JP3317916B2 - Mirror detection method and mirror detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror detecting method and a mirror detecting circuit for detecting a mirror portion existing between recording tracks in order to detect a recording track of an optical disk such as a CD.

[0002]

2. Description of the Related Art In an optical disk such as a CD, in order to control the position of the optical pickup to a required recording track of the optical disk, when the optical pickup moves on the optical disk,
It is necessary to recognize how many recording tracks have passed (track jump). In the optical disk, since a region having a high reflectance called a mirror portion exists between the tracks of the recording track, the recording track can be recognized by detecting the mirror portion. Conventionally, as a mirror detection circuit for detecting the mirror unit, there is a technique using an RF signal obtained from the optical pickup. For example,
In the technique disclosed in Japanese Patent Application Laid-Open No. HEI 8-115574, it has been proposed that an RF signal is subjected to peak detection and bottom detection, and the output signal of the subtracted circuit is compared and detected.

FIG. 4 is a block diagram showing an example of this type of conventional mirror detection circuit, and FIG.
It is each signal waveform diagram of 11- S16 . As shown in FIG. 5A, an optical pickup or RF amplifier (not shown) outputs R
An F signal is output. When the laser spot of the optical pickup is on the recording track, an output level having a large difference between the peak level and the bottom level corresponding to the recording pit provided on the recording track is obtained from this RF signal. When the signal is in the mirror section between the tracks, a signal in which the bottom level of the output level is increased by reflection at the mirror section (this signal is called a mirror signal)
Becomes Since the laser spot diameter is actually larger than the recording track width, an RF component exists in the mirror signal due to the influence (crosstalk) of the pit of the adjacent recording track. The output level is also changed by the mirror defect.

As shown in FIG. 4, the RF signal SRF is
The signals are input to the peak detection circuit 101 and the bottom detection circuit 102 as input signals. The peak detection circuit 10
1 performs peak detection by a time constant determined by the capacitor C11 and the current I11. The time constant at this time is a value that can follow the envelope of the rotation cycle of the optical disk. The output S11 of the peak detection circuit 101 is shown in FIG. On the other hand, the bottom detection circuit 1
02 performs bottom detection by a time constant determined by the capacitor C12 and the current I12. The time constant at this time is a value that can follow the traverse operation of the optical pickup. The output S12 of the bottom detection circuit 102 is shown in FIG. Then, the peak detection circuit 101
Of the bottom detection circuit 102 is connected to the in-phase input terminal of the subtractor 103.
Connected to the negative-phase input terminal of The subtracter 103 is the output of the output S13., It becomes a signal obtained by subtracting the output-S12 output S11, shows the waveform in FIG. 5 (D).

Next, the output S13 of the subtractor 103 is divided by the resistors 15 and 16, and the divided voltage signal S14
Is input to the peak detection circuit 105. In this case, the voltage is divided so as to have a value of 65% with respect to the peak of the output S14. Further, the time constant of the peak detection circuit 105 is set to a considerably slow time constant such that the voltage of the divided signal becomes DC. This peak detection circuit 105
5 (D) is connected to the in-phase input terminal of the comparator 104. The output S15 of FIG. The output S13 of the subtractor 103 is connected to an opposite-phase input terminal of the comparator 104. That is, the output S13 of the subtractor 103 is compared with the voltage of the output S15, and the output S16 of the comparator 104 becomes the output of the mirror detection circuit. This output S
16 (E) shows the waveform of the output S16.
Thus, the mirror detection, that is, the recording track can be detected.

[0006]

In recent years, DVDs have been developed as optical disks, and a CD / DVD reproducing apparatus capable of reproducing CDs has been demanded. A DVD is a disk of the same size as a CD, but the track pitch is reduced in order to increase the recording capacity. With respect to CDs, mirror signals have a standard that the OFF track level / ON track level of the RF signal is 50% or less. for that reason,
As described above, if the output S16 as the comparator voltage in the comparator 104 is set to be DC of about 65% of the amplitude, the mirror can be detected even when the level ratio is 50% in the worst case. However, in some DVDs, the track is narrower than the CD by about half, so that the level of the mirror signal is low and the OFF track level / ON track level is about 90% at worst. Therefore, when the detection is performed using the above-described conventional detection circuit, the level of the comparator voltage must be set to DC of about 95% of the amplitude of the RF signal. In this case, mirror detection is performed. The margin for the RF signal is about 5% of the RF signal, and it is difficult to stably detect the mirror signal by this method in consideration of the offset, variation, and the like generated in the RF signal.

A main object of the present invention is to provide a mirror detection method and a mirror detection circuit capable of stably detecting a mirror of an optical disk even when applied to a DVD / CD device capable of reproducing both DVD and CD. Is to provide.

[0008]

A mirror detection method according to the present invention comprises a step of obtaining a signal obtained by performing high-speed bottom detection on an RF signal obtained when a light spot crosses an optical disk made of a CD or DVD; Obtaining a signal obtained by performing low-speed bottom detection, subtracting both the bottom-detected signals, controlling the gain of the subtracted signal to a constant amplitude, and an intermediate value of the amplitude of the gain-controlled signal. And a step of comparing the gain-controlled signal using the level of the intermediate value as a comparison point. Here, it is preferable that the intermediate value as the comparison point is a level that is １ ／ of the amplitude of the signal whose gain is controlled.

A mirror detection circuit according to the present invention comprises: a high-speed bottom detection circuit for performing high-speed bottom detection of an RF signal obtained when a light spot traverses an optical disk made of a CD or a DVD; Detect bottom
A low-speed bottom detection circuit, a variable gain amplifier type subtractor for subtracting the high-speed bottom-detected signal and the low-speed bottom- detected signal and controlling the gain to a predetermined amplitude, and the gain variable amplifier type subtraction A signal processing unit for detecting an intermediate value level of the amplitude from the amplitude of the output of the filter, and an output of the variable gain amplifier type subtractor using the signal of the intermediate value level output from the signal processing unit as a comparison point. And a comparator for outputting a mirror detection signal by comparison.

Here, the signal processing unit includes a maximum value / minimum value detector for detecting a maximum value and a minimum value of the output of the variable gain amplifier type subtractor, and an intermediate value between the detected maximum value and the minimum value. And a calculation unit for detecting the level of In this case, it is preferable that the arithmetic unit detects a half level of the maximum value and the minimum value. Further, the signal processing unit includes a DVD / CD control circuit for variably controlling the gain of the variable gain amplifier type subtractor according to an optical disk of the DVD or CD. Alternatively, the signal processing unit includes a gain control circuit that variably controls the gain of the variable gain amplifier type subtractor according to each of the maximum value and the minimum value detected by the maximum value / minimum value detector. .

[0011] In the mirror detection circuit according to the invention is subjected to an amplification by switching the gain of the amplitude of the RF signal fast bottom detection were those signal which is obtained by subtracting the those slow bottom detection for each optical disc. When changing the gain, the gain is set large for a DVD with a small amplitude, and the gain is set small for a CD with a large amplitude so that the DVD and CD have substantially the same amplitude value. By detecting a mirror signal by comparing with a DC generated at an intermediate potential between the peak voltage and the bottom voltage of this amplitude, a stable mirror can be obtained regardless of the magnitude of the amplitude of the mirror signal of the RF signal which differs depending on each disk. Detection becomes possible.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block circuit diagram of a mirror detection circuit according to one embodiment of the present invention. The circuit configuration will be described with reference to FIG. The data recorded on the optical disk is read by an optical pickup, and the R generated through the RF amplifier in the RF amplifier and the AGC amplifier is used.
The F signal SRF is supplied to a high-speed bottom detection circuit 1 and a low-speed bottom detection circuit 2, respectively. The high-speed bottom detection circuit 1 performs bottom detection with a time constant T1 determined by the capacitor C1 and the current I1, and the time constant of this circuit is a value that can follow a traverse operation. The low-speed bottom detection circuit 2 has a time constant T determined by the capacitor C2 and the current I2.
2 is used for bottom detection, and the time constant T
2 is set to a considerably slow value such that the output is DC (direct current). The output S1 of the high-speed bottom detection circuit 1 is
The output S2 of the low-speed bottom detection circuit 2 is connected to the in-phase input terminal of the variable gain amplifier type subtractor 3 via the resistor 12,
The resistor 13 is connected to the negative-phase input terminal of the variable gain amplifier type subtractor 3. A voltage bias Vb having a voltage of DC1 is connected via a variable resistor 11 to the common-mode input terminal of the variable gain amplifier type subtractor 3. here,
The voltage gain of the variable gain amplifier type subtractor 3 is configured to be switched by a DVD / CD control circuit 21 in the digital signal processing circuit 20.

On the other hand, the output S3 of the variable gain amplifier type subtracter 3 is connected to the negative-phase input terminal of the variable gain amplifier type subtractor 3 via a variable resistor 14 to constitute a feedback circuit. . Further, the output S3 of the variable gain amplifier type subtracter 3 is connected to an in-phase input terminal of a comparator 4. The output S3 of the variable gain amplifier type subtracter 3 is the maximum value in the digital signal processing circuit 20.
The maximum value / minimum value detector 22 detects the maximum value and the minimum value of the amplitude. The detected maximum value and minimum value are input to the arithmetic unit 23, and by this calculation, an intermediate potential between the maximum value and the minimum value, for example, 5
Produces 0% value. The output S4 of the arithmetic unit 23 is connected to the negative phase input terminal of the comparator 4. Thus, the comparator 4 outputs the output S3 of the variable gain amplifier type subtractor 3 to the variable gain amplifier type
A signal obtained by comparison with a signal S4 having an intermediate potential of the output amplitude of the above is referred to as an output S5, which is the output of the mirror detection circuit.

Next, the mirror detection operation by the mirror detection circuit of FIG. 1 will be described with reference to FIG. FIG.
(E) shows the waveforms of the signals SRF and S1 to S5 in FIG. 1 for a CD-ROM disk and a DVD disk, respectively. FIG. 2A shows an RF signal SRF obtained from each of the disks, and a mirror signal of the RF signal at the time of a track jump, that is, when the optical pickup crosses a recording track on each disk, is a standard CD signal. −
In the ROM, as shown in FIG. 2 (A1), the OFF track level / ON track level is around 20%.
In the case of DVD, the OFF track level / ON track level is about 70% as shown in FIG. 2 (A2). Also, when the mirror is defective, the upper level of the RF signal disappears and there is almost no signal. However, here, the circuit configuration is such that detection is not performed when the mirror is defective.

When the RF signals SRF shown in FIGS. 2A1 and 2A2 are input, the high-speed bottom detection circuit 1 performs bottom detection with a time constant T1 determined by the capacitance value C1 of the capacitor C1 and the current value I1 of the current I1. And the output S1 has a waveform as shown in (B1) and (B2) of FIG. At this time, the time constant T1 for bottom detection can be controlled by the current I1 according to the rotation speed of the disk so as to follow the traverse operation. The time constant T1 is expressed by the following equation. T1 = C1 · V / I1 (1-1)

On the other hand, in the low-speed bottom detection circuit 2 to which the same RF signal SRF as described above is input, bottom detection is performed with a time constant T2 determined by the capacitance value C2 of the capacitor C2 and the current value I2 of the current I2. (C1), (C) of 2 (C)
The waveform becomes as shown in 2). The time constant T at this time
2 is set to a considerably slow time constant such that the lower level value of the RF signal is DC. Also, at this time, in order to stabilize the mirror output when the rotation speed is variable, the time constant of the low-speed bottom detection is set to change at the same rate as the time constant of the high-speed bottom detection. The time constant T2 is expressed by the following equation. T2 = C2 · V / I2 (1-2)

Next, the outputs S1 and S2 of the bottom detection circuits 1 and 2 are input to the variable gain amplifier type subtractor 3, respectively. The voltage gain of the variable gain amplifier type subtractor 3 is switched by a DVD / CD control circuit 21.
In the present embodiment, the DVD / CD control circuit 21 has a voltage of 12 [dB] in the DVD mode and 3.5 [dB] in the CD mode based on the standard OFF track level / ON track level of the DVD and CD. The resistance 11, the resistance 12, and the resistance 1 in the variable gain amplifier type subtracter 3 so that the gain becomes G.
3. The value of the resistor 14 is set. Here, assuming that the resistance of the resistor 11 is R1, the resistance of the resistor 12 is R2, the resistance of the resistor 13 is R3, and the resistance of the resistor 14 is R4, the voltage gain G1 from the signal of the output S1 at this time is: , The voltage gain G2 from the signal at the output S2 is expressed by the following equation. G1 = 20 log [{(R1 / (R1 + R2)} × {(R3 + R4) / R3}] (2-1) G2 = 20 log (R4 / R3) (2-2)

In the variable gain amplifier type subtractor 3, the output S1 and the output S2 are 12 [d
B], the signal amplified by 3.5 [dB] at the time of CD is subtracted. That is, the output S3 of the variable gain amplifier type subtracter 3 outputs a waveform in which a signal obtained by subtracting the output S2 from the output S1 to the DC1 voltage and multiplying the gain is output. By this operation, the output S3 of the variable gain amplifier type subtractor 3 is output.
As shown in (D1) and (D2) of FIG. 2 (D), a disc having a standard track pitch has a CD-ROM and a DVD.
Both have the same output amplitude. And this output S
3 is input to the maximum value / minimum value detection circuit 22 in the digital signal processing circuit 20, and the maximum value (peak value) and the minimum value (bottom value) of the detected amplitude are detected. Then, the detected maximum value and minimum value are input to the arithmetic unit 23, and the output S3
, An output S4 having a value of 50% in this case. The output S3 is compared with the output S4 as a comparison point of the comparator 4. As a result, (E1) and (E1) in FIG.
As shown in 2), “L”, O
“H” is output during the FF track.

As described above, even when the level of the mirror signal in the DVD RF signal is low, the difference between the peak value and the bottom value obtained from the mirror signal is expanded to the same level as the CD mirror signal, and the obtained difference is also increased. Since the mirror signal is compared based on the intermediate level between the maximum value and the minimum value of the signal, a stable mirror detection can be performed on DVDs as well as on CDs. In particular, even DVDs may be turned off due to variations in track pitch between individual disks.
Even when the track level / ON track level varies and becomes about 90% in the worst case, the signal is compared at the intermediate potential of the amplitude, so that the DUTY can perform a stable signal detection of 50%.

FIG. 3 is a block circuit diagram according to a second embodiment of the present invention. In the second embodiment of the present invention, the DVD / CD control circuit 21 in the first embodiment shown in FIG. 1 is replaced with a gain control circuit 24, and a maximum value / minimum value detection circuit is used as gain control means. It is characterized in that 22 detection outputs are used. As described above, even between DVDs, the track pitch varies among individual disks, and the OFF track level / ON track level is not constant. In this case, if the gain of the variable gain amplifier type subtractor 3 is constant, the amplitude may not be sufficiently enlarged, which may cause a problem in performing the above-described stable mirror detection. Therefore, in the second embodiment,
The output of the maximum / minimum value detection circuit 22 obtained by inputting the output S3 of the variable gain amplifier type subtractor 3 is input to the gain control circuit 24. As a result, the control signal of the gain control circuit 24 is determined based on the amplitude obtained from the maximum / minimum value detection circuit 22 so that the amplitude of the output S3 is constant. It is configured to determine the value of each of the resistors 11, 12, 13, and 14 in the vessel 3.

In the second embodiment, a CD-ROM,
Output S3 of variable gain amplifier type subtractor 3 in DVD
Is controlled so that the output amplitude becomes constant at a preset voltage value X [Vp-p] as shown in (D1) and (D2) of FIG. Using this signal, the first
Compared by the same means as in the embodiment, a stable mirror detection signal is output to the output S5 . Therefore,
In the second embodiment, the variable gain is set between DVD and CD.
Instead of performing the switching, the gain is changed according to the amplitude of the mirror signal. That is, since the pitch between the tracks on the optical disc is variable, the mirror detection can always be performed stably regardless of the type of the optical disc. Further, in the second embodiment, since the output amplitude voltage of the output S3 is constant at X [Vp-p] regardless of the type of the optical disk or the individual optical disk, an intermediate value between the maximum value and the minimum value is obtained. Is omitted and the comparator point of the comparator is set to D
Even if a fixed value of C1 + X [Vp-p] / 2 is set, there is no problem and the circuit configuration can be simplified.

Here, in the above-described embodiment, a configuration example in which the resistance value is varied is shown as the variable gain means in the variable gain amplifier type subtractor, but there is no problem with other means. Further, the present invention is not limited to the configuration of each of the above embodiments, and within the scope of the technical idea of the present invention,
Obviously, each embodiment can be appropriately changed.

[0023]

As described in the foregoing, according to the present invention, the high-speed bottom detection of the RF signal the light spot generated when traversing along the optical disk comprising a CD or DVD, pull the slow bottom detection signal Then, only the mirror signal is taken out, the gain variable amplifier is controlled so that the amplitude of this signal becomes constant, and the mirror signal is compared with DC of 振幅 of this amplitude as a comparison point, The comparison point can be set to an appropriate level for any optical disk, DVD or CD, or for an optical disk having a variation in track pitch, and there is an effect that stable mirror detection can be realized.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram according to a first embodiment of the present invention.

FIG. 2 is a diagram showing output waveforms of various parts of the circuit of FIG.

FIG. 3 is a block circuit diagram according to a second embodiment of the present invention.

FIG. 4 is a block circuit diagram of a conventional mirror detection circuit.

FIG. 5 is a diagram showing output waveforms of various parts of the circuit of FIG. 4;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 high-speed bottom detection circuit 2 low-speed bottom detection circuit 3 variable gain amplifier subtractor 4 comparator 11 to 14 resistor 20 digital signal processing circuit 21 DVD / CD control circuit 22 maximum / minimum value detection circuit 23 arithmetic unit 24 gain control circuit SRF RF signal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/085 G11B 21/08

Claims (7)

(57) [Claims] 1. A mirror portion of an optical disk is detected from an RF signal obtained when an optical spot crosses an optical disk formed of a compact disk (hereinafter, referred to as a CD) or a digital versatile disk (hereinafter, referred to as a DVD). Obtaining a signal obtained by performing high-speed bottom detection on the RF signal; obtaining a signal obtained by performing low-speed bottom detection on the RF signal; and subtracting both the bottom-detected signals; Gain controlling the signal obtained by the subtraction to a constant amplitude; obtaining an intermediate value level of the amplitude of the gain-controlled signal; and performing the gain control using the intermediate value level as a comparison point. And comparing a signal. 2. The intermediate value as the compare point is:
2. The mirror detection method according to claim 1, wherein the level of the signal is 1/2 of the amplitude of the gain-controlled signal. 3. A mirror detection circuit for detecting a mirror portion of the optical disc from an RF signal obtained when the light spot traverses an optical disc composed of a CD or a DVD. and fast bottom detection circuit for bottom detection at high speed, and slow bottom detection circuit for bottom detection of the RF signal to the low speed, and subtracting the signal bottom detection to the bottom detection signal and slow the speed and predetermined amplitude A variable gain amplifier type subtractor that controls gain, a signal processing unit that detects an intermediate value level of the amplitude from the amplitude of the output of the variable gain amplifier type subtractor, and the intermediate output from the signal processing unit. A comparator that outputs a mirror detection signal by comparing the output of the variable gain amplifier type subtractor with the signal of the value level as a comparison point. Mirror detection circuit for the butterflies. 4. A signal processing unit comprising: a maximum value for detecting a maximum value and a minimum value of an output of the variable gain amplifier type subtractor;
The mirror detection circuit according to claim 3, further comprising: a minimum value detector; and a calculation unit that detects a level intermediate between the detected maximum value and the minimum value. 5. The arithmetic unit according to claim 1, wherein the maximum value and the minimum value are 1 / min.
The mirror detection circuit according to claim 4, wherein two levels are detected. 6. The signal processing unit includes a DVD / CD control circuit that variably controls a gain of the variable gain amplifier type subtractor according to a DVD or CD optical disc. A mirror detection circuit according to claim 3. 7. The gain control unit variably controls a gain of the variable gain amplifier type subtractor according to each of a maximum value and a minimum value detected by the maximum value / minimum value detector. 6. A circuit according to claim 4, further comprising a circuit.
3. The mirror detection circuit according to 1.