JPS61120379A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To eliminate the adverse influence of variation in DC level by reproducing recorded information from the output of a pulse generating circuit which compares the output of a wide band amplifier with a constant reference level and generates pulses. CONSTITUTION:A level shifting circuit 23 receives a wide-band readout signal 102 and a data area signal 104 and compares the DC level of the wide-band readout signal 102 with the constant reference value VR1 when the data area signal is off to generate a level shift signal 105 which varies the DC level of the output of the wide-band amplifier 20 so that its deviation is corrected. When the data area signal 104 turns on, the level shifting circuit 23 stops comparison of the DC level of the wide-band readout signal and holds the value of the level shift signal 105 right before the data area signal 104 turns on. Namely, the level shifting circuit 23 corrects the output of the wide-band amplifier 20 so that the DC level of the wide-band readout signal 102 becomes equal to the constant reference value every time the data area signal 104 turns off, thereby suppressing variation in the DC level of the wide-band readout signal 102 due to variation in the reflection factor of a record carrier 7, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for reading and reproducing optically recorded information. Specifically, the present invention relates to a device for reading and reproducing optically recorded information. The present invention relates to an optical information reproducing device such as an optical disk file device, which reads recorded information by focusing and irradiating light and detecting changes in the intensity of reflected or transmitted light from a record carrier.

[Prior art]

A light beam is irradiated onto a record carrier on which information is optically recorded, and the reflected light is intensity-modulated by the recorded information (
In optical information reproducing devices such as optical disk devices and video disk devices, which receive light (or transmitted light) by a photodetector and reproduce the recorded information from the output of the photodetector, the recorded information It is necessary to receive frequency-modulated light and accurately amplify the signal components contained therein. Conventionally, such an amplifier circuit for outputting a photodetector has a simple circuit configuration and stable operation, as shown in Japanese Unexamined Patent Publication No. 58-6535 ``Record reading device for record carrier''. Since then, ACC-coupled amplifiers (high-frequency amplifiers), which cut low-frequency components and amplify only high-frequency components, have been widely used. However, the method of using such an AC-coupled amplifier as a readout amplifier assumes that the information signal does not contain low frequency components. This does not cause any problems when reproducing signals, but when reproducing digital data, the low-frequency components contained in the information are cut, resulting in a distorted readout waveform, which prevents accurate information from being reproduced. arise.

In addition, analog video information is recorded continuously over the circumference of the disk, and there is no phenomenon where recording is interrupted in the middle of the information track, but with optical disks that record digital data, the circumference of the disk is multiple times. It is divided into sectors, and between sectors there are areas where no information is recorded. When reading information from a record carrier on which information is recorded in divided parts, the DC component of the reflected light (or transmitted light) from the record carrier may be lost in the areas where no information is recorded. If the output of the photodetector at this time is amplified by an AC-coupled amplifier, the low frequency component will be cut, so a large spike-like level fluctuation will occur in the output of the amplifier where the DC component of the reflected light changes. arise. Such a situation similarly occurs when a defective portion of a record carrier is read, causing an excessively high data error rate when reproducing information in an optical disk device.

In order to solve the above problems, it is effective to use a wideband amplifier (DC amplifier) that flatly amplifies from the DC component to the high frequency component instead of using an AC coupled amplifier as the readout amplifier. The occurrence of offset drift is unavoidable, and it is difficult to accurately maintain the DC level of the output at a constant value.

Further, the reflectance of the surface of the record carrier is not uniform over the entire surface of the record carrier even when no information is recorded, and varies slightly depending on the location.

Therefore, in addition to being modulated by recorded information, the intensity of the reflected light from the record carrier varies relatively slowly in response to changes in the position of the light spot that illuminates the record carrier. Furthermore, it is difficult to keep the intensity of the laser beam that irradiates the record carrier strictly constant, and the intensity of the irradiated light varies, albeit slightly, which also causes the intensity of the reflected light to vary.

Since a DC amplifier accurately amplifies even slow changes in light intensity, fluctuations in reflected light intensity due to the above causes directly appear as level fluctuations in the amplifier output. For this reason, if the output of a readout amplifier using a DC amplifier is directly compared with a fixed reference level and converted into a pulse, the pulse width will fluctuate greatly due to output level fluctuations, resulting in a positive U.
(There is a great risk that the U information will not be reproduced. In other words, if the output of the photodetector is amplified with a DC amplifier, the low frequency components included in the recorded information will be amplified without being cut, so the waveform Distortion is eliminated, and spike-like level fluctuations at the boundary between areas where no information is recorded and areas where information is recorded are also eliminated. However, if a simple DC amplifier is used, the DC level of the amplifier output tends to fluctuate, and this can be If this happens, the pulse width will deviate significantly from its original value, making it difficult to reproduce information accurately.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned problems in conventional optical information reproducing devices, to amplify changes in the amount of reflected light or transmitted light over a wide band and flatly from direct current to high frequencies, and also to eliminate low frequency components. To provide an optical information reproducing device capable of faithfully reproducing a recorded information signal including a recording information signal, and accurately reproducing recorded information by eliminating the adverse effects of direct current level fluctuations due to reflectance fluctuations of a record carrier, etc. There is a particular thing.

[Structure of the invention]

In the present invention, a laser beam is focused and irradiated onto a record carrier on which information is optically recorded, a photodetector receives reflected light or transmitted light from the record carrier, and information is recorded from the output of the photodetector. an optical information reproducing device for extracting an information signal from the photodetector, the broadband amplifier is connected to the photodetector and flatly amplifies the output of the photodetector from direct current to high frequency components; a pulsing circuit for pulsing the output of the amplifier by comparing it with a certain reference level; a data area detection circuit that generates a data area signal indicating that there is a data area, and is connected to the wideband amplifier and the data area detection circuit, and while the data area signal is off, the DC level of the output of the wideband amplifier is a constant value. and a level shift circuit for shifting the level of the output of the broadband amplifier so that the output level of the wideband amplifier becomes 1, and the recorded information is reproduced from the output of the pulsing circuit.

[Effect]

In the optical information reproducing device of the present invention, the output of the photodetector is
A broadband amplifier flatly amplifies everything from direct current to high frequency components, and a data area detection circuit detects areas where no information is recorded on the record carrier. The shift circuit forcibly shifts the level of the output of the wideband amplifier to a constant value, suppressing fluctuations in the DC level of the output of the wideband amplifier, faithfully reproducing the information recorded on the record carrier, and A readout signal is obtained from which influences such as reflectance fluctuations of the carrier have been removed, and by pulsing this and reproducing information, extremely accurate reproduction of information is achieved. .

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the optical information reproducing apparatus of the present invention.

FIG. 2 is a diagram showing signal waveforms of various parts in the embodiment of FIG. 1.

A laser beam emitted from a laser diode 1 is converted into parallel light by a collimating lens 2, passes through a polarizing beam splitter 3, a 1/4 wavelength plate 4, is focused into a minute light spot by an objective lens 5, and is delivered to a recording carrier 7. irradiated onto the surface of The reflected light whose intensity has been modulated by the information recorded on the surface of the record carrier 7 passes through the objective lens 5 again and returns to parallel light, whose polarization angle is rotated by the quarter-wave plate 4, and the polarized beam splinter 3, the optical path is bent and the light passes toward the photodetector 10. A condensing lens 6 is arranged between the polarizing beam splitter 3 and the photodetector IO, and the reflected light is focused and made incident on the photodetector 10. Photodetector 10
is a photodiode that outputs a current corresponding to the intensity of incident light, and a + bias voltage is applied to it to operate stably and at high speed. The waveform (a) in Figure 2 is
The current waveform of the output current 101 of the photodetector 10 is shown. When reading out an area in which no information is recorded on the record carrier 7, which is divided into sectors and records information, the output current 101 changes only slowly.
When reading the area where information is recorded, the output current is 10
1, a high frequency positive pulse modulated by the recorded information appears. The DC level of the output current 101 fluctuates as shown, although relatively slowly, due to factors such as changes in the reflectance of the record carrier 7.

The broadband amplifier 20 receives the output current 101 from the photodetector 10 and flatly amplifies its DC component to a high frequency component indicating information recorded on the record carrier 7, thereby faithfully monitoring changes in the amount of light received by the photodetector 10. Wideband readout signal 10 reproduced in
Outputs 2. Since this broadband readout signal 102 also includes a DC component due to changes in the amount of reflected light from the record carrier 7, when reading out information that has been divided into sectors and recorded,
Changes from an area where no information is recorded to an area where information is recorded are also accurately reproduced, eliminating the occurrence of sudden spike-like level fluctuations at the boundaries of recording areas.

Further, even when a recording modulation method including low frequency components is used, the phenomenon in which the read waveform is distorted due to the low frequency components being applied during reading can be avoided. However, since the reflectance of the surface of the record carrier 7 is not constant over the entire surface of the record carrier 7, and the intensity of the laser beam emitted from the laser diode 1 is not strictly constant, the reflected light from the record carrier 7 is Apart from the modulation caused by recorded information, the intensity of
As the position of the light spot on the record carrier 7 changes or changes slowly over time, the photodetector 10
Simply amplifying the output current 101 flatly over a wide band will inevitably cause the DC level of the wideband readout signal 102 to fluctuate, and when this readout signal 102 is compared with a constant reference level and pulsed, the pulse width fluctuations, making it easy for errors to occur in the reproduction of information. For this reason, the wideband amplifier 20 is provided with a function of changing the DC level of the wideband read signal 102 by receiving a signal from the level shift circuit 23 described in f&. It is kept constant without being affected by reflectance fluctuations, etc.

The pulsing circuit 21 receives the wideband readout signal from the wideband amplifier 20, compares it with a certain reference level (voltage), converts it into a pulse, and outputs the readout pulse signal 103. This pulsing circuit 21 can be easily constructed using a voltage comparator.

The data area detection circuit 22 receives the read pulse signal 10
3, the light spot on the surface of the record carrier 7 generates a data area signal 104 indicating that the area where information is recorded is illuminated. When reading out the area in which information is recorded on the record carrier 7,
The broadband read signal 102 changes at a high frequency, and the pulse generator 21 outputs a high frequency read pulse signal 103.
is output, so by detecting a state in which high-frequency pulses appear continuously as the read pulse signal 103, it can be known that the area where information is recorded is irradiated with a light spot. On the other hand, when reading an area where no information is recorded, the pulse generator 2
Since the output of 1 does not change, if no pulse appears as the read pulse signal 103 for a certain period of time or more, it can be determined that the light spot is irradiating an area where no information is recorded. The data area detection circuit 22 is constituted by a re-riggable monostable multi-by-break (for example, ICμPB74123 manufactured by NEC Corporation),
When short cycle pulses are continuously input as the read pulse signal 103, the data area signal 104 is held in the on state, and when the pulse input stops for a certain period of time, the data area signal 104 is turned off. The waveform (b) in Figure 2 is
The waveform of this data area signal 104 is shown.

The level shift circuit 23 receives the broadband read signal 102 and the data area signal 104, and receives the data area signal 1
04 is off, that is, while reading an area where no information is recorded, the DC level of the wideband readout signal 102 is compared with a certain reference value VRI (for example, OV) and the deviation is corrected. A level shift signal 105 is generated to change the DC level of the output of the broadband amplifier 20. When the data area signal 104 turns on, the level shift circuit 23 stops comparing the DC level of the broadband readout signal 102, and holds the value of the level shift signal 105 immediately before the data area signal 104 turns on. That is, each time the data area signal 104 is turned off, the level shift circuit 23 modifies the output of the wideband amplifier 20 so that the DC level of the wideband read signal 102 is equal to a certain reference value, and adjusts the output of the wideband amplifier 20 to reduce the reflection of the record carrier 7. It functions to suppress fluctuations in the DC level of the broadband readout signal 102 due to rate fluctuations and the like. The waveform in FIG. 2(c) shows the waveform of this broadband readout signal 102. Due to the function of the level shift circuit 23, fluctuations in the DC level of the broadband readout signal 102 are suppressed to a small level, and since the broadband amplifier 20 flatly amplifies the output current 101 of the photodetector 10 from DC to high frequency, the photodetector 10 Since changes in the amount of reflected light incident on the recording medium are faithfully reproduced in the broadband readout signal 102, a signal having small level fluctuations and accurately indicating information recorded on the record carrier 7 can be obtained as the broadband readout signal 102. By comparing this broadband readout signal 102 with a constant reference level Vc and pulsing it by the pulsing circuit 21, a readout pulse signal 103 whose pulse width fluctuation is suppressed is obtained. The information recorded in 7 is accurately reproduced. Waveform (d) in FIG. 2 shows the waveform of this read pulse signal.

FIG. 3 shows a broadband amplifier 2 used in the embodiment of FIG.
Show details of 0. The wideband amplifier 20 includes a high frequency amplifier 30 that separates and amplifies the high frequency component of the output current 101 of the photodetector 10 , a low frequency amplifier 31 that separates and amplifies the low frequency component of the output current 101 , and a high frequency amplifier 30 that separates and amplifies the low frequency component of the output current 101 . a summing amplifier 32 that adds the output, the output of the low frequency amplifier 31, and the level shift signal 105 from the level shift circuit 23;
After separating and amplifying the high-frequency component and low-frequency component of the output current lot, the system performs additive synthesis, thereby flatly amplifying signals from direct current to high frequency signals. The configuration of the wideband amplifier 20 does not necessarily have to be such a configuration that separates and amplifies high frequency components and low frequency components, but since the output current 101 from the photodetector 10 is extremely weak, a single It is difficult to amplify this in a wide band and stably with an amplifier, so it is preferable to have a configuration in which the signals are amplified separately as in this example.

Separation of high frequency components and low frequency components of the output current 101 of the photodetector 10 is performed by a capacitor 40 and a resistor 41. Capacitor 40 passes only the high frequency component of output current 101 and inputs it to high frequency amplifier 30 . on the other hand,
The low frequency component of the output current 101 that cannot pass through the capacitor 40 is input to the low frequency amplifier 31 via the resistor 41. The crossover frequency fc that defines the boundary between the high frequency component and the low frequency component of this output current 101 is given by the following equation: where the capacitance value of the capacitor 40 is C1 and the value of the resistor 41 is R
It is given by 1/2πRC. The high frequency amplifier 30 amplifies the voltage change appearing at the terminal of the resistor 42 due to the high frequency current passing through the capacitor 40. The low frequency amplifier 31 is
It is a current-to-voltage conversion type amplifier that is constituted by an operational amplifier and converts a low-frequency current inputted through a resistor 41 into a voltage. The summing amplifier 32 has a configuration in which a voltage-current converter made up of an operational amplifier 47 and a transistor 48 is added to a differential amplifier made up of transistors 45 and 46. The constant current diode 49 is for supplying a constant bias current to the transistor 46, and may be a simple resistor. The output of the high frequency amplifier 30 is input to the bases of transistors 45 and 46, and a differentially amplified signal appears as a change in the collector voltage of the transistor 45. On the other hand, the output of the low frequency amplifier 31 is converted into a current signal by the operation of the operational amplifier 47 and the transistor 48, and changes the emitter current of the transistor 45. This change in emitter current appears as a change in the collector voltage of transistor 45. The level shift signal 105 inputted as a change in current value is applied to the emitter of the transistor 45, and changes the emitter current of the transistor 45, thereby changing the collector voltage of the transistor 45. Changes in the collector voltage of the transistor 45 due to the output of the high frequency amplifier 30, changes in the collector voltage due to the output of the low frequency amplifier 31, and changes in the collector voltage due to changes in the level shift signal 105 occur independently. The collector voltage is determined by the change in the output of the high frequency amplifier 30 and the change in the output of the low frequency amplifier 31.
This is the sum of the change in the output of and the change in the level shift signal 105.

The collector voltage of the transistor 45 is buffered by an emitter follower circuit constituted by the transistor 50 and output as a broadband read signal 102.

By adding again the signals that have been separated into high frequency components and low frequency components and amplified by the high frequency amplifier 30 and the low frequency amplifier 31, the collector of the transistor 45 receives the output current of the photodetector 10. A voltage change appears that faithfully reproduces the change from direct current to high frequency components. Furthermore, when the current value of the level shift signal 105 is changed, the collector voltage of the transistor 45 changes accordingly. Therefore, by changing the current value of the level shift signal 105, the DC level of the broadband readout signal 102 can be set to an arbitrary value. Can be set to

FIG. 4 shows details of the level shift circuit 23 used in the embodiment of FIG. 1. The level shift circuit 23 includes a low-pass filter 60 that receives the wide-band read signal 102 and extracts its low frequency components, and a level comparator 61 that compares the level of the low-pass filtered wide-band read signal with a constant reference voltage level VRI. Data area signal 104
a clock generation circuit 62 which generates a current clock signal 110 while the data area signal 104 is off in response to the clock signal;
The level comparator 61 receives the currant nox 110.
It is composed of an up/down counter 63 that performs an up-count or down-count operation according to the output of . From the interval when the data area signal 104 is on, the lock generation circuit 62 does not generate the count pulse 110, and the up/down counter 63 stops counting and holds the count value from the previous counting operation. , when the data area signal 104 turns off, a count pulse 110 is generated and the up/down counter 63
starts counting operation.

At this time, if the DC level of the wideband readout signal 102 is higher than the reference voltage level Vl11, the output of the level comparator 61 becomes high level and the knob down counter 63 performs a count-up operation. When the level is lower than the reference voltage level VRI, the output of the level comparator 61 becomes a low level and the up/down counter 63 performs a countdown operation.When the up/down counter 63 performs a count-up operation, the digital output value of the up/down counter 63 gradually increases, and the output current value of the D/A converter 64, that is, the value of the level shift signal 105 increases.When the current value of the level shift signal 105 increases, the transistor in the wideband amplifier 20 shown in FIG. The emitter current of the transistor 45 becomes thick (becomes), and the collector voltage of the transistor 45, that is, the DC level of the broadband readout signal 102 becomes low. The DC level of the signal 102 is the reference voltage level Vl
11, so the broadband readout signal 10
The level of the DC level 2 is shifted to match the reference voltage level VRI.

Although such a level shift operation is not performed while the data area signal is on, the level shift signal 105 continues to maintain the value that was modified immediately before that (waveform in Figure 2).
See C)].

As explained above, according to this embodiment, fluctuations in the DC level of the broadband readout signal 102 are suppressed to a small level, and changes in the amount of reflected light due to the information recorded on the record carrier 7 are included in the broadband readout signal 102. Since the pulse width is faithfully reproduced down to the low frequency components, a read pulse signal 103 can be obtained in which pulse width fluctuations are kept small and the noggle timing accurately indicates the information recorded on the record carrier. Information is then reproduced without error based on this read pulse signal 103.

〔Effect of the invention〕

As explained above, the present invention faithfully reads information recorded on a record carrier from the output of a photodetector down to low frequency components, and suppresses fluctuations in the DC level of the read signal due to changes in reflectance of the record carrier. This has the effect of minimizing negative effects such as areas where no information is recorded on the surface of the record carrier, missing recorded information, defects on the surface of the record carrier, and fluctuations in reflectance, thereby allowing information to be reproduced with fewer errors. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an optical information reproducing device according to an embodiment of the present invention. FIG. 2 is a diagram showing signal waveforms of each part in an embodiment of the present invention. FIG. FIG. 4 is a circuit diagram showing a detailed configuration of a wideband amplifier used in an embodiment of the present invention. FIG. 4 is a circuit diagram showing a detailed configuration of a level shift circuit used in an embodiment of the present invention. 1...Laser diode 2...Collimating lens 3...Polarizing beam splitter 4...1/4 wavelength plate 5...Objective lens 6... Condensing lens 7...Record carrier 10...Photodetector 20...Broadband amplifier 21...Pulsing circuit

Claims (1)

[Claims] (1) A laser beam is focused and irradiated onto a record carrier on which information is optically recorded, the reflected light or transmitted light from the record carrier is received by a photodetector, and the information is recorded from the output of the photodetector. An optical information reproducing device for extracting information signals includes: a wideband amplifier connected to the photodetector and flatly amplifying the output of the photodetector from direct current to high frequency components; a pulsing circuit that compares the output of the pulsing circuit with a certain reference level and pulsing it; and an area connected to the pulsing circuit and receiving the output of the pulsing circuit and recording data on the record carrier. a data area detection circuit that generates a data area signal indicating that the broadband amplifier is connected to the wideband amplifier and the data area detection circuit; an optical information reproducing apparatus comprising: a level shift circuit for shifting the level of the output of the wideband amplifier so that the level of the output of the wideband amplifier is such that the recorded information is reproduced from the output of the pulsing circuit;