JPH07311946A - Information recorder/player - Google Patents

Abstract

PURPOSE:To control the focus and tracking stably by providing means for varying the characteristics of an envelope detecting circuit. CONSTITUTION:Outputs from photoelectric conversion elements 1-a, 1-b for converting the light reflected on an optical disc into a current corresponding to the quantity of light are converted, respectively, through current/voltage conversion circuits 2-a, 2-b into voltage signals SO-a, SO-b which are then delivered to circuits 3-a, 3-b for compensating for the optical transmission characteristics. Output signals S1-a, S1-b therefrom are delivered to envelope detecting circuits 4-a, 4-b (simply shown as 4) which then output signals S2-a, S2-b. A seek circuit 8 is a main element of means for varying the characteristics of the envelope detecting circuit 4 and makes a decision whether the recorder/ player is in normal playing state or performing a seek operation before delivering a signal S3 for switching the characteristics of the envelope detecting circuit 4. The switching signal S3 switches the envelope detecting circuit 4 depending on the playing operation or the seeking operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus for optically recording / reproducing information, and in a general optical disk apparatus, a control signal generating circuit for generating a control signal for controlling the irradiation state of a light beam onto an optical disk. It is about.

[0002]

2. Description of the Related Art Generally, in an optical disk device, focus control is performed so that the optical beam always keeps a focused state on a recording film surface of an optical disk which is an information recording / reproducing medium, and the optical beam accurately tracks. It is necessary to perform tracking control for following up, and the control signals required for these controls are obtained from the reflected light from the optical disc using a control signal generation circuit.
In recent years, a read-only area (hereinafter referred to as a ROM area) that can only read a pre-recorded information signal, and a recordable and reproducible area (hereinafter referred to as a RAM area) that enables new additional recording or rewriting of the information signal. A convenient optical disc having the above has been proposed. As an example of the recording film of such an optical disc, a magneto-optical film made of an alloy of a transition metal and a rare earth metal is used. In this RAM area,
A guide groove for tracking control is provided in a spiral shape, and an information signal to be additionally recorded is recorded in the magneto-optical film between these grooves as a magnetic pit due to a difference in magnetic direction.

On the other hand, in the ROM area, as shown in FIG.
An information signal is previously recorded between the guide grooves as an uneven pit row (hereinafter referred to as an information pit) according to a modulation method of signal recording and a pattern of input information. In the ROM area of such an optical disc, since the guide groove for tracking and the information pit are mixed, there arises a problem that the control signal is deteriorated. This will be described below with reference to the drawings.

FIG. 18 shows reflected light obtained when an optical beam passes through a portion having no information pit (arrow A) and a portion having information pit (arrow B) in the ROM area shown in FIG. It is a figure showing intensity (signal SX, signal SY). The hatched portion in the figure corresponds to the case where the passage line of the optical beam is variously changed. As can be seen from the figure, the intensity of the reflected light from the optical disc greatly differs depending on the presence or absence of the guide groove and the information pit. Therefore, in the control signal generation circuit of the conventional optical disk device, the output of the photoelectric conversion means for converting the intensity of the reflected light into the electric signal is passed through the low-pass band designed in consideration of the difference in the frequency band of the control signal and the information pit. The control signal is input from the filter and the control signal is generated from the obtained signal (average value SA in FIG. 18). Therefore, the signal level is not lowered by the modulation method of signal recording and the pattern of input information. Inevitably, the gain of the control system changes as a result, which causes a problem that the pull-in operation of the control system and the tracking accuracy deteriorate.

As a method for solving such a problem, Japanese Patent Laid-Open No. 58-41447 discloses a configuration of a control signal generating circuit for tracking control having an envelope detection circuit. This is to selectively use the envelope detection circuit to selectively output the level (signal SX in FIG. 18) from the portion of the recording film surface of the optical disc having no information pits, which includes information as a control signal, from the output of the photoelectric conversion means. This is a method of reducing the amount of signal drop due to information pits by selecting, that is, detecting the envelope. FIG. 19 shows a configuration example of the envelope detection circuit of the control signal generation circuit, which includes the diode 4
0, capacitor C0, resistor R0 and buffer amplifier 41
It is composed of. The characteristic of the detection efficiency of this envelope detection circuit depends on the time constant determined by the capacitor C0 and the resistor R0 that are included. Therefore, the time constant is designed in consideration of the signal change due to the information pit, that is, the frequency band of the information signal and the frequency band required for the control signal. This allows
Even when the information is reproduced in the ROM area where the information signal and the control signal are mixed, it is possible to detect only the control signal component from the reflected light of the disc and obtain the control signal.

[0006]

However, in the control signal generating circuit having the conventional envelope detection circuit, the optical beam on the optical disk in the optical disk device moves from a certain track to a target track, that is, a seam. No consideration was given to the fact that the frequency of the tracking control signal changes when the tracking operation is performed. Hereinafter, this point will be described with reference to the drawings.

FIG. 20 is a schematic view of an optical disk, and FIG. 21 shows a ROM area in which guide grooves and information pits are mixed. The rotation speed of the optical disk shown in the figure is 3000 rp
m, the track pitch is 1.6 μm, and the disc eccentricity is 50 μm, the frequency of the tracking control signal during disc reproduction is about 3.1 kHz. On the other hand, the frequency of the tracking control signal during seek operation is 310 kHz when the seek speed is 0.5 m / s, which is about 100 times higher than that during reproduction.

FIG. 22 shows an input signal to the envelope detection circuit during disk reproduction. As shown in FIG. 22, the input signal to the envelope detection circuit at the time of reproducing the disc is a control signal frequency of 3.1 kHz and a frequency due to the information pits of several MHz (for example, in FIG. 21, the pit length is 2T and the pit interval is 2T). Pattern of 2T = 2T = 0.75 μm, the number of revolutions of the optical disk is 3000 rpm, and the reproduction position is the inner circumference (r
= 30 mm), the frequency due to the information pit is 6.
3 MHz). At this time, by setting the characteristics of the envelope detection circuit to be sufficiently larger than the period of signal change due to the information pit and sufficiently smaller than the band required for the control signal, the envelope detection circuit can The output (thick line in FIG. 22) synchronized with the control signal is detected. However, during seek operation, the frequency of the above-mentioned control signal is about 100 times that during reproduction, so that the control signal (3.1 kHz) and information signal (6.3 MH) during reproduction are used.
In the envelope detection circuit designed in consideration of the difference in the band of z), the output of the envelope detection circuit has a waveform as shown by the dotted line in FIG. 23, and the envelope synchronized with the control signal in the input signal is It cannot be detected sufficiently, and the control signal changes greatly accordingly, and the gain of the control system changes. When the gain of the control system changes, there arises a problem that the pulling operation of the system and the tracking accuracy are deteriorated.

[0009]

In the control signal generating circuit of the present invention, an information pit is provided in an envelope detection circuit for detecting the envelope of the output of the photoelectric conversion means or the output of the compensation circuit provided after the photoelectric conversion means. The characteristic of the envelope detection circuit is changed when the frequency band of the signal from 1 and the frequency band required for the control signal relatively change.

[0010]

By changing the characteristics of the envelope detection circuit set according to the frequency band of the information pit and the control signal at the time of reproducing the information pit signal, the signal frequency band from the information pit and the frequency band required for the control signal are changed. Even in a situation in which is relatively close, the envelope of the signal input to the envelope detection circuit is detected, a control signal of a nearly constant level is obtained after the envelope detection circuit, and the gain of the control system should be kept close to a constant level. You can This makes it possible to stabilize the pull-in operation and tracking accuracy of the system.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a first embodiment of a control signal generation circuit according to the present invention. The first embodiment has a configuration in which the characteristics of the envelope detection circuit are switched between normal reproduction and seek. In FIG. 1, 1-a and 1-b are photoelectric conversion elements that receive the reflected light from the optical disk and output a current according to the light amount. The outputs of the photoelectric conversion elements 1-a and 1-b are converted into voltage signals S0-a and S0-b by the current-voltage conversion circuits 2-a and 2-b, respectively, to compensate optical transfer characteristics. It is input to the compensation circuits 3-a and 3-b. The output signals S1-a and S1-b are signals S2- whose envelope components have been detected by the envelope detection circuits 4-a and 4-b.
It is output as a, S2-b. The current in the figure −
Voltage conversion circuits 2-a and 2-b, compensation circuits 3-a and 3-b
And the envelope detection circuits 4-a and 4-b have the same configuration. Here, the photoelectric conversion element 1 and the current-voltage conversion circuit 2 are elements constituting the photoelectric conversion means.

In FIG. 1, reference numeral 8 is a seek control circuit,
In the information recording / reproducing apparatus of the present invention, the seek operation for moving the optical beam to the target track is controlled. In the present embodiment, the seek control circuit 8 discriminates between the normal reproduction state and the seek operation, and outputs a switching signal S3 for switching the characteristics of the envelope detection circuit 4. To do. By the switching signal S3, the characteristics of the envelope detection circuit 4 are switched in correspondence with reproduction and seek.

FIG. 2 shows a configuration example of the compensation circuit 3 and the envelope detection circuit 4. The compensation circuit 3 includes an operational amplifier 30, a capacitor C1, and resistors R1 and R2. FIG. 3 shows the transfer characteristics of the optical system, the transfer characteristics of the compensation circuit 3, and the transfer characteristics from the optical system to the output of the compensation circuit 3. The transfer characteristic of the optical system is such that the gain decreases as the frequency of the recorded signal increases. That is, the characteristic is that the level of the reproduction signal decreases. Therefore, by setting the transfer characteristic of the compensating circuit 3 so that the gain increases (the output level increases) as the frequency of the input signal increases so as to compensate the transfer characteristic of the optical system, the compensation is performed as shown in FIG. Output signal S1 of circuit 3
It becomes possible to make the transfer characteristic of the constant level.

In the compensation circuit 3, the gain increase amount N (dB) in the high frequency portion is given by N = 20 × LOG (1 + R2 / R1). Also, the frequency Fs at which the gain starts to increase
(Hz) is given by Fs = 1 / (2π × C1 × (R1 + R2)). As a result, for example, R1 = 1.1 kΩ,
If R2 = 5.6 kΩ and C1 = 13 pF, N = 15.
It becomes 7 dB and Fs = 1.83 MHz.

Further, the envelope detection circuit 4 has a diode 40.
And capacitors C3 and C4, resistor R3 and buffer amplifier 4
It is composed of 1 and 1. In the envelope detection circuit 4, the switch 31 is a switching signal S3 from the seek control circuit 8.
The opening / closing is controlled by the switch, and the switch 31 is closed during normal disk reproduction. At this time, the resistance R
The time constant τ1 determined by 3 and the capacitors C3 and C4 is given by τ1 = (C3 + C4) × R3. On the other hand, when the seek operation is performed, the switch 31 is opened. At this time, the time constant τ2 determined by the resistor R3 and the capacitor C3 is given by τ2 = C3 × R3.

Here, the time constant τ also means a frequency determined by τ. FIG. 4 shows changes in the waveforms of the input signal S1 and the output signal S2 of the envelope detection circuit 4 during reproduction of the disc. The time constant τ1 determined by the capacitors C3 and C4 and the resistor R3 of the envelope detection circuit 4 is sufficiently larger than the period of the signal obtained from the information pit (hereinafter referred to as the information pit signal) and the frequency band required for the control signal. Is set to be sufficiently small. As a result, the input signal S1 including the information pit signal component is
In the envelope detection circuit 4, the output signal S in which only the envelope portion 100, which is the track crossing signal of the optical beam, is efficiently detected.
It becomes 2.

FIG. 5 shows an envelope detection circuit 4 for reproducing a disc.
6 shows the input and output waveforms of the envelope detection circuit 4 at the time of seeking. At the seek time of FIG. 6, when the envelope detection circuit 4 whose characteristics are set according to the disk reproduction of FIG. 5 is used, the frequency required for the control signal; fs becomes close to the frequency of the information pit signal; fp. Therefore, the output of the envelope detection circuit 4 has a waveform as shown by the dotted line in FIG. 6, and the input waveform cannot be sufficiently detected.

The thick line in FIG. 6 shows the output waveform when the characteristics of the envelope detection circuit 4 are switched according to the seek time. At this time, the time constant τ determined by the capacitor C3 and the resistor R3
2 is set smaller than the time constant τ1 during reproduction. In this way, the output waveform level of the envelope detection circuit 4 is improved by reducing the time constant determined by the capacitor and the resistance with respect to the frequency band required for the control signal.

FIG. 7 shows the detection efficiency with respect to the control signal frequency when the capacitor capacity is switched in the envelope detection circuit 4. Control signal frequency 400k
By setting the capacitor capacitance C = 0.047 μF of the envelope detection circuit 4 to 0.022 μF at Hz and R3 = 2.2 kΩ, the detection efficiency is approximately doubled. In this way, by switching the characteristics of the envelope detection circuit 4 between the time of disc reproduction and the time of seek, it becomes possible to obtain a control signal through the envelope detection circuit even during seek.
Stable control can be performed.

In the envelope detection circuits 4-a and 4-b, the envelope components of the input signals S1-a and S1-b are the signals S2-a and S2.
Detected as -b, and the subtraction circuit 5 and the addition circuit 6 are detected, respectively.
And a difference signal and a sum signal which are control signals used for the tracking servo. As described above, the detection efficiency of the envelope detection circuit depends on the frequencies of the information pit signal and the control signal. The first embodiment relates to a structure for coping with changes in the frequency of the control signal during seek and reproduction. Next, a description will be given of an embodiment corresponding to changes in both the information pit signal and the control signal that affect the detection efficiency of the envelope detection circuit.

FIG. 8 is a diagram showing the configuration of the second embodiment of the control signal generation circuit. In the information recording / reproducing apparatus, the frequency of the control signal at the time of reproduction does not change regardless of the reproduction position of the inner and outer circumferences of the disk in which the number of revolutions of the disk is constant. However, in a disc recorded at a constant linear velocity on the inner and outer circumferences, the number of rotations on the outer circumference with a large disc radius is smaller than that on the inner circumference with a smaller disc radius, and the control signal frequency changes depending on the playback position on the inner and outer circumferences of the disc. become. Further, the frequency range of the reproduction signal changes to the high frequency side on the outer circumference of the disk recorded with the pit interval at the outer circumference position made shorter than the inner circumference position in order to increase the recording capacity of the disk. Therefore, in these discs, the frequency of the information pit signal and the frequency of the control signal respectively change or relatively change. Therefore, if the characteristic of the envelope detection circuit is made constant, it is not possible to deal with the frequency change in the inner and outer circumferences of the disk. Therefore, the embodiment of FIG. 8 addresses the above problem by switching the characteristics of the envelope detection circuit according to the reproduction position of the disc. In FIG. 8, the same functional parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted unless particularly necessary.

In FIG. 8, 7 is a compensation circuit 3-a, 3-b.
Is an adder circuit for adding the output signals S1-a and S1-b of the adder circuit, and 8 is an address reproducer circuit for reproducing the address information of each track previously recorded on the disc from the output signal of the adder circuit 7 (the present invention). Corresponding to the position detecting means). The address reproduction circuit 8 determines the reproduction position of the disc based on the address information, and outputs a switching signal S3 for switching the characteristics of the envelope detection circuit 4. In the envelope detection circuit 4, the characteristics of the envelope detection circuit 4 when reproducing the inner circumference having a slow linear velocity or a long pit interval (the frequency of the information pit signal is low) by the switching signal S3 from the address reproducing circuit 8 The characteristics of the envelope detection circuit 4 are switched when reproducing the outer periphery having a high linear velocity or a short pit interval (the frequency of the information pit signal is high) or a small number of revolutions (the control signal is low).

FIG. 9 shows a configuration example of the envelope detection circuit 4.
2 except that the opening / closing control of the switch 31 is performed by the switching signal S3 from the address reproducing circuit 8 in FIG.
The configuration is exactly the same as. When reproducing the inner peripheral portion of the disc, the switch 31 is opened. At this time, the time constant τ2 determined by the resistor R3 and the capacitor C3 is given by τ2 = C3 × R3. On the other hand, when reproducing the outer peripheral portion of the disc, the switch 31 is closed. At this time, the time constant τ1 determined by the resistor R3 and the capacitors C3 and C4 is given by τ1 = (C3 + C4) × R3.

10 and 11 show changes in the waveforms of the input signal S1 and the output signal S2 of the envelope detection circuit 4 when the characteristics of the envelope detection circuit 4 are switched according to the inner and outer circumferences of the disk. In FIG. 10, the output waveform S2 is obtained by setting the time constant τ2 of the envelope detection circuit 4 according to the frequency f2 of the control signal. However, the frequency f1 of the control signal is higher than that in FIG. 10 (corresponding to the inner circumference).
Then, the time constant τ2 of the envelope detection circuit 4 set in FIG.
Is not sufficiently smaller than f1 and the envelope detection circuit cannot detect the envelope of the control signal S1.
The thick line in FIG. 11 shows the output waveform of the envelope detection circuit 4 when the characteristic of the envelope detection circuit 4 is switched according to the frequency of the control signal changed from f2 to f1. By resetting the time constant τ2 to τ1 which is smaller than the frequency of the control signal, the detection efficiency of the envelope detection circuit 4 is increased and the output waveform level is improved.

The characteristic switching of the envelope detection circuit 4 according to the frequency changes of the information pit signal and the control signal has been described above. In the envelope detection circuit 4, the time constant τ determined by the resistor and the capacitor is set to the frequency of the control signal. When set close to, there arises a problem that frequency components from the information pits remain in the output waveform after envelope detection. Therefore, an embodiment in which a low-pass filter is provided after the envelope detection circuit 4 in order to remove high frequency components close to the frequency of the information pit signal will be described below.

FIG. 12 is a diagram showing the structure of the control signal generating circuit. In FIG. 12, the same functional parts as those in FIGS. 1 and 8 are designated by the same reference numerals, and the description thereof will be omitted unless particularly necessary. Output signals S2 of the envelope detection circuits 4-a and 4-b
-A and S2-b are low-pass filters -9-a and 9-b.
Are input respectively. Low pass filter-9-a, 9
-B removes the high frequency components of the input signals S2-a and S2-b and outputs them as signals S4-a and S4-b. The signals S4-a and S4-b are input to the subtraction circuit 5 and the addition circuit 6, respectively, and the difference signal and the sum signal which are the control signals used for the tracking servo are output.

FIG. 13 shows a configuration example of the low pass filter-9. The low pass filter-9 is composed of an operational amplifier 90, a capacitor C9, and resistors R9 and R10. The frequency of the information pit signal is about several MHz, and the frequency of the control signal is 310 kHz at the seek time under the conditions of disk rotation speed: 3000 rpm, track pitch: 1.6 μm, and seek speed of 0.5 m / s. Therefore, for example, by setting R9 = 2.2 kΩ and C9 = 150 pF in the low-pass filter-9, the cutoff frequency becomes 480 kHz,
A frequency component close to the frequency of the information pit can be removed.

FIG. 14 shows changes in the waveforms of the input signal S2 and the output signal S4 of the low pass filter-9. In the envelope detection circuit 4, when the time constant determined by the resistance and the capacitor is set small with respect to the frequency of the control signal, the output signal S2 has a sawtooth-shaped high frequency component (ripple) associated with the frequency of the information pit signal. Is included. When this high frequency component is large, not only the pull-in operation and tracking accuracy of the system are deteriorated, but also an erroneous count of the number of tracks occurs at the time of seeking. S4 is a signal from which the above high frequency component has been removed by the low pass filter-9. By removing the high frequency component close to the frequency of the information pit signal in this way, the signal S4 including only the frequency component necessary for generating the control signal is obtained.

Although the case where the characteristic of the envelope detection circuit 4 is constant has been described here, the case where the characteristic of the compensation circuit 3 or the characteristic of the envelope detection circuit 4 is changed is not limited to this. By using -9, it is possible to obtain a signal from which high frequency components close to the information pit signal have been removed.

As described above, in the embodiments of FIGS. 1, 8 and 12, the output of the compensating circuit 3 is subjected to envelope detection, and then the subtracting circuit 5 and the adding circuit 6 obtain the difference signal and the sum signal. For example, as shown in FIG. 15, the current-voltage conversion circuit 2
It is also possible to perform the addition and subtraction processing on the output of 1 by the subtraction circuit 5 and the addition circuit 6 and then output it as a control signal via the compensation circuit 3 and the envelope detection circuit 4. The control signal may be output in the same manner when the low pass filter 9 is provided. Further, in FIG. 8, the address reproduction circuit 8 detects the reproduction position of the disc to switch the characteristic of the envelope detection circuit 4. However, the present invention is not limited to this, and the reproduction position of the disc is detected by an external sensor or the like and the envelope is detected. The characteristics of the line detection circuit 4 may be switched. Furthermore, in the present embodiment, the characteristic of the envelope detection circuit 4 is switched to two stages, but the present invention is not limited to this, and the characteristic may be changed in multiple stages or continuously.

Further, in the present embodiment, the configuration in which only the characteristic of the envelope detection circuit 4 is switched has been described, but the configuration is not limited to this, and the configuration in which only the characteristic of the compensation circuit 3 is switched or, for example, as shown in FIG. A configuration may be used in which the characteristics of both the circuit 3 and the envelope detection circuit 4 are switched. Further, in this embodiment, the compensating circuit 3 is provided before the envelope detection circuit 4, but the output of the photoelectric conversion means may be directly input to the envelope detection circuit 4 without providing it. Further, in the control signal generation circuit shown in the present embodiment, the case where the photoelectric conversion means is two has been described, but the present invention is not limited to this, and the photoelectric conversion means may be plural.

[0032]

INDUSTRIAL APPLICABILITY As described above, the present invention has, as a basic structure, an optical disk device, particularly an optical disk recording / reproducing apparatus having a tracking guide groove and information pits mixed therein, which is provided with a control circuit for reproducing. The control circuit is configured to change the characteristics of the detection means.
Therefore, even when the conditions for generating the control signal are different, the gain of the control system can be made substantially constant by changing the detection characteristic. Further, by providing a low-pass filter for extracting the low-pass component of the input signal after the envelope detection means of the control circuit, the saw blade with the frequency of the information pit signal included in the output waveform after the envelope detection. It is possible to remove a high frequency component (ripple) and obtain a stable control waveform.

Next, in the reproduction optical circuit of the optical disk, paying attention to the characteristic that the gain decreases as the frequency of the input signal increases, and a means for compensating for this characteristic is provided before the envelope detection means. By this, a constant gain can be obtained. Further, even when seeking, a stable control signal is obtained by detecting the seek state and switching between envelope detection means and compensation means. Further, a means for detecting the position of the optical head with respect to the recording / reproducing medium is provided, and by changing the characteristics of the envelope detection means and the characteristics of the compensation means, the control signal of the control signal caused by the difference in the peripheral speeds of the inner and outer circumferences of the optical disc is changed. The instability factor is removed and a certain gain is obtained.

Therefore, even if the conditions for generating the control signal are different, such as the change of the track traversing speed of the optical beam and the change of the disc reproducing position, the signal is almost constant and of a sufficient level to obtain the control signal. Can be obtained. This makes it possible to obtain a control signal at a substantially constant level and to bring the gain of the control system close to a constant level.
It is possible to stabilize the pull-in operation and tracking accuracy of the system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a control signal generation circuit of the present invention.

FIG. 2 is a diagram showing a configuration example of a compensation circuit 3 and an envelope detection circuit 4.

FIG. 3 is a diagram showing a relationship between a reproduction signal frequency and a reproduction signal level.

FIG. 4 is a diagram showing input / output waveforms of an envelope detection circuit.

FIG. 5 is a diagram showing input / output waveforms of an envelope detection circuit when reproducing a disc.

FIG. 6 is a diagram showing input / output waveforms of an envelope detection circuit during seek.

FIG. 7 is a diagram showing the relationship between the control signal frequency and the detection efficiency when the capacitor capacity of the envelope detection circuit is switched.

FIG. 8 is a block diagram showing another embodiment of the control signal generation circuit.

FIG. 9 is a diagram showing a configuration example of a compensation circuit 3 and an envelope detection circuit 4.

FIG. 10 is a diagram showing input / output waveforms of the envelope detection circuit when reproducing the outer circumference of the disc.

FIG. 11 is a diagram showing input / output waveforms of an envelope detection circuit at the time of reproducing the inner circumference of the disc.

FIG. 12 is a diagram showing another embodiment of the control signal generation circuit.

FIG. 13 is a diagram showing a configuration example of a low pass filter-9.

FIG. 14 is a diagram showing input / output waveforms of a low-pass filter.

FIG. 15 is a diagram showing another embodiment of the control signal generation circuit.

FIG. 16 is a diagram showing another embodiment of the control signal generation circuit.

FIG. 17 is a diagram schematically showing an optical disc having both guide grooves and information pits.

18 is a diagram showing an output waveform of a photoelectric conversion element obtained when an optical beam crosses a guide groove and an information pit formed on the disc of FIG.

FIG. 19 is a diagram showing a configuration example of an envelope detection circuit 4.

FIG. 20 is a diagram showing a moving direction of an optical beam on an optical disc during disc reproduction and seek.

FIG. 21 is a diagram showing a schematic configuration of guide grooves and information pits.

FIG. 22 is a diagram showing input / output waveforms of an envelope detection circuit when reproducing a disc.

FIG. 23 is a diagram showing input / output waveforms of the envelope detection circuit during seek.

[Explanation of symbols]

 1-a, 1-b Photoelectric conversion element 2-a, 2-b Current-voltage conversion circuit 3-a, 3-b Compensation circuit 4-a, 4-b Envelope detection circuit 5 Subtraction circuit 6 Addition circuit 7 Addition Circuit 8 Address reproduction circuit or seek control circuit 9-a, 9-b Low-pass filter-

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Inoue, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Video Media Research Laboratory, Hitachi, Ltd. (72) Inventor Motoyuki Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Bunch Co., Ltd. Hitachi Media Imaging Media Laboratory

Claims (5)

[Claims] 1. A light beam irradiating an information recording / reproducing medium with a control signal generating circuit for generating a control signal for controlling the irradiation state of the light beam onto the information recording / reproducing medium. Photoelectric conversion means for converting the reflected light from the information recording / reproducing medium into an electric signal, and an envelope detection means having the characteristic of detecting the envelope of the output of the photoelectric conversion means,
An information recording / reproducing apparatus comprising a signal calculating means for calculating the output of the envelope detecting means, characterized by including means for changing the characteristic of the envelope detecting means. 2. A light beam irradiating the information recording / reproducing medium with a control signal generating circuit for generating a control signal for controlling the irradiation state of the light beam onto the information recording / reproducing medium. Photoelectric conversion means for converting the reflected light from the information recording / reproducing medium into an electric signal, and an envelope detection means having the characteristic of detecting the envelope of the output of the photoelectric conversion means,
An information recording / reproducing apparatus comprising a signal calculation means for calculating the output of the envelope detection means, comprising a low-pass filter having a characteristic of extracting a low-frequency component of an input signal after the envelope detection means. An information recording / reproducing apparatus characterized in that 3. A compensating means having a characteristic that the amplitude of the output signal increases as the frequency of the input signal increases, in front of the envelope detecting means.
Alternatively, the information recording / reproducing apparatus described in 2. 4. A speed detecting means for detecting the speed of the optical beam across the track is provided, and at least one of the characteristic of the envelope detecting means and the characteristic of the compensating means is based on the output of the speed detecting means. 4. The information recording / reproducing apparatus according to claim 1, further comprising means for changing characteristics. 5. A position detecting means for detecting the position of the light beam applied to the information recording / reproducing medium is provided, and the characteristic of the envelope detecting means and the characteristic of the compensating means are selected based on the output of the position detecting means. 4. The information recording / reproducing apparatus according to claim 1, further comprising means for changing at least one characteristic.