JPS62204433A - Optical disk reproducing device - Google Patents

Abstract

PURPOSE:To make DC compensation of reproduced signals of inferior low frequency characteristic and excellently reproduce an address and data by providing a means that adds DC potential to reproduced signals at specified position of the reproduced signals. CONSTITUTION:Feeble reproduced signals from a light receiving element are amplified by a pre-amplifier 20. However, as the pre-amplifier circuit 20 is constituted by AC coupling, signal waveform after amplification becomes as waveform 31, and reproduced signals of inferior low frequency characteristic are obtained. When the reproduced signals are inputted to a DC compensating circuit 21, waveform in which DC component is restored as waveform 32 is outputted. That is, a gate signal 30 is inputted from a gate signal generating circuit 22 to the DC compensating circuit 21 at a clamp position, and signals are added to a circuit of next stage at the clamp position making clamp voltage reference voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for reproducing information recorded on an optical disc.

BACKGROUND OF THE INVENTION FIG. 6 is a functional block diagram of an optical disc recording and reproducing device using a conventional optical disc reproducing method. Further, in order to explain the operation of the conventional example, FIG. 6 shows an example of a track format of an optical disc, and FIG. 7 shows an output waveform of a reproduction signal. In FIG. 5, reference numeral 1 denotes an optical disk on which tracks for recording information are formed and a recording film is deposited on the surface.

Reference numeral 2 denotes a turntable fixed to the rotating shaft of a motor that rotates the optical disc 1. 3 is an optical head composed of a collimator lens, a beam splitter, a condensing lens, etc. 4 is a semiconductor laser attached to the optical head 3. 5 is a light receiving element also attached to the optical head 3.

6 is a laser drive circuit that controls the strength of the power of the semiconductor laser 4 according to write data. 7 modulates the write data (eg, known MFM).

3PM, etc.). 8 is the light receiving element 6 and 7
This is a preamplifier circuit that amplifies the weak signal that has been converted into an air signal. 9 is a waveform equalization circuit that compensates for a drop in amplitude at high frequencies. 1o is a demodulation circuit that demodulates reproduced data, and the operation of an optical disc recording and reproducing apparatus configured as above 1° will be explained.

The optical disc 1 is mounted on a turntable 2 and rotated at a constant rotation. On the surface of the optical disc 1, for example, the sixth
The address signal 11 shown in the figure is distributed on the track in the thickness direction of the substrate at a constant number of about 100 (depending on the wavelength of the semiconductor laser), and at a period longer than the pit length of the data to be recorded later. recorded in advance. A light beam (indicated by a broken line) from a semiconductor laser 4 fixed to the optical head 3 is focused onto the optical disk 1 by optical components such as a collimator lens and a condensing lens within the optical head 3. Similarly, the reflected light from the optical disc 1 is irradiated onto the light receiving element 5 by the optical head 3. Generally, the optical disc 1 rotates with the eccentricity of the wobbling track, so in order to record or reproduce information on a predetermined track, it is necessary to perform focus control to make the light beam follow the wobbling of the optical disc 1. requires tracking control to follow the With such focus control and tracking control being performed, the data to be written is processed by the modulation circuit 7 using, for example, the MFM method (Modified Frequency), which is a known modulation method.
Modulation). Further, in accordance with the output signal of the modulation circuit 7, the semiconductor laser 4 emits light by the laser 1 drive circuit 6, and the light beam is a high-power 0
The light becomes an N10FF signal and is focused on the optical disc 1, where data is recorded. For example, if a Te-based metal oxide film is deposited on the optical disc 1, a signal corresponding to the cycle of the data to be written after modulation is recorded as marks of different shadings with different reflectances. Next, the reproduced signal is generated by focusing a constant low-power laser beam on the recorded information track as described above, detecting the reflected light from the optical disc 1 with the light receiving element 6, converting it into an electric signal, and preamplifying it. The signal is amplified to a predetermined amplitude by the circuit 8. FIG. 7(-) shows an example of the reflectance distribution on the track during reproduction.

Based on the reflectance of the recording film in the evaporated state (also called as-deposited state), the reflectance of address 12 and data 13 is as shown in (-), and if ideal reproduction is possible, (a) ) is obtained from the output of the preamplifier circuit 8. Furthermore, the reproduced signal is compensated for high frequency characteristics by the waveform equalization circuit 9, and the demodulation circuit 1
The data is demodulated by o.

Problems to be Solved by the Invention However, with the above configuration, if the frequency characteristics of the preamplifier circuit are not ideal and low frequency components near DC are attenuated, the waveform of the reproduced signal will be deformed. , address 12.degree. data 13 in FIG. 7(a) is shown in FIG. It becomes an envelope like data 15. Disk substrates generally have defects such as "unevenness" in the recording film and pinholes, which are noticeable as low-frequency noise. Therefore, an AC-coupled preamplifier configuration is used to cut low frequency components for the purpose of noise reduction, and the reproduced signal becomes a distorted waveform with an envelope as shown in Figure 7(b), which is used to reproduce addresses and data. It had problems that degraded quality.

In view of the above, it is an object of the present invention to provide an optical disk reproducing apparatus that can recover waveform distortions caused by deterioration of low frequency characteristics of reproduced signals and reproduce good signals such as addresses and data.

Means for Solving the Problems The present invention is an optical disk reproducing apparatus that includes means for adding a DC potential to a reproduced signal at a predetermined position of the reproduced signal.

Operation The present invention performs DC compensation for a reproduced signal with poor low frequency characteristics by the above-described means, and enables good reproduction of addresses and data. Further, fluctuations in the DC component on individual disks or on the same disk surface are also reduced.

Embodiment FIG. 1 shows an embodiment of a reproducing circuit of an optical disk reproducing apparatus according to the present invention. Further, FIG. 2 shows an embodiment of the DC compensation circuit of the present invention, which will not be described in detail, and FIG. 3 shows the reproduced signal waveform. In FIG. 1, 2° is a preamplifier circuit that amplifies a weak reproduced signal converted into an electric signal by a light receiving element. 21 is a DC compensation circuit for compensating low frequency characteristics, 022 is a gate signal generation circuit for generating a gate signal, and 23 is an analog switch circuit for separating signals. 24 is a waveform equalization circuit that compensates for high frequency signal deterioration.

The operation of the reproducing circuit of the optical disc reproducing apparatus configured as above will be explained.

A weak reproduced signal from the light receiving element is amplified by the preamplifier circuit 2o. However, since the preamplifier circuit 20 is configured by AC coupling, the signal waveform after amplification produces a reproduced signal with poor low frequency characteristics as shown in the waveform 31 in FIG. Next, when this reproduced signal is input to the DC compensation circuit 21, a waveform in which the DC component has been recovered like the waveform 32 in FIG. 3 is output. That is, the gate signal 3o in FIG. 3 is input from the gate signal generation circuit 22 to the DC compensation circuit 21 at the clamp position, and the signal is applied to the next stage circuit at the clamp position using the clamp voltage as a reference voltage. FIG. 2 shows the configuration of a DC compensation circuit for performing the above operation.

In FIG. 2, 25 is an amplifier with a small output impedance. 26 is a coupling capacitance.

27 is an amplifier with a large input impedance R1.

28 is a switch that is opened/closed by a gate pulse.

29 is a reference voltage source. The output signal from the preamplifier is input to the amplifier 25, amplified, and output. When the ON signal of the gate pulse 3o is input, the switch 28 is closed, and the potential at the 0 point is fixed to the terminal voltage EC of the reference voltage source 29. Next, when the OFF signal is input, the switch 28 opens, but since the terminal voltage of the coupling capacitor 2b has been charged to the same value as EC while the signal is being passed, the next stage amplifier circuit 27 uses EC as a reference. The DC component is recovered. However, since the switch 28 is actually often composed of elements such as transistors and has a saturation resistance rg, it is necessary to make the potential at the 0 point approximately EC during the period when the gate pulse is ON. Time constant C(Ro
+ r s ) must be small compared to the ON time. In addition, during the period when the switch 28 is open, that is, during the signal passing period, the charge on the coupling capacitor C must be accurately stored until the next ON signal is input. constant C
Ri must be longer than the signal transit period. In reality, there is a transistor emitter follower circuit as an amplifier that satisfies the above input/output impedance conditions, and the above conditions can be satisfied. address and data are separated. Furthermore, the data is input to a waveform equalization circuit 24, compensates for deterioration of high frequency components, and is output.

In the above configuration, the position of the gate pulse input to the DC compensation circuit 21 is set between the address area and the data recording area, that is, the non-recording area. Since the reflectance value changes depending on the optical disk substrate, the voltage level after electrical signal conversion also changes. However, since the reproduced signal is clamped to the reference voltage at this position, the fluctuation is substantially suppressed. The gate pulse is generated by the gate signal generation circuit 22, and its position is determined by, for example, recording a pulse-shaped signal synchronized with the address in advance on the innermost circumference of the optical disc, and using the reproduced signal. There is also a method using an address signal, and it is easy to generate a gate pulse. It is also equally effective to synchronize the position of the gate pulse with a clamp area provided in advance within the address area or at a specific location. FIG. 4 shows an output example of a reproduced signal and a gate pulse when a clamp area is provided in the non-recording section.

As described in detail, according to the present invention, since the DC component of the reproduced signal is recovered, it is possible to reduce the deterioration of the reproduced signal near the beginning of addresses and data where the DC component changes significantly. Further, by setting the clamp position in the non-recorded area, fluctuations in the DC component due to variations in the optical disc can be reduced, which has a great practical effect.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram of a reproducing circuit of an optical disc reproducing apparatus according to the present invention, FIG. 2 is a circuit diagram showing an example of the configuration of a DC compensation circuit, and FIG. 3 is a reproduction waveform diagram that does not provide a detailed explanation of the present invention. Fig. 4 is an explanatory diagram showing an example of providing a clamp area, Fig. 5 is a functional block diagram of a conventional optical disc recording/reproducing device, Fig. 6 is an explanatory diagram showing an example of a track format, and Fig. 7 is an explanatory diagram showing a reproduction signal. It is a waveform. 20... Preamplifier circuit, 21... DC compensation circuit, 22... Gate signal generation circuit, 2
3...Analog switch circuit, 24...
・Waveform equalization circuit, 25...Amplifier, 26...
...Coupling capacitance, 27...Amplifier, 28...
...Switch, 29...Reference voltage source. Name of agent: Patent attorney Toshio Nakao and 1 other person
1111 Figure 2 2221 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) An optical disc reproducing apparatus characterized by comprising means for applying a DC voltage to a predetermined position of a reproduction signal from an optical disc to perform DC compensation. (2) The optical disc reproducing apparatus according to claim 1, wherein the predetermined position is a non-recording section. (3) The optical disc reproducing apparatus according to claim 1, wherein the predetermined position is a section recorded in advance at a specific location.