JPS61206933A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To detect always tracking errors with certain detection sensitivity by comparing phases of digital detection signals, into which detection signals are subjected to waveform shaping, by a phase comparing means 5. CONSTITUTION:A phase comparing means 5 compares phases of digital detection signals C and D with each other to output a phase difference signal E. A holding means 21 integrates a phase difference signal E1 by a resistance 22 and a capacitor 24; and when a pulse rises in a validity discrimination signal F1, an analog switch 26 is opened to hold said integral value, and a phase difference signal E2 is integrated by a resistance 23, a capacitor 25, and an analog switch 27, and the integral value is held similarly. When a pulse rises in the validity discrimination signal F1 again, constant current sources 30 and 31 are made operated, and capacitors 30 and 31 are discharged by a current i0, and outputs of buffers 28 and 29 are '1' until the potential becomes lower than a threshold. AND between outputs of buffers 28 and 29 and the validity discrimination signal F1 is operated and the difference is obtained by a differential amplifier 34 to obtain a tracking error signal G.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 a minute width, and accurate tracking control is generally required in order to reproduce the information. In order to perform tracking control, it is necessary to detect a tracking error, and this is normally performed using optical means. In order to detect this tracking error optically, there is a method that uses an auxiliary light spot different from the light spot for information reading, and a method that also detects 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 "positioning"). The optical system (referred to as the phase difference method) is characterized in that it has a simple optical system and is not easily affected by warping 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. 9 shows tracking error detection means using a phase difference method in a conventional optical information reproducing apparatus. In FIG. 9, 1 is a reading head, 2 is a recording medium, 1
ool! L and 100b are adders, 101a and 1
01b is a 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.

The reading head 1 outputs two types of detection signals human and B. Detection signal M and signal B are output signals from different parts of the photoelectric detector included in the reading head 1. In reality, each consists of multiple signals, and in many cases they are added externally, but here, one We will treat this as one 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). The same signal output from oscillator 103 is added to detection signals M and B by adders 100a and 100b, respectively. Waveform shaping means 101& and 101b shape the outputs of adders 1oOIL and 100b, respectively, to obtain digital detection signals. 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 M or B decreases due to a defect in the recording medium, the waveform shaping means 101a and Since the operation of 101b is stable and does not easily generate noise, the tracking control is stable. (For example, JP-A-58-160
(See Publication No. 144) 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 changes, Accordingly, 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 generated when large amplitude noise due to scratches on the recording medium is mixed 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-mentioned problems, and has little variation in tracking error detection f' sensitivity due to amplitude fluctuations of the detection signal, and suppresses noise in the tracking error signal caused by scratches on the recording medium. This stabilizes the control.

Means for Solving the Problems In order to solve the above problems, the optical information reproducing apparatus of the present invention shapes the waveforms of two detection signals into two digital detection signals, and the phase comparison means converts the two detection signals into two digital detection signals. The phases of the signals are compared and a phase difference pulse corresponding to the phase difference is output. In addition, the validity determining means determines that when the two digital detection signals are mutually equivalent to each other, the state is normal and the two digital detection signals are equal to one another. 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 difference 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 that passes through the approximate center of this far-field image is parallel to the direction in which the information track is projected, and a dividing line that is perpendicular to this. 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 occurs between the two detection signals obtained by adding the diagonals of these photoelectric detectors. ing.

Therefore, it is possible to always detect tracking errors with constant detection sensitivity regardless of the amplitude of the detection signal.

Furthermore, the present invention can suppress disturbances in tracking control due to dirt even when noise of the same amplitude is mixed into the detection signal due to scratches or the like.

This is because when large noises such as scratches mix into the detection signal, one digital detection signal may not change, but the other digital detection signal may continue to invert the state, and phase comparison means often do this. is regarded as a phase difference, and an erroneous phase difference pulse is generated. However, according to the present invention, by processing this erroneous phase difference pulse, its influence 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 the tracking error detection means in the optical information reproducing apparatus of the present invention.

In FIG. 1, 1 is a reading head and 2 is a recording medium.The reading head 1 reads information from an information track of the recording medium 2 and outputs two detection signals A and B. Detection signals A and B are signals output from two parts of the photoelectric detector included in the read head 1, and when the read head 1 has a tracking error with respect to the information track, a phase difference is created between these detection signals. arise. 42L and 4b are waveform shaping means which remove low frequency components from the detection signals A and B, and then perform waveform shaping by comparing with zero potential to output digital detection signals C and D. A phase comparison means 6 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 states are reversed from the mutually equivalent state to the other state,
If two digital detection signals are equal to each other, then 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 changed according to each case. A sex discrimination signal F is output. 7
is 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.

After this tracking error signal E is processed by the control circuit 9, it is supplied to the driving means 1o, and the driving means 1o drives the 1D 1 to read so as to cancel the tracking error. Tracking control is performed in this way. still,
The waveform shaping means 41L, 4b, the phase comparison means 5,
The validity determining means 6 and the output processing means 7 constitute the tracking error detecting means 3, and the control circuit 9 and the driving means 1o constitute the tracking control means 8.

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 determination 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 determination signal, respectively.
, and a validity determination signal F2.

The operation of this embodiment will be explained in more detail below with reference to FIG. In the following description, a high potential state of a digital signal will be expressed as "1", a low potential state as "0", and a negative potential state as "-1". Detection signals output from the reading head 1 and B are waveform shaping means 4a and 4b.
The digital detection signals C and D shown in the figure are obtained by waveform shaping. The state inversions of the digital detection signal C are sequentially state inversions 'I+'2 and C5, and the state inversions of the digital detection signal C are sequential state inversions d1 and d2.
+ d3 e d4 and d5. At this time, state inversion 'In state inversion C2 and state inversion C5 are respectively state inversion d1. It is paired with state inversion C2 and state inversion d5, and since the phase of the digital detection signal C is advanced in these state inversion parts, the phase difference signal E becomes "1" for a time corresponding to the phase difference. .

Furthermore, in these state inversion parts, the digital detection signal C
Since the state reversal of the digital detection signal and the digital detection signal are paired, the validity determining means 6 determines that the state is a normal state reversal. Until the state reversal appears in the validity determination signal 2. becomes “1”. That is, when the validity determination signal F1 is "1", the phase difference signal E
This state indicates that the is valid. However, this “1”
The length of can also be further shortened within the above-mentioned time. When the validity determination signal F1 is "1", the output processing means 7
When a pulse of "°1" stands in the phase difference signal E1 immediately before that, a pulse of "1" of the same degree as that is output as the tracking error signal G, and just before that, a pulse of "1" is output as the tracking error signal G.
When a pulse of ``1'' is generated at 2, a pulse of ``-1'' equivalent to that pulse is output as the tracking error signal G. On the other hand, looking at the state inversion d3 of the digital detection signal, the state of the digital detection signal is inverted from the state where the two digital detection signals C and D are equivalent, so the validity determining means 6 detects that the phase of the digital detection signal is advanced. 2 becomes "1" in the phase difference signal until the digital detection signal C9D becomes equivalent to the state inversion again due to the subsequent state inversion d4.

However, this state reversal d3. There is no state inversion in digital detection signal C that pairs with these in d4.

The state inversion d4 causes the digital detection signal 0. D is again in the same equivalent state as it was immediately before the state reversal d3. Therefore, in this case, the validity determining means 6 determines that the state reversal d3 + d4 is an abnormal state reversal, and determines that the state reversal d
4 until the next state reversal appears in the digital detection signal C or D, the validity determination signal F2 is set to ``°1''.
shall be. That is, the state in which the validity determination signal F2 is "1" indicates that the phase difference signal E is invalid. However, the length of "1" may be further shortened within the above-mentioned time. can. If the validity determination signal F1 is “
1°", the tracking error signal G has a pulse g of "-1", which is about the same as the 1" pulse θ of the phase difference signal E2, but in reality, the validity determination signal F1 is "
At OI+, the validity determination signal F2 becomes "1°", so the pulse g is not output. In this way, the pulse g, which can become noise in the tracking error signal G, can be eliminated.

In the above embodiment, the phase difference signal E is made up of two phase difference signals X1 and F2, but the phase difference signal E can also be made into one signal by generating bipolar pulses. . In addition, the validity determination signal F is also the validity determination signal F.
Although the validity determination signal F is made up of two signals, 1 and F2, the validity determination signal F may be made into one signal by generating bipolar pulses. 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, the effect can also be obtained by a configuration in which the magnitude of the pulse is substantially reduced.

FIG. 3 is a circuit diagram showing a specific example of the configuration of the output processing means in the above embodiment.

In FIG. 3, reference numeral 21 denotes a holding means which integrates the phase difference signal E1 using a resistor 22° capacitor 24, and when a pulse is generated in the validity determination signal F1, an analog switch 26 is opened to hold the integrated value. Resistance 23. capacitor 2
5 and analog switch 27, the phase difference signal E2 is similarly integrated and held. Further, when a pulse is generated in the validity determination signal F1, the constant current sources 30 and 31 are activated, and the capacitors 30 and 31 receive the current i. The buffers 28 and 29 are discharged until the potential falls below the threshold value.
The output of the buffers 28 and 29 is ANDed with the validity determination signal F1, and the differential amplifier 34 calculates the difference between them to obtain the tracking error signal G. .

FIG. 4 shows another specific example of the output processing means in the embodiment of FIG. 2. In FIG. 4, resistor 42.
The resistor 43 and the capacitor 44 are used to differentially integrate 1 and F2 into the phase difference signal, and constitute the holding means 21. When the validity determination signal F1 becomes "1", the analog switch 44 is closed and the charge accumulated in the capacitor 42 is transferred to the capacitor 46 having a larger capacitance.

Furthermore, if the resistance values of the resistor 49 and the resistor 6o are made sufficiently smaller than those of the resistor 4o and the resistor 41, most of the charge accumulated in the capacitor 45 is discharged through the resistor 49 and the resistor 6o, and the operational amplifier 48. Resistance 49. Resistance 50. Resistance 63. Resistance 54. The capacitor 51 and the capacitor 62 make it possible to obtain a tracking error signal that is proportional to the amount of charge stored in the capacitor 45 and has unnecessary high-frequency components removed.

Note that the holding means 2 in the examples shown in FIGS. 3 and 2 above
It is preferable that the integration time constant of 1 be set to approximately the time corresponding to the maximum value of the phase difference caused by the tracking error, thereby limiting the amplitude of noise mixed into the tracking error signal to below a certain value. 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
), so the time constant for the above 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 waveform shaping means 4a, 4b
By substantially stopping the operation, the effect can be further enhanced.

FIG. 5 shows a block diagram of waveform shaping means in another embodiment of the 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 a constant voltage source 62. The above high-pass filter 60. Comparator 61 and comparator 62 constitute waveform shaping means. FIG. 6 is a signal waveform diagram illustrating the operation of the waveform shaping means in the above embodiment. Signal waveforms A and B in FIG. 6 correspond to each part of A and B in FIG.
is the threshold value of the controller 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 amplitude of the output signal of the high-pass filter 60 will be such that the amplitude above and below the zero potential is the center. descend. 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 the 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. , there is no state reversal in the digital detection signal that is its output. At this time, even if the amplitude of the other detection signal is larger than the threshold value and there is a state reversal in the digital detection signal obtained by waveform-shaping the other detection signal, the false phase difference signal due to this is output to the output processing means 7.
Since this is suppressed by the following, 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 adversely affect the waveform shaping in the normal portion, and the above effect cannot be obtained when the amplitude decrease of the detection signal is small. In addition, in this embodiment, since the waveform is shaped using the potential V as the threshold after removing the low frequency component from the detection signal, the waveform of the detection signal is substantially set using 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. 7 shows a block diagram of waveform shaping means in still another embodiment of the present invention, which is an improvement on the above embodiment. In FIG. 7, reference numeral 7o denotes amplitude detection means for detecting the amplitude of the detection signal and outputting a corresponding detected amplitude;
Reference numeral 1 denotes a threshold value control means for controlling the threshold value of the comparator 61 in accordance with the amplitude detection signal. FIG. 8 is a signal waveform diagram for explaining the operation of the waveform shaping means in the above embodiment. Signals 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. 7 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 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. The threshold value control means 71 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. Note that the amplitude detection means To 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 band-pass filter.

Effects of the Invention As is clear from the above explanation, 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 layer detection signals from an equivalent state to a state where they are both equal to each other. When one digital detection signal is inverted and becomes equivalent to the other, it is a normal state reversal, and when one digital detection signal continues to invert and becomes equal again from a state in which these digital detection signals are equivalent to each other, it is a normal state reversal. After identifying an abnormal state reversal, a signal corresponding to the phase difference in the normal state reversal portion is output as a tracking error signal, and in the abnormal state reversal portion, the signal detected as the phase difference is corrected and used. It has a tracking error detection means that outputs a signal according to the tracking error signal as a tracking error signal, and is configured to perform tracking control according to this tracking error signal, so that the gain of the tracking control is stable and the recording medium is not scratched. An excellent effect can be obtained in that tracking control is less likely to be 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 transmitting the data as is and configuring it so that nothing is output when the state inversion is determined to be abnormal, the effect can be achieved with a simple circuit configuration.

Furthermore, the amplitude of the detection signal may be significantly reduced by setting the threshold value of the waveform shaping means to a value that is substantially the DC component of the detection signal plus an offset, or by controlling the threshold value according to fluctuations in the amplitude of the detection signal. When this occurs, the detection signal does not cross the threshold value and the operation of the waveform shaping means is substantially stopped, thereby achieving the effect that the stability of tracking control can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of an optical information reproducing apparatus in an embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part in the above embodiment, and FIG. 3 is a configuration of the output processing means in the above embodiment. FIG. 4 is a circuit diagram showing another example of the configuration of the output processing means in the above embodiment, FIG. 6 is a block diagram of the waveform shaping means in another embodiment of the present invention, FIG. FIG. 7 is a block diagram of a waveform shaping means in still another embodiment of the present invention. FIG. 8 is a signal waveform diagram of each part in the above embodiment. FIG. 9 is a diagram of the signal waveform of each part in the above embodiment. FIG. 3 is a block diagram of tracking error detection means in the optical information reproducing device. 1... Reading head, 3... Tracking error detection means, 4m, 4b... Waveform shaping means, 5... Phase comparison means, 6... ...Validity determining means, 7... Output processing means, 8...
・Tracking control means, 21...holding means,
θ0...High pass filter, 61...
·comparator. 7o...Amplitude detection means, 71
...Threshold value control means. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 Figure 4 Figure 2Fl Figure 5 Figure 7 Figure 8

Claims (6)

[Claims] (1) A light spot is formed by projecting irradiation light onto the information track of the recording medium, and the reflected light or transmitted light is detected and changes depending on the recorded information, and the tracking error of the light spot is detected. a reading head that outputs a plurality of signals including at least two detection signals whose phases change relative to each other according to the tracking error detection means that extracts a phase difference component of the detection signal and outputs a tracking error signal; tracking control means for adjusting the position of the optical spot according to the error signal, and the tracking error detection means includes waveform shaping means for respectively shaping the waveforms of the two detection signals and outputting 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 equal to each other, which digital detection signal was inverted first until the state becomes equal to each other again. Therefore, when the phase comparison means that generates phase difference pulses with substantially different polarities and the two digital detection signals are inverted from the mutually equivalent state to the other state, the two digital detection signals are determined to be valid. If one digital detection signal inverts its state twice in a row from a state in which the signals are equivalent to each other and returns to an equal state again, it is determined that the signal is invalid, and the validity determination signal takes a state corresponding to each case. a validity determining means for outputting a signal corresponding to a phase difference pulse output from the phase comparing means when the validity determining signal is in a state indicating validity; and a signal corresponding to the phase difference pulse outputted by the phase comparing means when the validity determining signal is in a state indicating invalid; An optical information reproducing device comprising: output processing means for outputting a signal according to a result of processing the phase difference pulse. (2) The output processing means has a holding means for holding a value obtained by integrating the phase difference pulse, and when the validity determination signal indicates validity, the output processing means outputs a pulse having a width corresponding to the value held by the holding means. The optical information reproducing device according to claim 1, wherein the optical information reproducing device outputs the pulse and does not output the pulse when the validity determination signal indicates invalidity. (3) The output processing means has a holding means for holding 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, The optical information reproducing apparatus according to claim 1, wherein the value held by the holding means is erased when the validity determination signal is in a state indicating invalidity. (4) In the waveform shaping means, a threshold value is set so that the detection signal does not cross the threshold value when the amplitude of the detection signal suddenly decreases. Information reproducing device. (5) The optical information reproducing device 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) 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. optical information reproducing device.