JPH09161285A - Tracking error detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tracking error detecting device with high detection precision. SOLUTION: A light receiving means 1 light receives reflected light of a light spot formed on an information track of a recording medium by irradiating irradiation light by photodetectors A-D, and outputs currents according to the light receiving amount of the photodetector A-D. Current/voltage conversion means 2A-2D convert the current outputs of the light receiving means 1 to voltage signals. Signal detection means 3a, 3b generate two detection signals varying according to information recorded on the recording medium and varying their phases each other according to the tracking error of the light spot from the voltage signals from the current/voltage conversion means 2A-2D. High band emphasis means 4a, 4b increase respective high frequency components of the two detection signals to supply them to waveform shaping means 5a, 5b. The waveform shaping means 5a, 5b waveform shape respectively two detection signals from the high band emphasis means 4a, 4b to generate two digital detection signals. Phase comparison means 6, 7 generate the tracking error signal based on the phase difference component of the two digital detection signals to output it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus for reproducing information recorded by phase pits on a recording medium such as an optical disk, for example, and detects a tracking error signal for tracking control performed during reproduction processing. And a tracking error detecting device.

[0002]

2. Description of the Related Art In recent years, an optical information reproducing apparatus for optically reading information from an optical disk such as a compact disk or a video disk has been widely used. In the above optical disk, information is recorded on a fine track by phase pits, and precise tracking control is necessary to accurately reproduce the information from this track. Also, in order to perform precise tracking control, it is necessary to detect a tracking error.
Usually, it is performed using optical means.

Therefore, the optical information reproducing apparatus shown in FIG.
The tracking error detection circuit 200 as shown in FIG. The tracking error detection circuit 200 uses, for example, a phase difference detection method.

The tracking error detection circuit 200 will be described below.

First, a light beam reflected from an optical disk (not shown) is made incident near the center of the four-division photodetector 201. Thus, from the four light receiving elements A, B, C, D of the four-division photo detector 201, a current according to the amount of light received by the light receiving elements is converted into a current-voltage converter 202.
It is output to each of A, 202B, 202C and 202D. Then, the current-voltage converters 202A, 202B, 2
The output currents from the light receiving elements A, B, C, and D are converted into voltage signals by the 02C and 202D, respectively.

Next, the adder 203a receives the voltage signal obtained by the current-voltage converter 202A and the current-voltage converter 202.
The voltage signal obtained at C is added. Also, the adder 20
3b adds the voltage signal obtained by the current-voltage converter 202B and the voltage signal obtained by the current-voltage converter 202D.

The addition signal (hereinafter referred to as A + C signal) obtained by the adder 203a is binarized by the binarizer 204a, and the binarized A + C signal is converted into a digital detection signal (A + C). It is supplied to the phase comparator 205. In addition, the addition signal obtained by the adder 203b (hereinafter,
This is called the B + D signal. ) Is also binarized by the binarizer 204b, and the binarized B + D signal is supplied to the phase comparator 205 as a digital detection signal (B + D).

Next, the phase comparator 205 includes a binarizer 20.
From the digital detection signal (A + C) from 4a and the digital detection signal (B + D) from the binarizer 204b,
The lead phase difference and the lag phase difference are detected, and the lead phase difference pulse and the lag phase difference pulse are respectively generated. And
The phase comparator 205 separately supplies the generated two pulses to the output processing circuit 206.

The output processing circuit 206 includes a phase comparator 205.
A tracking error signal is generated and output from the two pulses supplied separately from.

[0010]

By the way, the spatial frequency characteristic of the optical system for an optical disk is such as shown in FIG. 14, and as shown in FIG. 14, the shorter the pit, the lower the level of the reproduction signal. .

In the following description, the cut-off spatial frequency of the optical system is [νcutoff], the pit length corresponding to the cut-off spatial frequency of the optical system is [Lcutoff], the channel clock period is [T], and the channel clock is n times as large. A pit length having a period length is indicated by [L _nT ].

Therefore, for an optical disc having a short pit in which the pit length is close to [Lcutoff], the amplitude of the reproduction signal (hereinafter, referred to as reproduction amplitude) is small.
When the reproduction process is performed using the optical information reproducing device including the tracking error detection circuit 200 as described above,
According to the spatial frequency characteristics shown in FIG. 14, the pit asymmetry, that is, the fluctuation of the center level due to the pit asymmetry, the focus shift, the level reduction of the reproduction signal due to the inclination of the optical disc from the optical pickup optical axis, and the tracking error detection. The binarizer 204a of the circuit 200,
The change in the threshold value due to the change in the offset voltage of 204b has occurred. For this reason, the tracking error detection circuit 200 may not be able to accurately perform the binarization processing of the short pits. As a result, the tracking error signal obtained by the tracking error detection circuit 200 may have a reduced amplitude, increased noise, and It sometimes caused waveform distortion.

More specifically, for example, the spatial frequency characteristic of an optical system for a compact disk (hereinafter referred to as a CD: compact disk) is [νcutoff] to about 115.
0 / mm, which is the pit length [Lcutof
f] to 0.43 μm.

On the other hand, the CD has an EFM (Eight to Forte)
A signal digitized by the en modulation method is recorded in pits having a length of [3T] to [11T]. Therefore, of the pits recorded on the CD, the pit having a length of [3T] is the shortest pit, but according to the CD standard, [L _3T ] = 0.83 μm, and the spatial frequency characteristic is [L _3T ] −2 × [Lcutoff].

Here, in the reproduction signal obtained from the above CD, FIG. 15 shows an eye pattern in the case where the CD does not have pit asymmetry, and FIG. 16 shows the pit in the CD. It shows an eye pattern in the case of having asymmetry.

As shown in FIGS. 15 and 16 above,
The reproduction amplitude I _3T of the shortest pit is relatively large, [11
The reproduction amplitude of a pit having a length of [T] is about 70% of I _11T . Therefore, in such a case, the binarization process can be performed even for a CD having pit asymmetry.

However, the pit length of the shortest pit is [Lcu
toff], for example, when the spatial frequency characteristic is [L _3T ] to 1.5 × [Lcutoff],
As shown in FIG. 17, the reproduction amplitude I _3T of the shortest pit is
The amplitude I _11T of a pit having a length of [11T] is reduced to about 20%. Therefore, for a pit having a length close to the pit length corresponding to the cut-off spatial frequency of the optical system, there are cases in which the binarization processing cannot be performed due to the factors such as the pit asymmetry described above. It was

On the other hand, in order to solve the above-mentioned problems, for example, a device for increasing the amplitude of the input signal to the binarizer may be considered. The reproduction amplitude is also increased, and the reproduction amplitude of the long pit becomes very large. Therefore, a high power supply voltage is required, which leads to an increase in power consumption of the device.

Therefore, the present invention has been made in view of the conventional circumstances as described above, and has the following objects.

That is, an object of the present invention is to provide a tracking error detecting device having high detection accuracy.

Another object of the present invention is to provide a tracking error detecting device capable of improving the stability and control accuracy of tracking control.

[0022]

In order to solve the above problems, a tracking error detecting apparatus according to the present invention detects reflected light of a light spot formed by projecting irradiation light onto an information track of a recording medium. The light-receiving device receives light and outputs a current according to the amount of light received by the light-receiving device, the current-voltage converting device converts the current output of the light-receiving device into a voltage signal, and the current-voltage converting device. A signal detection unit that generates two detection signals that change from the voltage signal according to the information recorded on the recording medium and that change their phases according to the tracking error of the light spot, and the signal detection unit. A waveform shaping means for shaping each of the two generated detection signals to generate two digital detection signals; and two digital detection means generated by the waveform shaping means. And a phase comparing means for generating and outputting a tracking error signal based on the phase difference component of the signal. Further, it is characterized in that a high-frequency emphasizing means for generating two detection signals in which each high-frequency component is increased is provided before the waveform shaping means.

Further, the tracking error detecting device according to the present invention is characterized in that the high-frequency emphasis means is constituted by the current-voltage conversion means having high-frequency emphasis characteristics.

Further, the tracking error detecting apparatus according to the present invention is characterized in that the high frequency enhancing means is constituted by the signal detecting means having a high frequency enhancing characteristic.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The tracking error detecting device according to the present invention is applied to, for example, a tracking error detecting circuit 100 shown in FIG. 1 provided in an optical information reproducing device for reproducing information recorded on an optical disc.

The tracking error detection circuit 100 is
A phase-difference detecting method described later is used, and the four-division photodetector 1 including four light receiving elements A, B, C, and D and the respective outputs of the four light receiving elements A, B, C, and D are supplied. Four current-voltage converters 2A, 2B, 2C, 2D
And an adder 3a to which the output of the current-voltage converter 2A and the output of the current-voltage converter 2C are supplied, and an adder 3 to which the output of the current-voltage converter 2B and the output of the current-voltage converter 2D are supplied.
b and the high frequency emphasizing circuit 4a to which the output of the adder 3a is supplied.
And a high frequency emphasizing circuit 4b to which the output of the adder 3b is supplied.
And a binarizer 5a to which the output of the high-frequency emphasis circuit 4a is supplied.
And the binarizer 5b to which the output of the high-frequency emphasis circuit 4b is supplied.
And a phase comparator 6 to which the output of the binarizer 5a and the output of the binarizer 5b are supplied, and an output processing circuit 7 to which the output of the phase comparator 6 is supplied and which outputs a tracking error signal. There is.

First, for example, a light beam from an optical head 8 as shown in FIG. 2 enters the four-division photodetector 1.

That is, in the optical head 8 shown in FIG. 2, first, the divergent light emitted from the semiconductor laser 81 is reflected by the half mirror 82 and enters the collimator lens 83.

The collimator lens 83 converts incident light which is divergent light into parallel light and emits it. Collimator lens 8
The parallel light emitted from 3 is condensed on the optical disc 9 by the objective lens 84. At this time, a focusing control circuit (not shown) performs focus servo so that the diameter of the spot focused on the optical disc 9 is always minimized.

The light reflected from the optical disk 9 is
Again, it becomes convergent light through the objective lens 84 and the collimator lens 83, passes through the plane-parallel plate 85 for focus error detection by the astigmatism method, and then passes through the lens 86 for correction of difference as a light beam into four-part photodetector. Incident on 1.

The light beam emitted from the optical head 8 as described above is made incident on the vicinity C of the center of the four-divided photodetector 1 as shown in FIG.

Next, the above-mentioned phase difference detection method means that the detection light such as the reflected light from the optical disk 9 shown in FIG. This is a method of detecting a tracking error by using the phase difference between electric signals. In the tracking error detection circuit 100 using such a phase difference detection method, the phases of the electric signals corresponding to the respective light receiving amounts of the light receiving elements A, B, C, D of the four-division photodetector 1 are P _A , P _B , P. _C, when the P _D, the phase difference TE of the two electrical signals described above _{TE = (P a + P C} ) - are adapted to determine on the basis of (P _B + P _D) becomes equation.

That is, first, the light receiving element A receives the incident light from the optical head 8 and supplies the current corresponding to the received light amount to the current-voltage converter 2A. Similarly to the light-receiving element A, the other three light-receiving elements B, C and D respectively receive the incident light from the optical head 8 and output currents corresponding to the received light amounts to the current-voltage converters 2B and 2C. , 2D respectively.

Next, the current-voltage converter 2A includes the light receiving element A.
The current from is converted into a voltage signal, and the voltage signal is supplied to the adder 3a. In addition, the current-voltage converters 2B, 2C, 2
Similarly to the current-voltage converter 2A, D also converts the currents from the light receiving elements B, C, D into voltage signals and supplies the voltage signals to the adders 3b, 3c, 3d, respectively.

Therefore, the adder 3a is supplied with the respective voltage signals from the current-voltage converter 2A and the current-voltage converter 2C, and the adder 3b is supplied with the current-voltage converter 2B and the current-voltage converter 2D. Each voltage signal will be supplied.

Then, the adder 3a is connected to the current-voltage converter 2
The voltage signal from A and the voltage signal from the current-voltage converter 2C are added, and the added signal S _a1 is supplied to the high frequency emphasis circuit 4a. Further, the adder 3b adds the voltage signal from the current-voltage converter 2B and the voltage signal from the current-voltage converter 2D, and supplies the addition signal S _a2 to the high frequency emphasizing circuit 4b.

Here, the addition signal S _a1 output from the adder 3a, that is, the voltage signal corresponding to the amount of light received by the light receiving element A and the voltage signal corresponding to the amount of light received by the light receiving element C are obtained. Signal (hereinafter A + C signal S _a1
Say ) Has a waveform as shown in (1) of FIG. 3, for example. Further, a signal obtained by adding the addition signal S _a2 output from the adder 3b, that is, the voltage signal corresponding to the amount of light received by the light receiving element B and the voltage signal corresponding to the amount of light received by the light receiving element D (hereinafter , B + D signal S _a2 ) has a waveform as shown in (2) of FIG. 3, for example. As shown in (1) and (2) of FIG.
The A + C signal S _a1 and the B + D signal S _a2 each have a waveform corresponding to the presence or absence of a pit, and the A + C signal S _a1 and the B + D signal S _a2 are supplied to the high frequency emphasis circuit 5a and the high frequency emphasis circuit 5b, respectively. It

The high frequency emphasizing circuit 4a has, for example, a configuration as shown in FIG. 4 and has characteristics as shown in FIG.

That is, in the high frequency emphasizing circuit 4a, the capacitor 41 having the charge capacity C1, the resistor 42 having the resistance value R2, and the differential amplifier circuit 43 are provided in order between the input terminal I _in and the output terminal I _out. There is. Also, the input terminal I _in
Between the output terminal I _out and the capacitor 41, the resistor 42,
And a resistor 45 and a resistor 46 each having a resistance value R1 in parallel with the differential amplifier circuit 43. Further, the resistor 45 and the resistor 46 are connected, and the resistor 42 and the differential amplifier 43 are connected.

With the above configuration, as shown in FIG. 5, as the frequency of the input signal input from the input terminal I _in becomes higher from 1 / (2π (R1 + R2) C1) to 20 dB / dec. Gain is given, frequency 1 /
At (2πR2C1), the signal output from the output terminal I _out is given a gain represented by R1 / (R1 // R2).

The high frequency emphasizing circuit 4b has the same configuration as the high frequency emphasizing circuit 4a shown in FIG. 4 and has the characteristics shown in FIG. , Its detailed description is omitted. Further, the high frequency emphasizing circuits 4a, 4
A detailed description of the specific effect of b will be given later.

Therefore, A + C obtained by the adder 3a
The high frequency component of the signal S _a1 is increased by the high frequency emphasizing circuit 4 a and is supplied to the binarizer 5 a as an A + C signal S ^d _a1 . Further, B + D signal S _a2 obtained by the adder 3b, the high-frequency component is supplied as is increased B + D signal S ^d _a2 the binarizing unit 5b by the high-frequency emphasis circuit 4b.

The binarizer 5a is supplied with the A + C signal S ^d _a1 from the high frequency emphasizing circuit 4a, the direct current component of which is blocked by, for example, a capacitor (not shown). And
The binarizer 5a uses the A + C signal S ^{d with the} DC component cut off.
_{For a1} , the binarization process centered on the GND level, that is, the average DC level L as shown in (1) of FIG.
_A binarization process centered on ₁ is performed. As a result, the binarizer 5a obtains the digital detection signal S _b1 having the waveform as shown in (3) of FIG.

Further, in the binarizer 5b, similarly to the binarizer 5a, the B + D signal S ^d from the high frequency emphasizing circuit 4b in which the DC component is cut off by a capacitor (not shown ^).
_a2 is supplied. Then, the binarizer 5b is the binarizer 5
In the same manner as a, the B + D signal S ^d with the DC component blocked
_{For a2} , the binarization process centered on the GND level, that is, the average DC level L as shown in (2) of FIG. 3 above.
₂ binary processing with a focus on performing. As a result, the binarizer 5b obtains the digital detection signal S _b2 having the waveform as shown in (4) of FIG.

The digital detection signal S ^d _b1 obtained by the binarizer 5a and the digital detection signal S ^d _b2 obtained by the binarizer 5b as described above are supplied to the phase comparator 6, respectively. To be done.

The phase comparator 6 has a structure as shown in FIG. 6, for example, and has a digital detection signal S ^d _b1 from the binarizer 5a and a digital signal S ^d _b2 from the binarizer 204b. From this, a pulse with a lead phase difference and a pulse with a lag phase difference are generated, and the two generated pulses are output separately.

Each pulse generated by the phase comparator 6 will be specifically described below with reference to (3) to (6) in FIG. 3 and FIG.

Incidentally, (5) and (6) of FIG. 3 show waveforms of the pulse generated by the phase comparator 6, and in (3) to (6) of FIG. The state part and the state inversion part of the signal are denoted by b1-X, b2-X, and C, respectively.
1-X and C2-X.

First, in the phase comparator 6, the output signal A of the NAND gate 600 has the state parts b1-1 and b2.
As shown in -1, a digital detection signal S ^d _b1 from the binarizing unit 5a, when the digital detection signal from the binarizing unit 5b S ^d _b2 are both "1" only becomes "0". Also,
The output signal B of the OR gate 601, as shown in state portion b1-2 and b2-2, if the digital detection signal S ^d _b1 and digital detection signal S ^d _b2 are both "0" only "0". Further, as will be described later, the output signal of the NAND gate 612 normally becomes “0” only when both the digital detection signal S ^d _b1 and the digital detection signal S ^d _b2 are equal. Therefore, the output signal A of the NAND gate 600,
Alternatively, when the output signal B of the OR gate 601 is “0”,
The flip-flop 604 is set or reset and outputs the signal C.

That is, when both the digital detection signal S ^d _b1 and the digital detection signal S ^d _b2 are "1", the flip-flop 604 is set and outputs the signal C of "1", and the digital detection signal S _{When both b1} and the digital detection signal S _b2 are “0”, the flip-flop 604
Is reset and outputs a signal C of "0".

Therefore, for example, the digital detection signal S ^d
_{When both b1} and the digital detection signal S ^d _b2 are “1”, the flip-flop 604 is set and outputs the signal C of “1”. Therefore, the output signal D of the NAND gate 606 and the output of the NAND gate 608 are output. The signals F are both "0". Further, in this case, the output signal E of the OR gate 607 and the output signal G of the OR gate 609 are both “1”.

Therefore, as shown in the state portion C1-1, the digital detection signal S ^d _b1 and the digital detection signal S ^d
_When both _b2 are "1", the signal H, that is, the pulse S _C1 output from the output terminal I _{1 is} output as "0".
Further, as shown in the state portion C2-1, the signal I, that is, the pulse S _C2 output from the output terminal I ₂ is also output as “0”.

Next, when the digital detection signal S ^d _b1 or the digital detection signal S ^d _b2 becomes "0", for example, as shown in the state inversion part b1-3, the digital detection signal S ^d _b1
^{When d} _b1 becomes “0”, the pulse S _C1 becomes “1” as shown in the state inversion portion C1-2. At this time, the pulse S _C2
Is “0”.

As shown in the state inversion part b2-3, when the digital detection signal S ^d _b2 becomes "0" and both the digital detection signal S ^d _b1 and the digital detection signal S ^d _b2 become "0". As shown in the state inversion portion C1-3,
The pulse S _C1 becomes “0”. At this time, the pulse S _C2 is
It is "0".

When the digital detection signal S ^d _b1 and the digital detection signal S ^d _b2 both become "0", that is, when the digital detection signal S ^d _b1 and the digital detection signal S ^d _b2 both become the same state, , NAND gate 6
The output of 12 becomes "0", and the output signal B of the OR gate 601 also becomes "0". Therefore, the flip-flop 6
04 is reset. As a result, both the output signal D of the NAND gate 606 and the output signal F of the NAND gate 608 become "1". Also, the OR gate 607
And the output signal G of the OR gate 609 is
Both are “0”.

After that, when the digital detection signal S ^d _b1 or the digital detection signal S ^d _b2 becomes “1”, the pulse S _C1 or the pulse S _C2 becomes “1”, and the digital detection signal S ^d
_{When both b1} and the digital detection signal S ^d _b2 become “1”,
Both the pulse S _{C1 and the} pulse S _C2 become “0”, and the state returns to the initial state.

As described above, when only the state of the digital detection signal S _b1 supplied to the phase comparator 6 is inverted, the phase comparator 6 outputs the pulse S _C1 at "1",
When both the digital detection signal S ^d _b1 and the digital detection signal S ^d _b2 are in the same state, the pulse S _C1 becomes “0”. In addition, the digital detection signal S ^d _b supplied to the phase comparator 6
_When only the state of ₂ is inverted, the pulse S _C2 is output as “1” from the phase comparator 6, and the digital detection signal S ^d is output.
_{When both b1} and the digital detection signal S ^d _b2 are in the same state, the pulse S _C2 becomes “0”.

Then, "1" of the pulse S _C1 and the pulse S _C2
The difference in the length of time indicates the phase difference.

The pulse S _C1 and the pulse S _C2 obtained by the phase comparator 6 as described above are separately supplied to the output processing circuit 7.

Although not shown, the output processing circuit 7 comprises a low pass filter and a differential amplifier circuit. In the output processing circuit 7, the pulse S _C1 and the pulse S _C2 from the phase comparator 6 are supplied to the differential amplifier circuit via the low pass filter. Then, the differential amplifier circuit takes the difference between the pulse S _C1 and the pulse S _C2 that have passed through the low-pass filter, and generates a tracking error signal based on the difference. Therefore, the output processing circuit 7 outputs the tracking error signal S _d as shown in (7) of FIG.

As described above, in the tracking error detection circuit 100, the high-frequency emphasizing circuits 4a and 4b are provided in front of the binarizers 5a and 5b, and the high-frequency emphasizing circuit 4a is included in the binarizers 5a and 5b. , 4b are supplied.

The effect of providing the high frequency emphasizing circuits 4a and 4b will be specifically described below.

For example, it is assumed that the optical disc 9 shown in FIG. 2 has pit information of [3T] to [11T] length recorded by the EFM modulation method. The spatial frequency characteristic is [L _3T ] to 1.5 × [Lcutof
f] and [3T] length pits (hereinafter referred to as 3T pits) have a reproduction signal frequency of about 4.5 MH.
The reproduction signal frequency at the time of repeating z and [11T] pits (hereinafter referred to as 11T pits) is about 1.2 MH.
z. Further, the high frequency emphasizing circuits 4a and 4b are set to 1 MHz.
It gives a gain of about + 3db at z and about + 12db at 4MHz.
Shall be given.

First, under the conditions as described above, a reproduction signal having the eye pattern as shown in FIG. 17 is obtained from the optical disc 9. Further, the tracking error signal as shown in FIG. 7 is obtained from the optical disc 9 having the eye pattern shown in FIG. 17 by the tracking error detection circuit 100. This tracking error signal is obtained when the focus servo is applied to cross the track of the optical disc 9.

Next, for example, when the optical disk 9 is a disk having pit asymmetry, this optical disk 9
As shown in FIG. 8, a reproduction signal having an eye pattern in which the center level L _3T of the amplitude of the 3T pit greatly deviates from the center level L _11T of the amplitude of the 11T pit is obtained.

Therefore, when the tracking error signal is detected from the optical disk 9 having the pit asymmetry as described above, the difference between the tracking error signals depending on the presence or absence of the high frequency emphasizing circuits 4a and 4b is as follows.

FIG. 9 shows a tracking error detection circuit 100.
13 is a diagram showing a tracking error signal obtained when the high frequency emphasizing circuits 4a and 4b are omitted, that is, a tracking error signal obtained when the conventional tracking error detecting circuit 200 shown in FIG. 13 is used. is there. In addition, in this case, (a) and (b) of FIG.
It is the figure which showed the waveform of the signal input into a binarizer, and the waveform of the signal output from a binarizer.

The tracking error signal shown in FIG. 9 has lower amplitude, increased noise, and waveform distortion than the tracking error signal shown in FIG. Further, as shown in (a) of FIG. 10, the signal inputted to the binarizer has a portion E _r1 that cannot cross the threshold T because the reproduction amplitude of the short pit is deviated from the center. ~ E _r4
Has occurred. Therefore, as shown in FIG. 10B, the portions E _{r1 to} E that cannot cross the threshold T.
_r4 is output without being binarized.

On the other hand, FIG. 11 shows high frequency emphasizing circuits 4a and 4b.
FIG. 7 is a diagram showing a tracking error signal obtained when the tracking error detection circuit 100 including the above is used. 12A and 12B are waveforms of signals input to the binarizers 5a and 5b and the binarizer 5 in this case.
It is the figure which showed the waveform of the signal output from a and 5b.

The tracking error signal shown in FIG. 11 has lower amplitude, increased noise, and waveform distortion than the tracking error signal shown in FIG. 7, but the tracking error signal shown in FIG. Therefore, the amplitude reduction, the noise increase, and the waveform distortion are significantly improved. In addition, as shown in FIG. 12A, the high frequency emphasizing circuits 4a and 4b.
As a result, the reproduction amplitude of the short pit is increased. Therefore, as shown in (b) of FIG. 12, even if the reproduction amplitude of the short pit is deviated from the center, the threshold T can be crossed and the binarization can be surely performed.

As described above, by providing the high frequency emphasizing circuits 4a and 4b in front of the binarizers 5a and 5b, the reproduction amplitude of the short pit is increased, so that the binarization process and the phase comparison process are performed. Can be done accurately. Therefore, it is possible to reduce the amplitude reduction, noise increase, and waveform distortion of the tracking error signal obtained from the optical disc having the pit asymmetry.

Further, the amplitude of the tracking error signal is reduced due to the variation in the offset voltage of the binarizers 5a and 5b, the focus shift, and the reduction in the level of the reproduction signal caused by the inclination of the optical disc from the optical pickup optical axis.
Noise increase and waveform distortion can be reduced.

Therefore, the tracking error detection circuit 1
00 can obtain a good tracking error signal. Then, by using the tracking error signal obtained by the tracking error detection circuit 100, stable and highly accurate tracking control can be performed.

The tracking error detection circuit 1 described above is used.
In 00, the high frequency emphasizing circuit 4 is provided before the binarizers 5a and 5b.
The high-frequency emphasizing circuits 4a, 4b
The current-voltage converters 2 </ b> A to 2 </ b> D may each be provided with high-frequency emphasis characteristics without providing b. Alternatively, instead of the current-voltage converters 2A to 2D, the adders 3a and 3b may have high-frequency emphasis characteristics.

[0076]

In the tracking error detecting device according to the present invention, the light receiving means receives the reflected light of the light spot formed by projecting the irradiation light on the information track of the recording medium by the light receiving element, and the light receiving element The current is output according to the amount of received light. The current-voltage converting means converts the current output of the light receiving means into a voltage signal. The signal detection means changes from the voltage signal obtained by the current-voltage conversion means according to the information recorded on the recording medium, and the two detection signals whose phases change according to the tracking error of the light spot. To generate. The waveform shaping means shapes the waveforms of the two detection signals generated by the signal detecting means, and outputs 2
Generate two digital detection signals. At this time, the high frequency emphasizing means provided in front of the waveform shaping means generates two detection signals in which each high frequency component is increased and supplies the two detection signals to the waveform shaping means. The phase comparison means generates and outputs a tracking error signal based on the phase difference component of the two digital detection signals generated by the waveform shaping means. As a result, the two detection signals supplied to the waveform shaping means have high frequency components increased, and therefore the waveform shaping means can accurately perform the binarization process. Further, since the two digital detection signals obtained by the accurate binarization processing are supplied to the phase comparison means, the phase comparison means can accurately perform the phase comparison processing, and the tracking with good quality can be performed. An error signal can be generated. Therefore, it is possible to improve the detection accuracy of the tracking error detection device. Further, by using a high quality tracking error signal obtained by this tracking error detection circuit, stable and highly accurate tracking control can be performed.

Further, in the tracking error detecting device according to the present invention, the high frequency emphasizing means is composed of the current-voltage converting means having the high frequency emphasizing characteristic. This allows
The voltage signal in which each high frequency component is increased is supplied to the signal detection unit, and the signal detection unit can generate two detection signals in which each high frequency component is increased. Further, the waveform shaping means can accurately perform the binarization process. Further, the phase comparison means can accurately perform the phase comparison process and can generate a good quality tracking error signal. Therefore, it is possible to improve the detection accuracy of the tracking error detection device.

Further, in the tracking error detecting apparatus according to the present invention, the high frequency emphasizing means is composed of the signal detecting means having the high frequency emphasizing characteristic. As a result, the two detection signals supplied to the waveform shaping means have high frequency components increased, and therefore the waveform shaping means can accurately perform the binarization process. Further, the phase comparison means can accurately perform the phase comparison process and can generate a good quality tracking error signal. Therefore, it is possible to improve the detection accuracy of the tracking error detection device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a tracking error detection circuit to which a tracking error detection device according to the present invention is applied.

FIG. 2 is a block diagram showing a configuration of an optical head.

FIG. 3 is a waveform diagram for explaining each output signal of each component of the tracking error detection circuit.

FIG. 4 is a circuit diagram showing a configuration of a high frequency emphasis circuit of the tracking error detection circuit.

FIG. 5 is a diagram for explaining the characteristics of the high-frequency emphasis circuit.

FIG. 6 is a circuit diagram showing a configuration of a phase comparator of the tracking error detection circuit.

7 is a diagram for explaining a tracking error signal obtained from an optical disc having the eye pattern of FIG. 17 below.

FIG. 8 is a diagram for explaining an eye pattern of a reproduction signal obtained from an optical disc having pit asymmetry.

FIG. 9 is a diagram for explaining a tracking error signal obtained when the high-frequency emphasis circuit is not provided.

FIG. 10 is a waveform diagram for explaining input / output signals in the binarizer in the case where the high-frequency emphasis circuit is not provided.

FIG. 11 is a diagram for explaining a tracking error signal obtained when the high-frequency emphasis circuit is provided.

FIG. 12 is a waveform diagram for explaining input / output signals in the binarizer in the case where the high frequency emphasizing circuit is provided.

FIG. 13 is a block diagram showing a configuration of a conventional tracking error detection circuit.

FIG. 14 is a diagram for explaining a spatial frequency characteristic of an optical system for an optical disc.

FIG. 15 is a diagram for explaining an eye pattern of a reproduction signal obtained from an optical disc having no pit asymmetry.

FIG. 16 is a diagram for explaining an eye pattern of a reproduction signal obtained from an optical disc having pit asymmetry.

FIG. 17 is a diagram for explaining the reproduction amplitude of the shortest pit when the pit length of the shortest pit is closest to the pit length corresponding to the cutoff spatial frequency of the optical system.

[Explanation of symbols]

 1 4-division photodetector 2A-2D Current-voltage converter 3a, 3b Adder 4a, 4b High-frequency emphasis circuit 5a, 5b Binarizer 6 Phase comparator 7 Output processing circuit 100 Tracking error detection circuit

Claims (3)

[Claims] 1. A light receiving means for receiving reflected light of a light spot formed by projecting irradiation light onto an information track of a recording medium by a light receiving element and outputting a current according to the amount of light received by the light receiving element. A current-voltage converting means for converting the current output of the light-receiving means into a voltage signal, and the tracking of the light spot, which changes according to the information recorded on the recording medium from the voltage signal obtained by the current-voltage converting means. A signal detection means for generating two detection signals whose phases change depending on an error, and a waveform shaping means for shaping the two detection signals generated by the signal detection means to generate two digital detection signals. And a phase comparison means for generating and outputting a tracking error signal based on the phase difference component of the two digital detection signals generated by the waveform shaping means. For example, a tracking error detecting apparatus characterized by comprising a high band emphasis means for generating two detection signals which each high-frequency component is increased prior to said waveform shaping means. 2. The tracking error detecting device according to claim 1, wherein the high-frequency emphasis unit is constituted by the current-voltage conversion unit having a high-frequency emphasis characteristic. 3. The tracking error detection device according to claim 1, wherein the high-frequency emphasis unit is constituted by the signal detection unit having a high-frequency emphasis characteristic.