JP2600659B2 - Apparatus for detecting secondary distortion of recording signal and optical recording apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method for detecting the presence or absence of secondary distortion contained in information recorded on a recording medium such as an optical disk or a magneto-optical disk. The present invention relates to a distortion detection device.

(Prior Art) Conventionally, when information is recorded in the form of recording pits having mechanical irregularities on an optical disk by irradiating a laser beam based on the recorded information, or recording on a magneto-optical disk in a magnetization direction oriented vertically. When recording information in the form of bits, a binary signal having a duty ratio of 50% is recorded in order to obtain an appropriate laser drive power, and the duty ratio of the recorded information recorded on the medium is set to 50%. That is, the laser power is calibrated so as not to include the secondary distortion, and recording is performed using the calibrated laser power.

Incidentally, a spectrum analyzer is usually used for measuring the secondary distortion included in the information recorded on the optical disc. That is, information recorded on an optical disk is optically read by a read head and converted into an electric signal, and an information reproduction signal obtained from the read head is analyzed by a spectrum analyzer.

When recording information is analyzed by this spectrum analyzer, in a recording state by an ideal recording signal in which the duty ratio given by (Ta / T) shown in FIG. 8A is 50%, As shown in FIG. 9 (a), the measurement result of the recorded information by the spectrum analyzer shows that only the odd-order spectral components such as 3fs, 5fs,... Are obtained with respect to the recording frequency (fundamental frequency) fs.

On the other hand, when the duty ratio of the recording signal is smaller than 50% as shown in FIG. 8B, or when the duty ratio is larger than 50% as shown in FIG.
The recording information based on such a recording signal is obtained by the measurement result of the spectrum analyzer shown in FIG. 9 (b). In this case, the recording frequency fs has an even order such as 2fs, 3fs, 4fs. Spectral components are also generated, and the secondary spectral component of 2 fs is called secondary distortion.

(Problems to be Solved by the Invention) However, in the conventional secondary distortion detection method using the spectrum analyzer, for example, the secondary distortion is not generated, that is, the duty ratio of the recording information is maintained at 50%. As described above, it is difficult to automatically control the laser power serving as a recording signal for the following reasons.

First, as shown in FIGS. 8 (b) and 8 (c), the measurement results of the spectrum analyzer indicate that the duty ratio of the recording signal is less than 50% or less than 50%.
As shown in FIG. 2B, a second-order spectrum component representing second-order distortion appears, and the polarity cannot be detected. Therefore, it is not clear which of the duty ratios of the recording signals is shifted with respect to the duty ratio of 50% which does not cause the secondary distortion even if the secondary distortion can be detected, and it is not possible to judge the increase or decrease of the laser power.

Secondly, when the recording frequency is low, that is, when the number of recording bits is large, there is a problem that the detection accuracy of the secondary spectrum component by the spectrum analyzer is reduced. Therefore, it is necessary to increase the recording frequency fs.

However, when the recording frequency is increased to some extent, secondary spectrum components cannot be detected due to the MTF frequency characteristics of the reading optical system. That is, the MTF indicates the frequency characteristic of the sensitivity at which the optical system detects recorded information, and has the characteristic shown in FIG. As is clear from FIG. 10, the recording frequency fs
Is somewhat higher as shown in the figure, the MTF becomes zero at 2 fs which gives a secondary spectrum component, and a 2 fs signal cannot be detected.

(Means for Solving the Problems) The present invention has been made in view of such a conventional problem, and detects the presence or absence of secondary distortion included in information recorded on a recording medium such as an optical disk, and at the same time, detects polarity. That is, a recording signal secondary distortion detecting device and a secondary distortion detecting device that can easily detect in which direction the duty ratio of the recording signal causing the secondary distortion is deviated from the duty ratio of 50%. It is an object of the present invention to provide an optical recording apparatus capable of appropriately controlling the laser power at the time of recording by detection of the information.

In order to achieve this object, a first aspect of the present invention provides a reading unit for reading a signal from a recording medium on which the signal is recorded at two different frequencies, and a reading unit for reading the signal, the output being higher than a certain reference level. Amplitude difference detection means for detecting the difference between the amplitude and the lower amplitude, and determination means for determining the presence or absence and polarity of the secondary distortion included in the signal by comparing two outputs of the amplitude difference detection means. A configuration was provided.

Preferably, the amplitude difference detecting means includes an envelope detecting means.

Preferably, the amplitude difference detecting means includes a half-wave rectifier.

Preferably, the amplitude difference detecting means detects the difference after AC-amplifying the output of the reading means.

The second invention irradiates a laser beam,
Writing and reading means for writing a predetermined signal to a recording medium and reading the written predetermined signal and converting the read signal into an electric signal; and a second-order distortion included in an output from the writing and reading means. A determination means for determining presence / absence and polarity, and a laser power control means for controlling the power of a laser beam emitted from the writing and reading means at the time of writing based on the determination result by the determination means.

(Operation) According to the configuration of the first aspect, a low-frequency information reproduction signal and a high-frequency information reproduction signal are alternately obtained by optically reading recorded information, and the MTF frequency characteristic of the reading optical system is obtained. Depending on the frequency, the reproduction level is higher at a lower frequency and the reproduction level is lower at a higher frequency.

Also, looking at the change due to the duty ratio of the playback signal,
With respect to the same information bit variation, for example, the same diameter change of information pits having different diameters according to the magnitude of the frequency, the change in the duty ratio of the reproduced signal of the larger information pit (lower frequency) is small, and conversely, The change in the duty ratio of the reproduction signal of the smaller (higher frequency) becomes larger.
Therefore, based on a reproduced signal obtained from a low-frequency information bit having a small change in duty ratio, a change due to secondary distortion of a reproduced signal obtained from a high-information bit having a large change in duty ratio is detected. .

Further, although there is almost no change in the level of the low-frequency information reproduction signal serving as a reference with respect to the change from the duty ratio of 50%, the DC component of the high-frequency information reproduction signal decreases as the duty ratio decreases. As the duty ratio increases, the DC component increases. Therefore, looking at the amplitude center level of the low-frequency information reproduction signal,
The information reproduction signal of a high frequency shifts downward when the duty ratio decreases, and shifts upward when the duty ratio increases.

Therefore, according to the first aspect, the reproduced signal is AC-coupled so as to be shifted from the amplitude center level depending on the duty ratio, and then the envelope detection is separately performed on the upper side and the lower side of the amplitude center level.

If the duty ratio is 50%, the amplitude component is equal between the upper detection signal and the lower detection signal by this envelope detection, and if the duty ratio is smaller, the amplitude component of the upper detection signal is lower than that of the lower detection signal. When the duty ratio becomes larger than the amplitude component and the duty ratio further increases, a relationship occurs that the amplitude component becomes smaller on the upper side than on the lower side.

Therefore, the amplitude component is extracted by passing each envelope detection output through a band-pass filter to make a sine wave, and then the amplitude peak value is detected. From the magnitude comparison of the detected peak values, the presence or absence of secondary distortion and secondary distortion are generated. In this case, the magnitude relation with respect to the duty ratio of 50% is determined.

Further, according to the second aspect, the presence / absence and polarity of the secondary distortion of the signal are detected by the determination means, and the laser power can be appropriately controlled based on the result.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention.

First, the configuration will be described. Reference numeral 1 denotes a read head, which optically reads recorded information written on an optical disk 1a as a recording medium by a recording signal formed by irradiating a laser beam or the like, converts the information into an electrical signal, Is output.

Here, as information bits to be written on the optical disk 1a in order to detect the secondary distortion of the recorded information, information bits having two different frequencies are recorded alternately at the same time with a duty ratio of 50%. When the secondary distortion is detected, a portion in which the information bits having the two different frequencies are alternately recorded at the same time is reproduced.

The information bits to be recorded on the optical disk 1a for detecting the secondary distortion will be specifically described. For example, a low-frequency recording signal shown in FIG. 2A and a high-frequency recording signal shown in FIG. Record the signal. Here, assuming that the bit length of the high frequency signal shown in FIG. 2 (b) is T, the bit length of the low frequency signal shown in FIG. 2 (a) is set to 2T. Of course, the duty ratio of each recording signal having a bit length of 2T, T is set to 50%, but the duty ratio fluctuates as shown by a broken line due to variations in the laser power serving as the recording signal. Here, 2 having a bit length of 2T, T
Assuming that the same bit length variation ΔT occurs in one recording signal, the bit length is longer than that of a signal having a high frequency of bit length T.
The duty ratio of a signal having a low frequency of 2T does not change much. Therefore, the duty ratio of a recording signal having a low frequency and a bit length of 2T is approximately 50% even if some signal distortion occurs.
%, And a detection signal of a low frequency and a bit length of 2T is used as a reference signal in the detection of the second-order distortion which will be described later.

Referring again to FIG. 1, the information reproduction signal read by the read head 1 for secondary distortion detection is input to the amplifier 2 with AC coupling by the capacitor C1, and after the AC amplification by the amplifier 2, Similarly, it is input to each of the envelope detection circuits 3a and 3b via the AC coupling capacitor C2.

The envelope detection circuit 3a performs envelope detection on the information reproduction signal obtained from the amplifier 2 above the amplitude center level, while the envelope detection circuit 3b performs envelope detection below the amplitude center level.

Outputs of the envelope detection circuits 3a and 3b are respectively supplied to band-pass filters 4a and 4b, and the band-pass filters 4a and 4b respectively extract amplitude components of the envelope detection outputs and simultaneously convert the amplitude components into sine wave signals.

Outputs of the band-pass filters 4a and 4b are supplied to amplitude detection circuits 5a and 5b, and detect amplitude peak values in amplitude components of the envelope detection signals that have passed through the band-pass filters 4a and 4b, respectively.

The outputs of the amplitude detection circuits 5a and 5b are applied to a judgment logic 6 as judgment means for judging the degree of secondary distortion included in the information reproduction signal based on the magnitude of the detected peak value. Assuming that the amplitude peak value detected by the amplitude detection circuit 5a is h1 and the amplitude detection value detected by the amplitude detection circuit 5b is h2, the determination logic 6 performs the following determination processing based on the amplitude peak values h1 and h2. .

(A) When h1 = h2; It is determined that the duty ratio of the information reproduction signal is 50% and does not include the secondary distortion.

(B) When h1>h2; It is determined that the duty ratio of the information reproduction signal is smaller than 50% and that the secondary distortion is present.

(C) When h1 <h2: It is determined that the information reproduction signal has a duty ratio larger than 50% and that there is a second-order distortion.

That is, the judgment logic 6 selects one of the outputs a, b, c corresponding to the judgment conditions (a) to (c) based on the detected peak values h1, h2 from the amplitude detection circuits 5a, 5b. For example, when the laser power of the recording signal is controlled based on the output of the judgment logic 6, when the optimum output a is obtained, the duty ratio of the recording signal is 50%. The value at that time is maintained. On the other hand, when the judgment output b is obtained, since the duty ratio of the recording signal is small, the laser power is increased to control the duty ratio of the recording signal to 50% at which the optimum output a can be obtained. Conversely, when the judgment output c is obtained, since the duty ratio of the recording signal is larger than 50%, the laser power is reduced so that the optimum output a is obtained.

 Next, the operation of the embodiment of FIG. 1 will be described.

First, a recording signal having a bit length of 2T (low frequency) and a recording signal having a bit length T (high frequency) shown in FIG. 2 are alternately recorded at regular intervals on the optical disk 1a.
As shown in FIG. 3A, it is assumed that a signal having a bit length T is recorded alternately after a recording signal having a bit length 2T.

As described above, when information bits composed of two different frequencies recorded on the optical disk 1a are reproduced by the read head 1 to obtain an information reproduction signal, the detection sensitivity of the reading optical system shown in FIG. Bit length 2 depending on characteristics
The reproduced signal level differs between the reproduced signal of T and the reproduced signal of bit length T.

That is, since the recording frequency of the bit length 2T is low, the value of the MTF is large as is clear from the MTF frequency characteristic in FIG.
As a result, the reproduction level of the information reproduction signal from the recording bit having the bit length of 2T is increased as shown by the signal 7 in FIG.
On the other hand, since the frequency of the recording signal having the bit length T is high, the value of the MTF in FIG. 10 is small, and as shown in the signal 8 in FIG. As described above, the reproduction level becomes low, and the reproduction signal having the bit length T becomes a substantially sine wave because a signal having a frequency component more than twice the fundamental frequency cannot be detected from the optical system.

Therefore, as shown by the solid line 9 in FIG. 3A due to the MTF frequency characteristic of the reading optical system, the information reproduction signal of the information bit recorded at the duty ratio of 50% is shown in FIG.
The signal waveform shown in FIG. The signal waveform at the duty ratio of 50% is a reproduced signal waveform that is vertically symmetrical with respect to the center level 12 for both the bit length 2T and the bit length T.

Next, the duty ratio shown by the dotted line in FIG.
The information reproduction signal from the information bit recorded with the smaller recording signal 10 is as shown in FIG. 3 (c). That is,
Since the reproduced signal of bit length 2T is hardly affected by the duty ratio fluctuation, it has a symmetrical waveform above and below the center level 12, but the reproduced signal of bit length T has a duty ratio smaller than 50%. As a result, the waveform becomes a waveform in which the DC component decreases, the amplitude component above the center level 12 decreases, and the amplitude component below the center level 12 increases.

Further, as shown by a dashed line in FIG. 3A, the information reproduction signal of the information bit recorded by the recording signal 11 in which the duty ratio of the recording signal is larger than 50% is shown in FIG.
It becomes as shown in. That is, the reproduced signal having a bit length of 2T has almost no fluctuation due to the increase in the duty ratio, and thus has a substantially symmetrical waveform above and below the center level 12, but the reproduced signal having the bit length T has a DC component due to an increase in the duty ratio. Increases, the amplitude above the center level 12 increases, and conversely, the amplitude below the center level decreases.

Actually, as shown in FIG. 1, since the AC coupling is performed by the capacitors C1 and C2, when the magnitude of the DC component of the reproduction signal of the bit length 2T and the magnitude of the DC component of the reproduction signal of the bit length T are different, the fifth
As shown in the figure, the center level 12a of the reproduced signal having a bit length of 2T
A sag 13 is generated between the reproduced signal having the bit length T and the center level 12b. It must be detected while this sag is occurring. Therefore, the period τ for recording the signal having the bit length 2T and the signal having the bit length T cannot be made too large. In the present embodiment, the time for recording the signal having the bit length 2T and the time for recording the T signal are the same time in both directions (each τ / 2), because the final detection signal can be large. . Therefore, it is not always necessary to be the same time.

As described above, for detecting the secondary distortion of the information reproduction signal reproduced through the reading optical system of the reading head 1, the information reproduction signal when the duty ratio is smaller than 50% as shown in FIG. This will be described in detail using an example.

The information reproduction signal reproduced by the read head 1 when the duty ratio is smaller than 50% is AC-amplified by the amplifier 2 and then supplied to the envelope detection circuits 3a and 3b.
a produces a detection output of the upper envelope shown in FIG.
On the other hand, the envelope detection circuit 3b generates a detection output of the lower envelope shown in FIG. 6 (b).

In the upper and lower envelope detection signals shown in FIG. 6, a portion having a large amplitude represents a reproduced signal having a bit length of 2T, and a portion having a small amplitude component represents a reproduced signal having a bit length of T.

The upper and lower envelope detection signals detected by the envelope detection circuits 3a and 3b are input to the band-pass filters 4a and 4b. Here, the center frequency fc of the bandpass filters 4a and 4b
Is set to fc = 1 / τ, and the upper envelope detection signal shown in FIG. 9A passing through the bandpass filter 4a extracts the amplitude component shown in FIG. 6B. On the other hand, the lower envelope detection signal shown in FIG. 6B is a signal whose amplitude component is extracted and converted into a sine wave signal as shown in FIG. 7B. .

The amplitude component of the upper envelope detection output and the amplitude component of the lower envelope detection signal shown in FIGS. 7A and 7B obtained by passing through the band-pass filters 4a and 4b are converted to an amplitude detection circuit 5a. , 5b, the amplitude peak values h1, h2 are detected, and the determination logic 6 detects the presence or absence of secondary distortion and determines the duty ratio based on the magnitude relationship between the detected peak values h1, h2.
Judge the deviation from 50%.

That is, in the case of FIG. 7, since h1> h2, a judgment output b is generated indicating that secondary distortion has occurred and the duty ratio is smaller than 50%.

Of course, as shown in FIG.
When the duty ratio is larger than 50%, the detection peak values h1 and h2 obtained from the amplitude detection circuits 5a and 5b satisfy h1 <h2. Produces a decision output c. Furthermore,
When the duty ratio is 50%, h1 = h2. In this case, the optimum output a is generated.

In the above embodiment, the information reproduction signal of the information bit of the bit length 2T and the information bit of the bit length T recorded on the optical disk is taken as an example. Therefore, it is desirable to increase the difference between the bit lengths of recording signals having different frequencies within the range of the MTF frequency characteristic shown in FIG.

In the above embodiment, the control of the laser power serving as the recording signal based on the detection of the second-order distortion is taken as an example. However, the present invention is not limited to this. It may be used for measuring the ratio, or appropriate automatic control may be performed based on the detection output of the secondary distortion or duty ratio.

According to the above embodiment, after the outputs of the envelope detection circuits (3a, 3b) pass through the band-pass filters (4a, 4b), the amplitudes are detected by the amplitude detection circuits (5a, 5b). Although the difference is determined by the determination logic 6, the present invention is not limited to this. For example, the output of the half-wave rectifier circuit may be smoothed by a capacitor and the DC level may be compared and determined.

FIG. 11 shows an example in which the envelope detection circuit in FIG. 1 is composed of a half-wave rectifier circuit 20 and a smoothing circuit 21, and FIG. 12 is a diagram showing signal waveforms at various parts of the circuit. Reference numeral 12 denotes a signal amplitude center level, reference numeral 31 denotes an output waveform of the half-wave rectifier circuit 20, and reference numeral 32 denotes an output waveform of the smoothing circuit 21.

In short, the present invention is configured to detect the difference between the amplitudes of the reproduction information signal depending on the frequency above and below the amplitude center level, and to determine the magnitude relationship. The present invention can be applied to not only a rotating disk-shaped medium but also, for example, a card-shaped medium which moves linearly, and is not limited to the shape of the medium.

(Effects of the Invention) As described above, according to the present invention, the secondary distortion can be easily reduced based on the change in the DC component of the information reproduction signal due to the change in the duty ratio of the recording signal for the optical disk or the like from 50%. Whether the duty ratio can be detected and the secondary distortion is detected and the duty ratio is 50% at which no secondary distortion occurs,
Since it is possible to determine whether the duty ratio is larger or smaller than 50%, it is possible to correct the laser power at the time of recording, which has been difficult with, for example, the detection of secondary distortion by a conventional spectrum analyzer.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of recording signals having two different frequencies to be subjected to secondary distortion detection, and FIG. , 50
FIG. 4 is a signal waveform diagram showing the information reproduction signal when it is smaller than 50% and larger than 50%. FIG. 4 is a signal waveform diagram showing a change in the level of the reproduction signal due to the MTF frequency characteristic of the reading optical system.
FIG. 6 is a signal waveform diagram showing a zag of a reproduced signal caused by a difference in a DC component. FIG. 6 is an explanatory diagram of a waveform of the envelope detection signal of FIG. 1, and FIG. 7 is an output of the bandpass filter of FIG. FIG. 8 is a signal waveform diagram showing a change in the duty ratio of a recording signal, FIG. 9 is a spectrum distribution diagram showing a spectrum component with respect to a fundamental frequency obtained by a conventional spectrum analyzer, and FIG. MT of reading optical system
FIG. 11 is a graph showing F frequency characteristics, FIG. 11 is a circuit block diagram showing another embodiment, and FIG. 12 is a signal waveform diagram thereof. 1: Read head 1a: Optical disk 2: Amplifier 3a, 3b: Envelope detection circuit 4a, 4b: Bandpass filter 5a, 5b: Amplitude detection circuit 6: Judgment logic (judgment means)

Claims (5)

(57) [Claims] 1. Reading means for reading a signal from a recording medium on which a signal is recorded at two different frequencies, and a difference between an upper amplitude and a lower amplitude of a reference level of an output of the reading means. And a determination means for determining the presence or absence and the polarity of the secondary distortion included in the signal by comparing two outputs of the amplitude difference detection means. Signal second-order distortion detector. 2. The apparatus according to claim 1, wherein said amplitude difference detecting means includes an envelope detecting means. 3. The apparatus according to claim 1, wherein said amplitude difference detection means includes a half-wave rectification means. 4. An apparatus according to claim 1, wherein said amplitude difference detecting means detects the difference after AC-amplifying an output of said reading means. . 5. A writing and reading means for writing a predetermined signal on a recording medium by irradiating a laser beam, reading the written predetermined signal and converting it into an electric signal; Determining means for determining the presence or absence and polarity of the secondary distortion included in the output from the reading means; and controlling the power of the laser beam emitted at the time of writing from the writing and reading means based on the determination result by the determining means. And a laser power control means.