JPH0580053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical information reproducing device, and particularly to tracking control thereof.

2. Description of the Related Art In recent years, optical information reproducing devices that optically read information from recording media such as video discs and digital audio discs have been widely used. Information is recorded on information tracks with minute widths, and accurate tracking control is generally required in order to reproduce the information. In order to perform tracking control, it is necessary to detect tracking errors, and this is normally performed using optical means. In order to detect this tracking error optically, there is a method of using an auxiliary light spot different from the light spot for information reading, and a method of also detecting the tracking error using the same light spot as that for information reading. is known. Among the methods that do not use an auxiliary light spot, the tracking error is detected from the phase difference between the signals output from two parts of a photoelectric detector that receives detection light and outputs an electrical signal (hereinafter referred to as tracking error). The optical system (referred to as a phase difference method) has a simple optical system and is not easily affected by warpage of the recording medium.

An example of the above-mentioned conventional optical information reproducing device will be described below with reference to the drawings.

FIG. 10 shows tracking error detection means using a phase difference method in a conventional optical information reproducing apparatus. In FIG. 10, 1 is a reading head, 2 is a recording medium, 100a and 100b.
is an adder, 101a and 101b are waveform shaping means, and 102 is a phase comparison means. The operation of the conventional tracking error detection means configured as described above will be explained below.

Two types of detection signals A and B are output from the reading head 1. Detection signal A and signal B are output signals from different parts of the photoelectric detector included in the reading head 1, and each is actually composed of multiple signals, which are often added together externally, but here, one I will treat it as a signal. These detection signals are the sum of the diagonal directions obtained by dividing the far-field image of the detection light formed on the photoelectric detector into four in the direction in which the information track is projected and in the direction perpendicular thereto. It is known that a phase difference occurs between these detection signals due to a tracking error (for details, see Japanese Patent Laid-Open No. 52-93222). Oscillator 10 is used for detection signals A and B.
The same signals output from 3 are added by adders 100a and 100b, respectively. Waveform shaping means 101a and 101b waveform-shape the outputs of adders 100a and 100b, respectively, to obtain digital detection signals, respectively. By comparing the phases of these two digital detection signals by the phase comparison means 102, a tracking error signal can be obtained. Even if the amplitude of the detection signal A or B decreases due to a defect in the recording medium, the oscillator 1
Since the fairly large in-phase signal outputted from the waveform shaping means 101a and 101b is added to each detection signal, the operation of the waveform shaping means 101a and 101b is stable and less likely to generate noise, so the tracking control is stable. (For example, JP-A-58-150144
Problems to be Solved by the Invention However, in such a configuration, the detection sensitivity of the phase difference depends on the ratio of the amplitude of the detection signal to the output signal of the oscillator 103, so if the level of the detection signal fluctuates, Along with this, the tracking error detection sensitivity also fluctuates, resulting in a drawback that the tracking control gain also fluctuates. Furthermore, it is not very effective against noise that occurs when large amplitude noise such as scratches on the recording medium mixes into the detected amplitude, and there is also the problem that the stability of tracking control is not improved. .

The present invention has been made in view of the above points, and it is possible to reduce fluctuations in tracking error detection sensitivity due to amplitude fluctuations of the detection signal, and to control noise in the tracking error signal caused by scratches on the recording medium. , which stabilizes tracking control.

Means for Solving the Problems In order to solve the above problems, the optical information reproducing device of the present invention waveform-shapes the two detection signals to generate two detection signals.
The phase comparison means compares the phases of these digital detection signals and outputs a phase difference pulse corresponding to the phase difference. Further, the validity determining means determines that the state is normal when the two digital detection signals are inverted from the mutually equivalent state to the other state; If a signal reverses its state twice in a row and returns to its original equivalent state again, it is considered an abnormal state reversal, and in the former case the state is valid, and in the latter case it is invalid. Outputs a validity determination signal. The output processing means outputs a signal corresponding to the phase pulse as a tracking error signal when the validity determination signal indicates validity, and processes the phase difference pulse when the validity determination signal indicates invalidity. A signal corresponding to the result is output as a tracking error signal.

Effects The present invention has the following effects due to the above-described configuration.

That is, since the phase comparison means is configured to compare the phases of digital detection signals obtained by waveform-shaping the detection signals, an accurate phase difference can always be detected regardless of the amplitude of the detection signals. In addition, a far-field image is formed on a photoelectric detector by detecting the reflected light from the recording medium, and a dividing line parallel to the direction in which the information track is projected and a dividing line perpendicular to this are passed through the approximate center of this far-field image. It is already known that when the photoelectric detector is divided into four parts by a dividing line, a phase difference proportional to the tracking error will occur in the two detection signals obtained by adding the diagonals of these photoelectric detectors. Are known. Therefore, it is possible to always detect tracking errors with constant detection sensitivity regardless of the amplitude of the detection signal.

Further, the present invention can suppress disturbances in tracking control caused by noise when the detection signal is mixed with noise of the same amplitude due to scratches or the like. This is because when a large amount of noise from scratches or the like mixes into the detection signal, one digital detection signal often continues to invert its state even though the other digital detection signal does not change. In this case, this is regarded as a phase difference and an erroneous phase difference pulse is generated, but according to the present invention, by processing this erroneous phase difference pulse, the effect can be reduced. Therefore, it is possible to suppress large noises from being mixed into the tracking error signal due to scratches, etc., and it is possible to stabilize tracking control.

Embodiment FIG. 1 is a block diagram showing an embodiment of tracking error detection means in an optical information reproducing apparatus of the present invention. In FIG. 1, 1 is a reading head, 2 is a recording medium, and reading head 1 is a recording medium 2.
It reads information from the information track and outputs two detection signals A and B. Detection signals A and B
are the signals output from the two parts of the photoelectric detector included in the read head 1, resulting in a phase difference between these detection signals when the read head 1 has a tracking error with respect to the information track. 4
A and 4b are waveform shaping means which remove low frequency components from the detection signals A and B, and then perform waveform shaping by comparison with zero potential to output digital detection signals C and D. 5 is a phase comparison means which compares the phases of the digital detection signals C and D and outputs a phase difference signal E. Further, 6 is a validity determining means, which determines that the two digital detection signals are valid when the state is reversed from the mutually equivalent state to the other state, and when the two digital detection signals change from the mutually equivalent state to one If the digital detection signal is inverted twice in succession and becomes equivalent again, it is determined to be invalid and a validity determination signal F is output that assumes a state corresponding to each case. Reference numeral 7 denotes an output processing means which corrects the phase difference signal E according to the validity determination signal F and outputs a tracking error signal G. This tracking error signal E is processed by the control circuit 9 and then supplied to the driving means 10.
The driving means 10 drives the reading head 1 so as to cancel the tracking error. Tracking control is performed in this way. The waveform shaping means 4a, 4b, the phase comparison means 5, the validity determining means 6, and the output processing means 7 constitute the tracking error detection means 3, and the control circuit 9 and the driving means 10 constitute the tracking control means 8. Configure.

FIG. 2 is a signal waveform diagram showing the signals of each part of the above embodiment, and shows the waveforms of each part of waveforms A to G. However, in Fig. 1, the phase difference signal E and the validity discrimination signal F are each represented by one signal line, but these are the phase difference signal _E1 , the phase difference signal _E2 , and the validity discrimination signal _F1 , respectively. It is assumed that the validity determination signal _F2 is composed of two signals. The operation of this embodiment will be explained in more detail below with reference to FIG. In addition, in the following explanation,
The high potential state of the digital signal will be expressed as "1", the low potential state as "0", and the negative potential state as "-1". Detection signals A and B outputted from reading head 1 are waveform-shaped by waveform shaping means 4a and 4b to obtain digital detection signals C and D as shown in the figure. Digital detection signal C
Let the state inversions of be sequential state inversions c ₁ , c ₂ and c ₅ ,
Sequentially invert the state of digital detection signal D
Let d ₁ , d ₂ , d ₃ , d ₄ and d ₅ . At this time, state inversion c ₁ , state inversion c ₂ and state inversion c ₅ are paired with state inversion d ₁ , state inversion c ₂ and state inversion d ₅ respectively, and in these state inversion parts, the digital detection signal C is Since the phase is leading, it is a phase difference signal.
E ₁ becomes "1" for a time corresponding to the phase difference. Furthermore, in these state inversion parts, since the state inversions of the digital detection signal C and the digital detection signal D are paired, the validity determining means 6 determines that the state is a normal state reversal, and in this case, the slower state While the state reversal continues to appear on either the digital detection signal C or D after the reversal,
The validity determination signal _F1 becomes "1". That is,
A state in which the validity determination signal F ₁ is "1" is a state indicating that the phase difference signal E is valid. However, the length of this "1" can be further shortened within the above time. The output processing means 7 outputs a validity determination signal.
When F ₁ is "1", if a pulse of "1" stands in the phase difference signal E ₁ immediately before that, a pulse of "1" of the same level as that is output as the tracking error signal G, and the pulse of "1" stands just before that. “1” in phase difference signal E ₂
When the pulse is rising, a pulse of "-1" of the same level as that is outputted as the tracking error signal G. On the other hand, looking at the state inversion _d3 of the digital detection signal D, we see that the two digital detection signals C and D
Since the state of the digital detection signal D is inverted from the state in which they are equivalent, the validity determining means 6 determines that the phase of the digital detection signal D is advanced, and due to the subsequent state inversion _d4 , the digital detection signal C is changed again. ，
Phase difference signal until D becomes equivalent state inversion
E ₂ becomes "1". However, this state reversal d ₃ , d ₄
The digital detection signal C has no state inversion to pair with these, and the digital detection signals C and D are once again in the same equivalent state as immediately before the state inversion _d3 . Therefore, in this case, the validity determining means 6 determines that the state reversals d ₃ and d ₄ are abnormal state reversals, and a state reversal appears in the digital detection signal C or D after the state reversal d ₄ . Until then, the validity determination signal _F2 is set to "1". That is, a state where the validity determination signal _F2 is "1" is a state indicating that the phase difference signal E is invalid. However, the length of this "1" can be further shortened within the above time. If the validity determination signal is
If F ₁ is "1", the tracking error signal G will have a "-1" pulse g, which is about the same as the "1" pulse e of the phase difference signal E ₂ , but in reality, the effectiveness is Discrimination signal F ₁ is “0” and is a validity determination signal.
Since F ₂ becomes "1", pulse g is not output.
In this way, pulses g that can become noise in the tracking error signal G can be eliminated.

In the above embodiment, the phase difference signal E is composed of two phase difference signals _E1 and _E2 , but the phase difference signal E is made to generate bipolar pulses.
It can also be one signal. In addition, the validity determination signal F is also made up of two validity determination signals _F1 and _F2 , but the validity determination signal F can also be made into one signal by generating bipolar pulses. You can also do it. Further, in the above embodiment, the output processing means 7 outputs a pulse having a width comparable to that of the phase difference signal E when the validity determination signal F indicates validity. The waveform of the signal is not particularly limited as long as it has an integral value; for example, it may be configured to generate a constant width pulse whose height changes depending on the pulse width of the phase difference signal E. Moreover, although the pulse to be output is erased when the validity determination signal F is in a state indicating invalidity, it is also possible to obtain an effect by configuring the pulse size to be substantially reduced.

FIG. 3 is a circuit diagram showing a specific example of the configuration of the validity determining means in the above embodiment. In the figure, 80 is a first flip-flop which is set when both digital detection signals C and D are "1" and reset when both are "0". Reference numeral 81 designates a second flip-flop which is set when either of the digital detection signals C and D changes from the "1" state, and is reset when either state changes from the "0" state. The output signal _F1 is output from the digital detection signal C when the second flip-flop 81 is set and the digital detection signals C and D both become "0", or when the second flip-flop 81 is reset. and D become "1" when both become "1". Further, the output signal _F2 is output from the digital detection signal when the digital detection signals C and D both become "1" from the state in which the second flip-flop 81 is set, or from the state in which the second flip-flop 81 is reset. It becomes "1" when both signals C and D become "0".
By configuring as described above, the validity determining means 6 outputs signals F ₁ and F ₂ as shown in FIG. 2.

FIG. 4 is a circuit diagram showing a specific example of the configuration of the output processing means in the above embodiment. In FIG. 4, 21 is a holding means, a resistor 22, a capacitor 2
4 integrates the phase difference signal _E1 , and when a pulse is generated in the validity determination signal _F1 , the analog switch 2
6 is opened to hold the above integral value, and resistors 23,
Similarly, the phase difference signal _E2 is integrated and held by the capacitor 25 and analog switch 27.
Furthermore, when a pulse is generated in the validity determination signal _F1 , the constant current sources 30 and 31 are activated, and the capacitor 3
The outputs of the buffers 28 and 29 become "1" until the voltages 0 and 31 are discharged by the current i ₀ and the potential falls below the threshold value. Therefore, the outputs of these buffers 28 and 29 are ANDed with the validity determination signal _F1 ,
A tracking error signal G can be obtained by calculating the difference between these signals using a differential amplifier 34.

FIG. 5 shows another specific example of the output processing means in the embodiment of FIG. 1. In FIG. 5, a resistor 42, a resistor 43, and a capacitor 44 are used to differentially integrate the phase difference signals _E1 and _E2 , and constitute a holding means 21. Validity determination signal
When F ₁ becomes "1", the analog switch 44 is closed and the charge accumulated in the capacitor 42 is transferred to the capacitor 45 having a larger capacitance. Furthermore, if the resistance values of the resistor 49 and the resistor 5 are made sufficiently smaller than the resistors 40 and 41, most of the charge accumulated in the capacitor 45 is discharged through the resistor 49 and the resistor 50, and the operational amplifier 48 , resistor 49, resistor 50, resistor 53, resistor 54, capacitor 51, and capacitor 52 to obtain a tracking error signal that is proportional to the amount of charge accumulated in the capacitor 45 and removes unnecessary high-frequency components. I can do it.

In the examples shown in FIGS. 4 and 5 above, it is preferable that the integration time constant of the holding means 21 be approximately the time corresponding to the maximum value of the phase difference caused by the tracking error. The amplitude of noise mixed into the tracking error signal can be limited to a certain value or less. When the relative linear velocity of the information track is V and the period of the information track is P, the maximum value of the phase difference due to tracking error is P/(2V)
Therefore, the time constant of the above-mentioned integration may be set to approximately this level or less.

Furthermore, in the present invention, when the amplitude of the detection signal decreases due to a defect in the recording medium, the operation of the waveform shaping means 4a, 4b is substantially stopped, thereby further enhancing the effect. .

FIG. 6 shows a block diagram of waveform shaping means in another embodiment of the present invention. In FIG. 6, 60 is a high-pass filter that removes low frequency components from the detected amplitude, and 61 is a comparator that compares the output signal of this high-pass filter 60 with the output voltage V of the constant voltage source 62. The high-pass filter 60, comparator 61, and comparator 62 constitute waveform shaping means. FIG. 7 is a signal waveform diagram illustrating the operation of the waveform shaping means in the above embodiment. Signal waveforms A and B in FIG. 7 correspond to each part of A and B in FIG. 6, and 63 is the threshold value of the comparator 61.

A more detailed explanation will be given below with reference to FIG.

When the amplitude of the detection signal drops due to a defect in the recording medium, if the cutoff frequency of the high-pass filter 60 is sufficiently high, the high-pass filter 60
The amplitude of the output signal A decreases above and below the zero potential. If the comparator 61 were to perform comparison using zero potential as a threshold, the comparator 61 would generate random pulses as noise due to noise. However, in this embodiment, since the threshold value 63 is set to voltage V by the constant voltage source 62, the detection signal does not cross the threshold value in the defective portion of the recording medium, and the comparator 61 substantially stops. As a result, there is no state reversal in the output digital detection signal. At this time, even if the amplitude of the other detection signal is larger than the threshold and the state of the digital detection signal obtained by shaping the waveform of this signal is reversed, the phase difference signal due to this is output to the output processing means 7.
Since it is suppressed by , the influence on tracking control becomes extremely small. However, it is necessary to set the threshold value 63 not to be too high so as not to have an adverse effect on waveform shaping in the normal part.
The above effect cannot be obtained when the amplitude reduction of the detection signal is small. In this embodiment, after removing the low frequency component from the detection signal, the waveform is shaped using the potential V as the threshold. Therefore, the waveform of the detection signal is essentially set to the value obtained by adding the offset V to the DC component of the detection signal as the threshold. It's obvious that it will need some reshaping.

FIG. 8 shows a block diagram of a waveform shaping means in still another embodiment of the present invention, which is an improvement on the above embodiment. In FIG. 8, 70 is amplitude detection means for detecting the amplitude of a detection signal and outputting a detected amplitude corresponding to the detected amplitude, and 71 is threshold control means for controlling the threshold of the comparator 61 in accordance with the amplitude detection signal. FIG. 9 is a signal waveform diagram for explaining the operation of the waveform shaping means in the above embodiment, and the signals A, B, and C in FIG. 9 are the signals at each part of A, B, and C in FIG. 72 is the threshold value of the comparator 61.

The operation of the waveform shaping means shown in FIG. 8 will be explained below with reference to FIG.

When the amplitude of the detection signal drops due to a defect in the recording medium, if the cutoff frequency of the high-pass filter 60 is sufficiently high, the amplitude of the output signal A of the high-pass filter 60 will decrease as in the case of the previous embodiment. The vertical amplitude decreases around zero potential. At this time, the amplitude detection means 70 detects fluctuations in amplitude, and the amplitude detection signal changes accordingly. Threshold control means 7
1 sets the threshold value 72 to zero potential in a normal portion where the amplitude of the detection signal is constant, but when the amplitude detection signal changes, the threshold value 72 is changed as shown in the figure. Therefore, when the amplitude of the detection signal decreases due to a defect in the recording medium, the comparator 61 substantially stops operating. Furthermore, in this embodiment, since the threshold value 72 is at zero potential in the normal portion, ideal waveform shaping can be performed. The amplitude detection means 70 in this embodiment can be easily realized by a well-known envelope detector, and the threshold value control means 71 can be constituted by, for example, a bandpass filter.

Effects of the Invention As is clear from the above description, the present invention obtains a digital detection signal by waveform shaping the two detection signals output from the reading head, and changes the state of these digital detection signals from being equivalent to each other to inverting the states of both signals. When one of the digital detection signals becomes equivalent to the other, the state is reversed, and when the digital detection signals are equivalent to each other, one of the digital detection signals continues to be inverted, resulting in an equal state again. Sometimes, it is determined that there is an abnormal state reversal, and in the normal state reversal part, a signal corresponding to the phase difference is output as a tracking error signal, and in the abnormal state reversal part, the signal detected as the phase difference is corrected. It has tracking error detection means that outputs a signal corresponding to this as a tracking error signal, and is configured to perform tracking control according to this tracking error signal, so that the gain of tracking control is stable and the recording medium An excellent effect can be obtained in that tracking control is not easily disturbed even by large noises mixed into the detection signal due to scratches or the like.

Furthermore, the output processing means integrates the pulse generated according to the phase difference, and if the state reversal is determined to be normal, immediately thereafter generates a pulse with a time width corresponding to the above-mentioned integral value, or By configuring the configuration so that it is transferred as is and does not output anything if the state reversal is determined to be abnormal, it is possible to achieve the effect of being able to appear with a simple circuit configuration by configuring the configuration so that it does not output anything. It will be done.

Furthermore, if the threshold value of the waveform shaping means is substantially a value obtained by adding an offset to the DC component of the detection signal, or if the amplitude of the detection signal is significantly reduced, the detection signal does not cross the threshold value and the waveform shape is substantially reduced. By configuring the shaping means to stop its operation, it is possible to further improve the stability of tracking control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of an optical information reproducing apparatus in one embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part in the above embodiment, and FIG. 3 is a diagram of the effectiveness determining means in the above embodiment. FIG. 4 is a circuit diagram showing a configuration example of the output processing means in the above embodiment; FIG. 5 is a circuit diagram showing another configuration example of the output processing means in the above embodiment;
The figure is a block diagram of a waveform shaping means in another embodiment of the present invention, FIG. 7 is a signal waveform diagram of each part in the above embodiment, and FIG. 8 is a block diagram of a waveform shaping means in yet another embodiment of the present invention. 9 is a signal waveform diagram of each part in the above embodiment, and FIG. 10 is a block diagram of tracking error detection means in a conventional optical information reproducing apparatus. DESCRIPTION OF SYMBOLS 1... Reading head, 3... Tracking error detection means, 4a, 4b... Waveform shaping means, 5... Phase comparison means, 6... Effectiveness determination means, 7... Output processing means, 8... Tracking control Means, 21...
... Holding means, 60 ... High pass filter, 61
... Comparator, 70 ... Amplitude detection means, 71
...Threshold control means.

Claims (1)

[Claims] 1. A light spot is formed by projecting irradiation light onto an information track of a recording medium, and the reflected light or transmitted light is detected to change according to the recorded information, and the light spot is a reading head that outputs a plurality of signals including at least two detection signals whose phases change relative to each other according to a tracking error of a spot; and a tracking error detection means that extracts a phase difference component of the detection signal and outputs a tracking error signal. and tracking control means for adjusting the position of the optical spot according to the tracking error signal, and the tracking error detection means shapes the waveforms of the two detection signals and outputs two digital detection signals. When the state of one digital detection signal is reversed from the state in which the two digital detection signals are equivalent to each other, which digital detection signal is output first until the state of the two digital detection signals becomes equal to each other again. a phase comparison means that generates phase difference pulses having substantially different polarities depending on whether the two digital detection signals are inverted; If two digital detection signals are equivalent to each other, and one digital detection signal inverts its state twice in a row and becomes equal again, it is determined to be invalid and the state is set according to each case. validity determining means for outputting a sex determining signal; and when the validity determining signal indicates validity, outputting a signal corresponding to the phase difference pulse output from the phase comparing means, and determining that the validity determining signal is invalid. 1. An optical information reproducing device comprising: output processing means for outputting a signal according to the result of processing the phase difference pulse when in the state shown in FIG. 2. The output processing means has a holding means for holding a value obtained by integrating the phase difference pulse, and outputs a pulse having a width corresponding to the value held by the holding means when the validity determination signal indicates validity. 2. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus does not output a pulse when the validity determination signal is in a state indicating invalidity. 3. The output processing means has a holding means that holds a value obtained by integrating the phase difference pulse, and when the validity determination signal indicates validity, transfers and outputs the value held by the holding means, and determines the validity. 2. The optical information reproducing apparatus according to claim 1, wherein the value held by the holding means is erased when the discrimination signal indicates invalidity. 4. The optical information reproducing device according to claim 1, wherein the waveform shaping means has a threshold value set so that the detection signal does not cross the threshold value when the amplitude of the detection signal sharply decreases. 5. The optical information reproducing apparatus according to claim 4, wherein the waveform shaping means uses a value obtained by adding a DC offset to a DC value included in the detection signal as a threshold value. 6. Optical information according to claim 4, wherein the waveform shaping means comprises threshold control means for detecting the amplitude of the detection signal and controlling the threshold in response to fluctuations in the amplitude. playback device.