of the photodetector 18 shown in FIG.
, PDb, the voltage signal P&, the PbO difference voltage signal becomes a correct tracking error signal PP when the reflected spot of the reflected light on the photodetector 18 is at its center, but when the reflected spot is deviated from the center, it becomes a correct tracking error signal PP. A voltage corresponding to the deviation (offset voltage vPP) is added to the correct tracking error signal pp.

Further, the voltage signals Pa and Pb each change in level depending on the presence or absence of a pit, but their respective amplitude levels become different depending on the shift of the spot of the light beam with respect to the bit string. In other words, the voltage signal P&
, Pb, the tracking error signal can also be obtained by extracting the difference between the amplitude levels of Pb. Hereinafter, this tracking error signal will be referred to as the tracking error signal P.
Let P be a tracking signal RFPP. The tracking error signal RFPP obtained in this way is similar to the above-mentioned differential voltage signal. When the reflection spot is deviated from the center of the photodetector 18, the tracking error signal RFPP corresponding to the deviation (offset vRFPP) is converted into a correct tracking error signal. It is added to RFPP, and has a characteristic of being in an opposite phase to the tracking error signal PP.

Therefore, the tracking error signals PP and RF
PP and the respective offset voltages vPP and ”
By canceling out the RPPP, it is possible to obtain a correct tracking error signal regardless of the deviation of the reflected spot.

This principle will be explained in more detail.

FIG. 4 shows the reflection surface on the photodetector 18 corresponding to the position of the spot irradiated onto the pit. This shows the light amount distribution state of the light. That is, when the spot S is located on the right side of the pit P as shown in FIG. 4(-), the reflected spot H on the photodetector 8 as shown in FIG. A shadow (shaded area in the diagram) appears on the right side of the diagram. Next, as shown in Fig. 4(c), when spora)S is located at the center of gi)P,
As shown in FIG. 4(d), shadows are formed symmetrically over almost the entire reflection spora)H. When the spot S is located on the left side of the bit P as shown in FIG. 4(-), the reflected spora) H
A shadow appears on the left side of the figure.

In other words, if the position of spot S deviates from the center of P
is located at the center of the photodetector 18, each light receiving area PDa.

The amount of light received by PDb varies depending on the shading. Further, as described above, when the spot S is on the p)P, the amount of reflected light is the lowest, and conversely, when the spot S is completely off the p)P, the amount of reflected light is the maximum. That is, each light receiving area P of the photodetector 18
Da, P.D.

The voltage signals Pa and Pb output from the above reflection spora)
It changes depending on the distribution of H shading and the amount of light received depending on the presence or absence of bits.

From the above, it can be seen that the voltage signals Pa and P when the light beam traverses the spot at a constant speed with respect to multiple bit strings are
5 are as shown in FIGS. 5(a) and 5(b), respectively. That is, the voltage signals P,,P,.

As the spot passes over the bit string at times t1 and t2+t3, low-frequency components with opposite phases are generated, and this changes the amplitude level of the frequency component (information signal) corresponding to the presence or absence of the bit. , the tsuma civic level changes.

When the low-frequency signals (average voltage signals) LPa and LPb are extracted from such voltage signals P, , and Pb, respectively, the fifth
As shown in Figures (c) and (d), the envelopes fM and EPb at the peak level are used, respectively.
When tj& is output, the result is as shown in Fig. 5(e) and (f). When a difference signal between the low frequency signals LPa and LPb is generated, it becomes as shown in FIG. 5(g), which is the tracking error signal PP described above. Further, when a difference signal between the envelope signals EP, , and EP is generated, it becomes as shown in FIG. 5(h), which is the tracking error signal RFPP f described above.

That is, these two tracking error signals pp and RFPP have opposite phases to each other, but at the time jl+j! when the spot is on the bit string! The level is 0 [v] at yt8, and the level changes depending on the magnitude of the shift of the spot in the forward and reverse directions with respect to the bit string.

Next, a case will be described in which the reflection spot H on the photodetector 18 is offset from the center.

FIG. 6 shows the light amount distribution state of the reflective spora (H) on the photodetector 18 when the spot of the light beam is located at the center of the bit. In addition, the axis t in the figure is the light receiving area PD.
This is the dividing line of a and PDb, and the symbol m in the figure is the center line of reflection spora)H.

Now, classify the reflection spora) H according to the above axis and m! +7
1+72, and if signals Px and Py1+y2 corresponding to the light intensity of section X and section yl+yz are obtained, respectively, the tracking error signals pp and RFPP shown in FIG. . However, in reality, the division x + y 1 and the division y
Signal Px+A1 corresponding to the light amount of 2. P)'2 are obtained, so an offset voltage is generated in the tracking error signals PP and RFPP.

Here, assuming that the signal Py1 for the light intensity of the division y1 is obtained, each light receiving area PD, , PD.

One of them is obtained by adding the signal Py1 to the equal output shown in FIGS. 5(a) and 5(b), and the other is obtained by subtracting it. This signal Py, when the spot crosses a plurality of bit strings as in FIG. 5, and when the spot is at the center of the bit string as shown in FIG.
+tz +t3) Its amplitude level is maximum and minimum when it is in the middle between bit strings. Because of this, as shown in FIG. 8(a), the tracking error signal RFPP when the surface reflection spot s is at the center of the photodetector 18 is different from the actual tracking error signal (when it is off the center). RFPP is the envelope signal E of the peak level of the information signal obtained in the section yt.
Since Py1 becomes as shown in Figure 8(b),
As shown in figure (c), this Enhero' signal EPy1
If a voltage level twice that of RFPP has an offset voltage RFPP. Here, the important tracking error signal is the arrow A1 + A2 + All in the figure.
In this range AI + A2 t A3, the information signal obtained in the section y1 is almost constant, so the tracking error signal RFPP shown in FIG. 8(C) is substantially shifted by the offset voltage vRFPP. It turns out.

Next, considering the tracking error signal PP, the actual tracking error signal PP is shown in Fig. 5 (g).
This is the result of adding a low-frequency signal LPy, which is the low-frequency component of the signal Py1 obtained in the section y1 shown in FIG. 7, to the case where the reflection spot H shown in FIG. In this case, when the displacement of the reflection spot H is slight, the amount of light received in the section yl is proportional to its area. Therefore, as shown in FIG. 7, if the lower peak level of the signal Py1 when the spot is on the pit row is q, and the amplitude level of the information signal at this time is p, both q and p are classified. Y! is proportional to the area of

That is, while the offset voltage vRFPP of the tracking error signal RFPP due to the deviation of the reflection slide I (is p, the offset voltage of the tracking error signal VRPPP' (
= q). Above p.

Since q is in a proportional relationship, if q = -p, the above constant I can be expressed as follows. Therefore, the tracking error signal PP
Multiply by 2/k + 2 to obtain the tracking error signal RFPP
Its offset voltage vRFP by subtracting from
P can be removed. Incidentally, as explained in FIG. 5, the tracking error signal pp and RFP when
Since both P have opposite polarities, the positive tracking error signal resulting from the calculation as described above has a form in which only the offset voltage is removed and the tracking error component is added.

In the above case, the offset voltage is removed from the tracking error signal RFPP, but the offset voltage may be removed from the tracking error signal PP.

That is, a correct tracking error signal can be obtained by subtracting +2 times the racking en-signal RFPP by □ from the tracking error signal PP. However, tracking error signals PP and R
In FPP, the amplitude level is almost the same, but since the offset is the pressure VPPtVR, PPcasoresotttp+"-rp, that is, VP,
>V□, P, so the tracking error signal RFP
It is advantageous to remove the offset voltage from P.

If the above principle is pushed further, the following can be considered. In Figure 7 p.

Since q is in a proportional relationship as described above, p+q is naturally in a proportional relationship with p and q. That is, it can be seen that it is possible to compensate for the offset voltage even if P+Q is directly determined. This p+q can be calculated by detecting the respective peak values of the output signal Pa and Pb of the two light-receiving areas PD&, PD, and the total reflection level when the pulse spot is not on the bit, and calculating the difference between them. It is something that can be done.

FIG. 9 shows a tracking error signal generation circuit constructed based on the above principle. However, the same parts as in FIG. 1 are denoted by the same reference numerals, and only the different parts will be explained here.

That is, each light receiving area PD of the photodetector 18
, , Voltage signal P output from PDb.

Pb is the tracking error signal generation circuit 24, respectively.
It is also supplied to the offset voltage detection circuit 25.

First, the tracking error signal generation circuit 24 outputs the voltage signals PIL and Pb to the bypass filter 2, respectively.
The signal is supplied to the subtracter 243 via 41t, 241b and absolute value circuits 242m, 242b.

Among these, high/4' filter 241*, 241b
For example, as shown in FIG. 10, it can be constructed of a CR type consisting of a capacitor C1 and a resistor R1. Further, the absolute value circuits 242&, 242b can be configured with resistors R2, R3 and diodes DI+D2 for differential amplification of positive polarity outputs, as shown in FIG. 11, for example. The output signal of the subtracter 243 is then supplied to the subtracter 26.

Further, the offset voltage detection circuit 25 has a peak hold circuit 251 for each of the voltage signals P and lPb.
After being supplied to the subtracter 252 through subtracters 251b and 251b and subjected to subtraction processing, the signal is supplied to the subtracter 26 through a variable gain unit 253. Of these, the peak hold circuits 2518 and 251b can be configured with a time constant circuit including, for example, a transistor Q1, a resistor R41, and a capacitor C2. Further, the variable gain unit 253
can be configured with an attenuator made of a variable resistor, for example. The output signal of the subtracter 26 is supplied to the tracking control circuit 2θ.

The operation of the above configuration will be described below. That is, in the tracking error signal generation circuit 24, first, the voltage signals Pa and Pb are each passed through a high-noise filter 241m.

241b, and extracts an information signal corresponding to the presence or absence of pits, and outputs it to absolute value circuits 242a and 242b. The absolute value circuits 242 a and 242 b are for extracting the absolute value level of the information signal, as well as the aforementioned envelope signals EP and EPb, and output the envelope signals EP & and EPb to the subtracter 243 . This subtracter 243 generates a difference signal between the envelope signals EPa and EPb. The difference signal generated by this subtracter 243 is the tracking error signal RFPP described above, which includes the reflection signal J? on the photodetector 18? Cut H
It includes an offset voltage vRFPP due to the deviation of . Tracking error signal R generated in this way
FPP is output to subtractor 26.

On the other hand, in the offset voltage detection circuit 25, the voltage signals Pa and Pb are each passed through a peak hold circuit 251a.
+25 lb to hold the peak level value when the spot of the light beam is not on the pit and the totally reflected light is at the total reflection level, and the subtracter 252
Obtain the differential voltage by . That is, when each of the above-mentioned peak level values deviates from the center of the reflection spora) H on the photodetector 18, one increases and the other decreases in response to a change in the light receiving area.

By detecting such peak levels and taking the difference, a voltage corresponding to the deviation of the above-mentioned reflection spora)H can be obtained. This voltage is the offset voltage mentioned above■
It is PP. This onset voltage vPP is supplied to the variable gain unit 253, multiplied by the constant □, converted into an offset voltage of +2 vRFPP, and then output to the subtracter 26.

Then, the subtracter 26 subtracts the offset voltage VRFPP from the tracking error signal RFPP, and outputs a correct tracking error signal T that does not correspond to the positional deviation of the reflective spoiler) I to the tracking control circuit 2o. This allows accurate tracking to be performed at all times.

Therefore, with the above configuration, an accurate tracking error signal can be obtained even with the push-pull method. Further, since a tracking error signal having no off-nut voltage can be obtained even during the spot track jumping operation, it is possible to stably and reliably perform the tracking error signal at the end of the spot track jumping operation. In addition, since the above tracking error signal is not affected by the positional shift of the reflected spot on the photodetector, it is possible to increase the tolerance for disc tilt and distortion, which makes it possible to increase the tolerance for disc tilt and distortion. The tolerance for groove accuracy can also be increased.

Note that the tracking error signal generation circuit 24 of the above embodiment
may be configured as shown in FIG. That is,
The upper peak detectors 271h and 271b detect the maximum levels of the voltage signals p and +p, respectively, and at the same time, the lower peak detectors 272m and 272b detect the lower peak levels, and the lower peak levels are detected from the maximum level. By subtracting the peak level attenuators 273a and 273b, the envelope signal EP1. ．． EP. And this envelope signal EP.

A tracking error signal RFPP is obtained by generating a difference signal from EPb in a subtracter 274.

Further, in the above embodiment, the tracking error signal RFP
However, as shown in FIG. 14, the subtracter 28 generates the voltage signal Pa and the PbO difference signal to generate the tracking error signal pp, and the offset voltage vR2Pp is removed. The offset voltage vPP is output from the gain unit 253, and the subtracter 26
The offset voltage ■P from the tracking error signal PP
It is also possible to obtain a correct tracking error signal T by removing P. Further, as shown in the M2S diagram, the subtracter 28 generates the tracking error signal PP-, and the adder 29 and the bypass filter 3o extract the information signal, and then the level comparator 3 receives the total reflection of the reflected light. It is also possible to generate a pulse signal that deviates from t・irrepel, and use this pulse signal as an offset voltage VPP to be subtracted from the tracking error signal PP by the subtracter 26, or otherwise within the scope of the above gist. It goes without saying that it can be implemented with various modifications.

〔Effect of the invention〕

As described above, according to the present invention, an accurate tracking error signal can be obtained even if the Butshusol method is adopted, and the tracking error signal can be stably and reliably detected immediately upon completion of the spot track jumping operation. As a result, the tolerance for the inclination, deflection, and distortion of the disc is widened, and the tolerance for the accuracy of the pickup and the disc mounting machine groove is also increased, making it economically advantageous. It is possible to provide an extremely good tracking error signal generation circuit for a disc record playback device that can perform the following steps.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the tracking server means and track skip control means of a conventional disc record playback device, and FIG. 2 is a characteristic diagram illustrating the tracking error signal by the tracking serve means.
FIG. 3 is a waveform diagram illustrating changes in the above-mentioned tracking and tracking error signals during track skipping operation;
Figures 11 to 11 are for explaining an embodiment of the tracking error signal generation circuit of a disc record playback device according to the present invention, and Figures 4 to 8 are diagrams for explaining the present invention in detail. , FIG. 9 is a block diagram showing an embodiment of a tracking error signal generation circuit constructed based on the above principle, FIGS. 10 to 12 are circuit diagrams showing the circuit configuration of each main part of the above embodiment, and FIG. 13 to 15 are block circuit diagrams showing other embodiments of the present invention. 11...disc, 12...pickup, 13,
・, objective lens, 14... tracking direction, 15,
...Moving coil, 16...41 body laser, 17
... Beam screener, 18... Photodiode, 19... Differential amplifier, 2o... Tracking control circuit, 21... System controller, 22... Track skipping signal generation circuit, 23... ... Counter circuit, 24 ... Tracking error signal generation circuit, 241
a, 241b, 3o... bypass filter, 24,2
a, 242 b-absolute value circuit, 243.252,
26.28... Subtractor, 25... Offset voltage detection circuit, 251a, 251b... Peak hold circuit, 253... Variable gain unit, 29... Adder, 31...
...Level comparator, l...Dividing line, ■...Reflection spot, PD, L, PDb...Light receiving area, m...Reflection spot center line. Figure 2 4-Small) Silt. Figure 3 t4ts ts Figure 4 (a) (b) (C) (d) (e) (1) Figure 6 Figure 8 A1 A2 A3 22nd grade (C). 1 1 1” Figure 13 Figure 14 Figure 15

Claims (3)

[Claims] (1) A light beam is irradiated onto a disk on which digitized data obtained by encoding an information signal is recorded as a bit string, and reflected light that changes depending on the presence or absence of pits in the bit string is emitted in the tangential direction of the bit string. In the disc record playback device, the digitized data is read by receiving light with a light receiving section consisting of first and second light receiving areas arranged in rows and converting it into an electrical signal, wherein the first and second light receiving areas a first means for generating a tracking error signal corresponding to a shift in the forward and reverse directions of the light beam with respect to the bit string based on first and second signals outputted from the first and second signals; The offset voltage of the tracking error signal generated when the reflected light is shifted from the center of the light receiving section is detected by detecting the level when the reflected light is totally reflected and generating a voltage signal corresponding to the level difference. and a tracking error signal obtained by subtracting one voltage signal obtained by the second means from the tracking error signal obtained by the first means to substantially cancel out the outside of the offset voltage. A tracking error signal generation circuit for a disc record playback device, characterized in that it comprises a third means for generating a tracking error signal. (2) The first means generates the tracking error signal by extracting a difference signal between the first and second signals. A tracking error signal generation circuit for a disc record playback device. (3) The first means extracts first and second envelope signals corresponding to changes in the amplitude levels of frequency components depending on the presence or absence of bits from the first and second signals, respectively, and generates a difference signal between the first and second envelope signals. 11. The tracking error signal generation circuit for a disc record reproducing apparatus according to claim 10, wherein the tracking error signal is generated in such a manner as to generate the tracking error signal.