JP2008305515A - Optical disk player - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk player which has a simple circuitry and can increase the SN ratio of a transmission system by reducing disk noises, and can increase a recording capacity per one disk layer. <P>SOLUTION: The optical disk player is constructed in such a manner that a data track formed into a spiral shape with a track pitch Tp is irradiated with a laser beam, and recorded data is reproduced by the intensity of its reflected beam, and the optical disk player is provided with a high-pass filter for eliminating disk noises in a reproduced signal, and a DC reproduction circuit for detecting a low-pass component lost through the high-pass filter. With the use of a signal obtained by adding the output signal of the high-pass filter and the output signal of the DC reproduction circuit together, reproduced signal processing thereafter is carried out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical disk playback apparatus, and more particularly to an optical disk playback apparatus that improves disk-to-signal-to-noise ratio (SNR) by reducing disk noise that occurs when playing back an optical disk and improving the error rate of a playback signal. .

  As background art in this technical field, for example, there is a technique described in Patent Document 1. Patent Document 1 discloses a feedforward type quantized DC regeneration circuit (DFF), which includes a high-pass filter, a delay element, a first identification circuit, a low-pass filter, a volume, an addition circuit, It is disclosed that it comprises two identification circuits.

JP-A-6-309793 (FIG. 3 on page 3)

  In the optical disc market represented by DVD, the density has been increased to adapt to the increase in capacity of recorded information. Recently, Blu-ray and HD-DVD using a blue laser as a light source have been commercialized. . Of these, the Blu-ray disc standard uses a blue laser (wavelength of 405 nm) and an objective lens numerical aperture of 0.85 compared to the DVD with a laser wavelength of 660 nm and an objective lens numerical aperture of 0.60. A single-sided 25 GB recording capacity is realized. Also, recording of a multi-layer medium is possible by increasing the output of the blue laser. For example, 50 GB of information data can be recorded / reproduced on one side of a double-layer disc. It is predicted that the development for increasing the recording capacity will continue to be promoted mainly in the development of multilayer technology.

  By adopting a blue laser, the wavelength can be shortened and the recording density is improved. However, since the wavelength cannot be shortened any longer, the current signal transmission system will be improved to increase the linear recording density, or recording as described above. It is necessary to increase the capacity by increasing the number of layers of the film. Focusing on the signal transmission system among these, the Blu-ray disc has a problem that the noise in the low frequency band inherent to the disc is large and the SN ratio is greatly reduced.

  In the optical disk apparatus, it is necessary to transmit the low frequency up to about 1/2000 of the transmission signal bit frequency. If a high pass filter is inserted to reduce the low frequency disk noise, the low frequency component of the transmission signal itself is missing. As a result, the error rate of the transmission system is worsened.

  In such a high-density magnetic recording / reproducing apparatus using a rotating head with respect to such a disk reproducing apparatus, there is a signal deterioration due to the low-frequency cutoff characteristic of the rotary transformer, and therefore a data modulation method with a small DC component is used. Further, when a modulation method having a DC component is used, differential detection that does not require a DC component or a class 4 partial response is applied to the detection method, and in some cases, a rotary as described in Patent Document 1 is used. A DC regeneration circuit for compensating for the low-frequency cutoff characteristic of the transformer is applied.

  An object of the present invention is to provide an optical disk reproducing apparatus capable of improving the S / N ratio of a signal transmission system with a simple circuit configuration and increasing the recording capacity per one recording film.

  The above object can be achieved, for example, by the invention described in the claims.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  An optical disk reproducing apparatus according to the present invention is an optical disk reproducing apparatus in which a data track formed in a spiral shape on a disk is irradiated with a laser beam and data recorded by the intensity of reflected light is reproduced. A servo circuit that moves the beam in the radial direction with the beam on track, an amplifier that converts the reflected light intensity of the laser beam into a voltage, and a waveform equalization circuit that corrects intersymbol interference of the output signal of the amplifier; A high-pass filter for removing disc noise from the output signal of the waveform equalizer, a delay circuit for delaying the output signal of the high-pass filter, and an analog output signal of the waveform equalizer 2 A discriminating circuit for converting into a value, a low-pass filter for detecting a low-frequency component of an output signal of the discriminating circuit, and a low-pass filter And attenuator for varying the force signal level, and an adding circuit for adding the output signal of the output signal and the delay circuit of the attenuator circuit, performs reproduction signal processing after the output signal of the adder circuit.

  In the optical disk reproducing device according to the present invention, a second addition circuit for adding the analog output signal of the waveform equalization circuit and the output signal of the attenuator circuit is provided, and the output signal of the second addition circuit is identified. Input to the circuit is preferred.

  According to the present invention, it is possible to reduce the disk noise with a simple circuit configuration, improve the SN ratio of the transmission system, and increase the recording capacity per disk layer.

  Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following embodiments, and many parts and elements can be rearranged, changed, and replaced without departing from the spirit of the present invention.

  FIG. 1 is a block diagram of an optical disk reproducing apparatus according to the present invention. 1 is a disk, 2 is a motor, 3 is a servo circuit, 4 is a pickup, 5 is an RF amplifier, 6 is an equalizer circuit, 7 is a high-pass filter, 8 Is a low-pass filter, 10 is an attenuator circuit, 11 is an adder circuit, 12 is a delay circuit, 13 is a PLL circuit, 14 is a reproduction system signal processing circuit, 15 is a signal processing circuit, 16 is a laser beam, Reference numeral 17 denotes an optical disk playback device, and 18 denotes a drive control device.

  First, the basic operation of the optical disc playback apparatus 17 will be described. For example, when a BD-R disc 1, which is a Blu-Ray type one-time writing disc, is inserted, the disc 1 is rotated by the motor 2 and the servo circuit 3, and the laser beam 16 irradiated from the pickup 4, the RF amplifier 5, the equalizer Information such as control signals recorded on the disk 1 is read by the circuit 6, the PLL circuit 13 in the signal processing circuit 15 and the reproduction system signal processing circuit 14 to discriminate the disk medium. When the disc 1 inserted here is determined to be BD-R, the optical disc playback device 17 enters a state of waiting for operation, and thereafter is controlled to a data playback state based on a command of a drive control device 18 constituted by a host computer, for example. The

  During reproduction, the servo circuit 3 rotates the disk 1 at a predetermined speed, performs focus and tracking control of the laser beam 16 to scan one recording track formed in a spiral shape from the inner periphery to the outer periphery, A reflected signal from the laser beam 16 is detected and a reproduction signal is obtained from the RF amplifier 5.

  The output signal of the RF amplifier 5 is first sent to the equalizer circuit 6 for waveform equalization and then sent to the signal processing circuit 15. In the signal processing circuit 15, data reproduction is performed by a PLL circuit 13 that detects a transmission clock from the reproduced signal, a partial response reproduction circuit (not shown) that adapts the transmission system to a partial response, and the reproduced recording data. The column is temporarily stored in the buffer memory. In the reproduction system signal processing circuit 14, data stored in the buffer memory is sequentially read, and information recorded on the disk 1 by circuit operations (not shown) such as a synchronization signal detection circuit, a demodulation circuit, and an error detection / correction circuit. Play the data.

  FIG. 2 shows a noise frequency characteristic at an RF amplifier output of a general Blu-ray disc. FIG. 2 shows an example in which a 2T-2T repetitive signal having the highest frequency of the Blu-ray format is reproduced in the double speed mode and the noise spectrum at the output terminal of the RF amplifier 5 is measured. Is plotted as 0 dB. A portion that is greatly raised at a frequency of 20 MHz or less is due to the disk noise, and a frequency of 40 MHz or more is due to the frequency characteristics of the amplifier noise. These characteristics vary depending on the disc 1, pickup 4, and RF amplifier 5 used.

  The SN ratio of the transmission system can be expressed by the ratio between the equalized carrier signal level and the integrated value of the noise in the transmission band.

  FIG. 3 shows the noise spectrum measured at the output terminal of the equalizer circuit 6 by the same measurement method as in FIG. Since the equalizer circuit 6 has a high-frequency lifting characteristic, the influence of low-frequency noise is reduced as shown in FIG. 3, but noise of 10 MHz or less does not decrease and deteriorates the noise integrated value. If this low-frequency noise is reduced, the transmission signal-to-noise ratio increases, improving the error rate and improving the operational reliability of the apparatus. Further, higher density recording can be achieved by improving the SN ratio.

  In this embodiment, a high-pass filter 7 is connected to the output of the equalizer circuit 6 to reduce disk noise, and a low-frequency component of a transmission signal lost by passing through the high-pass filter 7 Restoration is performed by a DC regeneration circuit including an identification circuit 8, a low-pass filter 9, an attenuator circuit 10, an adder circuit 11, and a delay circuit 12 connected to the subsequent stage of the filter 7.

  The output signal of the equalizer circuit 6 is first input to the high-pass filter 7 to cut low-frequency disk noise. Next, the output signal is input to the discrimination circuit 8 and converted into a binary digital signal, and then the low-frequency component of the digital signal sequence input by the low-pass filter 9 is detected. Finally, the output signal amplitude of the low-pass filter 9 is adjusted to an appropriate value by the attenuator circuit 10 and added to the output signal of the high-pass filter 7 that has passed through the delay circuit 12. By this operation, the low-frequency component of the transmission signal lost by passing through the high-pass filter 7 is restored without deteriorating the SN ratio. Further, since the disk noise is reduced by passing through the high-pass filter 7, the SN ratio of the transmission signal can be improved comprehensively.

  FIG. 4 shows a circuit configuration of the identification circuit according to the present invention. In FIG. 4, 19 is a binarization circuit, and 20 is a D flip-flop circuit. The output signal of the equalizer circuit 6 is first converted into a digital signal of 1 and 0 by the binarization circuit 19, and the D flip-flop circuit 20 is operated at the timing of the output clock signal of the PLL circuit 13 to convert it into a digital signal sequence. Yes.

  FIG. 5 shows an example of each part signal waveform. Since the reproduced signal (a) subjected to the waveform equalization process passes through the high-pass filter 7, the low-frequency disk noise and the low-frequency component of the transmission signal are lost. Therefore, as shown in FIG. Becomes a thing that fluctuated in a direct current. Next, this signal is converted into a digital signal sequence by the discrimination circuit 8 and passed through the low-pass filter 9 to extract a DC component in the digital signal sequence (c). Finally, by adding the signals (b) and (c) by the adder circuit 11, the original reproduction signal from which the disk low-frequency noise has been removed can be obtained. This signal is binarized again or processed by a partial response method or the like. The delay circuit 12 is provided to compensate for the signal transmission delay time due to the low-pass filter 8.

  The attenuation ratio of the attenuator circuit 10 (addition ratio of the adder circuit 11) is controlled by the signal processing circuit 15, and specifically refers to information signals such as the detection rate of the synchronization signal and the error rate of the reproduction signal. In general, the output signal of the equalizer circuit 6 is at a constant level due to the operation of an AGC (Auto gain control) circuit. Therefore, once the attenuation ratio of the attenuator circuit 10 is determined at the time of disk loading or the like, the rest There is no need to change.

  Since the circuit shown in FIG. 1 has a feed-forward configuration, even if an inappropriate addition ratio is selected, there is an effect that a stable operation can always be obtained with simple control without oscillation. In particular, the playback signal level decreases when performing, for example, track jumping during special playback, etc., so it is possible to perform control to adjust the addition amount. Does not oscillate.

  The higher the cut-off frequency of the high-pass filter 7 and the low-pass filter 9 is, the more the disk noise can be reduced. However, in consideration of the operable range of the DC reproduction circuit, it is set to 1/30 or less of the signal transmission bit frequency. It is desirable. Basically, both cutoff frequencies are set to the same set value.

  FIG. 6 shows a second embodiment according to the present invention. The same parts shown in FIG. 1 are denoted by the same numbers, 21 is a second attenuator circuit, and 22 is a second adder circuit.

  In FIG. 6, after the amplitude of the low frequency component of the digital signal sequence extracted with respect to the embodiment of FIG. 1 is reduced by the second attenuator, it is added to the output signal of the waveform equalization circuit 7 by the second addition circuit. did. As described above, the low-frequency component detected also on the low-frequency component detection circuit side is feedback-added, thereby improving the operation stability of the PLL circuit 13 and improving the reproduction quality of the digital data string that is a DC detection signal. Therefore, the low-frequency signal detection accuracy can be increased. In this case, it is only necessary to detect the direct current component of the reproduction signal data string, and therefore it is not necessary to strictly control the output signal amplitude of the second attenuator circuit 21.

  In the embodiment of FIG. 6, the second attenuator circuit 21 is connected to the low-pass filter 9, but the output signal amplitude of the second attenuator circuit 21 is necessarily smaller than the output signal amplitude of the attenuator circuit 10. You may connect to.

  Although the circuit shown in FIG. 6 has a feedback configuration, stable operation can be obtained without oscillation by limiting the output signal amplitude of the second attenuator circuit 21. However, in the present embodiment, unlike the above-described example, when a track jump or the like is performed at the time of special reproduction or the like, if the output signal amplitude of the second attenuator circuit 21 is not controlled, the reproduction signal level is lowered. On the other hand, the amount of addition increases relatively, and the system may oscillate when the reproduction signal amplitude significantly decreases. Therefore, it is necessary to control the addition ratio by detecting the reproduction signal amplitude.

  The details of the present invention have been described above by taking the Blu-ray disc playback device as an example, but the recording medium is not limited to this, and the present invention can also be applied to disc playback devices such as HD-DVD devices, DVD devices, and CD devices.

1 is a block diagram of an optical disc playback apparatus according to a first embodiment of the present invention; The figure which shows the noise frequency characteristic at the time of pickup reproduction, The figure which shows the noise frequency characteristic after waveform equalization, The figure which shows one structure of the identification circuit in this invention, The figure which shows the disk reproduction waveform by this invention, It is a figure which shows 2nd Embodiment by this invention.

Explanation of symbols

1. Disk, 2. Motor, 3. Servo circuit, 4. Pickup,
5. RF amplifier, 6. Equalizer circuit, 7. High pass filter,
8... Identification circuit 9. Low pass filter 10 Attenuator circuit 11 Adder circuit 12 Delay circuit 13 PLL circuit 14 Regenerative signal processing circuit
15... Signal processing circuit, 16... Laser beam, 17.
18... Drive control device, 19... Binary circuit, 20.
21... Second attenuator circuit, 22.

Claims (2)

In an optical disk reproducing apparatus for reproducing data recorded by the intensity of reflected light by irradiating a data track formed in a spiral shape on a disk with a laser beam,
A servo circuit for moving the laser beam in the radial direction of the disk in an on-track state;
An amplifier for converting the reflected light intensity of the laser beam into a voltage;
A waveform equalization circuit for correcting intersymbol interference of the output signal of the amplifier;
A high-pass filter for removing disk noise from the output signal of the waveform equalization circuit;
A delay circuit for delaying the output signal of the high-pass filter;
An identification circuit for binarizing the analog output signal of the waveform equalization circuit;
A low-pass filter for detecting a low-frequency component of the output signal of the identification circuit;
An attenuator circuit for varying the output signal level of the low-pass filter;
An adder circuit for adding the output signal of the attenuator circuit and the output signal of the delay circuit;
An optical disk reproducing apparatus that performs subsequent reproduction signal processing on the output signal of the adder circuit.   2. The optical disk reproducing apparatus according to claim 1, further comprising: a second adder circuit that adds an analog output signal of the waveform equalizer circuit and an output signal of the attenuator circuit, and outputs the output signal of the second adder circuit. An optical disc reproducing apparatus, characterized by being input to an identification circuit.

Images