JP2769508B2 - Apparatus and method for detecting optimum recording power of optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus and a method for detecting an optimum recording power of an optical recording medium such as a rewritable optical disk.

2. Description of the Related Art Conventionally, as this type of apparatus, there is an apparatus disclosed in Japanese Patent Application No. 62-7734, and its block diagram is shown in FIG.

Referring to FIG. 2, 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 and converts it into an electric signal. Then, an information reproduction 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. 3A 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. 3B is T, the bit length of the low-frequency signal shown in FIG. 3A 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.

Now, assuming that the same bit length variation ΔT occurs in two recording signals having bit lengths 2T and T, the duty ratio of a low-frequency signal having a bit length of 2T is lower than that of a high-frequency signal having a bit length T. Does not change much. Therefore, the duty ratio of a 2T recording signal having a low bit length is maintained at approximately 50% even if some signal distortion occurs. A 2T recording signal is used as a reference signal.

Referring to FIG. 2 again, the information reproduction signal for secondary distortion detection read by the read head 1 is input to the amplifier 2 with AC coupling by the capacitor C1, and after 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 decision logic 6, when the optimum output a is obtained, the duty ratio of the recording signal is 5%. 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 greater than 50%, the laser power is reduced so that the optimum output a is obtained.

 Next, the operation of the embodiment of FIG. 2 will be described.

First, a recording signal having a bit length of 2T (low frequency) and a recording signal having a bit length of T (high frequency) shown in FIG. 3 are alternately recorded at regular intervals on the optical disk 1a.
As shown in FIG. 7A, it is assumed that two signals having a bit length T are alternately recorded following 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 becomes 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. 4 (a) due to the MTF frequency characteristic in 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. When the duty ratio is 50%, the signal wave system has a reproduced signal waveform that is vertically symmetric with respect to the center level 12 for both the bit length 2T and the hit length T.

Next, the duty ratio shown by the dotted line in FIG.
The information reproduction signal from the information bit recorded by the smaller recording signal 10 is as shown in FIG. 4 (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 the chain line in FIG. 4A, 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 12 decreases.

Actually, as shown in FIG. 2, 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 T of the reproduction signal of the bit length 2T differs,
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.

As described above, when detecting the secondary distortion of the information reproduction signal reproduced through the reading optical system of the reading level 1, the information reproduction signal when the duty ratio is smaller than 50% as shown in FIG. This will be specifically described with reference to 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. 7 (b).

In the upper and lower envelope detection signals shown in FIG. 7, 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. 7A that has passed through the bandpass filter 4a extracts the amplitude component shown in FIG. 7 (b). On the other hand, the lower envelope detection signal shown in FIG. 7 (b) is obtained by extracting the amplitude component and converting the signal into a sine wave signal as shown in FIG. 8 (b). Become.

The amplitude component of the upper envelope detection output and the amplitude component of the lower envelope detection signal shown in FIGS. 8 (a) and 8 (b) obtained by passing through the band-pass filters 4a and 4b are converted into 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. 8, since h1> h2, a second order distortion is generated, and a judgment output b indicating that the duty ratio is smaller than 50% is generated.

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.

[Problems to be Solved by the Invention] However, in such a conventional apparatus, when detecting the optimum recording power without the second-order distortion, the recording power that exactly satisfies h1 = h2 shown in FIG. Since it is impossible for the circuit to detect the recording power, it is determined that the recording power within the range of | h1−h2 | <α is actually appropriate for the predetermined value α (α is positive).

Therefore, when the optimum recording power is detected based on the secondary distortion detection, if the initial value of the recording power is excessively large or small, the recording is performed so that (| h1−h2 |) falls within the predetermined value α. When the power is corrected, it is determined that the optimum recording power has been reached at | h1-h2 | = α at the boundary where the boundary is always determined to be appropriate.

Therefore, in order to increase the detection accuracy of the secondary distortion, the predetermined value α
Must be reduced, but when the predetermined value α is reduced, there is a problem in that detection becomes difficult in a circuit.

Also, as shown in Fig. 11, the frequency characteristic of the MTF changes due to the difference in the resolution of the optical system, so that the low frequency f1
Is different from the amplitude difference of the signal of the high frequency f2.

For example, when the MTF frequency characteristics are as shown in FIG. 11, the outputs of the upper and lower envelope detection circuits 3a and 3b shown in FIG. 2 are as shown in FIG. 12 (a). Is the first
In the case of FIG. 1, the outputs of the upper and lower envelope detection circuits 3a and 3b are as shown in FIG. 12 (b). That is, the MTF of the optical system
The amplitude difference h 'changes depending on the frequency characteristics.

Therefore, when the amplitude h ′ becomes smaller than the predetermined value α indicating the detection accuracy of the secondary distortion, when | h1−h2 | = α, the waveform of the upper envelope detection output and the waveform of the lower envelope detection output The asymmetry increases, and the detection accuracy of the secondary distortion deteriorates.

Therefore, there is a problem that the detection accuracy of the secondary distortion changes due to a difference in resolution of the optical system.

The present invention has been made in view of such conventional problems, and always minimizes the secondary distortion without increasing the circuit accuracy of the secondary distortion detection and even when the optical resolution of the head varies. It is an object of the present invention to provide an optical recording medium optimum recording power detection device capable of detecting an optimum recording power.

Means for Solving the Problems To achieve this object, the invention of claim 1 writes a predetermined signal on a recording medium by irradiating a laser beam, and writes the predetermined signal on the recording medium. Writing and reading means for reading a signal and converting it to an electric signal; amplitude difference detecting means for detecting a difference between an upper amplitude and a lower amplitude of a reference level of an output of the writing and reading means; Laser power control means for controlling the power of the laser beam irradiated at the time of writing from the reading and reading means, and an output of the amplitude difference detecting means and at least two values (+
α and −α), and the power of the laser beam is changed by the laser power control means so that an output that matches the two values is obtained. Optimum power detecting means for setting an average of the obtained powers to an optimum value of the power of the laser beam.

Further, the invention according to claim 2 writes a predetermined signal on a recording medium by irradiating a laser beam, and then reads the written predetermined signal to generate a reproduction signal,
The presence / absence and polarity of secondary distortion included in the reproduction signal are determined by comparing the amplitude of the reproduction signal with at least two predetermined values, and based on the result of the determination, the laser beam irradiating the recording medium during writing is determined. Detect the optimal value of power.

[Operation] In the apparatus and method for detecting the optimum recording power of the optical recording medium according to the present invention having such a configuration, the outputs h1 and h2 of the two amplitude difference detection circuits when the recording power is changed.
The recording power at the boundary (upper limit and lower limit) of the range where | h1−h2 | <α, that is, each recording when the output difference (h1−h2) matches the value + α and the value −α The power is detected, and the average recording power at the center of the recording power giving + α and −α is detected as the optimum recording power.

 Specifically, by changing the recording power, a recording power A (upper limit) that satisfies h1−h2 = −α and a recording power B (lower limit) where h1−h2 = + α are detected, and (A + B) / 2 The average recording power is determined as the optimum recording power.

In detecting such an optimum recording power, it is not necessary to strictly set the predetermined value α to a smaller value, so that the load on the circuit is reduced, and without being affected by variations in the optical system, The optimum recording power that minimizes the secondary distortion, that is, the optimum recording power that satisfies | h1−h2 | ≒ 0 can be detected and set.

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

In FIG. 1, reference numeral 1 denotes a reading / recording head, which writes information by a recording signal by irradiating an optical disk 1a as a recording medium with a laser beam or the like, and optically reads the recorded information to convert it into an electric signal. To output an information reproduction signal.

The secondary distortion detection circuit 20 surrounded by a broken line has the same circuit configuration as the conventional device shown in FIG.

The output of the secondary distortion detection circuit 20, that is, the output of the judgment logic 6, becomes three judgment outputs of the recording power being excessive, appropriate and insufficient.

Specifically, based on the outputs h1 and h2 of the amplitude detection circuits 5a and 5b and the predetermined value α, a comparison judgment of | h1−h2 | <α is performed to generate a judgment output of excessive, proper and under.

Reference numeral 7 denotes a CPU. The CPU 7 changes or calculates the set value of the recording power at a certain fixed rate based on the judgment output of the secondary distortion detection circuit 20. The CPU 7 controls the optimum recording power by the control function. Is performed.

Reference numeral 8 denotes a D / A converter, which converts a digital value which is a laser recording power set value sent from the CPU 7 into an analog voltage. Reference numeral 9 denotes a laser drive, which generates a laser drive current according to the set value of the recording power of the laser by the analog voltage of the D / A converter 8.

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

First, the CPU 7 reads a judgment output of the secondary distortion detection circuit 20 based on an initial value of an arbitrary recording power set at that time.

At this time, if the determination output of the secondary distortion detection circuit 20 indicates that the determination output is too small, the CPU 7 increases the set value of the recording power at a certain constant rate, and performs recording and reproduction every time the certain rate is increased. When the judgment output of the secondary distortion detecting circuit 20 becomes appropriate repeatedly, the set value B of the recording power at that time is stored and held.

That is, the initial value of the recording power is too small when it is smaller than the lower limit value in the case of (h1−h2) <+ α. In this state, the appropriate output is obtained by increasing the recording power stepwise. , (H1−h2) = + α.

 This relationship can also be expressed as (h2−h1)> − α (h2−h1) = − α.

Subsequently, the CPU 7 further increases the set value of the recording power. When the judgment output of the secondary distortion detection circuit 20 becomes excessive, the CPU 7 changes the set value A of the recording power when the judgment output immediately before the judgment output was appropriate. Remember.

That is, the judgment output of the secondary distortion detection circuit 20 becomes excessive when the upper limit value is exceeded by (h1−h2)> − α, and immediately before that, h1−h2 ≒ −α The following relationship is obtained, and the set value A of the recording power at this time is stored and held.

In this way, the CPU 7 detects the set value A at which the recording power becomes the upper limit of the appropriate range and the set value B at which the recording power becomes the lower limit.

Subsequently, the CPU 7 calculates an average value of the upper limit set value A and the lower limit set value B in a range where the recording power is appropriate as (A + B) / 2, and uses the calculated average value as a set value for providing the optimum recording power. Is set in the laser drive circuit 9, and a series of processing for setting the optimum recording power is completed.

On the other hand, if the judgment output of the secondary distortion detection circuit 20 based on the initial value of the recording power is excessive, the CPU 7 similarly reduces the set value of the recording power stepwise at a certain rate, thereby similarly recording. Upper limit value A that determines the appropriate range of power
And the lower limit set value B is detected, and the set value of the optimum recording power can be detected as an average value of both.

Further, if the judgment output of the secondary distortion detection circuit 20 based on the initial value of the recording power is appropriate, the upper limit set value A is detected by increasing the set value of the recording power from a proper state, for example, at a certain rate, Thereafter, the lower limit set value B may be detected by decreasing the set value of the recording power.

[Effects of the Invention] As described above, according to the present invention, it is not necessary to tighten the accuracy of the circuit for detecting the secondary distortion, and the present invention is not affected by the variation in resolution of the head optical system. It is possible to detect and set the optimum recording power that minimizes the secondary distortion.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. 2 is a block diagram showing a conventional device; FIG. 3 is an explanatory diagram of two different frequency recording signals to be detected as secondary distortion; FIG. 4 is a signal waveform diagram showing a reproduced signal when the duty ratio of the recording signal is 50%, smaller than 50%, and larger than 50%; FIG. 5 is a diagram of the reproduced signal based on the MTF frequency characteristic of the reading optical system. FIG. 6 is a signal waveform diagram showing a sag of a reproduced signal caused by a difference in a DC component; FIG. 7 is a waveform explanatory diagram of an envelope detection signal in FIG. 2; FIG. 9 is a signal waveform diagram showing the output of the bandpass filter of FIG. 2; FIG. 9 is a signal waveform diagram showing a change in the duty ratio of the recording signal; FIG. 10 is a graph diagram showing the MTF frequency characteristics of the reading optical system; Fig. 11 is a graph showing the difference in MTF frequency characteristics due to the difference in resolution of the reading optical system. Full view; FIG. 12 is a waveform diagram of the upper and lower envelope detection output by the difference in MTF frequency characteristics of FIG. 11. 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 7: CPU 8: D / A converter 9: Laser drive circuit

Claims (2)

(57) [Claims] 1. 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, Amplitude difference detecting means for detecting a difference between an upper amplitude and a lower amplitude of a reference level of an output of the reading means; and laser power control for controlling power of a laser beam irradiated at the time of writing from the writing and reading means. Means, and an output of the amplitude difference detecting means and at least two values (+ α
And -α), and the laser power control means changes the power of the laser beam so as to obtain an output that matches the two values, and obtains an output that matches the two predetermined values. An optimum power detection means for setting an average of the respective powers when the power is applied to an optimum value of the power of the laser beam. 2. A predetermined signal is written on a recording medium by irradiating a laser beam, and then the read predetermined signal is read to generate a reproduced signal. The amplitude of the reproduced signal and at least two predetermined Determining the presence or absence and polarity of the secondary distortion included in the reproduced signal by comparing the value with a value, and detecting an optimum value of the power of the laser beam applied to the recording medium during writing based on the determination result. Optimum recording power detection method for optical recording media.