JPH0447529A - Signal processing circuit and optical information processing device - 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 [Industrial Application Field] The present invention relates to a signal processing circuit for converting an output current of an optical sensor of an optical information processing device into a voltage, and an optical processing circuit using such a circuit. The present invention relates to an information processing device.

[Prior Art] Conventionally, optical information processing devices using recording media such as optical disks as large-capacity memories are known. FIG. 2 shows a schematic configuration of such an optical information processing device.

In FIG. 2, 21 indicates an optical disc.

This optical disc 21 is placed on a turntable,
It is rotated by a spindle motor 22. An optical head 23 is provided so as to be movable in the radial direction of the rotated optical disk 21. The optical head 23 emits a light beam from a built-in semiconductor laser 24 toward an optical disk. The emitted light beam passes through collimator lens 2
5, it becomes parallel light, passes through the beam splitter 26,
The objective lens 27 forms an image on the optical disk as a minute spot. Information is recorded and/or reproduced on the optical disc 21 by this light beam.

On the other hand, the light reflected by the optical disk 21 passes through the objective lens 27 again, and the incident light beam is separated by the beam splitter 26. The separated reflected light passes through an anamorphic optical system 29 having different imaging positions in two orthogonal directions, and is received by a photoelectric conversion element 30. Photoelectric conversion element 30
consists of a plurality of optical sensors, and a signal processing circuit 31 converts the eight currents of the sensors into a current-to-voltage, and an error signal pressure detection circuit 40 generates a focusing error signal and a tracking error signal from the converted voltage. be done.

Here, the focusing error signal is used to accurately focus the light beam irradiated onto the optical disc onto the disc. An actuator 28 provided within the optical head 23 drives the objective lens 27 in the direction of its front axis in accordance with this focusing error signal to perform focusing control. The tracking error signal is used to control the light beam to accurately trace information tracks formed concentrically or spirally on the optical disc 21. This tracking error signal also
It is fed back to actuator 28 and used to drive objective lens 27 across the information track. A method for detecting such an error signal will be described below.

3(a) to 3(c) are front views of the photoelectric conversion element 30 shown in FIG. 21. FIG. The photoelectric conversion element is composed of four optical sensors 6.7 and 8.9, and reflected light from the optical disk enters the light receiving section as a spot 1o, as shown by the hatched area. The shape of this spot 10 changes depending on the focusing state of the light beam irradiated onto the optical disc. When the light beam is accurately focused on the disk, a circular spot 10 is formed as shown in FIG. 3(a), and the optical sensors 6 to 9 output equal currents.

When the light beam is focused in front of the disk and when it is focused behind the disk, the spot 10 becomes elliptical as shown in FIG. 3(b) and FIG. 3(c), respectively. . Therefore, a focusing error signal can be obtained from the difference signal between the sum of the outputs of the optical sensors 7 and 8 and the sum of the outputs of the optical sensors 6 and 9.

On the other hand, a bright and dark pattern is formed in the spot 10 according to the positional relationship between the light beam irradiated onto the disc and the information track. Also, optical sensor 6.7 and optical sensor 8.
The boundary line with 9 is provided parallel to the longitudinal direction of the image of the information track formed by the reflected light. Therefore, by subtracting the sum signal of the outputs of the optical sensors 6 and 7 and the sum signal of the outputs of the optical sensors 8 and 9, a tracking error signal is detected.

FIG. 4 is a diagram showing an example of the configuration of a conventional signal processing circuit that converts the output current of the photoelectric conversion element into voltage. Fourth
In the figure, 11.12°, 13.14 are differential amplifiers, and 15.16° and 17.18 are resistors having the same resistance value R, respectively. Current flowing through optical sensors 6.7 and 8.9 consisting of photodiodes etc. 1 a I L 711
This circuit converts a + l s into a voltage corresponding to each amount of current. Operational amplifier 11.12
, 13. Let the output voltages of 14 be v, , v, , v, , v, respectively.
Then, V, = R・ia, Vt = R' it,
The relationships Va = R' is and Ve = R-io are satisfied.

FIG. 5 shows that from the output voltage of the signal processing circuit shown in FIG.
This is an error signal detection circuit for detecting the aforementioned focusing error signal and tracking error signal. This circuit consists of summing amplifiers 32.33, 34, 35.38 and differential amplifiers 36.37. The focusing error signal S0 is output from the differential amplifier 37 by (V
t+V. )−(v, +v,).

On the other hand, the tracking error signal SAT is (vs +V
? )−(va +Vo) and the differential amplifier 36
It is output from Also, from the summing amplifier 38, Va
+V? A sum signal S and IF of +Vll + Ve is output. This sum signal SRF is a signal proportional to the total amount of light from the four optical sensors. The sum signal S++r is used, for example, to detect that the disk surface has come close to the in-focus position when performing focusing control. Also,
It is used to determine whether the light beam irradiated onto the disk is located on the information track or in the area between the information tracks (so-called on-land or on-group determination). Furthermore, in the reproduction mode, that is, in the case of reproducing information already recorded on the optical disc, the information signal can also be reproduced from the sum signals S and IF.

The signal detection method as described above is explained in detail in Japanese Patent Application Laid-Open No. 56-90434.

[Problems to be Solved by the Invention] In the conventional optical information processing device described above, the output current of each optical sensor changes depending on the amount of light reflected from the medium.

Therefore, the reflectance of the medium changes depending on the location,
If the output of the semiconductor laser changes due to the influence of temperature or the transmittance of the optical system decreases due to the adhesion of dust, the amount of light received by the optical sensor changes, causing problems such as the error signal detection sensitivity not being constant. was there.

An object of the present invention is to solve the above-mentioned problems of the prior art, to be able to detect focusing and/or tracking error signals with constant sensitivity even when the amount of light received by an optical sensor changes, and to detect a focusing and/or tracking error signal proportional to the amount of light received by the optical sensor. It is an object of the present invention to provide an optical information processing device that can be used as an optical information processing device, and a signal processing circuit for use in this device.

[Means for Solving the Problems] The object of the present invention is to provide a means for irradiating a recording medium with a light beam, a plurality of optical sensors that receive reflected light or transmitted light from the medium, and outputs of these optical sensors. It consists of a signal processing circuit that converts current into voltage, and a control circuit that generates a tracking and/or focusing error signal for a light beam from the output voltage of the signal processing circuit, and records and/or reproduces information on the medium. In the optical information processing device, the signal processing circuit includes a plurality of first converters that convert each of the output currents into a voltage based on a current-voltage conversion coefficient that changes according to a control signal, and the optical sensor. a second converter that is not connected to the first converter, has the same configuration as the first converter, and has a current-voltage conversion coefficient that changes according to the control signal; and an output of the first converter. a circuit that generates the control signal from a voltage and feeds the control signal back to each of the first and second converters so that the sum of the outputs of the first converter is constant; and the second converter. A differential circuit that differentiates the output voltage of the optical sensor from a reference voltage and outputs a voltage proportional to the total amount of light of the optical sensor, and a circuit that feeds back the output of the differential circuit to the input terminal of the second converter. This is achieved by doing.

[Example] Before describing the present invention in detail, the configuration of a signal processing circuit for preventing the sensitivity change of the control signal as described above will be described. FIG. 6 is a diagram showing an example of such a signal processing circuit. This circuit can be applied as is to the optical information processing device shown in FIG.

In FIG. 6, I, 2, 3.4 are variable coefficient current-voltage converters connected respectively to optical sensors 6.7, 8.9 consisting of photodiodes. The converter l is composed of a so-called double balanced mixer and a differential amplifier 39.

A double balanced mixer consists of multiple transistors, resistors, constant current sources, and voltage sources. The current value and resistance value of each part are as shown in the figure. converter 2,
3 and 4, although not shown in the drawings, each have exactly the same configuration as the converter 1. Therefore, converters 1-4 all exhibit the same characteristics.

Input terminals 1a, 2a, 3a, 4a of each converter have vc
A voltage of e is applied. Also, terminal 1d of each converter
, 2d, 3d, 4d, the converted voltages V+, V
! ,v,,v, are output. These output voltages are
A circuit such as that illustrated in FIG. 5 is used to generate focusing and tracking error signals. In addition, the output voltages V + , Vz , Vz ,
V4 is connected through resistors each having the same resistance value R5,
It is applied to the differential amplifier 19. The differential amplifier 19 converts the difference between this voltage and the reference voltage V into a control voltage ■. Output as . The control voltage VC is applied to the control terminals 1c, 2c, and 2c of each converter.
It is fed back to 3c and 4c. Each converter then changes its current-voltage conversion coefficient in response to this control signal.

Next, the operation of the converter 1 will be explained in detail. The collector current of each transistor is 1. ．． 1. ,I.

To, IE, IF, the current flowing through the resistor R1 is 1, . 1
．． , the photocurrent of the optical sensor 6 is i8, and the current flowing through the constant current source is calculated. Then, they satisfy the following relationship.

R1.

IA=IQ+ −・1 e
(1) R4.

1,=I. --・l g (2
)e Hatake 1b-VC IC-1+. ,(,-ヮ.・■・ (3)I
D = e a ve-vb l tene a l V C-V b l bow ^■.
= ea IVe-Vbl 10e Hatake (vC-vIl · l8 From the above equations (1) to (6), the following relational expression is obtained.

■. =IC +IE 1,=I.

+I.

here, a”q/kT, k is Boltzmann constant number, T is absolute temperature, q indicates the charge of the electron.

Above (1) ~(8) From the formula, Output voltage v1 Ba, Below It is required as below.

r·R2 1+ e ” ” b−vc (9) In this way, the converter 1 converts the current i6 into the voltage V+ with a conversion coefficient that changes according to the control voltage Vc. In exactly the same way, converters 2 and 3.4 have current f? , Ls+ii to voltage V2. Convert to V,,V4. On the other hand, since the differential amplifier 19 forms a negative feedback loop, the output voltage of each converter is controlled to be as follows. In other words, when a circuit like the one shown in Figure 6 is used, the sum of the output voltages becomes a constant value, and even if the amount of light received by the optical sensor changes, it is possible to always detect error signals with a constant sensitivity. .

According to the present invention, in the circuit shown in FIG. 6, it is further possible to obtain a signal proportional to the amount of light received at the edge of the optical sensor. In the circuit shown in FIG. 6, since the sum of the output voltages is controlled to be constant, this sum signal does not indicate the amount of light received by the optical sensor. Further, the control voltage vc is determined as follows from the relationship (ia÷L) (11). That is, the control voltage ■. However, the signal is not proportional to the amount of light received at the edge of the optical sensor.

FIG. 1 is a diagram showing an embodiment of a signal processing circuit according to the present invention, which can obtain a signal proportional to the amount of light received at the edge of an optical sensor. This embodiment has the same structure as the circuit shown in FIG. 6, except that a variable coefficient current-voltage converter 5 is provided. Also,
The operation of converting current into voltage is also exactly the same as the circuit shown in FIG. Therefore, in FIG. 1, the same parts as in FIG. 6 are given the same reference numerals, and detailed explanations will be omitted.

The circuit of this embodiment can be applied as is to the apparatus shown in FIG. Therefore, in the signal processing circuit 31 shown in FIG.
The circuit using the circuit shown in the figure is an embodiment of the optical information processing device of the present invention.

Further, by inputting the output voltage of the circuit shown in FIG. 1 to the circuit shown in FIG. 5, focusing and tracking error signals can be obtained. At this time, as in the case of the circuit shown in FIG. 6, the lateral ratio sensitivity of these error signals is maintained constant regardless of changes in the amount of light received by the optical sensor.

In FIG. 1, converter 5 has exactly the same configuration and characteristics as converters 1-4. This converter 5 is not connected to the optical sensor and has a drive voltage VC at the terminal 5a.
C is applied. Further, a control voltage VC is fed back to the control terminal 5c, similar to other converters. On the other hand, the voltage V5 output from the terminal 5d is input to the differential amplifier 20. This differential amplifier 20 has a voltage V6 and a reference voltage V.

Which difference signal is output as voltage v6? This voltage 6 is fed back to the terminal 5b of the converter 5 via the resistor R6, forming a negative feedback loop. Then, the output voltage Va is controlled to be equal to the reference voltage (2).

The voltage V is given by the following equation, similar to equation (9).

... (13) Also, since vc at this time is given by equation (12), therefore, voltage ■6 is Rp R・, (i6゜i?+i..i.> (15
)”” 4rVa. That is, the voltage V6 becomes a signal proportional to the total amount of light from the optical sensor.

In the embodiments described above, each transducer is preferably formed on the same chip and thermally coupled. This is because by making the temperature conditions of the converters the same, errors caused by heat can be compensated for and more accurate signal detection can be performed.

The present invention can be applied in various ways in addition to the embodiments described above. For example, the current-voltage converter is not limited to the circuit configuration of the embodiment, and may have any configuration as long as the conversion coefficient changes according to the control signal.

Further, although the so-called astigmatism method and the bush pull method have been described as examples of error signal detection methods, the present invention can also be applied to cases where error signals are detected using other methods. Further, in the embodiment, the optical sensor receives the reflected light from the medium, but if the medium is a transmission type, the optical sensor is configured to receive the transmitted light of the medium.

[Effects of the Invention] As explained above, the signal processing circuit and optical information processing device of the present invention use a variable coefficient current-voltage converter to control the sum of output voltages to be constant, so focusing and/or tracking error signals can now be detected with constant sensitivity. Furthermore, since a negative feedback loop was formed using a current-voltage converter not connected to the optical sensor, it became possible to detect a signal proportional to the total amount of light from the optical sensor.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the signal processing circuit of the present invention, FIG. 2 is a schematic diagram showing a configuration example of an optical information processing device to which the present invention can be applied, and FIG. 3 is a diagram showing the principle of error signal detection. Diagrams for explanation; FIG. 4 is a diagram showing an example of a conventional signal processing circuit; FIG. 5 is a diagram showing a configuration example of a circuit that detects an error signal from the output of the signal processing circuit; FIG. FIG. 3 is a diagram showing an example of the configuration of a signal processing circuit for making the detection sensitivity constant. 1.2, 3.4.5... Variable coefficient current-voltage converter 6.7, 8.9... Optical sensor

Claims (2)

[Claims] (1) Used in devices that record and/or reproduce information by irradiating a light beam onto a recording medium, the output current of a plurality of optical sensors that receive reflected light or transmitted light from the medium is A signal processing circuit for converting each of the output currents into an output voltage for generating a tracking and/or focusing error signal, comprising: a plurality of circuits for converting each output current into a voltage based on a current-voltage conversion coefficient that changes according to a control signal; a first converter; a second converter that is not connected to the optical sensor, has the same configuration as the first converter, and has a current-voltage conversion coefficient that changes according to the control signal; The control signal is generated from the output voltage of the first converter, and this control signal is fed back to each of the first and second converters so that the sum of the outputs of the first converter is constant. a differential circuit that differentiates the output voltage of the second converter from a reference voltage and outputs a voltage proportional to the total amount of light received by the optical sensor;
and a circuit that feeds back the output of the differential circuit to the input terminal of the second converter. (2) A means for irradiating a recording medium with a light beam, a plurality of optical sensors that receive reflected light or transmitted light from the medium, a signal processing circuit that converts the output current of these optical sensors into voltage, and a signal processing circuit that converts the output current of these optical sensors into voltage. and a control circuit that generates a tracking and/or focusing error signal of a light beam from an output voltage of a processing circuit, and an optical information processing device that records and/or reproduces information on the medium, the signal processing circuit comprising: a plurality of first converters that convert each of the output currents into a voltage based on a current-to-voltage conversion coefficient that changes according to a control signal;
a second converter having the same configuration as the converter and having a current-voltage conversion coefficient that changes according to the control signal, and generating the control signal from the output voltage of the first converter, A circuit that feeds back this control signal to each of the first and second converters so that the sum of the outputs of the first converter is constant; and a circuit that calculates the difference between the output voltage of the second converter and a reference voltage. , comprising a differential circuit that outputs a voltage proportional to the total amount of light received by the optical sensor, and a circuit that feeds back the output of the differential circuit to the input terminal of the second converter. Information processing device.