JPS63206915A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To ensure the accurate detection of levels by converting the output of a pulse generating means into a read pulse that provides the timing of a peak point for the change of the reflected light quantity. CONSTITUTION:A differential signal 102, i.e., the output of a differentiator 11 used for detection of a peak point is used to detect a level in order to assure the presence of the change of the reflected light caused by a pit. Thus, it is possible to eliminate the influence of the waveform distortions caused by the fluctuation of the DC level of a read signal or by the second order differentiation. At the same time, the detection due to noises, etc., can be avoided. Thus, it is possible to detect the timing of an accurate peak point and to perform the reproduction of information with high reliability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical information reproducing device, and specifically, the present invention relates to an optical information reproducing device, and specifically, irradiates information pits recorded on an optical disk with light, and measures the peak point of change in the amount of reflected light. The present invention relates to an optical disk device that reproduces multiple information by capturing timing.

[Conventional technology]

Several methods have been considered for recording and reproducing information on the optical disk surface of an optical disk device, one of which is to irradiate pulsed light to create approximately circular minute information pits. There is a method in which a large amount of information is recorded by forming a pit on the disk surface, and during reproduction, the timing of the center of the pit is determined by changes in the amount of reflected light, and the information is reproduced based on changes in the time interval. In such reproduction methods, a method is generally used in which the output of a sensor that receives reflected light is differentiated in order to capture the peak point of change in the amount of reflected light, and the zero-crossing point of the differential signal is detected using a comparator.

However, simply detecting the zero cross of the differential signal of the sensor output risks erroneously detecting a zero cross that does not correspond to the center of the υ pit due to slight fluctuations in the sensor output, external noise, etc. Some gating means will be required to ensure that the light change is at its peak.

Conventionally, such gating methods include a method in which zero cross detection is performed only when the raw signal before differentiation of the optical sensor output changes by a certain level or more, or a method in which a second-order differential signal is obtained by differentiating the signal after differentiation again. Methods have been considered in which gates are applied by detecting when the amount of change exceeds a certain level, but these methods have not always provided sufficient performance.

[Problem that the invention seeks to solve]

Among the conventional methods mentioned above, in the method of detecting a change in the optical sensor output exceeding a certain level, it is necessary to amplify the sensor output faithfully without changing the level. Since the change is unipolar, cutting the DC component will cause level fluctuations due to changes in the pit period, etc. For this reason, the amplifier must reproduce accurately up to the DC range, but even with this, level fluctuations due to changes in the reflectance of the disk surface, fluctuations in the amount of irradiated light, etc. cannot be avoided, and it is difficult to detect the presence or absence of pits. Detection was likely to be inaccurate.

On the other hand, the level detection method for second-order differential signals, which is another conventional method mentioned above, does not require accurate reproduction of the DC range, but because differentiation is performed twice to enhance the high frequency range, waveform distortion and noise of the sensor output Since the signal output appears by enlarging the signal, etc., the problem that the zero-cross point is likely to occur in a place other than the center of the burn pit has not been sufficiently eliminated.

In this way, in the conventional method, it is impossible to avoid detecting the peak of the reflected light output at a location different from the center of the pit, and therefore it is difficult to reproduce recorded information with high reliability. There were drawbacks.

[Means for solving problems]

The optical information reproducing device of the present invention includes an optical sensor that detects changes in the amount of reflected light, a differentiator that differentiates the output of the optical sensor, and detects that the output of the differentiator exceeds a first specified level. a first comparator; a time width comparing means for detecting that the time width of the output pulse of the first comparator exceeds a second specified value; and a pulse generating means that outputs a pulse when the output of the second comparator turns on after the output of the time width comparing means turns on, It is characterized in that the output of the pulse generating means is used as a read pulse.

According to the present invention, the level detection to confirm that the change in reflected light is caused by a pit is performed using the output (differential signal) of a differentiator for detecting the peak point, which eliminates the problem of conventional DC levels. The effects of waveform distortion due to fluctuations in the signal or second-order differentiation are removed, making it possible to accurately detect the level, and thus achieving highly reliable information reproduction.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the optical information reproducing apparatus of the present invention. A reading light beam is irradiated onto the optical disc 2 from the optical head 1, and information recorded on the optical disc 2 is read out. Inside the optical head 1 is a laser light source 3.
The reed emits a laser beam for readout. The emitted laser light passes through the beam splitter 4, is focused by the objective lens 6, and is irradiated onto the surface of the optical disk 2. The reflected light reflected by the disk 2 and modulated by the information pits passes through the objective lens 6 again, has its optical path bent by the beam splitter 4, and enters the optical sensor 5. The optical sensor 5 outputs a current corresponding to the amount of incident light, that is, a read current signal 100 that changes in accordance with the modulation by the information pits. A read current signal 100 from the optical cell/suction 5 is amplified by an amplifier 10 and a read signal 101 is output.

This amplifier 10 does not need to have operational performance up to the DC range, but only as long as operation in a band near the information signal frequency is ensured.

The differentiator 11 differentiates the readout signal 101 to obtain a differential signal 1.
Outputs 02. The comparator 12 detects the zero-cross point of the differential signal 102 and outputs a zero-cross signal 103 that rises at the timing of the peak point of the read signal 101. Ideally, by shaping this zero-crossing signal 103, a readout pulse that provides timing at the center of the information pit should be obtained. There is a risk that an erroneous pulse may be output at a timing different from that of the multi-information pit, and a gate means is required to ensure that the read pulse is output only at the center timing of the information pit.The device of the present invention The readout pulse output is gated by the means after the comparator 13 to ensure signal reproduction.

The comparator 13 sets the differential signal 102 to a constant negative level (-VR
), and the level detection signal 104 is turned on when the level of the differential signal 102 drops by −vR. Note that the reference level for comparison by the comparator 13 is negative in order to match the polarity of the differential signal 102, and if the polarity of the read signal 101 is reversed, a positive reference level will be used.

The level detection signal 104 output from the comparator 13 is input to the time width comparing means 14, and checked to see if it is on for a time width equal to or greater than a certain value. In this example, the time width comparison means 14 is composed of a resistor 41, a capacitor 42, and a NAND gate 43.

When the level detection signal 104 is input to the primary delay circuit composed of the resistor 41 and the capacitor 42, the capacitor 4
2 terminal voltage 105 begins to rise with a time constant (R-C) given by resistor 41 and capacitor 42. If the level detection signal 104 is on for a certain period of time or more, the terminal voltage 105 of the capacitor 42 exceeds the input threshold of the gate 43,
The output of the gate 43 is turned on (low level). From the above, the output of the gate 43 is turned on only when the amplitude of the differential signal 102 exceeds a certain level and the time period exceeding the level continues for a certain period of time or more. The fact that the differential signal 102 exceeds a certain level indicates that the falling edge of the readout signal 101 is steeper than the slope (vs. the rising edge), and if this state continues for more than a certain period of time, it means that the readout signal 101 This indicates that the peak level (or lowest level) of the signal 101 is higher than a certain value. Accordingly, when the output of the gate 43 turns on, it indicates that the peak level of the read signal 101 exceeds a certain value, and after the output of the gate 43 turns on, the zero cross signal 103
By capturing only the information, erroneous detection due to noise etc. can be eliminated and accurate readout pulses corresponding to the information bits can be obtained.

The clip 70 knob 15 is set by the output of the gate 43 and outputs the read gate signal 106. As mentioned above, the readout gate signal 106 turns on only after the differential signal 102 exceeds a certain level for a certain period of time or more, and only near the peak point of the fluctuation of light reflected by the pit. . Clip 70 knob 16 is gated with readout gate signal 106 and zero cross signal 1
Read pulse 110 at the rising edge of 03
Output. The shift flip 70 knob 15 is reset by the output of this read pulse 110, and the read signal 101
The state is in which the next peak is expected. The delay circuit 17 adjusts the pulse width of the read pulse 110 to be constant by outputting a signal for resetting the seven lip-flop 16 after a certain period of time from the rising edge of the read pulse 110.

This readout pulse 110 accurately indicates the peak point of the change in the amount of reflected light modulated by the information pit, excluding the detection of zero crossing due to noise etc. Based on this readout pulse 110, the center of the information pit is detected. The timing is accurately captured and the information recorded on the disc 2 is reliably reproduced.

FIG. 2 is a diagram showing examples of signal waveforms of various parts for explaining the operation of the apparatus shown in FIG. 1. When a light beam is irradiated onto a recording pit row on the disk surface as shown in A) of the same figure, the amount of reflected light decreases when the light hits the pit, so the readout signal 101 is as shown in B) of the same figure. Changes such that the lowest level (negative peak level) is at the center of the pit. Note that the signal polarity is reversed for information pits where the amount of reflected light increases at the pit portion. Read signal 1
A differential signal 102 obtained by differentiating 01 crosses the θ level from negative to positive at the negative peak point of the read signal 101, as shown in FIG. Further, the amplitude of the differential signal 102 corresponds to the steepness of the rise of the read signal 101, and the larger the amplitude of the read signal 101 and the higher the frequency, the larger the amplitude of the differential signal 102 becomes. This differential signal 102
A level detection signal 104 as shown in FIG.

As can be easily seen, this level detection signal 104 indicates that the fall of the read signal 101 is steep. Further, the period in which the level detection signal 104 is on always ends before the differential signal 102 crosses the zero level from negative to positive. If only the level of the differential signal 102 is detected, the level detection signal 104 may turn on even in response to thin pulse noise mixed in the readout signal 101. Therefore, it is necessary to check that the level detection signal 104 is on for longer than the runner time. This is confirmed by the time range comparing means 14.

When the level detection signal 104 is input to the primary delay circuit composed of the resistor 41 and the capacitor 42, the terminal voltage 105 of the capacitor 42 gradually rises as shown in E)K of the figure. When this terminal voltage 105 exceeds the input threshold (VTR) of the NAND gate 43, the output of the gate 43 is turned on and the flip-flop 15 is set.

As a result, as shown in the same figure F), the read gate signal 1
06 is turned on. As mentioned above, the level detection signal 10
4 is on only before the differential signal 102 crosses the zero level, so the read gate signal 1 is on.
The timing when 06 turns on always precedes the zero-crossing timing of the differential signal 102. On the other hand, comparator 12
The timing at which the differential signal 102 crosses the 0 level is detected, and the zero cross signal 1 as shown in G) in the same figure is detected.
03 is output.

The flip-flop 16 converts the zero-crossing signal 103 into a pulse while being gated by the readout gate signal 106, and outputs a readout pulse 110 as shown in FIG.

The timing of the rise of the read pulse 110 indicates the timing of the center of the information pit, and the read pulse 11 due to an erroneous zero cross signal 103 due to noise etc.
00 occurrences are excluded. By demodulating the data based on this read pulse 110, the information recorded on the disk 2 can be accurately reproduced.

〔Effect of the invention〕

As explained above, the present invention performs level detection to ensure that the change in reflected light due to the pit is at the peak.
Since this is done using the output of the differentiator (differential signal) to detect the peak point, it eliminates the effects of conventional problems such as fluctuations in the DC level of the read signal or waveform distortion due to second-order differentiation, and eliminates noise. It is possible to accurately detect the peak point timing by eliminating the detection by the above method, and therefore, highly reliable information reproduction is realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the optical information reproducing device of the present invention, and FIG. 2 is a diagram showing examples of signal waveforms of various parts to explain the operation of the device shown in FIG. 1. .

Claims (1)

[Claims] In an optical information reproducing device that reproduces information by irradiating light onto a record carrier on which optically readable information pits are formed and capturing the timing of the peak point of change in the amount of reflected light, changes in the amount of reflected light are captured. a readout optical sensor; a differentiator that differentiates the output of the optical sensor; a first comparator that detects that the output of the differentiator exceeds a first specified level; and an output pulse of the first comparator. a second comparator for detecting that the output of the differentiator has crossed the 0 level; and a pulse generating means for outputting a pulse when the output of the second comparator turns on after the output is turned on, and reads out the output of the pulse generating means to give the timing of the peak point of the change in the amount of reflected light. An optical information reproducing device characterized by using pulses.