JP2008004177A - Optical disk device - Google Patents

Abstract

An optical disc apparatus suitable for high-speed reproduction and capable of suppressing power consumption without using a semiconductor device having a complicated manufacturing process and high cost.
A slew rate limiting circuit is provided to limit a slew rate of a noise component in a high frequency region included in a reproduction signal, thereby suppressing an amplitude of the noise component and attenuating the noise component.
[Selection] Figure 1

Description

  The present invention relates to an optical disc apparatus capable of reproducing an optical disc such as a Blu-ray disc at a high speed.

  A conventional optical disk apparatus has removed an abnormal component (noise component) having a large slew rate included in a reproduction signal (RF signal) output from an optical pickup by an equalizer technique (see, for example, Patent Document 1). Hereinafter, the equalizer technique in the conventional optical disc apparatus will be described. FIG. 13 is a schematic block diagram of a reproduction signal processing system in a conventional optical disc apparatus.

  The conventional optical disk apparatus irradiates the optical disk 1 with laser light from the optical pickup 2, converts the return light reflected and returned to an electrical signal by a photodiode (not shown) in the optical pickup 2, and reproduces the reproduction signal ( A signal indicating information recorded on the optical disc 1), and the electric signal has an amplitude variation caused by variations in the type of the optical disc and the characteristics of the optical pickup. In the optical disc apparatus, the amplitude of the reproduction signal is normalized by an AGC circuit (auto gain control circuit) 3.

  The equalizer circuit 18 boosts a predetermined frequency band of the signal from the AGC circuit 3 so as to minimize intersymbol interference, equalizes the waveform of the signal, removes a noise component, and performs A / D conversion. Send to circuit 12. A DRC (digital read channel) circuit 13 decodes the signal converted into a digital signal by the A / D conversion circuit 12 and sends it to the interface circuit.

  FIG. 14 shows a block diagram of a conventional equalizer circuit 18. As shown in FIG. 14, the conventional equalizer circuit 18 is composed of a seventh-order equiripple filter, and a seventh-order low-pass filter circuit comprising second-order low-pass filter circuits 9, 19, 20 and a first-order low-pass filter circuit 21. Is provided. Further, the equalizer circuit 18 boosts a predetermined frequency band of the input signal by the secondary high-pass filter circuit 10 and the amplifier circuit 11.

  FIG. 15 shows the gain characteristics of the conventional equalizer circuit 18. According to the conventional equalizer circuit 18, for example, when a Blu-ray disc is reproduced at 10 × speed, the 2T signal that is the highest frequency among the reproduced signals (the frequency when reproduced at 10 × speed is 165 MHz) is amplified by about 3 dB. Is done. FIG. 16 shows the group delay characteristic of the conventional equalizer circuit 18. According to the conventional equalizer circuit 18, the group delay is flat without frequency dependency up to a frequency region exceeding the cut-off frequency fc.

  In order to reproduce a Blu-ray disc at 10 times speed with the configuration of the conventional optical disc apparatus, it is necessary to realize a cutoff frequency of 165 MHz in the conventional equalizer circuit 18. Therefore, a filter having the highest band among the filters constituting the seventh-order low-pass filter circuit requires a pass band of about 400 MHz from the transfer function of the equiripple filter.

  In order to realize the above characteristics, as a characteristic of a semiconductor analog device, ft (current gain cut-off frequency) should be 40 GHz or more (as a general guide, a device having an ft of about 100 times the necessary band is designed. (Desired) transistors are required, but such devices are costly due to the complexity of the manufacturing process.

Next, the power consumption of the conventional equalizer circuit 18 will be described.
FIG. 17 shows a circuit diagram of a gm-C type primary low-pass filter circuit. As shown in FIG. 17, the cut-off frequency fc of the first-order low-pass filter circuit composed of the gm amplifier circuit (conductance amplifier circuit) 22 and the capacitor 23 is
fc = gm / C1 (1)
Set by. However, gm is the gm value (mutual conductance) of the gm amplifier circuit 22, and C 1 is the capacitance value of the capacitor 23. For example, when the cut-off frequency fc is set to 400 MHz necessary for reproducing a Blu-ray disc at 10 times speed, if the capacitance value C1 of the capacitor 23 is assumed to be 1 pF, the gm amplifier circuit 22 of the gm amplifier circuit 22 is obtained from the equation (1). 400 μg mns is required as the gm value.

FIG. 18 shows a detailed circuit diagram of the gm amplifier circuit. The gm value of this gm amplifier circuit is
gm = Icnt / (Ia × R1) (2)
Is calculated by However, Ia is a current value flowing to the input part of the gm amplifier circuit, R1 is an input resistance value of the gm amplifier circuit, and Icnt is a control current value for controlling the gm value. Ia and R1 are determined by the input D range that the gm amplifier circuit must secure. That is,
Input D range = 2 x Ia x R1
Is calculated by

Therefore, for example, when a signal having an amplitude of 0.2 V is input, Ia and R1 are
0.2V = Ia × R1 (3)
Is calculated by If the value of R1 is 5 kΩ, the value of Ia is 40 μA. In addition, when the input D range is 0.4 V (the amplitude of the input signal is 0.2 V that is half that) and 400 μg mns is secured as the gm value, Icnt is obtained from the equations (2) and (3). 80 μA. Therefore, in this case, when the value of the current passed through the primary low-pass filter circuit is calculated, from FIG.
Itotal = Icnt + 2Ia + α = 160 μA + α
It becomes. Here, α is a current value required for the mirror current source. Here, 40 μA is considered. That means
Itotal = 200μA
Assuming that the power consumption in the case of designing with the power supply voltage 5V, 1 mW is required for each primary low-pass filter circuit. Therefore, the power consumption of the entire seventh-order low-pass filter circuit is 7 mW. In this case, if the power consumption by the secondary high-pass filter circuit 10 and the amplifier circuit 11 is 2 mW, the power consumption of the conventional equalizer circuit 18 is 9 mW, which is very large power consumption as one circuit in a large-scale IC. .

As described above, in an optical disc apparatus that reproduces a blue laser optical disc such as a Blu-ray disc, a 2T signal that does not exist in a DVD must be reproduced, and a conventional equalizer circuit having a seventh-order low-pass filter circuit is provided. In order to cope with high-speed reproduction, there is a problem that a manufacturing process is complicated and a high-cost semiconductor device is required, and power consumption is increased.
JP-A-11-345460

  In view of the above problems, the present invention implements noise removal, which is conventionally performed by a 7th-order low-pass filter circuit, by a slew rate limiting circuit, so that a manufacturing process is complicated and a high-cost semiconductor device is not used. An object of the present invention is to provide an optical disc apparatus suitable for high-speed reproduction and capable of suppressing power consumption.

  The optical disk apparatus according to claim 1 of the present invention is an optical disk apparatus including an optical pickup that irradiates a laser beam on the optical disk, receives the return light, and generates a reproduction signal indicating information recorded on the optical disk. An auto gain control circuit for normalizing the amplitude of the reproduction signal, an equalizer circuit for equalizing the waveform of the signal from the auto gain control circuit, and a through component for attenuating a noise component contained in the signal from the equalizer circuit. And a rate limiting circuit.

  An optical disk apparatus according to a second aspect of the present invention is the optical disk apparatus according to the first aspect, wherein the A / D conversion circuit converts the signal from the slew rate limiting circuit into a digital signal, and the A / D. And a digital read channel circuit for decoding the digital signal from the conversion circuit.

  An optical disc apparatus according to claim 3 of the present invention includes an optical pickup that irradiates a laser beam onto the optical disc, receives the return light, and generates a reproduction signal indicating information recorded on the optical disc. Amplifying the amplitude of the reproduction signal with a gain according to a gain control signal and normalizing the amplitude of the reproduction signal, and equalizing the waveform of the signal from the variable gain amplifier circuit An equalizer circuit, a slew rate limiting circuit for attenuating a noise component included in the signal from the equalizer circuit, an A / D conversion circuit for converting the signal from the slew rate limiting circuit into a digital signal, and the A / D A digital read channel circuit for decoding the digital signal from the conversion circuit, and the digital read channel circuit for decoding An amplitude detecting means for detecting an amplitude value of the signal output from the variable gain amplifier circuit, and a difference for detecting a difference from a predetermined reference amplitude value of the amplitude value detected by the amplitude detecting means And a gain control means for generating a gain control signal for controlling the gain of the variable gain amplifier circuit based on the difference detected by the difference detection means.

  According to the present invention, it is possible to provide an optical disc apparatus that is suitable for high-speed reproduction and can suppress power consumption without using a semiconductor device with a complicated manufacturing process and high cost. In addition, since a semiconductor device having a complicated manufacturing process is not used, design is facilitated. Furthermore, the circuit scale can be reduced as compared with a seventh-order low-pass filter circuit using a gm-C type first-order low-pass filter circuit. Therefore, it is possible to realize an optical disc apparatus capable of reproducing a blue laser optical disc at a high speed with a circuit having a low manufacturing cost, low power consumption, and a small circuit scale.

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic block diagram of a reproduction signal processing system of the optical disc apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the optical disc apparatus irradiates an optical disc 1 with laser light, receives the return light, and generates a reproduction signal (RF signal) indicating information recorded on the optical disc 1. And an AGC circuit (auto gain control circuit) 3 that normalizes the amplitude of the reproduction signal from the optical pickup 2, an equalizer circuit 4 that equalizes the waveform of the signal from the AGC circuit 3, and a signal from the equalizer circuit 4 And a slew rate limiting circuit 5 that attenuates an abnormal component (noise component) having a large slew rate.

The operation of the optical disk apparatus configured as described above will be described below.
The optical disc apparatus irradiates the optical disc 1 with laser light from the optical pickup 2 and converts the return light reflected and returned to an electric signal by a photodiode (not shown) in the optical pickup 2 to generate a reproduction signal. To do. The electric signal has an amplitude variation caused by the type of optical disc and the variation in characteristics of the optical pickup. In order to absorb the variation, the optical disc apparatus inputs the reproduction signal to the AGC circuit 3 and normalizes the amplitude. To do.

  However, since the AGC circuit 3 applies gain control at a frequency that does not follow a decrease in signal amplitude due to a defect or the like, an amplitude difference between codes is not absorbed. Therefore, the equalizer circuit 4 boosts a predetermined frequency band so as to minimize intersymbol interference and equalizes the waveform of the reproduction signal. FIG. 2 shows the gain characteristics of the equalizer circuit 4. For example, when the signal shown in FIG. 3 passes through the equalizer circuit 4, a predetermined frequency band is boosted to become a signal as shown in FIG. At this time, the noise component is also boosted.

  Further, the signal shown in FIG. 4 is input to the slew rate limiting circuit 5. The slew rate limiting circuit 5 limits the slew rate (rate of change) of each frequency component of the signal from the equalizer circuit 4 to a certain value (limit value) or less to attenuate the noise component. Specifically, the slew rate limiting circuit 5 limits the slew rate of the input signal to the limit value if the slew rate of the input signal is equal to or higher than the limit value, and outputs the limit value as it is if it is less than the limit value.

Hereinafter, the operation of the slew rate limiting circuit 5 will be described.
Here for the sake of simplicity
y = A x sin ωt
This will be described using the following signal. A is the amplitude (constant), ω is the angular frequency, and t is the time.

The slew rate SR (slope) of the signal y is
SR = A × ω × cos ωt (4)
The maximum value SRmax of the slew rate is
SRmax = Aω = A × 2πf
It can be expressed as. Note that f is a frequency.

The amplitude of the signal y when the slew rate is not limited is “A”, and the maximum amplitude A′max when the slew rate is limited is shown in FIG. As shown in
A′max = α × (T / 4) = α × (1 / 4f) (5)
It becomes. Note that T is a period. In practice, however, the slew rate of the signal y approaches zero when the phase is in the vicinity of 90 ° or 270 °. Therefore, the signal y when the slew rate is limited is not a triangular wave as shown in FIG. The maximum value of the amplitude is smaller than A′max.

FIG. 6 shows the relationship between the slew rate limit value α, the signal amplitude A, and the frequency f. As shown in FIG.
A = α / ω = α / 2πf
The upper side of the graph is an attenuation region of amplitude A, and the amplitude is limited as the signal has a higher frequency f.

FIG. 7 shows an embodiment of the slew rate limiting circuit 5. When the current value flowing through the constant current source 6 is I1, the current value flowing through the constant current source 7 is I2, and the capacitance value of the output load capacitor 8 is C3, the slew rate limit value α is the current value (I1-I2) and the capacitance value. It is determined by C3, and its relational expression is
α = (I1-I2) / C3
Can be expressed as

  As described above, in the optical disc apparatus, the amplitude of the reproduction signal from the optical pickup 2 is normalized by the AGC circuit 3, and the equalizer circuit 4 boosts a predetermined frequency band of the reproduction signal after the normalization, thereby reproducing the waveform of the reproduction signal. And the slew rate limiting circuit 5 attenuates the noise component of the reproduction signal after the equalization and sends it to the A / D conversion circuit.

Next, the operation will be described assuming that the Blu-ray disc is played back at 10 times speed.
In the case of a Blu-ray disc, the shortest mark length is 2T when 1 channel bit width is T, and the 2T signal when the repetition of the shortest mark is reproduced has a short pit length. On the other hand, the amplitude is about 13%. On the other hand, in the case of DVD, the shortest mark length is 3T, and the 3T signal has an amplitude of about 40% with respect to the amplitude of the 14T signal.

  When a conventional DVD drive was used to reproduce a DVD at 16 times speed and the signal waveform output from the optical pickup was observed to read the amplitude of the noise component, it was about 25% of the 3T signal. Assuming that the amplitude of the noise component does not change, in the case of a Blu-ray disc, the amplitude of the noise component is 77% with respect to the amplitude of the 2T signal. That is, when the amplitude of the 2T signal is 50 mVpp, the amplitude of the noise component is assumed to be 40 mVpp.

  First, a case where a noise component is attenuated using a conventional equalizer circuit composed of a seventh-order equiripple filter will be described. In this calculation, the amplitude of the 2T signal is 50 mVpp and the noise frequency is 1 GHz. FIG. 15 shows gain characteristics of a conventional equalizer circuit.

  As shown in FIG. 15, when the conventional equalizer circuit is used, the signal is amplified by about 3 dB at the frequency of the 2T signal (the frequency of 165 MHz when the Blu-ray disc is reproduced at 10 times speed), and the noise component frequency is 1 GHz. The signal is attenuated by about -10 dB. Therefore, the amplitude of the 2T signal after passing through the conventional equalizer circuit is amplified by 3 dB by 50 mVpp to become 70 mVpp, and the amplitude of the noise component is attenuated by −10 dB to become 13 mVpp.

  Next, the case where the equalizer circuit 4 and the slew rate limiting circuit 5 in the first embodiment are used will be described. As shown in FIG. 2, the equalizer circuit 4 boosts a signal having a frequency of 165 MHz or more by 6 dB.

  FIG. 8 shows an embodiment of the equalizer circuit 4. As shown in FIG. 8, the equalizer circuit 4 includes a secondary low-pass filter circuit 9, a secondary high-pass filter circuit 10, and an amplifier circuit 11. This equalizer circuit 4 also uses a filter in the same manner as the conventional equalizer circuit. However, since the order is low, the problem in the conventional configuration does not occur. The amplitude of the 2T signal after equalization by the equalizer circuit 4 is 50 mVpp, which is 100 mVpp, and the noise component amplitude is 40 mVpp, which is 80 mVpp.

Next, the slew rate limit value α is calculated so that the maximum value of the amplitude of the noise component is 13 mVpp which is the same as the output of the conventional equalizer circuit.
From the above formula (5),
α = A′max × 4f
= 0.0065 V x 4 x 1 GHz = 26 x 10 ⁶ [V / s]
It becomes. Therefore, if the slew rate limit value α is 26 × 10 ⁶ [V / s], the maximum value of the amplitude of the noise component of 1 GHz is 13 mVpp.

On the other hand, when the amplitude of the 2T signal when the slew rate is limited to 26 × 10 ⁶ [V / s] is calculated, when the 2T signal is considered as a sine wave, the slew rate is SR = A × ω × cosωt
It becomes.

Here, the angle at which the slew rate is 26 × 10 ⁶ [V / s] when the amplitude A of the 2T signal after equalization is 0.05 V and the frequency f of the 2T signal at 10 × speed reproduction is 165 MHz is:
26 × 10 ⁶ [V / s] = 0.05 V × 2 × π × 165 MHz × cos ωt
Should be calculated. as a result,
ωt = 60 °
It becomes.

Accordingly, 2T signal after equalizing is 0 because the slew rate of ° from up to 60 ° is a ^{26 × 10 6 [V / s} ] or more, 0 60 ° slew rate from ° is 26 × ¹⁰ 6 [V / s ]. That is, from 0 ° to 60 °, the 2T signal after equalization increases at 26 × 10 ⁶ [V / s]. Since the slew rate is smaller than 26 × 10 ⁶ [V / s] between 60 ° and 90 °, the original waveform of the 2T signal after equalization is output.

First, if the increment from 0 ° to 60 ° is y1, y1 = (60 ° / 360 °) × (1/165 MHz) × 26 × 10 ⁶ [V / s]
= 0.026V
It becomes.

Next, assuming that the increment from 60 ° to 90 ° is y2, y2 = 0.05 × sin 90 ° −0.05 × sin 60 °
= 0.007V
It becomes.

Therefore, the amplitude of the 2T signal after equalization with the slew rate limited to 26 × 10 ⁶ [V / s] is
Amplitude = (y1 + y2) x 2 = 0.066Vpp
It becomes.

  In summary, when a signal having a 2T signal amplitude of 50 mVpp (165 MHz) and a noise component amplitude of 40 mVpp (1 GHz) is passed through a conventional equalizer circuit, the amplitude of the 2T signal is 70 mVpp and the noise component amplitude is 13 mVpp. . On the other hand, in the first embodiment, the amplitude of the 2T signal is 66 mVpp and the amplitude of the noise component is 13 mVpp, and substantially the same characteristics are obtained.

  Next, assuming that the amplitude of the signal from the AGC circuit 3 is the amplitude shown in FIG. 9, the gain characteristics of the equalizer circuit 4 and the slew rate limiting circuit 5 as a whole will be described with reference to FIG. In FIG. 10, a thick solid line is a graph showing the gain characteristics of the equalizer circuit 4 and the slew rate limiting circuit 5 as a whole, and a thin solid line is a graph showing the gain characteristics of the conventional equalizer circuit. As shown in FIG. 10, according to the first embodiment, substantially the same characteristics as the conventional equalizer circuit can be obtained. As shown in FIG. 10, normalization of the reproduction signal by the AGC circuit 3 prevents a restriction on the slew rate of the reproduction signal.

  As described above, according to the first embodiment, by providing a slew rate limiting circuit for the purpose of noise removal, a Blu-ray disc can be designed with a circuit that is easy to design and has reduced power consumption and scale. And the like can be reproduced at a high speed.

  Specifically, when comparing power consumption, if the power consumption per primary low-pass filter circuit is 1 mW, the power consumption by the secondary high-pass filter circuit 10 and the amplifier circuit 11 is 2 mW in the conventional equalizer circuit, the overall power consumption The power is 9 mW. On the other hand, if the power consumption of the equalizer circuit 4 in the first embodiment is 4 mW and the power consumption of the slew rate limiting circuit 5 is 2 mW, the total power consumption is 6 mW, which is a reduction effect of about 33%.

  Regarding the circuit area, the slew rate limiting circuit is equivalent to one gm-C type first-order low-pass filter circuit, and the second-order component of the seventh-order low-pass filter circuit constituting the conventional equalizer circuit is the same as in the first embodiment. Since it is used as the equalizer circuit 4, there is a reduction effect of about 60%.

(Embodiment 2)
FIG. 11 is a schematic block diagram of a reproduction signal processing system of the optical disc apparatus according to Embodiment 2 of the present invention. However, the same members as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the optical disk apparatus according to the second embodiment, an A / D conversion circuit 12 that converts a signal from the slew rate limiting circuit 5 into a digital signal and a digital signal from the A / D conversion circuit 12 are provided at the subsequent stage of the slew rate limiting circuit 5. The difference from Embodiment 1 is that a DRC (digital read channel) circuit 13 for decoding a signal is provided.

  In the first embodiment described above, as shown in FIG. 10, a weak signal passes on the high frequency side as compared with a conventional equalizer circuit. For this reason, binarization of a reproduction signal by a data slicer without A / D conversion leads to signal quality deterioration such as jitter deterioration. On the other hand, when the A / D converted signal is processed by the DRC technique as in the second embodiment, the purpose is to serve as an anti-aliasing filter. Therefore, the signal is compared with the case where the data slicer is used. The impact on quality is reduced.

(Embodiment 3)
FIG. 12 is a schematic block diagram of the reproduction signal processing system of the optical disc apparatus according to Embodiment 3 of the present invention. However, the same members as those described in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

  The optical disk apparatus according to the third embodiment includes a VGA circuit (variable gain amplifier circuit) 14 instead of the AGC circuit as means for normalizing the amplitude of the reproduction signal, and performs feedback control of the gain of the VGA circuit 14. The difference from the second embodiment is that an amplitude detection unit 15, a difference detection unit 16, and a gain control unit 17 are provided.

  In other words, the VGA circuit 14 connected to the subsequent stage of the optical pickup 2 amplifies the amplitude of the reproduction signal with a gain corresponding to the gain control signal, normalizes the amplitude, and sends it to the equalizer circuit 4. The amplitude detector 15 detects the amplitude value of the signal output from the VGA circuit 14 based on the signal decoded by the DRC circuit 13. Further, the difference detection unit 16 detects a difference from a predetermined reference amplitude value of the amplitude value detected by the amplitude detection unit 15. The gain control means 17 generates a gain control signal for controlling the gain of the VGA circuit 14 based on the difference detected by the difference detection means 16. The amplitude detection unit 15, the difference detection unit 16, and the gain control unit 17 may be configured by a circuit or may be realized using a microcomputer.

The operation of the optical disk apparatus configured as described above will be described below.
In the same manner as in the first embodiment, the optical disk apparatus irradiates the optical disk 1 with laser light from the optical pickup 2 and reflects the return light that is reflected back to an electrical signal by a photodiode (not shown) in the optical pickup 2. To generate a reproduction signal. Then, the reproduction signal is input to the VGA circuit 14 and normalized to a constant amplitude. Thereafter, as in the first and second embodiments, the waveform of the reproduction signal is equalized, the noise component is attenuated, converted to a digital signal, the digital signal is decoded, and sent to the interface circuit at the subsequent stage.

  On the other hand, the amplitude detection means 15 detects the amplitude value of the signal output from the VGA circuit 14, the difference detection means 16 detects the difference from the predetermined reference amplitude value, and the gain control means 17 detects the difference. The gain of the VGA circuit 14 is set so as to compensate.

  The optical disk apparatus according to the present invention can provide an optical disk apparatus that is suitable for high-speed playback and can reduce power consumption without using a semiconductor device that has a complicated manufacturing process and is expensive. This is useful for disc drives that can be played on

1 is a schematic block diagram of a reproduction signal processing system of an optical disc apparatus in Embodiment 1 of the present invention. The figure which shows the gain characteristic of the equalizer circuit in Embodiment 1 of this invention The figure which shows an example of the input signal waveform to the equalizer circuit in Embodiment 1 of this invention The figure which shows an example of the output signal waveform from the equalizer circuit in Embodiment 1 of this invention The figure for demonstrating the amplitude of the signal which limited the slew rate by the slew rate limiting circuit in Embodiment 1 of this invention The figure for demonstrating the characteristic of the slew rate limiting circuit in Embodiment 1 of this invention 1 is a circuit diagram showing an example of a slew rate limiting circuit according to Embodiment 1 of the present invention. 1 is a circuit diagram showing an example of an equalizer circuit according to Embodiment 1 of the present invention. The figure which shows the amplitude of the input signal assumed in order to demonstrate the gain characteristic of the equalizer circuit and the whole slew rate limiting circuit in Embodiment 1 of this invention The figure which shows the gain characteristic of the equalizer circuit and the whole slew rate limiting circuit in Embodiment 1 of this invention Schematic block diagram of the reproduction signal processing system of the optical disc apparatus in Embodiment 2 of the present invention Schematic block diagram of a reproduction signal processing system of the optical disc apparatus in Embodiment 3 of the present invention Schematic block diagram of a reproduction signal processing system in a conventional optical disc apparatus Block diagram of a conventional equalizer circuit The figure which shows the gain characteristic of the conventional equalizer circuit The figure which shows the group delay characteristic of the conventional equalizer circuit Circuit diagram of gm-C type first-order low-pass filter circuit used in conventional equalizer circuit Detailed circuit diagram of gm amplifier circuit used in conventional equalizer circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Optical pick-up 3 AGC (auto gain control) circuit 4, 18 Equalizer circuit 5 Slew rate limiting circuit 6, 7 Constant current source 8 Capacitance 9, 19, 20 Secondary low-pass filter circuit 10 Secondary high-pass filter circuit 11 Amplifier circuit 12 A / D conversion circuit 13 DRC (digital read channel) circuit 14 VGA (variable gain amplifier) circuit 15 Amplitude detection means 16 Difference detection means 17 Gain control means 21 Primary low-pass filter circuit 22 gm amplifier circuit 23 Capacitance

Claims (3)

An optical disc apparatus including an optical pickup that irradiates a laser beam on an optical disc, receives a return light thereof, and generates a reproduction signal indicating information recorded on the optical disc,
An auto gain control circuit for normalizing the amplitude of the reproduction signal;
An equalizer circuit for equalizing the waveform of the signal from the auto gain control circuit;
A slew rate limiting circuit for attenuating a noise component included in the signal from the equalizer circuit;
An optical disc apparatus comprising: The optical disc apparatus according to claim 1,
An A / D conversion circuit for converting a signal from the slew rate limiting circuit into a digital signal;
A digital read channel circuit for decoding a digital signal from the A / D conversion circuit;
An optical disc apparatus further comprising: An optical disc apparatus including an optical pickup that irradiates a laser beam on an optical disc, receives a return light thereof, and generates a reproduction signal indicating information recorded on the optical disc,
A variable gain amplifier circuit that amplifies the amplitude of the reproduction signal with a gain according to a gain control signal and normalizes the amplitude of the reproduction signal;
An equalizer circuit for equalizing the waveform of the signal from the variable gain amplifier circuit;
A slew rate limiting circuit for attenuating a noise component included in the signal from the equalizer circuit;
An A / D conversion circuit for converting a signal from the slew rate limiting circuit into a digital signal;
A digital read channel circuit for decoding a digital signal from the A / D conversion circuit;
Based on the signal decoded by the digital read channel circuit, amplitude detecting means for detecting the amplitude value of the signal output from the variable gain amplifier circuit;
Difference detection means for detecting a difference from a predetermined reference amplitude value of the amplitude value detected by the amplitude detection means;
Gain control means for generating a gain control signal for controlling the gain of the variable gain amplifier circuit based on the difference detected by the difference detection means;
An optical disc apparatus comprising:

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