JPH0580054B2 - - 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, there is a method that detects the tracking error from the phase difference of each signal 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. 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, 100a and 100b are adders, 101a and 101b are waveform shaping means,
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 signals A and 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 is often 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). 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 considerably 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 noise is hardly generated, so that the tracking control is stable.

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 when the level of the detection signal changes, There was a drawback that the tracking error detection sensitivity also varied, and therefore the tracking control gain also varied. 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 cannot be improved. .

The present invention has been made in view of the above-mentioned problems.The present invention has been made in view of the above-mentioned problems, and it is possible to reduce fluctuations in tracking error detection sensitivity due to fluctuations in the amplification of the detection signal, and to suppress 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 apparatus of the present invention waveform-shapes two detection signals to
The phases of these digital detection signals are compared and a tracking error signal is obtained according to the phase difference. However, since the two digital detection signals are equivalent to each other, one digital detection signal If the state is subsequently reversed and the state returns to the original equivalent state again, the phase difference at the state-inverted portion is considered to be substantially zero.

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

In other words, since the configuration is such that the phases of digital detection signals obtained by shaping the waveforms of two detection signals are compared and the phase difference is detected, an accurate phase difference can always be detected regardless of the amplitude of the detection signals. I can do it. 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 occurs in the two detection signals obtained by adding the diagonals of these photoelectric detectors. known (e.g.
(Refer to Japanese Patent Application Laid-Open No. 52-93222). 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 large noises such as scratches mix 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 a large error occurs in the phase difference signal, but according to the present invention, the influence can be reduced by suppressing such erroneous detection of phase difference. . 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. A phase comparison means 5 compares the phases of the digital detection signals C and D and outputs a phase difference signal F. Further, 6 is a validity determining means, which outputs an invalid signal F when the two digital detection signals are in an equivalent state, and one digital detection signal is inverted twice in a row and becomes equal again. do. The phase difference signal F is used as a tracking error signal, and based on this, the control circuit 9 operates the driving means 10 so as to cancel out the tracking error of the reading head 1. The waveform shaping means 4a, 4b, phase comparison means 5 and validity determining means 6 constitute tracking error detection means 3, and the control circuit 9 and drive means 10 constitute tracking control means 8.

FIG. 2 is a signal waveform diagram showing the signals of each part of the above embodiment, and waveforms A to F show the waveforms of each part of A to F in FIG. The operation of this embodiment will be explained in more detail below with reference to FIG.
In the following explanation, the positive potential of the digital signal will be expressed as '1', the zero potential as '0', and the negative potential as '-1'. Detection signal A output from reading head 1
and B are waveform-shaped by the waveform shaping means 4a and 4b to produce a digital detection signal C as shown in the figure.
and D are obtained. The state inversions of the digital detection signal C are sequentially state inversions c ₁ , c ₂ and c ₅ , and the state inversions of the digital detection signal D are sequentially state inversions d ₁ ,
Let d ₂ , d ₃ , d ₄ and d ₅ . At this time, the state is reversed
c ₁ , state inversion c ₂ and state inversion c ₅ are paired with state inversion d ₁ , state inversion d ₂ and state inversion d ₅ respectively, and in these state inversion parts the digital detection signal C is advanced in phase. Therefore, the phase difference signal F becomes '1' only for a time corresponding to the phase difference. On the other hand, in the state inversion _d3 of the digital detection signal D, the state inversion appears in the digital detection signal D first from the state where both the digital detection signals C and D are '0', so the digital detection signal D is ahead in phase. The phase comparator 5 determines this and attempts to output a '-1' phase difference signal. However, since there is no state inversion of the digital detection signal C corresponding to the state inversion _d3 of the digital detection signal D, and a state inversion _d4 of the digital detection signal D appears subsequently, the validity determining means 6
determines that these state inversions d ₃ and d ₄ are invalid, and the invalid signal E becomes '1'. Therefore, the phase comparison means 5
erases the portion f based on the state inversions d ₃ and d ₄ of the phase difference signal F to '0'. Conventionally, the pulse f of this phase difference signal F has become noise in the tracking error signal, but by doing so, the noise in the tracking error signal can be suppressed.

Incidentally, as is clear from the above explanation, even if the state of the two digital detection signals is reversed from the state where they are equivalent to each other,
Its effectiveness will not be known until we see whether the next state reversal appears on either digital detection signal.
Therefore, in order to prevent an erroneous phase difference signal from being output due to an abnormal state inversion such as one digital detection signal inverting its state twice in a row from a state in which two digital detection signals are equivalent to each other. To achieve this, it is necessary to either accumulate and hold the phase difference signal until the validity of the state inversion can be determined, or to delay the phase comparison operation using a delay element. Therefore, the specific configuration of the phase comparison means will be described next.

FIG. 3 is a circuit diagram showing a specific configuration of the phase comparing means 5 and the validity determining means 6, and FIG. 4 is a signal waveform diagram of each part A to Q in the circuit diagram. below,
The operations of the phase comparing means 5 and validity determining means 6 shown in FIG. 3 will be explained with reference to the signal waveform diagram shown in FIG. 4. First, the operation of the phase comparison means 5 will be explained. Assume that the digital detection signals output from the waveform shaping means 4a and 4b are as shown in A and B in FIG. 4, respectively. Here, part a of digital detection signal A and digital detection signal B
Part b is a state inversion caused by malfunction of the waveform shaping means 4a and 4b due to noise or the like.
At this time, the output of the NAND gate 20 becomes '0' only when both the digital detection signals A and B are '1', so it becomes the signal C, and the output of the OR gate 21 becomes '0' when both the digital detection signals A and B are '0'. Since it becomes '0' only when , it becomes signal D. As will be clear from the explanation that follows, the NAND gate 32 is normally '0' when the digital detection signals A and B are both equal, so when the signal C or D becomes '0', the flip-flop 24 is set or reset.
Outputs signal E. That is, when digital detection signals A and B both become '1', flip-flop 24 is set and signal E becomes '1', and when digital detection signals A and B both become '0', flip-flop 24 is reset and signal E becomes '1'.
becomes '0'. Therefore, for example, if digital detection signals A and B are both '1', the flip-flop 24 is set to '1', so the signal F output from the NAND gate 26 and the signal F output from the NAND gate 28 are set to '1'. The signal H becomes '0', and the signal G output from the OR gate 27 and the signal I output from the OR gate 29 become '1'. Therefore, signals J and K are '0' at this time. Next, when digital detection signal A or B becomes '0', signal J or K becomes '1'.
When digital detection signals A and B both become '0', signals J and K both become '1'. Therefore, the output of NAND gate 32 is '0'
Since the output D of the OR gate 21 also becomes '0', the flip-flop 24 is reset, and the signals F and H become '1' and the signals G and I become '1'.
0' and the signals J and K become '0' again. Thereafter, when digital detection signal A or B becomes '1', signal J or K becomes '1', respectively, and when digital detection signals A and B both become '1', signals J and K become '0' again. Return to the initial state. As explained above, the signal J or K becomes '1' only when the state of the digital detection signal A or B is reversed, and the difference in the length of the '1' time of the signals J and K is the difference between the lengths of the '1' times of the digital detection signals A and B. This indicates the phase difference of state inversion of B, and the difference is taken by the differential amplifier 46 and output as a phase difference signal. Further, the holding means 45 stores a signal corresponding to the phase difference detected at the immediately previous state inversion portion. Further, when the validity determining means 6 detects an abnormal state reversal of the digital detection signal A or B, the invalid signal becomes '1', and at that time, the holding means 45 transfers the stored value from the output of the differential amplifier 46. By subtracting with the differential amplifier 47, the phase difference portion detected at the abnormal state inversion portion can be canceled out from the already output phase difference signal. The above is the operation of the phase comparison means 5. The NAND gate 32 mentioned above is for feeding back the states of the signals J and K so that when the digital detection signals A and B are both inverted, the signals J and K become '0' after both are inverted. By doing this, both signals J and K generate a complete rising pulse even for an extremely small phase difference, and it becomes possible to detect this phase difference without producing a dead zone.

Next, the operation of the validity determining means 6 will be explained. Both digital detection signals A and B are '1'
If so, the flip-flop 24 is set and the signal E becomes '1'. At this time, when either the digital detection signal A or B is inverted and becomes '0', the signal C becomes '1', and therefore the signal L, which is the output of the NAND gate 34, becomes '0' and the flip-flop 36 is set. The signal N becomes '1'. At this time, OR gate 3
8 to 41 are all '1', and NAND gate 4
The signals P and Q outputted by the circuits 2 and 43 are both '0'. Thereafter, when the other of the digital detection signals A and B is inverted and both become '0', the output of the OR gate 41 becomes '0', and the signal Q output from the NAND gate 43 becomes '1'. That is, when the digital detection signals A and B are both normally inverted from the ``1'' state to the ``0'' state, the signal Q becomes ``1''. However, from the state where both digital detection signals A and B are '1', one of the signals inverts its state twice in succession and becomes both '1' again.
When there is an abnormal state reversal such as 1',
The output of the OR gate 38 becomes '0', and the signal P output from the NAND gate 42 becomes '1'. Conversely, when the digital detection signals A and B are both '0', the OR gate 40
becomes '0', the signal Q output from the NAND gate 43 becomes '1', and from the state where both digital detection signals A and B are '0', one of the signals inverts its state twice in a row and becomes '1' again. When the abnormal state is reversed such that it becomes '0', the OR gate 39 becomes '0' and the signal P output from the NAND gate 42 becomes '0'.
1'.

As is clear from the above explanation, when the digital detection signals A and B reverse their normal states, that is, when they have a similar state reversal although they contain a phase difference, the NAND gate 43 When the output signal Q becomes '1' and the two digital detection signals A and B reverse abnormally, that is, when one of these signals inverts twice in a row, teeth
The signal P output from the NAND gate 42 becomes '1'. That is, this signal P is
This is equivalent to the invalid signal E in the figure.

As described above, when the validity determining means 6 detects an abnormal state reversal of the digital detection signal A or B, it is possible to cancel the phase difference portion detected at the abnormal state reversal portion from the already output phase difference signal. can. With the simple configuration described above,
The noise in the tracking error signal generated at the abnormal state reversal portion is immediately canceled out, and the period of time is extremely short, making it possible to prevent tracking control from being disturbed by the noise.

It should be noted that the validity determining means 6 is not limited to the configuration of the above embodiment, and the same digital detection signal continues to be detected after one of the digital detection signals inverts the state and before the other digital detection signal inverts the state. Any configuration may be used as long as it detects a state reversal.

In the above embodiment, the noise in the tracking error signal generated at the abnormal state reversal portion is canceled out afterwards, but it is also possible to prevent noise from being mixed into the tracking error signal from the beginning at the abnormal state reversal portion. . FIG. 5 is a block diagram showing another embodiment of the tracking error detection means which prevents noise from being mixed into the tracking error signal at an abnormal state reversal portion. In Figure 5, 50
Delay means a and 50b respectively delay the digital detection signals output from the waveform shaping means 4a and 4b. Reference numeral 51 denotes phase comparison means, which has the same function as the embodiment described above, but operates in a slightly different manner in response to the output of the validity determination means 6. The rest of the structure is the same as the embodiment shown in FIG. FIG. 6 is a signal waveform diagram showing signals of each part of the above embodiment,
Waveforms A to H show the waveforms of each part of A to H in FIG. The operation of this embodiment will be explained in more detail below with reference to FIG. Detection signals A and B output from the reading head 1 are waveform-shaped by waveform shaping means 4a and 4b to become digital detection signals C and D, which are output by delay means 5.
The signals E and F are delayed by 0a and 50b. The phase comparison means 51 detects a phase difference in the state inverted portions of these signals E and F. On the other hand, the validity determining means 6 determines whether the state reversal is normal or abnormal from the digital detection signal before being delayed, and in the case of abnormality, the invalid signal G to be outputted from now on becomes '1'. shall become. Since the phase comparing means 51 compares the phases of the state inverted portions of the delayed signals E and F, before performing this comparison operation, the validity determining means 6 determines whether the state inverted portions are normal or not. It is possible to determine the Therefore, the phase comparison means 51 uses the invalid signal G
When is '1', the phase comparison operation is controlled to be substantially stopped. By doing so, it is possible to prevent noise from being mixed into the tracking error signal at an abnormal state inversion portion of the digital detection signal.

Effects of the Invention As is clear from the above description, the present invention waveform-shapes the two detection signals output from the reading head to obtain a digital detection signal, and converts the digital detection signals from an equivalent state to a state in which they are both inverted. 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 tracked. Since it has a tracking error detection means that does not output as an error signal and is configured to perform tracking control according to this tracking error signal, the gain of tracking control is stable and it is possible to prevent scratches on the recording medium. Even with large noise mixed into the detection signal by
This provides an excellent effect in that tracking control is less likely to be disturbed.

Further, a holding means for temporarily storing the output of the phase comparison means is provided, and when the validity determining means determines that the state reversal is abnormal, the value stored in the holding means is subtracted from the tracking error signal. As a result, it is possible to suppress the noise of the tracking error signal with a simple configuration.

Furthermore, by comparing the phases after delaying the digital detection signal, it is determined whether the state inversion part is normal or not before the phase comparison is performed using the state inversion part, so noise is generated based on the abnormal state inversion. The effect is that the tracking control signal is not mixed with the tracking control signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tracking control means of an optical information reproducing apparatus according to 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 concrete diagram of the main parts of the above embodiment. A circuit diagram showing a configuration example, FIG. 4 is a signal waveform diagram of each part of the above circuit diagram, FIG. 5 is a block diagram of a tracking control means of an optical information reproducing apparatus in another embodiment of the present invention, and FIG. It is a signal waveform diagram of each part in the said Example. DESCRIPTION OF SYMBOLS 1... Reading head, 3... Tracking error detection means, 4a, 4b... Waveform shaping means, 5... Phase comparison means, 6... Effectiveness determination means, 8... Tracking control means, 45... Holding means , 50...
Delay means.

Claims (1)

[Scope of Claims] 1. Projecting irradiation light onto an information track of a recording medium to form a light spot, detecting the reflected light or transmitted light, and changing the light spot according to the recorded information. a reading head that outputs a plurality of signals including at least two detection signals whose phases change relative to each other in accordance with a tracking error; and 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 tracking error signal, and the tracking error detection means outputs two digital detection signals by shaping the waveforms of the two detection signals, respectively. It includes a waveform shaping means and a phase comparison means for detecting a phase difference between two digital detection signals and outputting a phase difference signal, and one digital detection signal is output twice in a row from a state in which the two digital detection signals are equivalent to each other. chemical information, characterized in that when the state is reversed and the state becomes equivalent again, the phase comparison means is configured so as not to output a phase difference signal corresponding to the state reversal portion. playback device. 2. The phase comparison means has a holding means that holds a phase difference signal part corresponding to the immediately previous state inversion part of the two digital detection signals, and outputs a signal corresponding to the phase difference signal, and also outputs a signal corresponding to the phase difference signal and If one of the digital detection signals inverts the state twice in a row from a state where they are equivalent to each other and becomes equal again, the value held by the holding means is subtracted from the phase difference signal. The optical information reproducing device according to claim (1), which outputs a signal. 3. The phase comparison means has a delay output that delays the two digital detection signals, and from a state in which the two digital detection signals are equivalent to each other, one digital detection signal inverts the state twice in a row and becomes equal again. Claim (1) characterized in that the phase difference detection operation is substantially stopped when
The optical information reproducing device as described in .