JPH07296395A - Tracking signal detecting method for information reproducing apparatus - Google Patents

Abstract

PURPOSE:To reduce man-hour required for adjustment of an analog multiplier or the like by binarizing the signal from a quartering sensor, processing the binarized signal at logic level, and suppressing fluctuation in the level of tracking detection signal, thereby performing the operation logically. CONSTITUTION:A read spot traces the pit row on a disc and the light diffracted by the pit is condensed toward modulation sensors 10A-10D. A 4cH signal detected by the sensor 10 is fed to a level comparator 14 (or an amplifier 12 and a limiter 13) where the signal is binarized. The 4cH signal outputted from the level comparator is fed to phase comparators 16A, 16B where the phase difference is detected. The phase difference is fed to a differential operating circuit 19 which differentiates the phase difference signal to produce a tracking error signal fluctuating between plus and minus levels. The phase comparator 16, e.g. a phase detecting circuit being employed in PLL, pulsates the phase difference to produce a DC voltage through a low-pass filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking signal detecting method for an information reproducing apparatus, and more particularly to a tracking signal detecting method capable of reducing the adjustment man-hour and stabilizing with time by digital processing.

[0002]

2. Description of the Related Art As shown in FIG. 5, there is a tracking detection method using an analog circuit for multiplying a high frequency signal by using an analog multiplier. Also, as shown in FIG.
There is a phase difference detection method in which a diagonal sum signal is converted into a digital signal and the phase difference is detected. In the detection method using the analog multiplication circuit shown in FIG. 5, when the signal level fluctuates, the level of the tracking signal fluctuates due to its squared characteristic, so that the influence of the level fluctuation is too large.

That is, if there is a defect such as a fingerprint on the disc and the intensity of the luminous flux is reduced to 0.7, the level of the tracking signal is 0.7 because the respective level fluctuations are multiplied in the analog multiplication method. × 0.7 =
The gain variation becomes large because it becomes 0.5 and is reduced to half.

[0004]

In order to correct this, 4C which controls the level fluctuation of the 4CH analog signal is used.
The circuit becomes complicated because the H AGC is required. Also,
The fluctuation is problematic even in the unit of ms, just as the fluctuation of 1 ms is a problem when the servo band is 1 kHz. Therefore, the response of the AGC is required to have high speed, and it is difficult to obtain the characteristics.

Further, the analog method requires an initial adjustment for setting the operating point of the multiplier, and in consideration of its variation, adjustment man-hours and changes with time are problems. In the analog system, the RF signal level and the tracking signal are proportionally related to each other, and the reading signal is directly affected by the fluctuation of the MTF, so that the tracking signal level fluctuates in the signal cycle. In the conventional phase difference method, since the signal components are summed, a phase difference corresponding to the depth of the disk is added as a coefficient to the signal amplitude, and there is a condition that a tracking signal is difficult to be output depending on the pit shape of the disk.

This condition will be further described below by modeling a four-divided signal. For example, JP-A-57-19
In 1839, the signal is modeled as follows. S1 = Acos (ωt + φo + 2πδr / p) + Bcos (ωt + φo) +
Ccos (ωt + 2πδr / p) S2 = Acos (ωt + φ0-2πδr / p) + Bcos (ωt + φo) +
Ccos (ωt-2πδr / p) S3 = Acos (ωt-φo + 2πδr / p) + Bcos (ωt-φo) +
Ccos (ωt + 2πδr / p) S4 = Acos (ωt-φo-2πδr / p) + Bcos (ωt-φo) +
Ccos (ωt-2πδr / p)

The analog detection system uses this signal to
The calculation of S1.S4-S2.S3 was performed to detect the tracking signal. However, since each signal contains a phase change due to off-track, a tracking signal can be formed by detecting this. A case of a general phase difference method for CD will be described. FIG. 6 shows a phase difference detection circuit.

On-track and when δr = 0, S1 = Acos (ωt + φo) + Bcos (ωt + φo) + Ccos (ω
t) S2 = Acos (ωt + φo) + Bcos (ωt + φo) + Ccos (ω
t) S3 = Acos (ωt-φo) + Bcos (ωt-φo) + Ccos (ω
t) S4 = Acos (ωt-φo) + Bcos (ωt-φo) + Ccos (ω
t), and the phases are compared by taking the diagonal sum here. S1 + S3 = 2 {(A + B)
cos (φo) + C} cos (ωt) S2 + S4 = 2 {(A + B) cos (φo) + C} cos (ωt), and the diagonal sum signal is in-phase on the reference axis in the on-track state. .

Next, δr changes, and 2πδr / p = + 0.1
Looking at φo, S1 = Acos (ωt + 1.1 φo) + Bcos (ωt + φo) + Cco
s (ωt + 0.1 φo) S2 = Acos (ωt + 0.9 φo) + Bcos (ωt + φo) + Cco
s (ωt-0.1 φo) S3 = Acos (ωt-0.9 φo) + Bcos (ωt-φo) + Cco
s (ωt + 0.1 φo) S4 = Acos (ωt-1.1 φo) + Bcos (ωt-φo) + Cco
s (ωt-0.1 φo)

Therefore, S1 + S3 = 2A cos (φo) ・ cos (ωt + 0.1 φo) + 2B cos (φo) ・ cos (ωt) + 2C cos (ωt + 0.1 φo) phase lead component S2 + S4 = 2A cos (φo) ・ cos (ωt) -1.1 φo) + 2B cos (φo) ・ cos (ωt) + 2C cos (ωt-0.1 φo) Phase lag component.

Next, δr changes, and 2πδr / p = -0.1
Looking at φo, S1 = Acos (ωt + 0.9φo) + Bcos (ωt + φo) + Cco
s (ωt-0.1 φo) S2 = Acos (ωt + 1.1 φo) + Bcos (ωt + φo) + Cco
s (ωt + 0.1 φo) S3 = Acos (ωt-1.1 φo) + Bcos (ωt-φo) + Cco
s (ωt-0.1 φo) S4 = Acos (ωt-0.9 φo) + Bcos (ωt-φo) + Cco
s (ωt +0.1 φo)

Therefore, S1 + S3 = 2A cos (φo) .cos (ωt-0.1 φo) + 2B cos (φo) ・ cos (ωt) + 2C cos (ωt-0.1 φo) phase delay component S2 + S4 = 2A cos (φo) ・ cos (ωt) +1.1 φo) + 2B cos (φo) ・ cos (ωt) + 2C cos (ωt + 0.1 φo).

From the above equation, it can be seen that the phase of the diagonal sum signal is changed and the signals are switched off-track. Therefore,
If this is detected by phase comparison, the tracking signal can be detected. Further, since the phase changes centering on the reference axis and there is no DC component, it can be detected by a normal phase comparator that detects the phase from 0 °.

However, looking at each component, the co
Since s (φo) is multiplied by the amplitude, φo is π / 2,3π
For depths near / 2, there is a drawback that the signal characteristics deteriorate because the level decreases. Further, since the signal pattern changes due to the lens shift, fluctuations occur due to signal crosstalk.

[0015]

SUMMARY OF THE INVENTION In order to improve the above drawbacks, the present invention binarizes a signal of a four-division sensor and processes it at a logic level, thereby changing the level of a signal from a disk, and , The level fluctuation of the tracking detection signal due to the signal pit length (signal cycle) is reduced, and the calculation is logically performed, thereby reducing the adjustment man-hours of the analog multiplier and the like.

FIG. 1 shows the tracking detection method.
Along with this will be described below. First, the signal component is obtained, vectorized, and examined. Unlike the conventional phase difference method, the method of the present invention detects front and rear phase differences. On-track, when δr = 0, S1 = Acos (ωt + φo) + Bcos (ωt + φo) + Ccos (ω
t) S2 = Acos (ωt + φo) + Bcos (ωt + φo) + Ccos (ω
t) S3 = Acos (ωt-φo) + Bcos (ωt-φo) + Ccos (ω
t) S4 = Acos (ωt-φo) + Bcos (ωt-φo) + Ccos (ω
t).

Here, the phases are compared between S1 and S4 and S2 and S3. On-track, S1, which is a combination of the amplitude A and B components with phase lead of φo and the component on the reference axis,
S2 is compared with S4 and S3 in which the components having amplitudes A and B and a phase of .phi.o delay and the components on the reference axis are combined. Therefore, phase difference (S1, S4) = 2 x Θ (composite phase of 2φo and 0) Phase difference (S2, S3) = 2 x Θ (composite phase of 2φo and 0) where Θ is Θ = tan-1 ((A + B) sin φo / ((A + B) cos φ
o + C)) In this way, there is a signal phase difference on-track,
Not an in-phase signal.

Then, off-track, δr changes, and
Looking at πδr / p = + 0.1φo, S1 = Acos (ωt + 1.1φo) + Bcos (ωt + φo) + Cco
s (ωt + 0.1 φo) S2 = Acos (ωt + 0.9 φo) + Bcos (ωt + φo) + Cco
s (ωt-0.1 φo) S3 = Acos (ωt-0.9 φo) + Bcos (ωt-φo) + Cco
s (ωt + 0.1 φo) S4 = Acos (ωt-1.1 φo) + Bcos (ωt-φo) + Cco
It becomes s (ωt-0.1 φo).

Here, when S1 and S4 are compared in phase, the mutual signals change by 0.1 φ in opposite directions. Therefore, from the reference phase, the phase difference (S1, S4) = 2 × θ (2φ o phase The combined phase of the component and the reference phase component) + 2 × ΔΘ Phase difference (S2, S3) = 2 × Θ (The combined phase of the 2φo phase component and the reference phase component) −2 × ΔΘ. This is the opposite phase, changing to a complement.

On the contrary, when offtracking, δr changes and 2πδr / p = -0.1φo, S1 = Acos (ωt + 0.9φo) + Bcos (ωt + φo) + Cco
s (ωt-0.1 φo) S2 = Acos (ωt + 1.1 φo) + Bcos (ωt + φo) + Cco
s (ωt + 0.1 φo) S3 = Acos (ωt-1.1 φo) + Bcos (ωt-φo) + Cco
s (ωt-0.1 φo) S4 = Acos (ωt-0.9 φo) + Bcos (ωt-φo) + Cco
It becomes s (ωt + 0.1 φo).

Here, when S1 and S4 are compared in phase, the mutual signals are changed by 0.1 φo in opposite directions. Therefore, from the reference phase, the phase difference (S1, S4) = 2 × θ (2φo phase The composite phase of the component and the reference phase component) -2 * [Delta] [Theta] phase difference (S2, S3) = 2 * [Theta] (2 [phi] o composite phase of the phase component and the reference phase component) + 2 * [Delta] [theta]. Therefore, it can be seen that if the deviation from the center phase is detected, the deviation from the track center can be detected, and if they are mutually differential, they can be detected at twice the level.

Unlike the conventional phase difference method, the method of the present invention in which the phases are compared at each component level does not include a component whose amplitude changes with depth and can be said to have little depth dependence.
In the phase detection according to the present invention, the central phase is not 0, so its study is necessary. The phase comparison circuit has a wide detection phase range and a narrow detection phase range. The configuration changes depending on which circuit is used. When the phase detection range is linear with approximately one cycle, there is no problem unless the central phase during operation is 180 °.

0 ° used in ordinary PLL circuits and the like
A delay circuit is required before a signal is input to the phase comparison circuit centered on. Further, it is necessary to use a phase shift circuit that makes this phase constant depending on the input frequency.

Up to now, the signal of the four-division sensor has been calculated by using the analog multiplier, but the difference in the case of using the digital system will be described below. The signal to be multiplied is approximated as a sine wave, the amplitude is A and B, and the phase is θ and θ +
Let be α. The signal after multiplication is e = Asin θ × B sin (θ + α) = A × B {-cos (2θ + α) + cosα} / 2 When calculated by the EX-OR circuit, it becomes a PWM waveform in which the pulse width changes depending on the phase difference α , Servo band 30K
When the LPF is used to extract components below Hz, an error signal proportional to α is detected. The signal is expressed as an e-avr average value as follows.

E-avr = C × 2 × α / 360 ° C: Amplitude of pulse When the above is arranged, the graph shown in FIG. 7 is obtained. That is, in the case of the analog method, a signal is formed with both the phase and the amplitude of the waveform. In the digital method, since the pulse amplitude is constant, the calculation result is determined only by the phase difference. In the case of digital, it is a unipolar signal, so it becomes a signal having a bias voltage. In addition, as a result, although the phases are different between analog and digital, they are signals that basically constitute a cycle with a phase difference of 360 °.

[0026]

As described above, according to the present invention, since the front and rear phases of the left and right signals in the track direction are compared with each other, the respective signals are compared with each other as a binary signal from the analog signal by the level comparator, and the direct current component is compared. Phase difference is centered around the phase difference, and the AC phase difference that changes in proportion to the amount of off-track is detected.Using a phase comparator that can linearly detect the phase within approximately one cycle of the signal, the left and right phase detections are performed. The tracking error signal can be detected by differentially calculating the signals.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic structure to which the tracking signal detecting method of the information reproducing apparatus of the present invention is applied will be described with reference to FIG. The reading spot traces the pit train of the disc, and the modulation due to diffraction by the pit is detected by the sensor 10A.
4CH focused on 10D and detected by this sensor 10
Is supplied to the level comparator 14 (or the amplifier 12 and the limiter 13) to be binarized. Since the sensor output is supplied to the level comparator 14 via the capacitors 11A to 11D, only the AC component is supplied, and thus the binarization is performed by the simple average value of each signal.

The 4CH signal output from the level comparator is supplied to the phase comparators 16A and 16B, and the phase difference between them is detected. The phase difference signal is supplied to the differential operation circuit 19, and the differential is taken to be a tracking error signal that changes to + and −. The phase comparator 16 is a phase detection circuit such as that used in a PLL, which makes a phase difference into a pulse and converts it into a DC voltage through a low-pass filter (not shown).

Next, a specific embodiment to which the tracking signal detecting method of the information reproducing apparatus of the present invention is applied will be sequentially described below with reference to FIGS. The reading spot traces the pit row of the disc, and the modulation due to the diffraction by the pit is focused on the sensor 10, and the sensors 10A to 1A
The signal of 4CH detected at 0D, such as a and b shown in FIGS. 3A and 3B, is supplied to the level comparator 1
4A to 14D, for example, binarization is performed as shown as signals c and d in FIGS. 3C and 3D.

The output of the sensor 10 is capacitors 11A-1
Since it is supplied to the level comparators 14A to 14D via 1D, only the AC component is supplied, and thus the binarization is performed by the simple average value of each signal.
The output signals of the level comparators 14A to 14D are phase comparators 16A, 16 configured by, for example, EX-OR circuits.
It is supplied to B respectively. 1CH, 2CH signals directly 4
The CH and 3CH signals are supplied to the phase comparators 16A and 16B via the phase shift circuits 15D and 15C, respectively.

In the digital type, the phase shift circuits 15D and 15C use, for example, pulse delay lines. However, in the case of using the analog type, for example, the phase shift circuits 15D and 15C having the LPF configuration may be installed in front of the level comparators 14D and 14C, respectively.

As the phase comparators 16A and 16B, E
When the X-OR circuit is used, the phase reference is when the duty of the input signal is 50% and the phase difference is 90 °. When the phase difference becomes larger than that, it becomes a high-level voltage when advanced and becomes a low-level voltage when delayed.
The dynamic range where the detection area is linear is ±
It is 90 °.

Further, in the case of the set-reset type flip-flop type phase comparison circuit, only the edge is used as the input signal, and the phase difference is 0 ° as a reference. Depending on whether it is advanced or delayed, it becomes high level or low level. The dynamic range is ± 180 °. When the phase difference due to diffraction is about 90 ° ± 90 °, there is no problem because the operating point is the middle point of the dynamic range even if it is detected by the EX-OR circuit. However, when it changes like 180 ° ± 90 °, it is not preferable because it extends over a positive slope and a negative slope. Therefore, a phase shift circuit is inserted in order to compress the phase difference of the input signal (because the phase difference 0 is the reference, the phase is delayed).

The output signal of the phase comparator, eg FIG.
(E), e and f shown in FIG. 3 (f) are the gate circuit 1
It is supplied to the differential operation circuit 19 via 7A, 17B and LPFs 18A, 18B to output a tracking error signal indicated by g in FIG. This gate circuit 17A,
Reference numeral 17B is provided to gate such an inconvenient signal by a gate signal and remove it, although an error occurs in track-to-track detection when performing track counting or track jump.

Next, regarding the method of generating the gate signal,
This will be described with reference to the waveform diagram of the gate circuit control signal of the tracking detection signal shown in FIG. The 4CH summation signals from the sensors 10A to 10D are supplied to the adder 21. The output signal of the adder 21 is shown by p in FIG. 4 (A), is converted into a signal shown by q in FIG. 4 (B) via the level comparator 22, and is output as the retriggerable monomultivibrator 2
3 is supplied.

The output signal of the retriggerable monomultivibrator (MM) 23 indicated by r in FIG. 4C is supplied to the control input terminals of the gate circuits 17A and 17B as gate signals. The phase difference signal is supplied to the differential operation circuit 19, and the differential signal is taken to become an error signal that changes to + and −, which is indicated by g in FIG. The phase comparator is a phase detection circuit used in PLL,
The phase difference is pulsed and is converted to a DC voltage through the low pass filters 18A and 18B.

As described above, according to the tracking signal detecting method of the information reproducing apparatus of the present invention, the following excellent operational effects can be exhibited. By performing digital processing, it is possible to reduce the number of adjustment steps and stabilize with time. Further, the generation of the error detection signal generated as a result of binarization can be dealt with by the gate processing circuit, and the tracking signal can be stabilized.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram to which a tracking signal detecting method of an information reproducing apparatus of the present invention is applied.

FIG. 2 is an embodiment to which the tracking signal detection method of the information reproducing apparatus of the present invention is applied.

FIG. 3 is a waveform diagram of a tracking detection signal.

FIG. 4 is a waveform diagram of a gate circuit control signal of a tracking detection signal.

FIG. 5 is a diagram showing an analog circuit for multiplying a high frequency signal by using a conventional analog multiplier.

FIG. 6 is a diagram showing a conventional diagonal sum signal converted into a digital signal,
It is the figure which showed the circuit of the phase difference detection system which detects the phase difference.

FIG. 7 is a graph showing a comparison between digital and analog phase comparison differences.

[Explanation of symbols]

10, 10A-10D, S1, S2, S3, S4 ... Sensor 11A-11D ... Capacitor 12A-12D ... Amplifier 13A-13D ... Limiter 14, 22 ... Level comparator 15C, 15D ... Phase shift circuit 16A, 16B ... Phase comparator 17A, 17B ... Gate circuit 18A, 18B ... LPF 19 ... Differential operation circuit 21 ... Adder 23 ... Retriggerable mono-multivibrator (MM)

Claims (3)

[Claims] 1. When the four-division sensor is rotated clockwise from left front to S1, S2, S3, and S4 with respect to the traveling direction of the truck, phase comparison is performed between the left and right signals in the truck direction. Of the signal of the level comparator,
S1 and S4 and S2 as binary signals from analog signals
Phase is detected linearly within approximately one cycle of the signal by comparing the phases between S3 and S3 and detecting the AC phase difference that changes in proportion to the off-track amount, centering on the DC phase difference. A tracking signal detecting method for an information reproducing apparatus, characterized in that a tracking error signal is detected by differentially calculating each of the left and right phase detection signals using a phase comparator that can be used. 2. The phase comparator is linear within a range of ± 90 °, and a phase shift circuit for delaying the phase of the comparison signal is provided to make the signal detection operation linear near on-track. A tracking signal detecting method for an information reproducing apparatus as set forth in claim 1. 3. The sum signal from the four-division sensor is binarized at a predetermined level or higher to detect continuity of the binarized signal and prevent generation of an erroneous detection signal in a discontinuous portion. The tracking signal detecting method for an information reproducing apparatus according to claim 1, further comprising a gate circuit.