JPS58155532A - Tracking servo signal detecting method of optical pickup - Google Patents

Abstract

PURPOSE:To improve S/N ratio and to stabilize a servo, by superimposing a DC component formed on the basis of a tracking error signal on the tracking error signal, and increasing the entire level of the tracking error signal. CONSTITUTION:In an optical pickup detecting a tracking error signal at each pit of a disc information surface from the difference between optical sensor outputs divided into two depending on the optical spot scanning direction, the positive/negative part only of the tracking error signal Te is detected at half- wave linear detection circuits 21 and 22 respectively and inputted to limiter amplifiers 31, 32, and summed at an adder AD1 via clamp circuits 41, 42. The tracking error signal Te is superimposed on the summing output at an adder AD2, and after the entire level is increased, the resulting signal is inputted to a bridge detection circuit 50, allowing to make the level of the tracking servo signal Ts equal to the peak value of the tracking error signal Te. Thus, unstable servo due to the DC vomponent is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a tracking serve signal of an optical pickup.
In an optical pickup that detects a tracking error signal for each pit on the disc information surface from the difference between the optical sensor outputs, each half-wave linear detection circuit, limiter/amplifier, and clamp are used for the positive and negative parts of the tracking error signal. The signals of the obtained positive and negative parts are added together, the tracking error signal is added thereto, and the added signal is passed through a full wave detection circuit to detect a tracking surge signal. The present invention relates to a tracking radar signal detection method for optical pickup. 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 6, and is made into circularly polarized light by a quarter-wave plate 4. Deflection prism 5
, 7 through the objective lens 6 driven by the orcus F and the tracking T, and is focused 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. Objective lens 6. Passes through a 90° deflection prism 5, becomes linearly polarized light orthogonal to the incident light at a 174-wavelength filter 4, is deflected by 90° at a polarizing beam slittor 6, and convergent lens 9. Cylindrical lens 10f tilted at 45°; After that, the light is received by the four-split sensor 11. The tracking error signal Te is transmitted through the adder AD and the subtracter SBi to the cloth part (10'+2) and the left part ("3+"4) of the 4-split sensor 11, which is divided into two by the light spot scanning direction, that is, the Y axis.
) The 7-occasion error signal Fe detected from the difference output between the
It is detected from the difference output between P2+hand 4) and the diagonal part ("1+"3).

Although the pit signal (LP) is not shown, it is detected from the sum output of the right part (≠1+≠2) and the left part (S3+≠4) via an adder. In such detection, a light spot S that irradiates a pit P on the disc information surface 8 is diffracted by the pit P, is reflected, and enters the objective lens 6 . The intensity distribution of the reflected light diffracted by the pit P is
The depth of the pit P is one-fifth of the wavelength λ of the light spot S, and the diameter of the light spot S is three times the width of the pit P. Figure 2 shows the spatial intensity distribution when observed through the 6 surfaces of the objective lens, that is, the diffraction nomiturn.From this pattern, the tracking error signal Te (T) and the pin (P) shown in Figure 3 (a) are optical spora). 8 scans stubbornly, Fig. 3 (c
) will result in a waveform as shown below. 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 0 represents the overall modulation degree, and the other numbers represent the objective lens 6. It represents the total amount of light reflected on the lens 6 surface, that is, each light 11 in the area of the 4-split sensor 11 when the number surrounded by 0 is taken as 1. Furthermore, the numbers with a square mark represent the respective areas of the four-part sensor 11, and E α, etc. correspond to A and α in FIG. 3(a).

Next, the method of obtaining the tracking error signal Tet- shown in FIG. 3(c) from the diffraction nomiturn shown in FIG. 2 will be explained.

The α position of A in Fig. 3(a) corresponds to E α in Fig. 2, and the tracking error signal Te =
((su1++2) (from peak 30th month April x overall modulation degree ((0,15+0.55)-(0,19+0.11)
)XO, 15=0,06 is obtained. Also, regarding the β position of pit P, ((0,42+0.42)−(0,08+
0.08))Xo, 23=0.156, similarly pit P
γ position of i (then + (0,55 + 0.15) -
(0,19+0.11 month X O,15=0,06
get.

Also, where there is no pit P, ((0,25+0.25) −
(0,25+0.25))X1=0. In this way, a tracking error signal Te f for each valley pit P as shown in FIG. 3(C) is obtained.

However, in the prior art, the tracking error signal 'l'e f obtained in this way is directly passed through a low-pass filter LPF to remove all high frequency components to produce a tracking A signal Ts, but the tracking A signal TS is a tracking error signal Te Since it does not reach the peak value of , there is a problem that 8/N becomes low, and the direct current component due to the inclination of the disc information surface 8 also enters the tracking error signal Te, making the serve unstable. There was a problem.

This 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 to increase the overall level of the tracking error signal. The aim is to solve the above problems.

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

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

21 and 22 are half-wave linear detection circuits, each of which receives a tracking error signal Te on its input side.

The half-wave linear detection circuit 21 receives the tracking error signal Te.
Only the positive portion of the waveform is detected, and the output waveform is as shown in FIG. 3(d). The half-wave linear detection circuit 22 detects only the inner negative portion of the tracking Moller signal Te, and its output waveform E is as shown in FIG. 3(e).

51 and +2 are limiters/amplifiers, and the outputs of half-wave linear detection circuits 21 and 22 are applied to the input terminals of both of them. The limiter/amplifier 61 suppresses the upper and lower sides of the output waveform of the half-wave linear detection circuit 21 to make the output waveform a constant amplitude and amplifies it.

The limiter/amplifier 62 suppresses the upper and lower sides of the output waveform of the half-wave linear detection circuit 22 to make the output waveform a constant amplitude and amplifies it. And both have constant amplitude and
The degree of amplification is determined by the tracking error signal Te f where the amplitude of the tracking error signal Te is small, that is, between A and the mouth or between the mouth and C in FIG. 3(a).
The low yR of the peak value that occurs when the tracking error signal T'e is directly passed through the full-wave detection circuit described later as a reference.
It is determined to compensate for the

41 and 42 are clamp circuits, and the outputs of limiter/amplifiers 61 and 62 are applied to their input ends.

Clamp circuits 41 and 42 are both limiter/amplifier 3
This is to shift the output level of 1.32 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 are shown in FIG.
), the waveform will be as shown in (g). AD is an adder, and the outputs of clamp circuits M41 and M42 are added to the input side, and the outputs of clamp circuits M41 and M42 are added together. The output waveform H of the adder AD1 has a waveform as shown in FIG. 3(h). AD2 is an adder, and the output of the adder AD and the tracking error signal Te are added to the input terminal, and the output of the adder 5ADx and the tracking error signal T are added.
evi - is added.

As a result, the level of the tracking error signal Te is increased by the output level of the adder AD.

The output signal from adder AD2 has a waveform as shown in FIG. 3(i). Reference numeral 50 denotes a full wave detection circuit, which receives the output of the adder AD2 at its input terminal, removes high frequency components contained in the output of the adder AD2, and detects the tracking servo signal Tsf. The waveform of the tracking search signal Ts is as shown in FIG. 3(j).

In this way, the DC component formed based on the tracking error signal Te is superimposed on the tracking error signal Te to raise the level as a whole, and then the full-wave detection circuit 5
By adding it to 0, the tracking servo signal Ts
can be made equal to the peak value of the tracking error signal Te, improving 8/N and eliminating servo instability due to DC components. Note that the tracking servo signal Ts is phase-compensated, and the tracking drive coil is operated by current drive to perform tracking servo communication.

As explained above, the present invention detects all the tracking error signals for each bit on the disc information surface from the difference in the optical sensor output divided into two by the optical spot scanning direction.・For the negative part, pass through each half-wave linear detection circuit, limiter/amplifier, and clamp circuit, add up the obtained signals of each positive and negative part, and add the tracking error 1g to this, By passing this added signal through a full-wave detection circuit and detecting the tracking error signal ∆, it is possible to increase the level of the tracking error signal. This has the effect of being able to resolve instability within itself.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the optical system of the original pickup and a diagram showing the No. 13 processing system of a conventional 4-split sensor. Figure 2 is diffraction at the objective lens surface when the pit depth is λ/2) ξ Figure showing the turn, 3rd
) is a diagram showing the waveform of the tracking error signal, (d) is a diagram showing the output waveform of the half-wave linear detection circuit 21, (C) is a diagram showing the output me of the half-wave linear detection circuit 22, and (f) is a diagram showing the output waveform of the half-wave linear detection circuit 22. The diagram shows the output waveform of the circuit 41, (g) shows the output waveform of the clamp circuit 42, and (h) shows the output of the adder AD. Figure 4 is a block diagram showing an embodiment of the present invention. 1... Semiconductor laser, 2...Collimator lens, 6
...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,
51.52...Limiter/amplifier, 41.42...
Clamp circuit, 50...Full wave detection circuit, ADI, AD
2... Adder patent applicant Akai Electric Co., Ltd. Figure 1 Y-axis Figure 2

Claims (1)

[Claims] 1. In an optical pickup that detects a tracking error signal for each pit on the disc information surface from the difference in the optical sensor output divided into two by the optical spot scanning direction, each half-wave straight line is detected for the positive and negative parts of the tracking error signal. Detection circuit, limiter/amplifier and clamp circuit,
The signals of the positive and negative parts obtained are added together with the tracking error signal, and this added signal is passed through a full-wave detection circuit to detect a tracking surge signal. Features a tracking serve signal detection method for optical pickup.