JPH0227737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a tracking servo signal of an optical pickup, and in particular, detects the difference between the optical sensor outputs divided into two by the optical spot scanning direction. In an optical pickup that detects a tracking error signal and also detects a pit signal for each pit on the disk information surface from the sum of the optical sensor outputs, the phase-inverted pit signal is converted into a positive pulse by a zero cross comparator. , a rising pulse and a falling pulse are generated from the positive pulse, the tracking error signal is sampled and held using the rising pulse and the falling pulse, and both sample and hold signals are added, and from this added signal, the tracking error signal is sampled and held. The present invention relates to a tracking servo signal detection method for an optical pickup, which is characterized in that the tracking servo signal is detected by removing high frequency components.

Detection of a tracking error signal and a focus error signal in an optical pickup of a conventional optical video/audio disk player has been carried out by the method shown in FIG. To explain the optical system based on FIG. 1, linearly polarized light from a semiconductor laser 1 is made into parallel light by a collimator lens 2, goes straight through a polarizing beam splitter 3, and is made into circularly polarized light by a 1/4 wavelength plate 4. ° Deflection prism 5, focus F
The reflected light passes through the objective lens 6 driven by the tracking T and focuses on the disk information surface 8 rotated by the disk rotation motor 7, and the reflected light becomes circularly polarized light rotating in the opposite direction to the incident light.
After passing through a 90° deflection prism 5, it becomes linearly polarized light orthogonal to the incident light at a quarter-wave plate 4, and is deflected by 90° at a polarizing beam splitter 3, passing through a converging lens 9 and a cylindrical lens 10 tilted at 45°, to a 4-split sensor. The light is received at 11. The tracking error signal Te is then passed through an adder AD and a subtracter SB to a four-split sensor 11 which is divided into two along the optical spot scanning direction, that is, the Y axis.
It is detected from the difference output between the right part (#1 + #2) and the left part (#3 + #4), and the focus error signal Fe is detected from the diagonal part (# 2+#4) and the diagonal section (#1+#3).

Although the pit signal RF is not shown, it is sent to the right (#1+#2) and left (#3+) via an adder.
#4) is detected from the sum output. In this detection, a light spot S that illuminates a pit P on the disk information surface 8 is diffracted and reflected by the pit P and enters the objective lens 6. The intensity distribution of the reflected light diffracted by the pit P changes depending on the relative positional relationship between the pit P and the light spot S, and the depth of the pit P is one-fifth of the wavelength λ of the light spot S.
Figure 2 shows the spatial intensity distribution, that is, the diffraction pattern, when observed through six objective lenses under the condition that the diameter of the light spot S is large and three times the width of the pit P. From this pattern, the tracking error can be determined. signal
Te is the pit P shown in Fig. 3a, which is the light spot S.
When scanning at an angle, the waveform becomes as shown in FIG. 3f. To briefly explain FIG. 2, the A column shows the positional relationship between the pit P and the light spot S, and the B column shows the intensity distribution on the objective lens 6 surface. In addition, in column B, the part indicated by fine diagonal lines represents the dark part of the reflected light amount distribution, the circle represents the aperture of the objective lens 6, the number surrounded by (〓〓) represents the overall modulation degree, and the other The numbers represent the total amount of light reflected on the objective lens 6 surface, that is, the amount of light in each area of the four-divided sensor 11 when the number surrounded by (〓〓) is set to 1. Furthermore, the numbers with # represent the respective areas of the four-part sensor 11, and A-α, etc. correspond to A and α in FIG. 3A.

Next, obtaining the tracking error signal Te shown in FIG. 3 f from the diffraction pattern shown in FIG. 2 will be explained.

The α position of pit P in Fig. 3a corresponds to E-α in Fig. 2, and the tracking error signal
Te={(#1+#2)-(#3+#4)}×total modulation degree {(0.15+0.55)-(0.19+0.11)}×0.15=
get 0.06. Also, regarding the β position of pit P, {(0.42+0.42)-(0.08+0.08)}×0.23=0.156,
Similarly, for the γ position of A of pit P, {(0.55+
0.15) - (0.19 + 0.11)} x 0.15 = 0.06.

Also, where there is no pitt P, {(0.25+0.25)-(0.25
+0.25)}×1=0. In this way, a tracking error signal Te for each pit P as shown in FIG. 3f is obtained.

However, in the prior art, the tracking error signal Te obtained in this way is directly passed through a low-pass filter LPF to remove the high frequency component and become the tracking servo signal Ts. There was a problem that the servo became unstable because it entered the tracking error signal Te.

This invention was made by focusing on the problems of the prior art, and involves converting a tracking error signal into two waveforms using sample and hold, and then superimposing the two to increase their level. Therefore, the purpose is to solve the above problems.

The present invention will be explained below based on the drawings.

FIG. 4 is a diagram showing an embodiment of the present invention. 20 is a comparator, which is a zero-cross comparator when inputted is an inversely phased pit signal RF having a waveform as shown in FIG. 3b, and the reference voltage is 0V. The pit signal RF is converted by the comparator 20 into a positive pulse waveform having a constant amplitude as shown in FIG. 3c.

31 is a rising pulse generator, and comparator 2
It takes an output of 0 as an input and generates a pulse when the output of the comparator 20 rises from the 0 level to a certain level. This rising pulse has a waveform as shown in FIG. 3d. 32 is a falling pulse generator which receives the output of the comparator 20 as an input and generates a pulse when the output of the comparator 20 falls from a certain level to 0 level. This falling pulse has a waveform as shown in FIG. 3e. 41 and 42 are analog switches, to which a tracking error signal Te having a waveform as shown in Fig. 3f is applied to the input side of both.
The output side is connected to the input side of adder AD.

The analog switch 41 is turned on and off by a rising pulse, and the analog switch 42 is turned on and off by a falling pulse.

The tracking error signal Te is sampled and held by turning on and off the analog switches 41 and 42. Note that the sampling period is set to be much shorter than the hold period. The waveform of the tracking error signal Te sampled and held by the analog switch 41 becomes a converted waveform as shown in FIG. The converted waveform will be as shown in Figure 3h. Adder AD is analog switch 4
The outputs of 1 and 42 are added, and the output waveform is as shown in FIG. 3i. Comparing the levels of the tracking error signal Te ₁ detected in this way and the tracking error signal Te which has not been processed according to the present invention at the position α in A of FIG. 3A, Te is 0.060. On the other hand, Te ₁ is 0.120. Therefore Te ₁ is Te 2
(6dB), and the tracking error signal Te ₁ can be detected with high sensitivity.

The LPF is a low-pass filter that receives the output of the adder AD, removes high frequency components contained in the tracking error signal Te ₁ , and detects the tracking servo signal Ts.

The waveform of the tracking servo signal Ts is shown in Figure 3j.
The waveform will be as shown in . In this way, instead of adding the tracking error signal Te directly to the low-pass filter LPF, the tracking error signal Te
By converting the waveform and increasing its level and adding it to the low pass filter LPF, it is possible to eliminate servo instability caused by the DC component.

Note that the tracking servo signal Ts is phase compensated, and the tracking drive coil is operated by current drive to apply the tracking servo.

As explained above, the present invention detects a tracking error signal for each pit on the disk information surface from the difference in the optical sensor output divided into two by the optical spot scanning direction, and also detects the tracking error signal for each pit on the disk information surface from the sum of the optical sensor outputs. In an optical pickup for detecting a pit signal for each pit on the disk information surface, converting the phase-inverted pit signal into a positive pulse by a zero-cross comparator, and generating a rising pulse and a falling pulse from the positive pulse, The tracking error signal is sampled and held using the rising pulse and the falling pulse, and both sample and hold signals are added together, and high frequency components are removed from the added signal to detect the tracking servo signal. Therefore, it is possible to increase the level of the tracking error signal, and accordingly, it is possible to obtain the effect that instability of the servo caused by the DC component can be resolved.

[Brief explanation of drawings]

Figure 1 is a perspective view of the optical system of the optical pickup and the signal processing system of the 4-split sensor. Figure 2 is a diagram showing the diffraction pattern on the objective lens surface when the pit depth is λ/5. Figure 3a is a diagram showing the optical spot scanning the pit, b is a diagram showing the reverse phase waveform of the pit signal, and c is a diagram showing the output waveform of the comparator.
d is a diagram showing the waveform of the rising pulse, e is a diagram showing the waveform of the falling pulse, f is a diagram showing the waveform of the tracking error signal, g is a diagram showing the output waveform of the analog switch 41, and h is a diagram showing the output waveform of the analog switch 42. i is a diagram showing the output waveform of the adder, j is a diagram showing the waveform of the tracking servo signal, and FIG. 4 is a block diagram showing an embodiment of the present invention. 1... Semiconductor laser, 2... Collimator lens, 3... Polarizing beam splitter, 4... 1/4 wavelength plate, 5... 90° deflection prism, 6... Objective lens, 7... Disk rotation motor, 8...Disk information surface, 9...Converging lens, 10...Cylindrical lens, 11...4-divided sensor, 20...Comparator, 31, 32...Pulse generator, 41, 42...
...analog switch, AD...adder, LPF...
low pass filter.

Claims (1)

[Claims] 1. Detect the tracking error signal for each pit on the disk information surface from the difference in the optical sensor output divided into two by the optical spot scanning direction, and
In an optical pickup that detects a pit signal for each pit on the disk information surface from the sum of the optical sensor outputs, the phase-inverted pit signal is converted into a positive pulse by a zero-cross comparator, and a rising pulse and a rising pulse are converted from the positive pulse. A falling pulse is generated, the tracking error signal is sampled and held using the rising pulse and the falling pulse, and both sample and hold signals are added together, and high frequency components are removed from the added signal to perform tracking. A tracking servo signal detection method for an optical pickup characterized by detecting a servo signal.