JPH0229930A - Optimal recording power detection device and method for optical recording media - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optimum recording power detection device for an optical recording medium such as a rewritable optical disc.

[Prior Art] Conventionally, this type of device includes the device disclosed in Japanese Patent Application No. 1987-7734, whose block diagram is shown in FIG.

In FIG. 2, first, the configuration will be explained. Reference numeral 1 denotes a reading head, which optically reads recorded information written on an optical disk 1a as a recording medium by a recording signal formed by irradiation with a laser beam, etc., and converts it into an electrical signal. and outputs an information reproduction signal.

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

To specifically explain the information bits recorded on the optical disc 1a to detect secondary particles, for example, a low frequency recording signal shown in FIG. 3(a) and a high frequency recording signal shown in FIG. 3(b) Record the signal.

Here, if the bit length of the high frequency signal shown in FIG. 3(b) is T, the bit length of the low frequency signal shown in FIG. 3(a) is set to 2.Of course, the bit length is 2T. , T
The duty ratio of each recording signal is set to 50%, but due to variations in the laser power used as the recording signal, the duty ratio varies as shown by the broken line.

Now, if two recording signals with bit lengths 2T and T have the same bit length fluctuation Δt, the duty of the low frequency signal with bit length 2 is higher than that of the high frequency signal with bit length T. The ratio does not change much. Therefore, the duty ratio of the recording signal of two bit lengths with low frequency is maintained at approximately 50% even if some Shintan distortion occurs.
In secondary child detection, which will be explained later, a recording signal with a low frequency and a bit length of 2T is used as a reference signal.

Referring again to FIG. 2, the information reproduction signal for second-order distortion detection read by the reading head 1 is input to the amplifier 2 with AC coupling by the capacitor C1, and after being AC amplified by the amplifier 2, Also capacitor C2 for AC coupling
The signal is inputted to each of the envelope detection circuits 3a and 3b via.

The envelope detection circuit 3a performs envelope detection of 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.

The outputs of the envelope detection circuits 3a and 3b are given to bandpass filters 4a and 4b, respectively.
4b, the amplitude component of the envelope detection output is extracted and simultaneously converted into a sine wave signal.

The outputs of the bandpass filters 4a and 4b are sent to the amplitude detection circuit 5a.
, 5b, and detects the amplitude peak values of the amplitude components of the envelope detection signals that have passed through the bandpass filters 4a and 4b.

The outputs of the amplitude detection circuits 5a and 5b are provided to a judgment logic 6 as a judgment means for judging the degree of quadratic included in the information reproduction signal based on the magnitude of the detected peak value. The judgment logic 6 performs the following judgment process based on the amplitude peak values hl and h2, assuming that the amplitude peak value detected by the amplitude detection circuit 5a is hl and the amplitude detection value detected by the amplitude detection circuit 5b is h2. .

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

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

(c) When hl<h2; It is determined that the duty ratio of the information reproduction signal is greater than 50% and there is secondary content.

That is, the judgment logic 6 uses the detected peak values i1. (a) to (C) above based on h2
For example, when outputting one of the corresponding outputs a, b, and c under the judgment conditions of , and controlling the laser power of the recording signal based on the output of the judgment logic 6, the optimum output a was obtained. Sometimes, the duty ratio of the recording signal is 50%, so the laser power is maintained at the value at that time, while when a judgment output is obtained, the duty ratio of the recording signal is small, so the laser power is kept at that value. By increasing the duty ratio of the recording signal, the duty ratio of the recording signal is controlled to 50% where the optimum output a is obtained, and conversely, when the judgment output C is obtained, the duty ratio of the recording signal is greater than 50%, so the laser power is lowered. control is performed so that the optimum output a is obtained.

Next, the operation of the embodiment shown in FIG. 2 will be explained.

First, the optical disc 1a has a bit length of 2T as shown in FIG.
A recording signal (low frequency) with a bit length T (low frequency) and a recording signal @ (high frequency) with a bit length T are alternately recorded at regular intervals. For example, as shown in Figure 4 (a), a recording signal with a bit length T Assume that two signals of bit length T are subsequently recorded alternately.

When the information bits of two different frequencies recorded on the optical disk 1a are reproduced by the reading head 1 to obtain an information reproduction signal, the detection sensitivity of the reading optical system shown in FIG. 10, that is, the MTF with respect to the recording frequency Depending on the characteristics, the reproduced signal level of the reproduced signal with a bit length of 2 and the reproduced signal with the bit length T is different.

In other words, since the recording frequency for two bit lengths is low, the 10th
As is clear from the MTF frequency characteristics shown in the figure, the value of MTF is large, and as a result, the reproduction level of the information reproduction signal from the recording bits with a bit length of 2 becomes high as shown in signal 7 of FIG. On the other hand, since the frequency of the recording signal with bit length T is high, the value of MTF in FIG. 10 becomes small, and as shown in FIG. The playback level becomes lower as shown in
Furthermore, the reproduced signal with bit length T becomes a substantially sinusoidal wave because signals with frequency components that are twice the fundamental frequency or more cannot be detected by the optical system.

Therefore, due to the MTF frequency characteristics in the reading optical system, the duty ratio is 50%, as shown by the solid line 9 in Fig. 4(a).
The information reproduction signal of the information bits recorded in FIG.
) is the signal waveform shown.

The signal waveform when the duty ratio is 50% is bit length 2.
For both signals with a bit length of 1 and a bit length of T, the reproduced signal waveforms are vertically symmetrical with respect to the center level 12.

Next, the duty ratio shown by the dotted line in Fig. 4(a) is 50%.
The information reproduction signal from the information bits recorded with the smaller recording signal 10 is as shown in FIG. 4(C). In other words, since the reproduced signal with a bit length of 2 bits is hardly affected by the duty ratio fluctuation, the center level is 1.
2, the waveform is symmetrical above and below, but for the reproduced signal with bit length T, when the duty ratio becomes smaller than 50%, the DC component decreases, and the upper amplitude component of center level 12 decreases, while at the same time the lower amplitude component decreases. The resulting waveform has an increased amplitude component.

Furthermore, as shown by the dashed line in FIG. 4(a), the recording signal 11 whose duty ratio is greater than 50%
The information reproduction signal of the information bits recorded in FIG.
> is shown. In other words, since the reproduced signal with a bit length of 2T has almost no fluctuation due to an increase in the duty ratio, it has a waveform that is approximately symmetrical above and below the center level 12, but the reproduced signal with a bit length T has a DC current as the duty ratio increases. As the component increases, the amplitude above the center level 12 increases and conversely the amplitude below the center level 12 decreases.

Actually, as shown in Figure 2, capacitors C1 and C2
Since the AC coupling is performed at
As shown in FIG. 6, a rig 13 is generated between the center level 12a of the reproduced signal with bit length 2T and the center level 12b of the reproduced signal with bit length T. This rig must be detected while it is occurring. Therefore, the period for recording a signal with two pill lengths and a signal with a bit length T cannot be made very large.

Regarding the second-order distortion detection of the information reproduction signal reproduced through the reading optical system of the reading head 1, for example, FIG.
), the information reproduction signal having a duty ratio smaller than 50% will be specifically explained.

The information reproduction signal reproduced by the reading head 1 when the duty ratio is smaller than 50% is AC amplified by the amplifier 2 and then applied to the envelope detection circuits 3a and 3b. The envelope detection circuit 3b produces a detection output of the upper envelope shown in FIG. 7(b).

In the upper and lower envelope detection signals shown in FIG. 7, a portion with a large amplitude component represents a reproduced signal with a bit length of 2T, and a portion with a small amplitude component represents a reproduced signal with a bit length of T.

The upper and lower envelope detection signals subjected to envelope detection by the envelope detection circuits 3a and 3b are input to band pass filters 4a and 4b. Here, the center frequency fc of the bandpass filter 4b is set to fc=1/τ, and the upper envelope detection signal shown in FIG. 7(a) that has passed through the bandpass filter 4a is The amplitude component shown in Fig. 8(a) is extracted and converted into a sine wave, and the lower envelope detection signal shown in Fig. 7(b) is the signal shown in Fig. 8(b). The amplitude component is extracted and the signal is converted into a sine wave signal.

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 obtained by the amplitude detection circuit 5a. , 5b, the amplitude peak value h1.
h2 is detected, and in the judgment logic 6, the detected peak value h1. Based on the magnitude relationship of h2, the presence or absence of a secondary child is detected and the deviation of the duty ratio from 50% is determined.

That is, in the case of FIG. 8, since hl>h2, a determination is made that a secondary child is generated and the duty ratio is smaller than 50%.

Of course, as shown in FIG. 4(d), the duty ratio is 50.
%, the detected peak value h1. obtained from the amplitude detection circuit J a t5b. Since h2 is hl<h2, the decision logic 6 determines the occurrence of a secondary child and at the same time generates a decision output C in which the duty ratio is greater than 50%. Furthermore, when the duty ratio is 50%, h
l,=h2, and in this case, the optimum output a is produced.

[Problems to be Solved by the Invention] However, in such a conventional device, when detecting the optimal recording power without secondary particles, the recording power that strictly satisfies h1=h2 as shown in FIG. Since it is impossible to detect it due to the circuit, it is actually determined that the recording power that falls within the range of hl-h2<α for a predetermined value α (α is positive) is appropriate.

Therefore, when detecting the optimum recording power based on second-order distortion detection, if the initial value of the recording power is too large or too small, the When the power is corrected, it is determined that the optimum recording power is reached at hl-h2+=α at the boundary where it is always determined to be appropriate.

Therefore, in order to improve the accuracy of secondary child detection, it is necessary to reduce the predetermined value α, but if the predetermined value α is reduced, there is a problem in that detection becomes difficult due to the circuit.

Also, as shown in Figure 11, the frequency characteristics of the MTF change due to differences in the resolution ability of the optical system, so the amplitude difference between the low frequency f1 signal and the high frequency f2 signal will differ. .

For example, when the MTF frequency characteristic is ■ in Figure 11, the second
The outputs of the upper and lower envelope detection circuits 3a and 3b shown in the figure are J in FIG. 12(a), while the MTF
When the frequency characteristics are shown in Figure 11 (■), the outputs of the upper and lower envelope detection circuits 3a and 3b are as shown in Figure 12 (b).
become that way. That is, the amplitude difference changes depending on the MTF frequency characteristics of the optical system.

Therefore, when the amplitude decreases with respect to a predetermined value α that indicates the detection accuracy of the quadratic, when hl-h21-α, there is an asymmetry between the waveform of the upper envelope detection output and the waveform of the lower envelope detection output. becomes large, and the secondary child detection accuracy deteriorates.

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

The present invention was made in view of these conventional problems, and it is possible to always minimize the secondary distortion even if there are variations in the optical decomposition of the head without increasing the circuit accuracy of secondary distortion detection. It is an object of the present invention to provide an optimal recording power detection device for an optical recording medium that can detect the optimal recording power.

[Means for Solving the Problems] In order to achieve this object, the present invention optically records binary information with a scheduled duty ratio of 50% using two different frequencies on a recording medium alternately, and , recording reading means for optically reading the recorded information and converting it into an electric signal; AC amplifying means for AC amplifying the output signal of the recording reading means; and above the amplitude center level of the output of the AC amplifying means. two amplitude difference detection means for detecting each of the amplitude differences hl and h2 caused by the difference in recording frequency on the lower side; an output difference (hl-h) of the two amplitude difference detection means;
2) Judgment means that compares 2) with predetermined values +α and -α to determine the presence or absence and polarity of secondary distortion included in the recorded information; and: laser drive means that generates a current necessary to emit recording power. and: The output difference (old -h2) of the two amplitude difference detection means from the judgment means is the value +α and the value -
The recording power is changed by the laser driving means so as to obtain a judgment output that matches α, and the optimum recording power is determined as the average value of each recording power when an output difference that matches α and −α is obtained. and a control means for detecting and setting the laser driving means.

[Function] In the optimum recording power detection device for an optical recording medium of the present invention having such a configuration, it is possible to determine the difference between the outputs of the two amplitude difference detection circuits h2 and h2 when the recording power is changed. , each recording power that is the boundary (upper limit and lower limit) of the range where hl-h21<α, that is, the output horn difference (hl-h2) is the value +α and the value -α.
Detect each recording power when it matches, and calculate the +α and −
The average recording power that is the center of the recording powers that give α is detected as the optimum recording power.

Specifically, by changing the recording power hl-h2=-α To the recording power (upper limit), hl-h2. =+α Detect the recording power B (lower limit) that becomes (A+8)/2 Find the average recording power that gives the optimum recording power.

In detecting such optimal recording power, a predetermined value α
Since there is no need to strictly set the value of
That is, it is possible to detect and set the optimum recording power that satisfies hl-h21tanO.

[Example] FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, numeral 1 denotes a reading/recording head, which writes information in the form of a recording signal by irradiating an optical disk 1a as a recording medium with a laser beam or the like, and optically reads the written recording information and converts it into an electrical signal. and outputs an information reproduction signal.

A secondary distortion detection circuit 2o surrounded by a broken line has the same circuit configuration as the conventional device shown in FIG.

The output of the second-order distortion detection circuit 20, that is, the output of the determination logic 6, becomes three determination outputs: excessive, appropriate, and insufficient recording power.

Specifically, the output h1, [1
2 and a predetermined value α, a comparison judgment of hl−h21<α is performed to generate judgment outputs of excessive, appropriate, and insufficient.

7 is a CPU, and the CPU 7 changes or modulates the setting value of the recording power at a certain rate based on the judgment output of the secondary distortion detection circuit 20, and the control function of the CPU 7 determines the optimal recording. Power detection processing is performed.

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

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

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

At this time, if the judgment output of the secondary distortion detection circuit 20 indicates that the output is too low, the CPU 7 increases the set value of the recording power at a certain rate, and performs recording/reproduction every time the set value of the recording power is increased by a certain rate. Repeatedly, when the judgment output of the secondary distortion detection circuit 20 becomes appropriate, the recording power setting value B at that time is stored and held.

In other words, when the initial value of recording power is too small, (hl-h2)
<10α, which is the case, is smaller than the lower limit value, and by increasing the recording power stepwise in this state, a proper output is achieved when (hl−h2)=+α.

This relationship is (h2-hl)>-α (h2-hl)=-α It can also be expressed as

Next, the CPU 7 further increases the setting value of the recording power,
When the judgment output of the secondary distortion detection circuit 20 becomes excessive, the set value A of the recording power when the judgment output immediately before was appropriate is stored and held.

That is, the determination output of the second-order distortion detection circuit 20 becomes excessive when (hl-h2)>-α exceeds the upper limit value, and just before that, hl
A relationship of -h2 to -α is set as 1q, and the set value A of the recording power at this time is stored and held.

In this way, the CPU 7 detects the setting value A that is the upper limit of the recording power range and the setting value B that is the lower limit of the appropriate recording power range.

Next, the CPU 7 calculates the average value of the upper limit setting 1aA and the lower limit setting B in the range where the recording power is appropriate as (A+B)/2, and uses this calculated average value as the setting value that provides the optimum recording power. The optimum recording power is set in the laser drive circuit 9, and a series of optimum recording power setting processes are 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 conversely decreases the set value of the recording power step by step at a certain rate to perform the same recording process. It is possible to detect the upper limit setting value A and the lower limit setting value B that determine the appropriate range of power, and to detect the optimum recording power setting value as the average value of both.

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

[Effects of the Invention] As explained above, according to the present invention, there is no need to tighten the accuracy of the circuit for detecting second-order distortion, and it is not affected by variations in the resolution of the head optical system, and the second-order distortion is always It is possible to detect and set the optimum recording power that minimizes the order distortion.

[Brief explanation of the drawing]

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 recording signals with two different frequencies to be detected as secondary distortion; Figure 4 is a signal waveform diagram showing the reproduction signal when the duty ratio of the recording signal is 50%, less than 50%, and greater than 50%. Figure 5 shows the reproduction signal according to the MTF frequency characteristics of the reading optical system. Signal waveform diagram showing level changes: Figure 6 is a signal waveform diagram showing dips in the reproduced signal caused by differences in DC components; Figure 7 is an explanatory diagram of the waveform of the envelope detection signal in Figure 2; Figure 8 Figure 9 is a signal waveform diagram showing the output of the bandpass filter in Figure 2. Figure 9 is a signal waveform diagram showing changes in the duty ratio of the recording signal. Figure 10 is a graph diagram showing the MTF frequency characteristics of the reading optical system. : Figure 11 is a graph showing the difference in MTF frequency characteristics due to the difference in the resolution of the reading optical system; Figure 12 is a graph showing the waveforms of the upper and lower envelope detection outputs due to the difference in the MTF frequency characteristics in Figure 11. This is a clear diagram. 1: Reading head 1a: Optical disk 2: Amplifier 3a, 3b: Envelope detection circuit 4a, 4b: Band pass filter 5a, 5b: Amplitude detection circuit 6: Judgment logic 7: CPU 8: D/A converter 9: Laser drive circuit

Claims (1)

[Claims] (1) A recording/reading means for optically recording alternately binary information with a scheduled duty ratio of 50% at two different frequencies on a recording medium, and optically reading the recorded information and converting it into an electrical signal. and; AC amplifying means for AC amplifying the output signal of the recording/reading means; and detecting amplitude differences h1 and h2 that occur based on the recording frequency above and below the amplitude center level of the output of the AC amplifying means. two amplitude difference detection means; the output difference (h1-h2) of the two amplitude difference detection means is compared with a predetermined maximum value +α and minimum value −α to determine the presence or absence of secondary distortion contained in the recorded information; a determination means for determining polarity; a laser drive means for generating a current necessary to emit recording power; and a determination means for detecting an output difference (
The recording power is changed by the laser driving means so that a judgment output in which h1-h2) matches the maximum value +α and the minimum value -α, and the output difference that matches the maximum value +α and the minimum value -α is An apparatus for detecting optimum recording power for an optical recording medium, comprising: a control means for detecting an optimum recording power as an average value of the respective recording powers obtained and setting the optimum recording power to the laser driving means;