JPH02775B2 - - 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, the positive and negative parts of the tracking error signal are passed through a half-wave linear detection circuit, a limiter/amplifier, and a clamp circuit, and the obtained signals of the positive and negative parts are The present invention relates to a method for detecting a tracking servo signal of an optical pickup, which comprises adding the tracking error signal to the tracking error signal, and detecting the tracking servo signal by passing the added signal through a full-wave detection circuit. 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 quarter-wave plate 4.
The reflected light passes through an objective lens 6 driven by a 90° deflection prism 5, focus F, and tracking T, and is focused on a disk information surface 8 rotated by a disk rotation motor 7, and the reflected light is rotated in the opposite direction to the incident light. It becomes circularly polarized light, passes through an objective lens 6 and a 90° deflection prism 5, becomes a linearly polarized light perpendicular to the incident light at a quarter-wave plate 4, is deflected by 90° at a polarizing beam splitter 3, and is tilted at a converging lens 9 at a 45° angle. Cylindrical lens 10
The light is then received by the four-part sensor 11. The tracking error signal Te is output from the adder AD and the subtracter.
The right part of the 4-split sensor 11 (# 1
+#2) and the left side (#3+#4), and the focus error signal Fe is detected from the difference output between the left side (#2+#4) and the diagonal side (#2+#4) through the adder AD and subtractor SB.
4) and the diagonal portion (#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. 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 three times the width of
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. 3c. 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. moreover#
The numbers with marks represent the respective areas of the four-part sensor 11, and A-α, etc. correspond to A and α in FIG. 3a.

Next, it will be explained how to obtain the tracking error signal Te shown in FIG. 3c from the diffraction pattern shown in FIG. 2.

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)} x total modulation degree {(0.15 + 0.55) - (0.19 + 0.11)} x 0.15 =
We get 0.66. 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 = 0.66.

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. 3c 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 high frequency components and become a tracking servo signal Ts, but the tracking servo signal Ts is not a tracking error signal. Since it does not reach the peak value of Te, there is a problem that it is small and the S/N becomes low, and the DC component due to the tilt of the disk information surface 8 also enters the tracking error signal Te, making the servo unstable. There was a problem with that.

The present invention was made by focusing on the problems of the prior art, and involves superimposing a DC component formed based on a tracking error signal on the tracking error signal, thereby reducing the overall tracking error signal. The aim is to solve the above problems by raising the level.

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

FIG. 4 is a block diagram showing one embodiment of the present invention.

21 and 22 are half-wave linear detection circuits, both of which have a tracking error signal Te applied to their input sides.
The half-wave linear detection circuit 21 generates a tracking error signal.
It detects only the positive part of Te, and its output waveform D is as shown in Figure 3d. The half-wave linear detection circuit 22 generates a tracking error signal.
It detects only the inner negative part of Te, and its output waveform E is as shown in FIG. 3e.

31 and 32 are limiters/amplifiers, to which the outputs of the half-wave linear detection circuits 21 and 22 are applied to the input sides. The limiter/amplifier 31 suppresses the top and bottom of the output waveform of the half-wave linear detection circuit 21, makes the output waveform a constant amplitude, and amplifies it.
The limiter/amplifier 32 suppresses the top and bottom of the output waveform of the half-wave linear detection circuit 22 to make the output waveform a constant amplitude and amplifies it. In both cases, the constant amplitude and degree of amplification are determined based on the tracking error signal Te between A and B or between B and C in Figure 3a, where the amplitude of the tracking error signal Te is small. It is determined to compensate for the reduction in peak value that occurs when the error signal Te is directly passed through a full-wave detection circuit, which will be described later.

41 and 42 are clamp circuits, and the outputs of the limiter/amplifiers 31 and 32 are applied to the input sides of both of them. The clamp circuits 41 and 42 both shift the output level of the limiter/amplifiers 31 and 32 to match the diode level of a full wave detection circuit, which will be described later.

The output waveforms F and G of the clamp circuits 41 and 42 have waveforms as shown in FIG. 3 f and g. AD ₁ is an adder, and the outputs of the clamp circuits 41 and 42 are added to the input side, and the outputs of the clamp circuits 41 and 42 are added together. The output waveform H of adder AD ₁ is the third
The waveform will be as shown in Figure h. AD ₂ is an adder,
The output of the adder AD ₁ and the tracking error signal Te are added to the input side, and the output of the adder AD ₁ and the tracking error signal Te are added.
As a result, the level of the tracking error signal Te is increased by the output level of the adder _AD1 .

The output waveform I of the adder AD ₂ has a waveform as shown in FIG. 3i. Reference numeral 50 denotes a full wave detection circuit, to which the output of the adder AD ₂ is added to the input side, and detects the tracking servo signal Ts by removing high frequency components contained in the output of the adder AD ₂ . The tracking servo signal Ts has a waveform as shown in FIG. 3j. In this way, by superimposing the DC component formed based on the tracking error signal Te on the tracking error signal Te to raise the level as a whole, and then adding it to the full wave detection circuit 50, the tracking servo signal The level of Ts can be made equal to the peak value of the tracking error signal Te, improving the S/N ratio and eliminating servo instability due to DC components. In addition, tracking servo signal
The phase of Ts is compensated, the tracking drive coil is activated by current drive, and the tracking servo is applied.

As explained above, the present invention provides a tracking error signal in an optical pickup that 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. The positive and negative parts of the signal are passed through each half-wave linear detection circuit, limiter/amplifier, and clamp circuit, and the obtained positive and negative parts are
The level of the tracking error signal is determined by adding the signals of each negative part and adding the tracking error signal thereto, and passing this added signal through a full wave detection circuit to detect the tracking servo signal. Accordingly, it is possible to improve the S/N ratio and eliminate servo instability caused by DC components.

[Brief explanation of drawings]

Figure 1 is a perspective view of the optical system of the optical pickup and a diagram showing the signal processing system of a conventional 4-split sensor. Figure 2 is a diagram showing the diffraction pattern on the objective lens surface when the pit depth is λ/5. , FIG. 3 a shows the optical spot scanning the pit, b shows the negative phase waveform of the pit signal, c shows the waveform of the tracking error signal, and d shows the output waveform of the half-wave linear detection circuit 21. , e is a diagram showing the output waveform of the half-wave linear detection circuit 22, f is a diagram showing the output waveform of the clamp circuit 41, g is a diagram showing the output waveform of the clamp circuit 42, and h is a diagram showing the output waveform of the adder AD ₁ . FIG. 4 is a block diagram showing an embodiment of the present invention; i is a diagram showing the output waveform of the adder AD ₂ ; j is a diagram showing the waveform of the tracking servo signal; FIG. 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-split sensor, 21, 22... Half-wave linear detection circuit, 31, 32... Limiter/amplifier, 41, 42... ...Clamp circuit, 50...Full wave detection circuit, _AD1 , _AD2 ...Adder.

Claims (1)

[Claims] 1. In an optical pickup that 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, the positive and
The negative part is passed through each half-wave linear detection circuit, limiter/amplifier, and clamp circuit, and the obtained signals of the positive and negative parts are added together, and the tracking error signal is added thereto, and this added signal is A tracking servo signal detection method for an optical pickup, which comprises detecting the tracking servo signal by passing it through a full wave detection circuit.