JPH06267079A - Apparatus for reproducing optical data - Google Patents

Abstract

PURPOSE:To obtain an optical data reproducing apparatus which simplifies the design of a differential circuit including a current/voltage converting part, and effectively restricts unnecessary high frequency noises in a simple structure. CONSTITUTION:According to the apparatus, optical data is read by converting the change in the amount of light detected by a photodiode to electric signals, and a reproducing signal is obtained based on at least either of a primary differential signal obtained by differentiating the read signal and a secondary differential signal obtained by differentiating the primary differential signal again. A differential means for generating the primary or secondary differential signal is a transformer 3 having a first coil 4 and a second coil 5 magnetically coupled by a magnetic core 6. An electric signal corresponding to the change of the amount of light detected by a photodiode 2 is fed to the first coil 4 of the transformer 3, and a differential signal is output from the second coil 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing device used for reproducing optical information such as an optical disk device.

[0002]

2. Description of the Related Art For example, in an optical information reproducing apparatus used for a CD, a magneto-optical disk, etc., in order to read recorded information from a recording medium, a recording medium is irradiated with a laser beam focused on an extremely small spot, and the medium is read. The change in the light reflection intensity due to the presence or absence of pits formed on the surface and the change in the polarization plane due to the magnetization direction of the recording film are converted into the change in the light amount according to the recording signal by the optical element of the optical pickup, and this change in the light amount is changed. Recorded information is reproduced by detecting with an optical sensor such as a photodiode.

FIG. 10 shows an example of a conventional optical information reproducing apparatus, in which an output from a photodiode 101 for detecting a change in light quantity according to a recording signal output from an optical element of an optical pickup is converted into a current-voltage converter. To the current-voltage converter 10 for converting the change in light quantity into a predetermined voltage.
The output of 2 is first-order differentiated by the first-order differentiating circuit 103, and the first-order differentiating signal is given to the second-order differentiating circuit 104 to re-differentiate the first-order differentiating circuit 103 and the second-order differentiating circuit 104. At least one of the signal and the secondary differential signal output is given to the comparator discriminating circuit 105 and compared with a signal of a predetermined level to obtain a reproduction signal of recorded information.

In this case, the current-voltage conversion circuit 102 is constituted by a negative feedback amplifier 1021 as shown in FIG. 11 for reproduction because the current change corresponding to the light amount change obtained by the photodiode 101 is as small as about 1 μA. It forms the first stage amplifier circuit of the circuit system. Further, as the primary or secondary differential circuits 103 and 104, a CR type differential circuit including an operational amplifier OP, resistors R1 and R2, capacitors C1 and C2 as shown in FIG. 12 is used. The frequency characteristic of the CR type differential circuit here is as shown in FIG. 13, and the ideal differential time characteristic is a circuit excluding R1 and C2, and is represented by a broken line of frequency f0 or more determined by the differential elements C1 and R2. As shown. Then, the optical information reproducing apparatus configured as described above obtains a reproduction signal of the recorded information of the disc.

By the way, generally, as a recording method for recording data on a disc, encoded data generated by modulating the original data shown in FIG. 14 (a) to the original data shown in FIG. 14 (b). The pit position recording method in which the center position of the pit recorded in "1" of the coded bit is associated with "1" each time the coded bit "1" as shown in FIG. "0" is inverted, so-called N
A pit edge recording method is known in which RZI modulation is coded and the "1" portion is made to correspond to the leading edge or trailing edge of the recorded pit. The method of generating the binarized reproduction data is also different.

In the pit position recording method, the logic of a gate pulse obtained by slicing an original waveform or a differential waveform of the original waveform at a constant level for peak detection of an analog reproduction signal and a differential pulse obtained by slicing the differential waveform at zero level A method in which a differential detection method and an amplitude detection method are combined to obtain a data pulse by operation has been put to practical use. For example, a method has been proposed in which a reproduced original waveform as shown in FIG. 14 is second-order differentiated and the second-order differentiated signal is sliced at a constant level.
(JP-A-63-291263)

In FIG. 15, (a) is a reproduced analog signal, and the differential signal (b) of this reproduced analog signal is sliced at appropriate slice levels Vt1 and Vt2 to obtain a zero-cross signal (c). Here, the gate pulse is obtained by slicing the signal (e) obtained by second-order differentiating the original waveform (a) at the slice level Vt3 (FIG. 15).
(F)). Thus, if the logical product of the zero-cross signal of FIG. 15C and the gate signal of FIG.
Data indicating the peak position of the original waveform such as 5 (g) can be reproduced.

As described above, according to the method of obtaining the gate pulse by using the second differential, compared with the method of obtaining the gate pulse by slicing the reproduced original waveform, the envelope caused by the low frequency component contained in the original waveform is compared. It has the characteristic that it is not easily affected by fluctuations.

On the other hand, in the pit edge recording system,
An Erice method that slices the reproduced analog signal with a level signal that fluctuates depending on the envelope of the reproduced waveform or the reproduction waveform to obtain the pit edge position, or a zero-cross differential pulse and a first-order differentiated signal that are obtained by differentiating the reproduced analog signal two-dimensionally. A second-order differential method is used to obtain an edge position by a logical operation with a gate pulse obtained by slicing at a level.

FIG. 16 shows an example of a reproducing method by the second differential method. In this case, a zero cross signal (e) obtained by second differentiating the reproduced analog signal (a) and a first differential signal ( By performing logical operation processing on the gate pulse (c) obtained by slicing b), reproduced data as shown in (g) is obtained.

[0011]

However, according to the conventional optical information reproducing apparatus, the CR type differential circuit is used to obtain the zero-cross signal or the gate signal for separating the zero-cross signal as described above. Therefore, due to the frequency characteristics of the differentiating circuit, high frequency noise is easily amplified,
Especially in the second-order differentiation, the high-frequency noise due to the superposition of differentiating circuits becomes more prominent, and when the optical information is recorded at a high density or the transfer rate is increased, the jitter of the reproduced signal increases and There is a problem that it is impossible to reproduce various signals.

That is, in such a CR type differential circuit,
As described above, assuming that it has an ideal differential time property,
Differentiating elements C1 and R2 except R1 and C2 shown in FIG.
It is conceivable that the frequency is more than the frequency f0, which is determined by, as shown by the broken line. However, in this case, the frequency characteristic of the output becomes an output proportional to the frequency, so that the high frequency noise is greatly amplified.

Therefore, the actual CR type differential circuit is shown in FIG.
By adding R1 and C2 to compensate for the phase delay in the feedback circuit and operate stably as shown in Fig. 13, the frequency characteristics shown by the solid line in Fig. 13 We also try to reduce the noise in the.

In order to realize high density recording of optical information and high transfer rate, it is necessary to make the time constants C1 and R2 of the differentiating elements as small as possible so that the differentiating operation can be performed at high speed even with a high frequency signal. , But this time constant C1, R
When 2 is decreased, the output of the circuit decreases and S of the differential signal
/ N decreases, and if the signal differential frequency band is secured at a high frequency and high frequency noise is reduced by R1 and C2, R1 and C2 must be reduced, and phase compensation becomes insufficient. Therefore, the circuit operation at high frequency may become unstable. Therefore, in order to satisfy all of these conditions, it is extremely difficult to set the respective values of the time constants C1 and R2 of the differential element and the circuit elements R1 and C2 for phase compensation, which makes the circuit design difficult. There was a problem.

Further, the high frequency cutoff characteristic obtained by R1 and C2 is as shown in A of FIG. 13, and is -20 dB / de.
Since it is about c, it is not very effective in effectively cutting unnecessary high-frequency noise. For this reason, it is necessary to use a filter with a sharp high-frequency cutoff characteristic, but this further complicates the circuit. However, there is a problem in that it becomes expensive in terms of cost.

Further, in the conventional optical information reproducing apparatus, there is a circuit including an amplifier such as a current-voltage converter from the photodiode 101 to the differentiating circuits 103 and 104. There is also a problem that the induced line noise increases.

The present invention has been made in view of the above circumstances, and simplifies the design of a differentiating circuit including a current-voltage converting section, has a simple structure, and effectively suppresses unnecessary high-frequency noise. It is an object of the present invention to provide an optical information reproducing device capable of performing the above.

[0018]

SUMMARY OF THE INVENTION According to the present invention, optical information is read by converting a change in the amount of light received by a photosensor into an electric signal, and the read signal is differentiated to obtain a first-order differential signal and the first differential signal. An optical information reproducing apparatus for obtaining a reproduction signal based on at least one of a secondary differential signal obtained by differentiating a secondary differential signal again,
The differentiating means for generating the second derivative signal or the second derivative signal is
It comprises a transformer in which a first coil and a second coil are magnetically coupled with a core of a magnetic material, and an electric signal according to a change in the amount of light received by the photosensor is applied to the first coil of the transformer, and The second coil is configured to output the differential signal.

[0019]

As a result, according to the present invention, a current that changes according to the amount of light received by the photosensor is applied to the primary coil of the transformer, and the change in the magnetic flux generated in the core of the transformer by the primary coil is changed to the secondary coil. By converting the voltage into a voltage and outputting it as a differential signal, the time constants C1 and R2 of the differentiating element and the circuit element R for phase compensation, as in the conventional CR differentiating circuit.
The troublesome work of setting each value of 1 and C2 separately so as to satisfy the predetermined condition is eliminated, and the design of the differentiating circuit can be simplified, and the current of the photosensor output can be simplified. Since the voltage conversion and the differentiation operation can be performed at the same time, the circuit from the photosensor to the differentiation circuit can be downsized and simplified.

Further, since a transformer is used as the differentiating circuit and is affected by the frequency characteristic of the magnetic permeability of the magnetic material of the core, by selecting the magnetic characteristic of the magnetic material to be used,
It is possible to easily block only unnecessary high frequency components above the signal band without adding a filter having excellent high frequency cutoff characteristics.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. (First embodiment)

FIG. 1 shows the appearance of the optical information reproducing apparatus according to the first embodiment. In the figure, reference numeral 1 denotes a printed circuit board. On the printed circuit board 1, a photodiode 2 for detecting a change in light quantity according to a recording signal output from an optical element of an optical pickup, and a transformer 3 in proximity to the photodiode 2 are provided. It is provided. This transformer 3 is basically a first coil 4 and a second coil 5 magnetically coupled by a core 6 made of a magnetic material, and a current drive circuit 7 is provided between the first coil 4 and the photodiode 2. , The second coil 5
A voltage amplifier 8 is connected to.

As a result, the signal pattern recorded on the optical information recording medium is received by the photodiode 2 as a light amount change corresponding to the recording signal pattern by the optical element of the optical pickup (not shown), and this light amount change is caused by the current. It is applied as a current change to the first coil 4 of the transformer 3 via the drive circuit 7, a differential signal is output from the second coil 5, and is taken out through the voltage amplifier 8. FIG. 2 shows a circuit configuration of such an optical information reproducing apparatus.

In this case, the photodiode 2 which is a photo sensor is a current source which is applied with a reverse bias voltage by the DC power source 20 through the resistor 21 constituting the current drive circuit 7 and which changes in accordance with the amount of received light. . The photodiode 2 is connected to the first coil 4 of the transformer 3 in series. Then, the second coil 5 of the transformer 3 is connected to the voltage amplifier 8
It is connected to the output terminal 22 via.

However, if the resistance value R of the resistor 21 constituting the current drive circuit 7 is set to a value sufficiently larger than the impedance ωL1 of the inductance L1 of the first coil 4 of the transformer 3, the first coil 4 of the transformer 3 is photo-coupled. It can be driven by the current source of the diode 2.

However, if the internal resistance of the photodiode 2 is larger than the impedance of the impedance Impedance ωL1, the resistance R can be omitted. Further, in the present embodiment, the current drive circuit 7 for the first coil 4 is only a resistor, but a circuit for current-driving the first coil 4 of the transformer 3 based on an electric signal corresponding to a light quantity change of the photo sensor. For this, an optimal current drive circuit may be configured according to the elements of the photo sensor.

Next, when the current i corresponding to the change in the light amount flows in the first coil 4 of the transformer 3, a magnetic flux φ proportional to the current i is generated in the core 6 of the transformer 3 and the second coil of the transformer 3 is generated.
A voltage output v2 is induced in the coil 5 in proportion to the time variation Δφ / Δt of the magnetic flux.

The voltage v between the terminals of the second coil 5
2 is amplified by the voltage amplifier 8 up to a predetermined voltage v0, whereby the output voltage v0 can be taken out as a differential signal of the amount of received light which changes according to the recording signal pattern of the photodiode 2.

When the number of coil turns is small and the inductance L is small, the transformer 3 can be replaced with the equivalent circuit shown in FIG. 3A, ignoring the leakage inductance and the line capacitance. In this case, the response voltage v2 when the current i corresponding to the change in light amount is input to the first coil 4
Becomes a differential waveform as shown in FIG. 3 (b), and the time constant L /
The smaller R is, the more completely differentiating operation is possible with respect to the high frequency input signal.

In this way, a current that changes according to the amount of light received by the photosensor 2 is passed through the primary coil 4 of the transformer 3 to change the magnetic flux generated in the core 6 of the transformer 3 by the primary coil 4. Since it can be converted into a voltage by the secondary coil 5 and taken out as a differential signal, the respective values of the time constants C1 and R2 of the differentiating element and the circuit elements R1 and C2 for phase compensation as in the conventional CR type differential circuit. Is eliminated, and the troublesome work of having to set each of them separately so as to satisfy the predetermined condition is eliminated, and the design as a differentiating circuit can be simplified.

Further, since the transformer 3 is used as the differentiating circuit, the frequency characteristic of the differential signal is affected by the change in the inductance, that is, the frequency characteristic of the magnetic permeability of the magnetic material of the core 6, and therefore the magnetic material used. By selecting the magnetic characteristics of, the high frequency cutoff characteristic does not affect the stability of the amplifier unlike the conventional CR type differential circuit, and a filter with excellent high frequency cutoff characteristic is added to the differential circuit. Even if it does not, it is possible to easily block only unnecessary high frequency components above the signal band.

For example, when the signal band is 3 MHz as shown in FIG. 4 as the core material of the transformer 3, the magnetic permeability is flat up to 10 MHz which is about three times this, and when it becomes a high band of 10 MHz or more. If a metal magnetic thin film such as an amorphous alloy having a frequency characteristic of magnetic permeability that rapidly decreases the magnetic permeability is used, the inductance is rapidly decreased and the differential signal output is decreased in an unnecessary high region of 10 MHz or more. Like In this case, a sharp high-frequency cutoff characteristic can be obtained by connecting a capacitor in parallel with the coil and utilizing resonance.

Further, if the transformer 3 is used to form a differentiating circuit, even if an excessive amount of light is incident on the photodiode 2 due to a large fluctuation of the reflectance of the optical information recording medium, the magnetic characteristics of the core 6 and By changing the shape of the core, the magnetic saturation level is controlled and the output of the second coil 5 is suppressed, so that the output can be kept below a certain value.

Further, the transformer 3 is adapted to perform the current-voltage conversion and the differential operation of the photodiode at the same time, and constitutes a differentiating circuit including the current-voltage converting section, so that the conventional CR-type differentiating circuit is used. Compared to the one used, it is not necessary to separately provide a circuit for current / voltage conversion of the photodiode in the preceding stage of the differentiating circuit, and it is possible to suppress the generation of noise due to current / voltage conversion and simplify the circuit.

Moreover, the transformer 3 is replaced by the photodiode 2
By arranging them close to, the signal line from the photodiode 2 to the differentiating circuit, which is easily affected by external noise, can be shortened, and noise can be reduced. (Second Embodiment) FIGS. 5 and 6 show the schematic construction of the second embodiment. In FIG. 5, the basic configuration is the same as that of the first embodiment, but the transformer and the amplifier are integrated and integrally formed with the photodiode to reduce the size.

In this case, in FIG. 5A, the transformer 52 formed of a thin film is formed inside the case 56 on the substrate 54 integrally with the semiconductor chip 51 of the photodiode. Here, the transformer 52 is composed of a thin film coil 52a of a conductive material composed of a first coil and a second coil, and a magnetic thin film core 52b. Further, an integrated circuit 53 such as an amplifier circuit for amplifying the voltage of the second coil and a current drive circuit for driving the first coil of the transformer is formed on the side surface of the substrate 54 opposite to the mounting surface of the transformer 52.

A lead wire 55 for connecting to an external circuit is connected to the substrate 54 and the case 56, and
A light receiving window 57 is opened in the case 56 so that light corresponding to a recording signal pattern enters the semiconductor chip 51 of the photodiode.

Here, as shown in FIG. 5B, in the thin film transformer 52, after the magnetic thin film core 52b is formed on the substrate 54, the surface is insulated with an insulating film such as SiO2, and the terminal 58 is formed thereon. The thin-film coil 52a made of a conductive material, which is composed of a first coil connected to and a second coil connected to the terminal 59, is spirally formed.

In this case, the thin film core 52b and the thin film coil 52a may be formed by a film forming method such as a sputtering method or a vapor deposition method. The substrate 54 is a silicon substrate and the semiconductor chip 51 of the photosensor and an integrated circuit such as an amplifier are formed. It is also possible to simultaneously generate the same film forming apparatus and process as 53. On the other hand, FIG. 6 shows a configuration in which the device of the present invention is built in an optical pickup 60 using a hologram element.

In this case, the optical pickup 60 is provided with a condenser lens 62 and a hologram element 6 in a case 68 provided on a fixed base 69b so as to face the optical information recording medium 61.
3, the laser diode 64a formed on the substrate 65,
A photodiode 64b, a transformer 66 and a signal processing circuit 67 are provided.

The optical pickup 60 constructed in this way
Causes the laser light emitted from the laser diode 64a to pass through the hologram element 63 and be condensed on the optical information recording medium 61 by the condenser lens 62, while the optical information recording medium 6 is
The light modulated into the recording information reflected by the beam No. 1 passes through the condenser lens 62 and is diffracted by the hologram element 63 so as to be converged on the photodiode 64b. Then, the recording signal is reproduced by converting the light amount change into an electric signal by the photodiode 64b.

Here, if the thin film transformer 66 and the signal processing circuit 67 such as an amplifier circuit are integrally formed on the substrate 65 on which the photodiode 64b is formed as described in FIG. 5B, It is possible to integrally configure a reproduction circuit including a current-voltage conversion of a reproduction signal and a differentiating circuit inside the optical pickup 60.

Therefore, in this way, by integrally forming the photodiode 64b, the transformer 66, and the signal processing circuit 67 such as the width width device, the reproducing circuit including the photodiode 64b can be miniaturized and integrated, and the semiconductor manufacturing process. Like the above, mass production is easy and cost reduction is possible.

Further, by forming the transformer 66 with a thin film, the time constant of the differential operation can be reduced, and the differential operation can be performed at a higher frequency, so that the recording / reproducing apparatus can be made higher in density and faster.

Further, since it is possible to shorten the connection signal line including the transformer 66 and electrically shield the photodiode 64b to the differentiating circuit including the transformer 66 with a metal case, the influence of external noise is reduced. At the same time, noise generated in the reproducing circuit can be reduced. (Third Embodiment) FIGS. 7 and 8 show the schematic construction of the third embodiment.

FIG. 7 shows a basic circuit of the third embodiment. In this case, the first coil of the transformer 70 is 71, 72
Is divided into two, and each terminal has two photodiodes 7
4, 75 are connected, and the output from the second coil 73 is taken out through the voltage amplifier 76.

For example, conventionally, when the outputs from a plurality of photodiodes are used to detect a reproduction signal, the current outputs of the two photodiodes 81 and 82 are converted into current-voltage conversion circuits 83 and 84 as shown in FIG. After converting to voltage,
The differential amplifier 85 obtains the difference signal, and the differentiating circuit 86 performs processing such as peak detection.

On the other hand, in FIG. 7, the current outputs i1 and i2 of the two photodiodes 74 and 75 are applied to the first coils 71 and 72 of the transformer 70. Then, in the core of the transformer 70, the proportional magnetic flux φ of the coils 71 and 72 is generated.
Therefore, if the coils 71 and 72 are anti-coupled to each other, the total magnetic flux φ generated in the core is φ = φ1.
-Φ2, and the amplified output v0 of the second coil 73
Is an output proportional to Δφ / Δt = Δ (φ1−φ2) / Δt. In this case also, the photodiodes 74 and 7
If the internal resistance of 5 is sufficiently larger than the impedance of the first coil, the resistor 77 can be omitted.

Therefore, the output v0 from the second coil 73 shown in FIG. 7 becomes an output corresponding to the differentiation of the difference in the light amount changes received by the two photodiodes 74 and 75, and FIG.
It can be seen that the output is equivalent to the output obtained by the conventional method.

As a result, according to the third embodiment, current-voltage conversion of the photodiode output, calculation of difference or sum, and differentiation can be performed at once in the transformer 70, so that the reproducing circuit can be miniaturized and the cost can be reduced. It is easy to reduce noise. (Fourth Embodiment) FIG. 9 shows a schematic configuration of the fourth embodiment.

FIG. 9A shows the basic circuit of the third embodiment. In this case, the two transformers 91 and 92 are used, and the differential output of the first transformer 91 is input to the second transformer 92 again via the voltage-current conversion circuit 93 and redifferentiated to obtain the second-order differential output. I am configuring.

That is, in FIG. 9A, the differential output obtained by the first transformer 91 is input to the primary side of the second transformer 92 via the voltage-current conversion circuit (current drive circuit) 93, After differentiating again, the voltage amplifier 9 connected to the secondary side
By amplifying to a predetermined voltage by 4, it becomes possible to obtain an output v0 proportional to the second-order differential signal of the current output of the photodiode 90.

At this time, as shown in FIG. 9B, if the magnetic paths are separated so that the magnetic fluxes φ1 and φ2 generated in the cores of the first transformer 91 and the second transformer 92 do not cross each other, Two transformers 91, 92 on a common core 95
Can also be formed.

Therefore, in this way, the second-order differential signal of the photodiode output can be obtained, and also in this embodiment, the circuit can be simplified and downsized, and the differential operation by the transformer and the signal line. By shortening, it is possible to reduce noise. The present invention is not limited to the above-mentioned embodiments, and can be implemented by appropriately modifying it without changing the gist.

[0055]

According to the present invention, a current that changes according to the amount of light received by the photosensor is applied to the primary coil of the transformer, and the change of the magnetic flux generated in the core of the transformer by the primary coil is changed by the secondary coil. Since the signal is converted into a voltage and outputted as a differential signal, the respective values of the time constants C1 and R2 of the differentiating element and the circuit elements R1 and C2 for phase compensation are set to predetermined conditions as in the conventional CR type differential circuit. The troublesome work of having to separately set each of them to be satisfied is eliminated, and the design of the differential circuit can be simplified.
Moreover, since the current-voltage conversion of the photosensor output and the differentiation operation can be performed at the same time, the circuit from the photosensor to the differentiation circuit can be downsized and simplified.

Further, since the transformer is used as the differentiating circuit and is influenced by the frequency characteristic of the magnetic permeability of the magnetic material of the core, the magnetic characteristic of the magnetic material to be used is selected, whereby a filter having an excellent high cutoff characteristic is obtained. Without adding
Only unnecessary high-frequency components above the signal band can be blocked easily.

Further, by arranging the photo sensor and the transformer in close proximity to each other and shortening the line from the photo sensor to the differentiating circuit, high-frequency noise generated in the reproducing circuit or intruding from the outside is reduced and stable. Differentiated operation is possible.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a circuit configuration of a first embodiment.

FIG. 3 is a diagram for explaining the first embodiment.

FIG. 4 is a diagram showing frequency characteristics of magnetic permeability of the transformer used in the first embodiment.

FIG. 5 is a diagram showing a schematic configuration of a second embodiment of the present invention.

FIG. 6 is a diagram showing a schematic configuration of a second embodiment of the present invention.

FIG. 7 is a diagram showing a schematic configuration of a third embodiment of the present invention.

FIG. 8 is a diagram showing a conventional example corresponding to the third embodiment.

FIG. 9 is a diagram showing a schematic configuration of a fourth embodiment of the present invention.

FIG. 10 is a diagram showing an example of a conventional optical information reproducing device.

FIG. 11 is a diagram showing an example of a current-voltage conversion circuit of a conventional optical information reproducing device.

FIG. 12 is a diagram showing an example of a conventional CR type differential circuit.

FIG. 13 is a diagram showing frequency characteristics of a conventional CR type differential circuit.

FIG. 14 is a diagram illustrating conventional pit position recording and pit edge recording.

FIG. 15 is a diagram for explaining a reproduction method of pit position recording.

FIG. 16 is a diagram for explaining a reproducing method of pit edge recording.

[Explanation of symbols]

1 ... Printed circuit board, 2 ... Photodiode, 3 ... Transformer, 4 ... 1st coil, 5 ... 2nd coil, 6 ... Core, 7 ...
Current drive circuit, 8 ... Voltage amplifier, 21 ... Resistor, 51 ... Semiconductor chip, 52 ... Transformer, 52a ... Thin film coil, 5
2b ... Magnetic thin film core, 53 ... Integrated circuit, 55 ... Lead wire, 54 ... Substrate, 56 ... Case, 57 ... Light receiving window, 58,
59 ... Terminal, 60 ... Optical pickup, 61 ... Optical information recording medium, 62 ... Condensing lens, 63 ... Hologram element, 64
a ... laser diode, 64b ... photo diode, 6
5 ... Board, 66 ... Transformer, 67 ... Signal processing circuit, 68
... case, 70 ... transformer, 71, 72 ... first coil,
73 ... 2nd coil, 74, 75 ... Photo diode, 7
6 ... Voltage amplifier, 91, 92 ... Transformer, 93 ... Voltage-current conversion circuit, 94 ... Voltage amplifier, 95 ... Core.

Claims (3)

[Claims] 1. An optical signal is read by converting a change in the amount of light received by a photosensor into an electrical signal, and the read signal is differentiated to obtain a primary differential signal and the primary differential signal is differentiated again. In an optical information reproducing apparatus adapted to obtain a reproduction signal based on at least one of the obtained secondary differential signals, the differentiating means for producing the primary differential signal or the secondary differential signal includes a first coil and a second coil. It is composed of a transformer magnetically coupled with a core of a magnetic material, an electric signal corresponding to a change in the amount of light received by the photosensor is given to the first coil of the transformer, and a differential signal is output from the second coil of the transformer. An optical information reproducing device characterized in that 2. The optical information reproducing apparatus according to claim 1, wherein the photo sensor and the transformer are arranged close to each other. 3. The photosensor is composed of a plurality of transformers, and the transformer has a plurality of first coils. The photosensors are separately connected to the first coils, and the second coil of the transformer is used to connect the photosensors to the photosensors. An optical information reproducing apparatus characterized in that a differential signal of a sum or a difference of electric signals which changes according to the amount of received light is output.