JP2008090977A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably read a signal of a recording area continuous with an unrecorded area and to suppress the resolution of an AD converter from degrading. <P>SOLUTION: The optical disk drive 1 is provided with an optical pickup unit 10 which irradiates an optical disk 2 with a laser beam, detects the catoptric light from the optical disk 2, and outputs an RF signal introducing an AC component and a DC component from the catoptric light. Then, the RF signal including the AC component and the DC component output from the optical pickup unit 10 is output to an AGC section 20 which is DC coupled to the optical pickup unit 10. Also, a VGA 21 of the AGC section 20 controls the amplitude of the RF signal to prescribed magnitude by using the maximum value of the voltage of the RF signal output from a peak hold circuit 22 and outputs the value to a level shift circuit 30. In the level shift circuit 30, the voltage of the RF signal of 80% in modulation percentage output from the AGC section 20 is shifted so as to have the same voltage level as that of the D range of the AD converter 41 and is then output to the AD converter 41. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus that reproduces information recorded on a recording surface of an optical disc.

  Usually, the level of a signal obtained from the reflected light of an optical disc differs between a recording area where information is recorded and an unrecorded area where information is not recorded. Therefore, when reproducing information recorded on the optical disc, AGC (Auto Gain Control) processing is performed to control the amplitude of the RF signal extracted from the reflected light of the optical disc to be substantially constant. Hereinafter, an optical disc apparatus 101 according to a conventional example that performs AGC processing and controls the amplitude of an RF signal to be substantially constant will be described with reference to FIG. FIG. 4 is a block diagram of an optical disc apparatus according to a conventional example.

  In the conventional optical disc apparatus 101, reflected light from a recording area where information on the optical disc 102 is recorded is detected by an optical pickup unit 110, and an RF signal which is a reproduction signal is extracted. The extracted RF signal is input to a VGA (Variable Gain Amplifier) 121 of the AGC unit 120 and input to the RF signal amplitude detector 122. The optical pickup unit 110 and the AGC unit 120 are AC-coupled by a capacitor 131, and the AGC unit 120 and the signal processing unit 140 are AC-coupled by a capacitor 151. Therefore, the AGC unit 120 outputs only the AC component of the RF signal extracted from the reflected light of the optical disc 102 to the subsequent signal processing unit 140. At this time, as shown in FIG. 5, the RF signal voltage is ½ or less maximum with respect to the dynamic range (hereinafter referred to as D range) of the AD converter (Analog Digital Converter) by adjusting the gain of the VGA 121. Is set to the voltage of

  Specifically, first, the reference potential determined by the resistors 123a and 123b of the AGC unit 120 is set as a target value, and the amplitude of the RF signal detected by the RF signal amplitude detector 122 and a reference of a preset amplitude are set. Compare the value. When the amplitude of the input RF signal is smaller than the reference value, the voltage supplied to the VGA 121 is controlled to increase the gain. If the amplitude of the input RF signal is larger than the reference value, the voltage supplied to the VGA 121 is controlled to lower the gain. In this way, the RF signal output from the AGC unit 120 is set to a substantially constant amplitude and supplied to the AD converter 141 through the capacitor 151. The capacitor 151 constitutes a time constant circuit 150 together with the resistor 152. The capacitor 131 that AC-couples the optical pickup unit 110 and the AGC unit 120 constitutes a time constant circuit 130 together with the resistor 132.

  On the other hand, when reflected light from an unrecorded area where no information is recorded is detected by the optical pickup unit 110, an RF signal cannot be extracted. Therefore, the AGC unit 120 increases the gain of the VGA 121 in order to set the voltage of the capacitor 150 to the same signal level as the reference value, but as a result, it converges to the maximum gain.

  By the way, as shown in FIG. 4, the AGC unit 120 is provided with a time constant circuit 125 including a capacitor 125a and a resistor 125b so as to delay the response. For this reason, when the recording area is reproduced from the unrecorded area of the optical disc 102, due to this response delay, the VGA 121 has a maximum gain set when detecting reflected light from the unrecorded area, and from the recording area. The amplitude of the acquired RF signal is adjusted. As a result, the RF signal extracted from the recording area continuous to the unrecorded area is adjusted with the maximum gain, and the signal extracted from the recording area continuous to the unrecorded area is saturated and cannot be read. was there.

  Therefore, when detecting the reflected light from the unrecorded area, the VGA gain is fixed to prevent the increase of the VGA gain and the saturation of the RF signal extracted from the recording area continuous to the unrecorded area is prevented. An information reproducing apparatus has been proposed (see, for example, Patent Document 1). In the information reproducing apparatus disclosed in Patent Document 1, when reproducing an unrecorded area, the gain of the VGA is fixed to prevent saturation of the RF signal from the unrecorded area to the beginning of the recorded area. .

JP-A-5-62346

  However, in Patent Document 1, the fixed gain is not a uniform value but needs to be individually adjusted according to pickup variations and optical disk reflectivity. Further, when the AGC fixed gain is appropriately set in the information reproducing apparatus disclosed in Patent Document 1, the RF signal is read from the beginning of the recording area from the unrecorded area as shown in FIG. In addition, there is a disadvantage that only half of the D range of the AD converter can be used. As a result, there is a problem that the resolution of the AD converter is lowered.

  The present invention has been made to solve the above-described problems, eliminates the need for individual adjustment of the gain of the AGC unit, stably reads a signal in a recording area continuous to an unrecorded area, and provides an analog signal. The purpose is to suppress a decrease in the resolution of the digital converter.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, an optical disc apparatus according to the present invention is a pickup that irradiates an optical disc with light, detects reflected light from the optical disc, and outputs a reproduction signal including an AC component and a DC component from the reflected light. And a peak hold circuit that outputs the maximum value of the reproduced signal voltage, and a DC coupling with the pickup, and using the maximum value of the reproduced signal voltage output from the peak hold circuit, the amplitude of the reproduced signal is set to a predetermined magnitude. The AGC unit that is controlled and output, the analog-digital converter that converts the reproduction signal that is an analog signal into a digital signal, and the voltage of the reproduction signal that is output from the AGC unit with the maximum modulation rate is the dynamic range of the analog-digital converter. Shift the voltage level of the playback signal so that it becomes the same voltage level as And a level shift circuit that force.

  In the optical disc apparatus according to the present invention, as described above, the pickup and the AGC unit are DC-coupled so that the reproduction signal including the AC component and the DC component output from the pickup is not AC-coupled in the AGC unit. AGC processing can be performed. In other words, since the reproduction signal extracted from the unrecorded area of the optical disk contains a DC component, the voltage level output from the peak hold circuit becomes the TOP level, and the gain of the AGC unit is prevented from being maximized. Can do. Further, the response is not delayed by this DC coupling. As a result, the reproduction signal of the recording area continuous to the unrecorded area is not adjusted to an appropriate gain and is not saturated, so that the signal of the recording area continuous to the unrecorded area can be read stably. Further, if the output level of the reproduction signal is adjusted and confirmed at the design or production stage, it is not necessary to adjust the gain of the AGC unit every time the optical disk is replaced.

  Also, by using the maximum value of the voltage of the reproduction signal output from the peak hold circuit and controlling the amplitude of the reproduction signal to a predetermined level, an AGC unit is provided to output the reproduction signal output from the AGC unit. The amplitude of the signal can be kept within a predetermined range. Then, by using the level shift circuit to shift the voltage of the reproduction signal having the maximum modulation rate output from the AGC unit to the same voltage level as the dynamic range of the analog-digital converter, the dynamic range can be effectively used. Can do. As a result, it is possible to suppress a decrease in the resolution of the analog-digital converter.

  In the above optical disk apparatus, preferably, the level shift circuit uses the maximum value of the reproduction signal voltage output from the peak hold circuit as a reference voltage, and the voltage of the reproduction signal output from the AGC unit having the maximum modulation rate is analog. The voltage level of the reproduction signal is shifted so as to be the same voltage level as the dynamic range of the digital converter and output to the analog-digital converter. With this configuration, the voltage level of the reproduction signal output from the AGC unit can be accurately shifted using the maximum value of the voltage of the reproduction signal output from the peak hold circuit as a reference voltage. As a result, the dynamic range can be used more effectively, and the degradation of the resolution of the analog-digital converter can be further suppressed.

  In the optical disc apparatus, preferably, the level shift circuit includes an operational amplifier, and the reproduction signal output from the AGC unit is input to the inverting input terminal of the operational amplifier. This is because the frequency characteristic of the operational amplifier is better when configured in this way.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of an optical disc apparatus according to an embodiment of the present invention. FIG. 2 is a waveform diagram of a signal output from the AGC unit of the optical disc apparatus shown in FIG. FIG. 3 is a waveform diagram of signals output from the level shift circuit of the optical disc apparatus shown in FIG. The configuration of the optical disc apparatus 1 will be described in detail with reference to FIGS.

  An optical disc apparatus 1 according to this embodiment is a disc reproducing apparatus that reads an RF signal extracted from reflected light from an optical disc 2 by irradiating an optical disc 2 on which information is recorded with laser light. As shown in FIG. 1, the optical disc apparatus 1 includes an optical pickup unit 10, an AGC unit 20, a level shift circuit 30, and a signal processing unit 40.

  The optical pickup unit 10 is provided for irradiating the recording surface of the optical disc 2 with laser light, detecting reflected light from the optical disc 2 irradiated with the laser light, and generating an RF signal as a reproduction signal. Yes. The optical pickup unit 10 includes a laser diode 11 that emits laser light, a lens 12 that condenses the laser light emitted from the laser diode 11 on a recording surface of the optical disc 2, and reflected light from the optical disc 2 irradiated with the laser light. A photodiode 13 for receiving light, and an IV conversion circuit 14 including an operational amplifier 14a and a feedback resistor 14b are provided.

  The laser light emitted from the laser diode 11 and collected by the lens 12 is reflected by the recording surface of the optical disc 2 and received by the photodiode 13. The photodiode 13 converts the received optical signal into an electric (current) signal and outputs it to the IV conversion circuit 14. The IV conversion circuit 14 converts the input current signal into a voltage signal and outputs the voltage signal to the AGC unit 20 at the subsequent stage. When the reflected light from the recording area where the information on the optical disk 2 is recorded is detected, an RF signal is generated. When the information on the optical disk 2 detects the reflected light from the unrecorded area, the RF signal is generated. No signal is generated. The RF signal (voltage signal) includes an AC component and a DC component.

  The AGC unit 20 controls the amplitude of the RF signal output from the IV conversion circuit 14 of the optical pickup unit 10 to a predetermined magnitude, and converts the RF signal having a voltage waveform as shown in FIG. Output to. As shown in FIG. 1, the AGC unit 20 includes a VGA (variable gain amplifier) 21, a peak hold circuit 22, a target value setting circuit 23, a comparator 24, and a time constant circuit 25. . In the present embodiment, the AGC unit 20 is DC coupled to the IV conversion circuit 14 of the optical pickup unit 10 described above, and an RF signal (hereinafter, referred to as an AC signal and a DC component output from the IV conversion circuit 14). RF (DC) signal) is connected to VGA21 → peak hold circuit 22 → comparator 24 → VGA21 to form a negative feedback loop.

  The peak hold circuit 22 has a function of detecting and outputting the peak value (maximum value) of the voltage of the input RF signal, and is provided for acquiring a reference voltage used in the level shift circuit 30 described later. It has been. The peak value of the voltage of the RF signal output from the peak hold circuit 22 is input to the inverting input terminal 24a of the comparator (operational amplifier) 24, and at the same time, the non-inverting input terminal 35b of the operational amplifier 35 of the level shift circuit 30 described later. Is input. In the present embodiment, since the IV conversion circuit 14 and the AGC unit 20 are DC coupled, AC coupling as in the conventional capacitor 131 shown in FIG. 4 is not performed. As shown in FIG. 2, the peak value of the voltage at the TOP level can be detected in an unrecorded area in which information on the optical disc 2 is not recorded.

  Further, as shown in FIG. 2, the peak hold circuit 22 has a peak voltage of the TOP level even in the recording area where the information on the optical disc 2 is recorded, even when the average of the DC component differs depending on the modulation rate of the RF signal. The value can be detected. As a result, a control voltage applied to the VGA 21 can be obtained in the recording area by a target value setting circuit 23 and a comparator 24 described later.

  The target value setting circuit 23 is composed of resistors 23a and 23b, and the target value of the potential determined by the resistors 23a and 23b is determined by the level shift circuit 30 in the subsequent stage so that an RF signal whose modulation factor is maximum (80%) (see FIG. 2. The voltage level of the modulation rate: Max (80%)) is set to a value that makes the same voltage level as the D range of the AD converter 41. As shown in FIG. 2, the modulation rate is a ratio between the amplitude of an RF signal that does not include a DC component (hereinafter referred to as an RF (AC) signal) and the amplitude of the RF (DC) signal. Information is written on the optical disc 2 within a modulation rate (for example, 40% (Min) to 80% (Max)) determined by the standard.

  As shown in FIG. 1, the comparator 24 is composed of an operational amplifier, and compares the potential determined by the resistors 23 a and 23 b of the target value setting circuit 23 and the peak value of the voltage of the RF signal output from the peak hold circuit 22. In comparison, the control voltage applied to the control terminal (VGACONT) 21c of the VGA 21 is determined.

  The time constant circuit 25 includes a resistor 25a and a capacitor 25b.

  The VGA 21 is configured such that the gain changes according to the magnitude of the applied control voltage, and the magnitude of the amplitude (voltage level) of the output RF signal can be changed. The input terminal 21a of the VGA 21 is connected to the IV conversion circuit 14 of the optical pickup unit 10 at the preceding stage, and the output terminal 21b is connected to the level shift circuit 30 at the subsequent stage. A comparator 24 is connected to the control terminal (VGACONT) 21 c of the VGA 21, and a control voltage determined by the comparator 24 is applied.

  Here, in this embodiment, the level shift circuit 30 has a function of shifting the voltage of the RF signal output from the AGC unit 20 to a predetermined voltage level and outputting it to the AD converter 41 in the subsequent stage. Specifically, with the peak value of the voltage of the RF signal output from the peak hold circuit 22 as a reference voltage, the voltage of the RF signal with the maximum modulation rate (80%) output from the AGC unit 20 is the AD converter 41. The voltage level of the RF signal is shifted so as to be the same voltage level as that of the D range and output to the AD converter 41. Since the voltage level of the RF signal input to the level shift circuit 30 is controlled by the AGC unit 20 in the previous stage, the level shift circuit 30 can easily adjust the voltage of the RF signal having the maximum modulation rate (80%) to AD. The voltage level can be the same as the D range of the converter 41.

  The level shift circuit 30 includes four resistors 31 to 34 and one operational amplifier 35. In the present embodiment, the RF signal output from the AGC unit 20 is input to the inverting input terminal 35a of the operational amplifier 35, and the RF signal output from the peak hold circuit 22 is input to the non-inverting input terminal 35b. The peak value of the voltage is input. As described above, the frequency characteristic of the operational amplifier 35 is better when the RF signal is inverted and input than when the RF signal is not inverted.

  The signal processing unit 40 includes an AD converter 41 that converts an RF signal (analog signal) output from the level shift circuit 30 into a digital signal, and a signal processing circuit 42 that decodes and outputs the digital signal. The D range of the AD converter 41 is determined by the reference potentials VL and VH.

  In the present embodiment, as described above, the RF signal including the AC component and the DC component output from the IV conversion circuit 14 of the optical pickup unit 10 is obtained by DC coupling of the optical pickup unit 10 and the AGC unit 20. In the AGC unit 20, AGC processing can be performed without AC coupling. That is, since the DC signal is included in the RF signal extracted from the unrecorded area of the optical disc 2, the voltage level output from the peak hold circuit 22 becomes the TOP level, and the conventional AGC unit 120 shown in FIG. As described above, the gain can be prevented from being maximized. Further, the response is not delayed by this DC coupling. As a result, the RF signal in the recording area continuous to the unrecorded area is adjusted to the maximum gain and does not saturate, so that the signal in the recording area portion continuous to the unrecorded area can be read stably. Further, if the output level of the reproduction signal is adjusted and confirmed at the design or production stage, it is not necessary to adjust the gain of the AGC unit 20 every time the optical disk 2 is replaced.

  Further, in the present embodiment, by using the maximum value of the voltage of the RF signal output from the peak hold circuit 22, the AGC unit 20 is provided that controls and outputs the amplitude of the RF signal to a predetermined magnitude. The amplitude of the RF signal output from the AGC unit 20 can be kept within a predetermined range. Then, the level shift circuit 30 is used to shift the voltage of the RF signal with the maximum modulation rate (80%) output from the AGC unit 20 to the same voltage level as the D range of the AD converter 41, so that the D range Can be used effectively. As a result, a decrease in the resolution of the AD converter 41 can be suppressed.

  Further, in the present embodiment, the level shift circuit 30 that shifts the voltage level of the RF signal with the peak value of the voltage of the RF signal output from the peak hold circuit 22 as a reference voltage is provided, thereby being output from the AGC unit 20. The voltage level of the RF signal can be accurately shifted. As a result, the D range can be used more effectively, and the decrease in the resolution of the AD converter 41 can be further suppressed.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims for patent, and includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the present embodiment, an example in which the optical disc device of the present invention is applied to a disc playback device that plays back information stored on the optical disc has been described. However, the present invention is not limited to this, and recording is performed in addition to playback. It may be a disc playback / recording apparatus.

1 is a block diagram of an optical disc apparatus according to an embodiment of the present invention. It is a wave form diagram of the signal output from the AGC part of the optical disk apparatus shown in FIG. FIG. 2 is a waveform diagram of a signal output from a level shift circuit of the optical disc apparatus shown in FIG. 1. It is a block diagram of an optical disc device according to a conventional example. FIG. 6 is a waveform diagram of a signal output from an AGC unit of the conventional optical disc apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 2 Optical disk 10 Optical pick-up unit (pickup)
20 AGC section 22 Peak hold circuit 30 Level shift circuit 35 Operational amplifier 35a Inverting input terminal 41 AD converter (analog / digital converter)

Claims (3)

A pickup that irradiates the optical disc with light, detects reflected light from the optical disc, and outputs a reproduction signal including an AC component and a DC component from the reflected light;
A peak hold circuit for outputting a maximum value of a reproduction signal voltage including an AC component and a DC component output from the pickup;
An AGC unit that is DC-coupled to the pickup and uses the maximum value of the voltage of the reproduction signal output from the peak hold circuit to control and output the amplitude of the reproduction signal to a predetermined magnitude;
An analog-digital converter that converts the reproduction signal, which is an analog signal, into a digital signal;
The analog-to-digital converter shifts the voltage level of the reproduction signal so that the voltage of the reproduction signal output from the AGC unit has the same voltage level as the dynamic range of the analog-to-digital converter. An optical disc apparatus comprising: a level shift circuit for outputting to a disc.   The level shift circuit uses the maximum value of the voltage of the reproduction signal output from the peak hold circuit as a reference voltage, and the voltage of the reproduction signal output from the AGC unit having the maximum modulation rate is converted to the analog-digital converter. 2. The optical disc apparatus according to claim 1, wherein a voltage level of the reproduction signal is shifted so as to be the same voltage level as that of the dynamic range and output to the analog-digital converter. The level shift circuit includes an operational amplifier,
3. The optical disc apparatus according to claim 1, wherein the reproduction signal output from the AGC unit is input to an inverting input terminal of the operational amplifier.

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