JPS63257923A - Tracking circuit for optical disk device - Google Patents

Abstract

PURPOSE:To prevent the amplitude of a tracking error signal from decreasing at the time of high speed accessing by using a value which is in proportion to a total reflection light quantity signal from a recording medium at the time of the follow-up control of an objective lens 4 and using a value which is in proportion to a difference between the total reflection light quantity and the shift speed signal of the objective lens at the time of accessing as a gain control signal. CONSTITUTION:A speed detector 17 obtains the shift speed of the objective lens 4 by dividing the counted value of a counting circuit 12 by a time. For executing tracking servo without a shift instruction (s), a switch 16 is turned off and an ACG (automatic control of gain) is executed with setting the total reflection light quantity signal (y) as the gain control signal (z) as it is. If the shift instruction (s) is received, the switch 16 is turned on and an operation amplifier circuit 15 operates the total reflection light quantity signal (y) and the shift speed signal (p) of the objective lens 4, which the speed detector 17 outputs, and the AGC is executed with said difference as the gain control signal (z), whereby the amplitude reduction corresponding to the speed of the tracking error signal (x) is compensated. Thus, the stable tracking error signal can be obtained even at the time of high speed accessing.

Description

[Detailed Description of the Invention] [Summary] The present invention solves the drawback that the output amplitude of an automatic gain control circuit that generates a tracking error signal decreases during high-speed access of an optical head in an optical disk device by using a total reflection light amount signal from a recording medium. The correction is made by using a gain control signal as a value proportional to the difference in the moving speed signals of the optical heads.

[Industrial application field]

The present invention relates to an optical disc device, and more particularly to a tracking circuit that outputs a stable tracking error signal during high-speed access.

Optical disk devices serve as external storage devices for computers.
Although it has the advantage of being small and has a large capacity, it has the disadvantage that the access time is slower than that of a magnetic disk device, and shortening the access time is important for expanding the range of applications for optical disk devices.

[Conventional technology]

FIG. 3 shows a conventional tracking circuit configuration diagram.

In the figure, light emitted from a laser diode 1 is turned into parallel light by a collimating lens 2, passes through a beam splitter 3, and forms a light spot at a predetermined track position on a recording medium 5 via an objective lens 4.

An actuator 6 has a function of moving the objective lens 4 to a predetermined track position, and here it is assumed that it includes both coarse access and fine access functions.

The light beam reflected by the recording medium 5 travels backward along the optical path and is reflected by the beam splinter 3, and a portion of the reflected light is incident on the two-split photodetector 7. The output of the two-split photodetector 7 is input in parallel to a subtracting amplifier 8 and a summing amplifier 9, and the output of the subtracting amplifier 8 is a tracking error signal X.
, the output of the summing amplifier 9 is used as the total reflected light amount signal y.

The tracking error signal
The signal is input to a circuit 10 (abbreviated as 1 or less AGC), where division of X/y is performed. That is, the total reflection light amount signal y is used as the gain control signal 2 of the tracking error signal X.

The output of the AGC circuit 10 is branched into two branches, one of which is connected to the actuator 6 via a servo circuit 11 and a changeover switch 14.
A servo drive system is configured to drive the servo drive system, and the other is manually operated by the colorant circuit 12 to detect the trunk position of the objective lens 4, and its output is input to the movement control circuit 13. When the movement control circuit 13 receives a movement command S from a higher level system (not shown), it calculates the difference between the current track position and the destination track position, and sends a control signal corresponding to the movement amount to the actuator via the changeover switch 14. Enter 6.

The recording medium 5 of an optical disc device is usually provided with a groove called a pre-group in advance, and the diffraction phenomenon of this groove is used to detect a radial position signal (tracking error signal X).

FIG. 4 is a diagram for explaining the pregroup method. As shown in the figure, λ/8 (
If a groove with a depth of λ is the wavelength of the irradiated light is provided, the intensity distribution of the reflected light from the recording medium 5 will be affected by the diffraction phenomenon as shown in the upper diagram of each objective lens 4 depending on the relative position of the groove and the light spot. This takes advantage of the fact that it changes due to

The tracking error signal X can be obtained by simply receiving the reflected light of this intensity distribution with the two-split photodetector 7 shown in FIG. 3 and finding the difference between the two using the subtracting amplifier 8.

Further, by calculating the sum of the two using the summing amplifier 9, the total reflected light amount signal y can be obtained.

FIG. 5 shows a waveform diagram of the third response section, and the operation of the circuit shown in FIG. 3 will be explained below with reference to FIG.

In FIG. 5, the horizontal axis represents the distance in the radial direction of the recording medium.

The vertical axis is the voltage, and X is the waveform of the tracking error signal,
y indicates the total reflection light amount signal. In the figure, position iP
The zero-crossing points of the tracking error signal Servo control is possible by controlling the position with the actuator 6. Further, by counting the number of zero crossing points by the counting circuit 12, the number of traversed tracks, that is, the current position signal on the recording medium 5 is determined.

The total reflected light amount signal y includes a DC component, and has a maximum value at positions P2 and P4 corresponding to the trunk center position of the tracking error signal X, and a minimum value at intermediate positions PI, P3, and P between adjacent trunks. . That is, both waveforms are characterized by having a phase difference of approximately 90 degrees.

Conventional optical disc devices use a laser diode 1 as a light source, and the emitted light is controlled to have high power during recording and low power during playback.

Therefore, the trunking error signal X during recording and playback
sensitivities are different. However, if this continues, the servo control will become unstable, so the total reflection light my from the recording medium 5 is detected, and automatic gain control of the tracking error signal X is performed using this signal.

[Problem that the invention seeks to solve]

According to the configuration of the conventional tracking circuit, since a DC amplifier is used in the subtraction amplifier 8 for detecting the tracking error signal X, the band is narrow, and during high-speed access, the amplitude of the tracking error signal X decreases and the count circuit 12 The disadvantage is that the input signal is weak and the reliability of counting is reduced.

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a tracking circuit in which the amplitude of the tracking error signal X does not decrease even during high-speed access.

[Means for solving problems]

As shown in FIG. 1, the tracking circuit of the present invention converts a tracking error signal X obtained when moving an objective lens 4 to a desired position on a recording medium 5 of an optical disk device and connecting light points into a gain control signal 2. AGC that makes the gain of the tracking error signal X constant by dividing by
In the circuit a(I), as the gain control signal 2, a value proportional to the total reflection light amount signal y from the recording medium 5 is used when tracking the objective lens 4, and when accessing, a value proportional to the total reflection light amount signal y and the objective lens 4 is used. A configuration using a value proportional to the difference in the moving speed signal p of the lens 4 is adopted.

[Effect]

As shown in the waveform diagram of each part in Fig. 2, both end positions d of the distance,
, d3, the moving speed is slow and d2 is fast, then the tracking error signal X during high-speed access decreases in amplitude as the speed increases, like an envelope. The total reflected light amount signal y is constant regardless of speed changes. The moving speed signal of the objective lens, as shown by waveform p, is large near position d2 and becomes small at both ends d, d. Therefore, if waveform p is subtracted from waveform y, waveform 2
It becomes small near position d2 as shown in FIG. Therefore, when waveform X is divided by waveform 2, the decrease in amplitude is corrected as in waveform r.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 shows a configuration diagram of a tracking circuit according to the present invention. The difference from FIG. 3 is that an operational amplifier 15 is provided to input the total reflection light amount signal y output from the summing amplifier 9, and the other input terminal of the operational amplifier 15 is connected to the objective lens 4 output from the speed detector 17. The moving speed signal p is inputted via the switch 16, and the output of the operational amplifier 15 is inputted as the gain control signal 2 to the AGC circuit 10, and the AGC circuit 10 divides the tracking error signal X by the gain control signal 2 and outputs the result. The parts that are different are different.

The speed detector 17 calculates the moving speed of the objective lens 4 by dividing the count value of the counting circuit 12 by time.

When tracking servo is performed without a movement command S, the switch 16 is turned off and AGC is performed using the total reflection light amount signal y as it is as the gain control signal 2.

When the movement command S is received, the switch 16 is turned on, and the operational amplifier 15 outputs the total reflected light amount signal y and the speed detector 1.
By calculating the difference between the moving speed signal p of the objective lens 4 outputted by the tracking error signal 7 and performing AGC using this as the gain control signal 2, it is possible to compensate for the amplitude decrease corresponding to the speed of the tracking error signal X.

Figure 2 shows the waveform diagram of the first answering part. In each figure, the horizontal axis shows distance, and the vertical axis shows voltage, and the same level Wt, d1
．． The waveforms at dt and ds are compared.

Since both the tracking error signal X and the output waveform 2 of the arithmetic unit 15 have the same changing tendency of decreasing near the center position d, it is possible to correct the decrease in the amplitude of the tracking error signal X by dividing X/Z. can.

〔Effect of the invention〕

As described above in detail, according to the tracking circuit of the optical disc device of the present invention, a stable tracking error signal can be obtained even during high-speed access, and the reliability of the counting circuit can also be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the tracking circuit of the present invention, Fig. 2 is a waveform diagram of the first response section, Fig. 3 is a block diagram of a conventional tracking circuit, and Fig. 4 is for explaining the conventional pregroup method. Figure 5 shows the waveform diagram of the third answering section. In FIG. 1, 4 is an objective lens, 5 is a recording medium, and 10 is an objective lens.
is an automatic gain control (AGC) circuit, p is a moving speed signal, and X
denotes a tracking error signal, y denotes a total reflection light amount signal, and 2 denotes a gain control signal, respectively. ＞CL LI

Claims (1)

[Claims] A tracking error signal (x) obtained when moving an objective lens (4) to a desired position on a recording medium (5) of an optical disk device and connecting light points is converted into a gain control signal (z). In an automatic gain control circuit (10) that keeps the gain of the tracking error signal (x) constant by dividing by
During follow-up control, a value proportional to the total reflected light amount signal (y) from the recording medium (5) is used, and during access, the total reflected light amount signal (y) and the moving speed signal (p) of the objective lens (4) are used. A tracking circuit for an optical disc device, characterized in that a value proportional to the difference between the two is used.