JPS59146487A - Generating circuit of tracking servo signal - Google Patents

Abstract

PURPOSE:To attain the accurate tracking control by performing the subtraction with a desired ratio between the difference signals of upper and lower envelope components to generate a tracking servo signal and therefore eliminating the effect of disturbance to the tracking error signal. CONSTITUTION:The outputs A1 and A2 of amplifiers 10a and 10b are impressed to upper envelope extracting circuits 17a and 17b and lower envelope extracting circuits 18a and 18b respectively. The outputs Ue1 and Ue2 of the circuits 17a and 17b are supplied to a differential amplifier 19, and this difference output F is impressed to an input of a differential amplifier 22 via a variable resistor 21. While the outputs Le1 and Le2 of the circuits 18a and 18b are led to a differential amplifier 20, and this difference output H is impressed to the other input of the amplifier 22. The output of the amplifier 22 is changed into a tracking servo signal I and supplied to a driving amplifier 14 via an equalizer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking servo signal generation circuit in an information reading device.

For example, a tracking servo control device for an optical information reading device has a configuration as shown in FIG. That is, the irradiated light beam from the laser light source 1 passes through the lens 2, the beam splitter 3, the 1/4 wavelength plate 4, and the objective lens 5, and then enters the recording surface of the recording disk 6. Objective lens 5
As a result, the laser beam is converged to form a pickup light spot as a minute information detection point on the recording surface. The reflected light (or transmitted light) by this disk 6 is separated by a beam splitter 3 and sent to a set of photoelectric conversion elements 9a.
, 9b are irradiated onto each light receiving surface. Both photoelectric conversion elements 9a
, 9b is the amplifier ioa.

10b and LPF (low pass filter) 11a.

11b and are applied to the differential amplifier 12.

This differential output is input to the drive amplifier 14 via the equalizer 13, and serves as a drive signal for the drive coil 8 for moving the objective lens 5 in a direction perpendicular to the track.

A pair of photoelectric conversion elements 9a and 9b are mounted so that their light-receiving surfaces are divided by a single dividing line 9C, as shown in FIG. These elements 9a are parallel to - indicated by the arrow Y and with respect to the optical axis 7' of the reflected light of the light spot.
, 9b are arranged symmetrically. In addition, 7 is the optical axis of the incident light, and 15 is a spindle motor for rotating the disk.

Due to this M4 configuration, if the center of the pickup optical spot is shifted from the center of the rack in the direction perpendicular to the track,
According to this shift, the intensity distribution of the light tA entering the photodetectors 9a and 9b becomes asymmetrical, and a difference occurs between the output horns of both detectors. Therefore, by obtaining the difference between the low-frequency components of these two detectors using the differential amplifier 12, a so-called tracking error signal is obtained, and this error signal is used to move the objective lens 5 from I to the rack orthogonal direction (disk radial direction). ), the pickup moonlight subol
- is biased accordingly, making accurate tracking possible at all times.

However, in such an apparatus, due to the inclination of the recording surface of the disk 6, the movement of the objective lens 5 in the disk radial direction, etc., the detector 9a of the reflected light 16 from the disk, as shown by the dotted line in FIG. This has the drawback that the center on 9b deviates from the dividing line 9C, causing serious target deviation in the tracking servo control system.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tracking servo signal generation circuit that can eliminate the adverse effects of disturbance factors on tracking error signals and perform accurate tracking control.

The tracking servo signal generation circuit according to the present invention includes a set of detection signals provided in order to detect the amount of deviation of the information detection point in the direction perpendicular to the track, so that a difference occurs between the detection outputs corresponding to the amount of deviation. means for extracting the upper envelope component and lower envelope component of each detection output of the set of detection means, and means for obtaining a difference signal between these upper envelope components and a difference signal between the lower envelope components. and a means for subtracting these difference signals at a desired ratio to generate an i~ racking servo signal.

The present invention will be explained below using the drawings.

FIG. 3 is a block diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals.

In this example, the outputs A+ and A2 of the amplifiers 10a and 10b are applied to the upper envelope extraction circuits 17a and 17b and the lower envelope extraction circuits 18a and 18b, respectively, and the output j of the upper envelope extraction circuits 17a and 17b is applied to the upper envelope extraction circuits 17a and 17b.
le I and lJe 2 are led to a differential amplifier 19, and the difference output F is applied to one input of a differential amplifier 22 via a variable resistor 21. Also, a lower envelope extraction circuit 18a.

The outputs Le+ and Le2 of 18b are led to a differential amplifier 20, and the difference output F is applied to the other input of the differential amplifier 22. The output of the differential amplifier 22 becomes the tracking signal I, which is input to the drive amplifier 14 via the equalizer 13.

FIG. 4(a) is an example of a circuit for extracting the lower envelope, in which the input signal is applied to the cathode of the diode D1,
output from its anode. Anode and power supply +Vcc
A resistor R1 and a capacitor C1 are connected in parallel between.

Figure 4 (b) is an example of a circuit for extracting the upper envelope, in which the input signal is applied to the anode of diode Q2,
output from its cathode. The cathode is grounded by a resistor R2, and the continuum C2 is connected in parallel to the resistor R2. Figure 5(a) to width are the operation waveforms of each part of the circuit blocks in Figures 1 and 3. These waveforms indicate that due to disturbance, the center of the reflected light beam from the disk is located at the photodetectors 9a and 9b.
In a state displaced from the dividing line 9C, that is, in a state as shown by the dotted line in FIG. 2, the tracking revolve loop is open and the light spot moves diagonally across the recording track on the disk surface. It shows the time changes of each waveform when

In the figure, to indicates the time when the light spot coincides with the center of one track, and L-1 and t+1 indicate the times when the light spot coincides with the center of both tracks adjacent to the rack and the inner and outer peripheries of the rack. The vertical axis is the signal level.

In Fig. 5(a), the crests indicate the amplified signals AI and A2 of the detection outputs of the -phase photoelectric conversion elements 9a and 9b, respectively, and the output Δ1 of the detector 9a, which is a person with an irradiation area, is smaller. With respect to the output A2 of the detector 9b, the amplitude of the component and the DC component (average value component) are both large, and they are in a substantially proportional relationship.

Note that both signals Δ1. The phase relationship of the envelope components of A2 has a phase difference from each other from the center of the 1-rack as shown by the peak in FIG. This phase difference is caused by the fact that the intensity distribution of the light reflected from the disk becomes asymmetrical with respect to the optical axis due to the deviation from the center of the optical slot.

Figure 5 (C1 shows the waveforms of the signals B+ and B2 in Figure 1, with only the low-frequency components of the signals A+ and A2 extracted. Figure d+ shows the difference between the two signals B+ and B2. This is the waveform of the l-racking error signal in the conventional example shown in Fig. 1, and as seen in the figure, the 1-racking servo cannot lock due to the existence of a DC offset. The DCC off-sera component indicates the influence of disturbance, and the signal of this embodiment shown below cancels this.The signal Δ+, A2 is input to the envelope extraction circuit shown in Fig. 4. Capacitor C+ in Figure 4.

The value of C2 is set so as to hold the maximum or minimum value of the signals AI and A'2, and as a result, the base envelope component is extracted. Figure 5(e) shows the signals A+, A
A signal Ue+, which is obtained by extracting only the upper envelope component of 2,
Figure (9) shows the waveform of signal 1-e+, Lez, in which only the lower envelope component is extracted. jlel, IJc! 2゜1-el, Le
2 can be approximated by the following equation.

(Je + = ni + = (Yo 1y (ωj +
δ))...(1) Ue 2 = 2 ・(Yo +V <ωt-δ))
......(2) [e I = + ・(XO'+X ((Z)t+δ'
))... (3) L, e 2 = 2 ・(Xo +x (ωt-δ')
)・・・・・・ (4) Here, + and 2 are proportional constants that change due to disturbances,
Yo, Xo are DC components, 17 ft), × + t + t are AC components, ω is 11~ rack interval scanning time is one cycle, l
This is the angular frequency of δ, δ′ (the phase difference is one step above the other).

FIG. 5 (f> is the waveform of the difference component F between the signals Ue+ and Uez, F=LJel −Ue 2−(Kt −Kz )・Y
o + to + ・y(ωt+δ)− to 2・y (ωt−δ
)...(5). Figure 5<IX) is the waveform of the difference component 1-1 of the signal e+ and L4z, and 1-1=Le l -Le 2 = (2 to Kl -
)・Xo++・X (ωt+δ) −Kz・× (
ω is one δ)...(6). Comparing the waveforms in FIG. 5(f) and (h), the time to
Since the DCC off-cellar 1 is in phase, both signals F and H
By mixing the two in an appropriate ratio and taking the difference component, DCC offcera 1 to 1 can be removed.

In this case, since the DC offset component y of signal F is large, the variable resistor 21 creates a signal by multiplying the signal F by an appropriate attenuation constant α, and the differential amplifier 22 obtains the difference between the signal F and the signal F. That is, the signal passing through the variable resistor 21 is α・F=α・(Kl−2)・Yo+α・K1・
y〈ω to 10δ) - 2゜・y(ω t −δ ) ) ・・・ ・・・
(7), so from equations (6) and (7), (2 to Kl -) -x○- = α- (2 to Kl -)
・Yo・・・・・・(8) By selecting the value of α that satisfies the formula, the difference signal I=]]−α・F with the DC offset removed is expressed as Figure +i
〉 can be obtained as follows.

■ and α are as follows.

I=to+(X (ωt+δ)−α・y(ωt+δ
)) − to 2 ・(x (ω[−δ)□ −α・□
shi(ωt-δ))...(,'9)α-Xo/
Yo-' (10) 'The AC components of the signals ゛F and 1-1 are also in phase □, and by taking the difference, the signal I
Therefore, the alternating current component also decreases, but in reality, the rate at which the upper envelope component of the signal □ signal A'+ ``'', ``A2'' is modulated by the recording track is that the lower envelope component is modulated by the recording track. The reduction in the alternating current component of the difference signal I can be ignored because it is sufficiently small compared to the modulation rate.
It is clear from equation 9 that the signals for the optical switch 1 to the drive wheel 8 for position deviation, that is, the tracking servo signal 1-1, are shown in Figure 5+i. It can be seen that the DC'A offset caused by the disturbance is removed and a good tracking signal with no target deviation is obtained.

Figure 6 shows amplifiers 10a and 1'Ob that are added to Figure 3.
This shows an example in which the circuit configuration from 1 to 22 to the differential amplifier 22 is put to practical use. In FIG. 6, the amplifier 10a is the same as that in FIG. ,
Dionide D-, which is connected with the opposite polarity, and □D! 'V
The output envelope extraction circuit i, which is biased to cc and is composed of a resistor R'aJj and a conde laser C3, is connected to a diode D4 and OV connected in opposite polarity. Standardized R4 and Mondenza C4
The output J signal is -U'e2. The signal A1 is the same as the above example. The signals Le1 and -Le2 are input to the inverting input of the positive differential amplifier 23' via the resistors Ry' and Ra, and are added by the differential amplifier 23 to produce the signals "!Le'+, le2.,"
). Then, the 2 of the differential fan 25 is added to the 2 of the differential amplifier 25 via the 4-variable resistor 24 and the resistor MR''s and R6.The values of the resistors R5 to R9 are all variable □ If the resistor 24 at'vx is R, the value of the feedback resistance of the differential amplifier 25 is Rf, and the values of the feedback resistor 27 of the differential amplifier 25 are R, f, □, the differential amplifier 25
The output signal J' is ・J '''Rf'/R'V ・(Lel'''−'L'
e”,!’)-’Rf/”RX (’U’e
+"-Ue 2)'"□ ・・・・・・
・(1・1)= (RT /R'Y') "H-(Rf
'/Rx)・F'. Since the □ signal I from which the DCC off-serato is removed is expressed as 1-14-αF: □, the coefficient Rf of H and F in equation (11) is
/ RY: If R-f/Rx is set to the ratio of 1:α, then at the signal port (7), [! Each time the DC offset can be removed. That is, the value RY of the variable resistor may be set so as to satisfy the following equation.

Rf/RY:Rj7Rx,,,='i:'':α,''that is, RY-α·RX...□...(12□) However, from equation 10)', α-XO/YO.

In the embodiment shown in FIG. 6, by changing the amplifier 10b' to an inverting amplifier, the number of subtraction circuits can be reduced and the loss can be reduced.
. . . can be further reduced, and the same effect as in FIG. 3 can be obtained.

Of course, various other circuit configurations are possible. In addition, so far we have explained the case of completely removing disturbances such as the offset caused by movement of the objective lens in the direction perpendicular to the track, but below we will explain the case of actively utilizing the offset. .

Consider a case where the objective lens is supported by a spring or the like in the tracking direction. At this time, when the objective lens is displaced to follow the recording track, a steady deviation occurs due to the restoring force due to the stiffness component of the support spring. This steady deviation, or offset, is proportional to the lens displacement. Therefore, the proportionality constant β determined by the stiffness of the support spring and the tracking surf loop gain is adjusted to the right.On the other hand, an offset proportional to the lens position occurs in the signal if (=H−αF) mentioned above. This amount of offset can be freely determined by changing the reduction constant α. In other words, the proportionality constant γ can be freely determined depending on the relationship between the displacement of the lens and the offset amount. Therefore, The damping constant α is expressed as ゛γ−−β・・・
By setting (13) so that it is satisfied, it is possible to cancel the steady deviation caused by the stiffness of the support spring. The circuit configuration C in FIG. 3 or FIG. 6 can be demonstrated by adjusting the variable resistor 21 or 24, respectively.

In this way, it is possible to cancel the steady-state deviation component that occurs in the 1-racking servo lube due to the stiffness of the lens support system, so that accurate tracking servo is always possible even when the eccentric weight of the recording track is large.

According to the present invention, the difference in the upper envelope component and the difference in the lower envelope component of each detection output of the - set of detection means each contain components due to disturbance in phase. By simply covering the electrical processing, it is possible to prevent the tracking mebo from malfunctioning due to disturbances, and there is no need to use any additional optical components. [The circuit configuration is simple and the accuracy J = < disturbance can be removed.

In the above description, the objective lens is moved as the light spot deflecting means, but other means such as a tracking mirror may be used. In addition, it is not limited to optical information reading devices; any other type of information reading device can be used as long as the reproduction method generates equivalent tracking error signal information, and the recording medium does not need to be a disk. do not have.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional racking servo device, Fig. 2 is a diagram showing the relationship between a photoelectric conversion element and a light spot, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a block diagram of a conventional racking servo device. Third
FIG. 5 is a circuit diagram of a specific example of a part of the block in the figure, FIG. 5 is a waveform diagram of each part of the block in FIG. 3, and FIG. 6 is a circuit diagram showing another modification of the circuit block in FIG. 3. Description of symbols of main parts 1...Laser light source 5...Objective lens 6...Disc 9...Photodetector 12, 19.2'0. 22...Differential amplifier 1
718... Envelope extraction circuit, b concave, Figure 5

Claims (1)

[Claims] A servo signal generating device for a 1-racking servo control device configured to bias an information detection point of a pickup in a direction substantially orthogonal to the recording track so that the information detection point of the pickup accurately tracks the recording track, a set of detection means provided to detect the amount of deviation of the information detection point in the direction perpendicular to the track, and a set of detection means provided such that a difference occurs between detection outputs corresponding to the amount of deviation; means for extracting the upper envelope component and lower envelope 1cope component of each detection horn, means for obtaining a difference signal between these upper envelope components and a difference signal between lower envelope components, and a means for obtaining a difference signal between these upper envelope components and a difference signal between the lower envelope components, and A tracking servo signal generation circuit comprising means for generating a tracking servo signal by subtracting the ratio.