JP4614699B2 - Signal processing apparatus for optical disk system - Google Patents

Description

  The present invention relates to a signal processing apparatus for an optical disc system.

  An optical pickup is an apparatus that records or reproduces information on an optical disk using an optical system that combines a light source, a lens, a photodetector, and the like. A signal (hereinafter referred to as “photodetection signal”) obtained from the optical disc by this optical pickup is characteristic variation such as reflectance of the optical disc, manufacturing variation of the optical system including the optical detector of the optical pickup, and recording / reproduction. -Level fluctuation may occur due to a change in the amount of light based on a difference in erasing operation mode. For this reason, in an optical disc system that performs optical disc recording or reproduction, an AGC (Auto Gain Control) circuit (for example, refer to Patent Document 1 shown below) is usually used to make the level of the light detection signal coincide with a predetermined reference level. Provided.

 FIG. 7 is a diagram showing a configuration of an optical disc system having a conventional AGC circuit 40. As shown in FIG. Information recorded on the optical disk 10 is read out as return light of the laser light by the optical pickup 20, and further subjected to photoelectric conversion to obtain a light detection signal. This photodetection signal becomes a signal source for performing various optical disc reproduction processes (decoding process, servo process, etc.) in the DSP 50. From this photodetection signal, an RF signal, an FE (Focus Error) signal, and a TE (Tracking Error) A signal or the like is generated.

  Since the level of the light detection signal at the stage detected by the optical pickup 20 is very small, the front stage amplifier 30 amplifies it to a level that can be handled by a subsequent stage DSP (Digital Signal Processor) 50 and the like. Then, the light detection signal amplified by the pre-stage amplifier 30 is supplied to the AGC circuit 40, and the level fluctuation is absorbed. As a result, a light detection signal stabilized to a substantially constant level is supplied to the DSP 50, and after being subjected to decoding processing according to the optical disc 10, a reproduction signal (audio signal, CD-ROM signal, video) is supplied to the speaker 60 or the like. Signal, etc.) are output.

The AGC circuit 40 is detected by the VCA (Voltage Control Amplifier) 41 that amplifies or attenuates the light detection signal with a variable gain according to the control voltage, the detector 42 that detects the output of the VCA 41, and the detector 42. In order to make the output of the VCA 41 coincide with a predetermined reference level, it is constituted by an analog circuit having a VCA control circuit 43 that generates a control voltage to the VCA 41 and supplies it to the VCA 41. The reference level in the VCA control circuit 43 is normally an internally generated voltage obtained by dividing the power supply voltage VCC by a predetermined amount.
Japanese Patent No. 3272003

  By the way, in the conventional mechanism that stabilizes the level of the light detection signal such as the AGC circuit 40 shown in FIG. 7, the amount of reflected light due to characteristic variation due to environmental conditions of the optical disk or optical pickup, dirt or scratches on the optical disk, etc. Unexpected level fluctuations in the photodetection signal can occur due to various noise factors such as changes in. However, the conventional mechanism is in a state where the specification is fixed by the analog circuit configuration, so that it is not flexible enough to cope with an unexpected level fluctuation of the light detection signal. As a result, the light detection signal is used. There has been a problem that the optical disk reproduction process cannot be performed properly.

  A main aspect of the present invention for solving the above-described problems is that, in a signal processing apparatus of an optical disc system having an analog signal processing unit and a digital signal processing unit, the analog signal processing unit performs reproduction processing obtained from the optical disc. And a gain variable amplifying unit that amplifies the photodetection signal level based on a variable gain so as to coincide with a predetermined reference level, and the digital signal processing unit is amplified by the variable gain amplifying unit. An A / D conversion unit that samples the light detection signal and performs A / D conversion, a comparison unit that compares the level of the light detection signal after the A / D conversion with the reference level, and a result of the comparison Accordingly, the counter is configured to count up or count down based on the counter clock, and the variable gain is set based on the count value of the counter. Has a gain adjusting unit for integer, a, to vary the ratio of the clock frequency of the counter clock and the sampling frequency in the A / D conversion, to.

  ADVANTAGE OF THE INVENTION According to this invention, the signal processing apparatus of the optical disk system suitable for an optical disk reproduction | regeneration processing can be provided.

<Optical disk system>
A configuration / operation of an optical disc system according to an embodiment of the present invention will be described with reference to FIG.
An optical disc system that performs recording / reproduction with respect to an optical disc 10 compliant with CD standards (CD-ROM, CD-R / RW, etc.), DVD standards (DVD ± R / RW, DVD-RAM), etc. , Optical disk signal processing LSI 70, microcomputer (hereinafter referred to as microcomputer) 200, various servo control actuators such as focus / tracking / spindle and their driver circuits (all not shown), and reproduction of speaker 60, etc. An output device.

  The optical pickup 20 is a device that records / reproduces information to / from the optical disc 10 using an optical system in which a light source, a lens, a photodetector, and the like are combined. Information recorded on the optical disk 10 is read out as return light of the laser beam by the optical pickup 20, and a photodetection signal is obtained by performing photoelectric conversion. The photodetection signal serves as a signal source for performing various reproduction-system digital processing in the digital signal processing unit 90, and an RF signal, an FE signal, a TE signal, and the like are generated from the photodetection signal.

  The microcomputer 200 controls the entire optical disc system. In particular, the microcomputer 200 includes a reference level register 201 for storing a reference level serving as a determination criterion for stabilizing the VCA 82 output, and a timing control unit 202 for controlling various timings in the optical disc signal processing LSI 70.

  Examples of timing signals inside the optical disk signal processing LSI 70 controlled by the timing control unit 202 include a counter clock supplied to the VCA control unit 95 to generate a control voltage to the VCA 82, and an A / D conversion unit. An A / D sampling control signal for controlling sampling in 94, a D / A sampling control signal for controlling sampling in the D / A converter 93, and the like. That is, the timing control unit 202 supplies information for controlling the timing signal as described above (hereinafter referred to as timing control information) to the timing signal generation unit 96 via the microcomputer interface unit 97. .

  The optical disk signal processing LSI 70 is an integrated circuit in which an analog signal processing unit 80 and a digital signal processing unit 90 are integrated into a one-chip CMOS device by CMOS process technology. Note that the analog signal processing unit 80 and the digital signal processing unit 90 may be implemented as separate chips. However, as shown in FIG. 1, as a single chip, the power consumption is reduced, the chip area is reduced, and the cost is reduced. Down etc. are planned.

  The analog signal processing unit 80 performs analog signal processing such as waveform shaping of the light detection signal detected by the optical pickup 20, APC (Automatic Power Control) of the laser emission output of the optical pickup 20, and the like. The analog signal processing unit 80 shown in FIG. 1 has, in particular, a pre-amplifier 81, a VCA 82, a peak level detector 83, and a decoder 84 as a mechanism for compensating (absorbing) the level fluctuation of the light detection signal. I will do it.

The pre-amplifier 81 is provided between the optical pickup 20 and the VCA 82, that is, in the pre-stage of the VCA 82. The level of the light detection signal obtained from the optical disk 10 by the optical pickup 20 is set to a level that the optical signal processing LSI 70 can handle. Amplifies up to.
The VCA 82 amplifies or attenuates the level of the light detection signal with a variable gain according to the control voltage. The VCA 82 is an embodiment of the “gain variable amplification section” according to the present invention.
The peak level detector 83 detects the peak level of the VCA 82 output. In addition to the peak level detection unit 83, a mechanism for detecting the bottom level of the VCA 82 output or a mechanism for detecting a peak level that is a difference level at the bottom level from the peak level of the VCA 82 output may be adopted.
The decoder 84 decodes the control signal output from the VCA control unit 95 and generates a control voltage for controlling the VCA 82.

  The digital signal processing unit 90 performs reproduction digital signal processing such as decoding processing such as EFM or EFMPLUS demodulation and error correction, servo control such as focus / tracking, encoding processing such as EFM modulation and error correction coding, and write strategy. Performs digital signal processing of the recording system such as control. The functions of the digital signal processing unit 90 are implemented as a DSP dedicated program using so-called DSP hardware or DSP MAC (Multiply and Accumulation).

  In particular, the digital signal processing unit 90 includes a waveform shaping unit 91, a decoding processing unit 92, and a D / A conversion unit 93 as a mechanism for performing digital signal processing in the reproduction system, and absorbs fluctuations in the level of the light detection signal. As a mechanism for achieving this, an A / D conversion unit 94 and a VCA control unit 95 are provided, and a timing signal generation unit 96 and a microcomputer interface unit 97 that exchanges signals with the microcomputer 200 are provided. .

  First, a mechanism for performing reproduction digital signal processing in the digital signal processing unit 90 will be described. The waveform shaping unit 91 converts the output of the VCA 82 into a binary value and converts it into an EFM or EFMPLUS signal. The decode processing unit 92 performs a predetermined decode process according to the standard of the optical disc 10 on the EFM or EFMPLUS signal. As a reproduction signal obtained by this decoding process, for example, an Lch / Rch audio signal is converted into an analog signal by the D / A converter 93 and output to the speaker 60.

  Next, a mechanism for absorbing the level fluctuation of the light detection signal in the digital signal processing unit 90 will be described. First, it is assumed that the reference level is preset by the microcomputer 200 in the VCA control unit 95. In the A / D converter 94, the peak level of the VCA 82 output detected by the peak level detector 83 is sampled based on the A / D sampling control signal supplied from the microcomputer 200, and a predetermined quantization is performed. Quantization is performed based on the number. In the following description, unless otherwise specified, the “peak level of VCA 82 output” is the peak level of VCA 82 output after being sampled and quantized by the A / D converter 94.

  Here, the VCA control unit 95 increases the control voltage supplied to the VCA 82 by one step when the peak level of the VCA 82 output is below the reference level, and the control voltage supplied to the VCA 82 when the peak level of the VCA 82 output exceeds the reference level. Is lowered one step. By repeatedly performing such VCA control, the level fluctuation of the light detection signal is absorbed.

  Next, the timing signal generator 96 will be described. The timing signal generation unit 96 generates various timing signals inside the optical disc signal processing LSI 70 based on timing control information supplied from the microcomputer 200 via the microcomputer interface unit 97. Note that the timing signal generated by the timing signal generation unit 96 includes the counter clock supplied to the VCA control unit 95 and the A / D sampling for controlling the sampling in the A / D conversion unit 94 as described above. Control signals and the like.

  Here, as the counter clock generated by the timing signal generator 96, any one of a plurality of predetermined counter frequencies is arbitrarily set. In this case, the timing signal generation unit 96 is configured by a well-known PLL circuit including, for example, a voltage controlled oscillator, a frequency divider capable of setting the frequency division number, a phase comparator, and the like. A counter clock is obtained from the oscillation output of the oscillator. In other words, by varying the frequency dividing number in the frequency divider of the PLL circuit, the clock frequency of the counter clock (hereinafter referred to as counter clock frequency) can be arbitrarily set.

  A predetermined sampling frequency is arbitrarily set as the A / D sampling control signal generated by the timing signal generator 96.

<VCA control unit>
The configuration / operation of the VCA control unit 95 according to an embodiment of the present invention will be described with reference to FIG. 3 as appropriate and based on FIG. The VCA control unit 95 is an embodiment of the “gain adjustment unit” according to the present invention. As shown in FIG. 2, the VCA control unit 95 includes a comparison unit 951 and a counter 952.
The comparison unit 951 compares the peak level of the VCA 82 output supplied from the A / D conversion unit 94 with the reference level supplied from the microcomputer 200 via the microcomputer interface unit 97. As shown in FIG. 3, the comparison unit 951 outputs an H level for setting the counter 952 to the count-up mode when the peak level of the VCA 82 output is equal to or lower than the reference level. On the other hand, when the peak level of the VCA 82 output exceeds the reference level, the L level for causing the counter 952 to enter the countdown mode is output.
The counter 952 includes an up / down counter, a U / D terminal for inputting the output of the comparison unit 951, a CLK terminal for inputting the counter clock output from the timing signal generation unit 96, a count up / It has a Q terminal for outputting the count value that has been lowered.
As shown in FIG. 3, the counter 952 enters either the count-up / count-down operation mode based on the output of the comparison unit 951. That is, the counter 952 counts down when the output of the comparison unit 951 is L level, and counts up when the output of the comparison unit 951 is H level.

<Relationship between counter clock frequency and sampling frequency>
In the present invention, for example, the timing control unit 202 of the microcomputer 200 arbitrarily varies the ratio between the counter clock frequency in the counter 952 and the sampling frequency in the A / D conversion unit 94. The operation of the optical disk signal processing LSI 70 in this case will be described based on the specific examples shown in FIGS.

  4 shows the case where the counter clock frequency is set equal to the sampling frequency, FIG. 5 shows the case where the counter clock frequency is set lower than the sampling frequency, and FIG. 6 shows the case where the counter clock frequency is higher than the sampling frequency. Is set to. 4, 5, and 6, (a) is the output waveform of the peak level detector 83, (b) is the waveform of the sampling control signal of the A / D converter 94, and (c) is the comparison. The output waveform of the unit 951, (d) shows the waveform of the counter clock of the counter 952, and (e) shows the output waveform of the counter 952.

<< Counter clock frequency = Sampling frequency >>
A case where the counter clock frequency is set equal to the sampling frequency will be described with reference to FIG.

  It is assumed that the peak level of the VCA 82 output of the signal whose information is read from the optical disk 10 by the optical pickup 20 is “A”. At this time, when the VCA control is started, the peak level of the VCA 82 output detected by the peak level detector 83 starts to increase stepwise. At this time, the A / D converter 94 performs sampling and quantization for each sampling point at which the peak level of the VCA 82 output is determined by the A / D sampling control signal. The comparison unit 951 compares the peak level of the VCA 82 output with the reference level for each sampling point in synchronization with the A / D conversion unit 94.

  The counter 952 counts up or down based on the counter clock having the same frequency as the sampling frequency slightly delayed in phase from each sampling point based on the comparison result in the comparison unit 951. The counter 952 may be adjusted to synchronize with the A / D conversion unit 94 and the comparison unit 951, that is, to adjust the phase of the counter clock and the A / D sampling control signal with certainty. As a result, the response of the level change of the photodetection signal by the VCA control is improved.

  By the way, at the sampling points A to D, since the sampled peak level of the VCA 82 output is equal to or lower than the reference level, the output of the comparison unit 951 continues to be at the H level. That is, in sampling at the sampling points A to D, the count value of the counter 952 continues to be counted up by the counter clock.

  At the sampling point E, since the sampled peak level of the VCA 82 output exceeds the reference level, the output of the comparison unit 951 switches from the H level to the L level, and the count value of the counter 952 is counted down by the counter clock within the sampling period. To do. At the sampling point F, since the sampled peak level of the VCA 82 output is below the reference level, the output of the comparison unit 951 switches from the L level to the H level, and the count value of the counter 952 is changed by the counter clock within the sampling period. Count up.

  At the sampling point G, the sampled peak level of the VCA 82 output exceeds the reference level, so the output of the comparison unit 951 switches from the H level to the L level, and the count value of the counter 952 is counted down by the counter clock within the sampling period. To do. Thereafter, since the sampled peak level of the VCA 82 output continues to exceed the reference level, the count value of the counter 952 is continuously counted down by the counter clock.

<< Counter clock frequency << Sampling frequency >>
Based on FIG. 5, a case where the counter clock frequency is set to “½ times the sampling frequency” will be described as an example when the counter clock frequency is set to a frequency lower than the sampling frequency.

  As shown in FIG. 5, when the counter clock frequency is set to “½ times” the sampling frequency, the counter 952 counts up or down with respect to “twice” sampling in the A / D converter 94. It will be performed only once. For this reason, compared with the case where the counter clock frequency is set equal to the sampling frequency, the response of the level change of the photodetection signal by the VCA control is delayed.

  Therefore, for example, when the peak level of the light detection signal is suddenly caused by noise and a steep pulse-like change occurs, the counter clock frequency may be intentionally set to a frequency lower than the sampling frequency. preferable. That is, the opportunity for the counter 952 to operate based on the peak level caused by the noise of the VCA 82 output, that is, the opportunity for the VCA control to follow the noise is reduced.

<< Counter clock frequency >> Sampling frequency >>
Based on FIG. 6, a case where the counter clock frequency is set to “twice” the sampling frequency will be described as an example of the case where the counter clock frequency is set higher than the sampling frequency.

  As shown in FIG. 6, when the counter clock frequency is set to “twice” the sampling frequency, the counter 952 counts up or counts down to “2” for “one time” sampling in the A / D converter 94. Times "will also be performed. That is, the amount of change in the control voltage supplied to the VCA 82 is “doubled” based on the amount of change in the count value of the counter 952 and thus the count value of the counter 952. In other words, as compared with the case where the counter clock frequency is set equal to the sampling frequency, the resolution of the level adjustment of the photodetection signal in the VCA control is “½ times”.

  That is, compared with the case where the counter clock frequency is set equal to the sampling frequency, the level setting accuracy of the photodetection signal by the VCA control is deteriorated, and the response of the level change of the photodetection signal by the VCA control is accelerated. . Therefore, for example, when the VCA control is started, the level setting accuracy of the photodetection signal is ignored, and the counter clock frequency is set to the sampling frequency when it is desired to rapidly bring the photodetection signal level close to the target reference level. It is preferable to intentionally set to a higher frequency.

<Examples of effects>
In the above-described embodiment, when the counter clock frequency is set to a frequency lower than the sampling frequency, for example, by changing the ratio between the counter clock frequency and the sampling frequency, the level change of the light detection signal by the VCA control is changed. Responsiveness can be intentionally slowed. Conversely, when the counter clock frequency is set to a frequency higher than the sampling frequency, the accuracy of the level setting of the photodetection signal by the VCA control can be intentionally deteriorated. That is, by changing the ratio between the counter clock frequency and the sampling frequency, it is possible to intentionally change the behavior of the level change of the photodetection signal by the VCA control. As a result, the flexibility of the level adjustment of the light detection signal by the VCA control can be improved, and the level adjustment of the light detection signal by the VCA control can be appropriately and easily performed.

  In the above-described embodiment, by setting the counter clock frequency equal to the sampling frequency, the level setting accuracy of the light detection signal and the level change responsiveness can be improved in a balanced manner and easily in the VCA 82.

  In the embodiment described above, the ratio between the sampling frequency and the counter clock frequency can be easily adjusted by adopting a mechanism for changing only the counter clock frequency.

  In the embodiment described above, the timing control unit 202 of the microcomputer 200 can easily set an appropriate counter clock frequency according to the specifications of the optical disk system.

  Although the present embodiment has been described above, the above-described examples are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed / improved without departing from the spirit thereof, and the present invention includes equivalents thereof.

It is a figure which shows the structure of the optical disk system concerning one Embodiment of this invention. It is a figure which shows the structure of the VCA control part concerning one Embodiment of this invention. It is a figure for demonstrating operation | movement of the VCA control part concerning one Embodiment of this invention. It is a figure for demonstrating operation | movement of the digital signal processing part concerning one Embodiment of this invention. It is a figure for demonstrating operation | movement of the digital signal processing part concerning one Embodiment of this invention. It is a figure for demonstrating operation | movement of the digital signal processing part concerning one Embodiment of this invention. It is a figure which shows the structure of the conventional optical disk system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk 20 Optical pick-up 30 Preamplifier 40 AGC circuit 41 VCA 42 Detector 43 VCA control circuit 50 DSP
60 Speaker 70 Signal processing LSI for optical disc
80 Analog signal processing unit 81 Pre-amplification unit 82 VCA 83 Peak level detection unit 84 Decoder 90 Digital signal processing unit 91 Waveform shaping unit 92 Decoding processing unit 93 D / A conversion unit 94 A / D conversion unit 95 VCA control unit 951 Comparison unit 952 Counter 96 Timing signal generation unit 97 Microcomputer interface unit 200 Microcomputer 201 Reference level register 202 Timing control unit

Claims (4)

In a signal processing apparatus of an optical disc system having an analog signal processing unit and a digital signal processing unit,
The analog signal processing unit is configured to amplify a level of a light detection signal for performing reproduction processing obtained from an optical disc based on a variable gain so as to match a predetermined reference level; and
A level detection unit for detecting the peak or bottom level of the photodetection signal, and
The digital signal processing unit samples an optical detection signal amplified by the variable gain amplification unit and performs A / D conversion; and
A comparison unit that compares the level of the photodetection signal after the A / D conversion with the reference level;
A counter that counts up or counts down based on a counter clock according to a result of the comparison, and a gain adjusting unit that adjusts the variable gain based on a count value of the counter, and
A signal processing apparatus for an optical disc system, wherein a ratio of a sampling frequency in the A / D conversion and a clock frequency of the counter clock is varied according to a detection result from the level detection unit .   2. The signal processing apparatus of the optical disc system according to claim 1, wherein a clock frequency of the counter clock is set equal to a sampling frequency in the A / D conversion.   3. The signal processing apparatus of the optical disc system according to claim 1, wherein only the clock frequency of the counter clock is varied with respect to a predetermined sampling frequency in the A / D conversion.   The signal processing device is connected to a microcomputer that performs overall control of the optical disk system, and the counter clock having a variable clock frequency is supplied to the gain adjusting unit by the microcomputer. Item 4. A signal processing apparatus for an optical disc system according to Item 3.

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