JPH0447531A - 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
The signal processing circuit 31 converts the output current of the optical sensor from a current to a voltage, and an error signal detection circuit 40 generates a focusing error signal and a tracking error signal from the converted voltage. Ru.

Here, the focusing error signal is used to accurately focus the light beam irradiated onto the optical disc onto the disc. The actuator 28 provided in the optical head 23 drives the objective lens 27 in the direction of its optical axis according to this focusing error signal to perform focusing control.The tracking error signal is formed concentrically or spirally on the optical disc 21. This is to control the light beam so that it accurately traces the information track. 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. 2. FIG. The photoelectric conversion element is composed of four optical sensors 6.7 and 8.9, and the light receiving section has the following:
The reflected light from the optical disk enters as a spot 10 as shown by the shaded 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.

If the light beam is imaged in front of the disk and if it is imaged in the back of the disk, the spot 10 will be 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. In addition, the optical sensor 6.7 and the 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° and 13.14 are differential amplifiers, respectively, and 15 and 16° and 17.18 are resistors having the same resistance value R, respectively. Current 1 a + 17 Hi flowing through optical sensors 6.7 and 8.9 consisting of photodiodes etc.
This circuit converts a and io into voltages corresponding to the respective amounts of current. Operational amplifier 11.12, 13.1
If the output voltages of 4 are Ve, Vs, Vt, Va, respectively, then 6=R・ia, Vt=R-it, Vs
=R-is, and satisfy the relationships of V*=R-1g.

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 is composed of summing amplifiers 32, 33, 34, 35.38 and differential amplifiers 36.37. The focusing error signal S AF is generated by the differential amplifier 37.
It is obtained as an output of (Vy +Vs) - (Vs +Vs). On the other hand, the tracking error signal SAT is
(Vs +V?) - (Vs +Vw) I.

The signal is output from the differential amplifier 36. Also, from the summing amplifier 38, Va +V? +Va +Vs sum signal 5
IIF is added. This sum signal S□ is a signal proportional to the amount of edge light received by the four optical sensors. Sum signal S FI
F is used, for example, to detect that the disk surface has come close to the in-focus position when pulling in the focusing control. It is also 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, when reproducing information already recorded on the optical disc, it is also possible to reproduce the information signal from this sum signal S□.

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 eight elements of the semiconductor laser change due to temperature, or if the transmittance of the optical system decreases due to adhesion of dust, the amount of light received by the optical sensor will change, causing problems such as the error signal detection sensitivity becoming inconsistent. There was a point.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above, and to provide an optical information processing device that can detect focusing and/or tracking error signals with constant sensitivity even when the amount of light received by an optical sensor changes. An object of the present invention is to provide a signal processing circuit for use in the present invention.

[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 current mirrors into which each output current of the optical sensor is input, and each of the current mirrors.
a plurality of current switches that shunt the output current of the mirror at a shunting ratio that changes according to the same control signal; a plurality of current-to-voltage converters that convert the current shunted by each of the current switches into voltage; a circuit that generates the control signal based on a signal obtained by adding the outputs of the plurality of converters, and feeds back the control signal to each of the current switches so that the sum of the outputs of the plurality of converters is constant; This is achieved by configuring.

[Embodiment] FIG. 1 is a diagram showing the configuration of an embodiment of a signal processing circuit of the present invention. The circuit of this embodiment can be applied as is to the apparatus shown in FIG. Therefore, an embodiment of the optical information processing apparatus of the present invention uses the circuit shown in FIG. 1 for the signal processing circuit 31 shown in FIG. 2.

In FIG. 1, reference numerals 6, 7, 8.9 are optical sensors consisting of photodiodes. A driving voltage vac is applied to these optical sensors. 1, 2, 3.4 are current-voltage conversion circuits into which the photocurrent detected by each optical sensor is input. Although not shown in the drawings, the conversion circuits 2, 3.4 each have the same configuration as the conversion circuit 1. Therefore, conversion circuits 1 to 4 all exhibit the same characteristics.

From terminals 1a, 2a, 3a, 4a of each conversion circuit, voltage V1. V2. Vz and V4 are output respectively. These output voltages are used to generate focusing and tracking error signals using a circuit such as that illustrated in FIG. In addition, the output voltages Vr, Vx, Vx
, V4 are resistors 50°51 each having the same resistance value.
．． 52 and 53 and input to the differential amplifier 47. The differential amplifier 47 uses this added voltage and the reference voltage V
The difference from 1 is the control voltage ■. Bind and output. Control voltage V
C is fed back to control terminals 1c, 2c, 3c, and 4c of each conversion circuit.

The conversion circuit 1 is composed of a Wilson type current mirror 43, a current switch 44, and a current-voltage converter consisting of a differential amplifier 45 and a feedback resistor 46.

The current mirror 43 consists of a transistor Q and a multi-emitter transistor Q2 having ten emitters. The collector current of transistor Q2 is ten times that of transistor Q1. That is, the current input from the optical sensor is amplified ten times by this current mirror 43.

An offset current is applied from a constant current source 41 to the input of the current mirror 43 . This offset current is for making the current mirror 43 active even when the input current from the optical sensor is very small. On the other hand, a constant current source 42 is provided to reduce the offset current from the current mirror 43. mirror 4
3, the offset current is also amplified ten times, so the current value of the constant current source 42 is set to be ten times the current value of the constant current source 41.

The current amplified by the current mirror 43 is
The signal is input to the switch 44. The current switch 44 is composed of two transistors, and the ratio of the amount of current flowing through each transistor is determined by the magnitude relationship between the control voltage VC input from the terminal IC and the reference voltage V. That is, the ratio between the input current of the current switch 44 and the input current is controlled by the control voltage (6).

The output current of the current switch 44 is
and a feedback resistor 46, the voltage V,
is converted into and output from terminal 1d.

Next, the operation of the circuit shown in FIG. 1 will be explained. Assuming that the output photocurrent of the optical sensor 6 is Ag and the current value of the constant current source 41 is 1 μA, a current of i6+1 μA flows through the transistor Q1 of the current mirror 43, and a current of i6+1 μA flows through the transistor Q2.
A current of 10X (i, +1 μA) flows. Constant current source 42
When the current value of is set to 10 μA, the input current i to the current switch 44 is subtracted and becomes I Qx ia. In other words, the output current of the optical sensor is amplified ten times.

The current i is shunted by the current switch 44, and the current ia is input to the differential amplifier 45. This current i6 is expressed as follows.

(1) Here, k is the Boltzmann constant, T is the absolute temperature, and q is the charge of the electron.

The above-mentioned current i6 is converted to voltage ■1 by the above-mentioned current-voltage converter.
is converted and output. Here, current mirror 4
3, the photocurrent is amplified by a factor of 10. Therefore, if the same voltage output as that without amplification is obtained, the resistance value of the feedback resistor 46 may be reduced to one-tenth. Therefore, higher frequency photocurrent can be converted into current-to-voltage.

The current-voltage conversion coefficients of conversion circuits 1 to 4 are all equal, 1 and 2, respectively (2 is the shunt ratio due to the current switch, and 2 is the other fixed coefficient) of the optical sensor 7.8.9. The output current is 01? + 1111 19, the following relational expression can be obtained.

V + =K +・K *・l s
(2) V, = 1・2・i,
'(3) V * = K +・K
*・is (4)V4
= to 1・to 2・i * (
5) On the other hand, the conversion coefficient is controlled by the control signal so as to satisfy the following relationship.

: v, (6) From equation (6), the output voltage of each conversion circuit is determined as follows.

V゛“ 4■・ L+ L+ La+ Ll ”V
, =4V, 61" zs+ it+ x6 + L (8) Vl=
4V,-,'・,. +1? + la + i. (9) V4 = 4V
g, "la+L+ia+i. (lO) That is, the output of each current-voltage conversion circuit is normalized by the total photocurrent value. Therefore, such a circuit can be used as an optical information processing device. When used in , it is possible to detect focusing and/or tracking error signals with a certain sensitivity.

The above is the configuration for converting the output current of the optical sensor into voltage, but in the embodiment shown in FIG. 1, a current-voltage conversion circuit 5 is further provided. This conversion circuit 5 is for obtaining an output voltage proportional to the total amount of light received by the optical sensor.

The conversion circuit 5 has the same configuration and characteristics as the conversion circuits 1 to 4. This conversion circuit 5 is not connected to the optical sensor, and a driving voltage Vcc is applied to the terminal 5a. In addition, the control voltage V is fed back to the control terminal 5c, similar to other conversion circuits.On the other hand, the voltage V output from the terminal 5d is fed back to the differential amplifier 4.
8 is input. Then, this differential amplifier 48 outputs a difference signal between the voltage V and the reference voltage ■ as a voltage v6. This voltage v6 is fed back to the terminal 5b of the conversion circuit 5 via the resistor 49, forming a negative feedback loop. Then, the output voltage V is the reference voltage ■.

is controlled to be equal to

The input current i to the conversion circuit 5 is expressed as follows, assuming that VIE is the base-emitter voltage of the transistor.

V, -2V,! f*: (11)
Therefore, the output voltage V, is Vs - 2 VIE V, = 1 to 1, (12) Since this voltage forms a negative feedback loop via the differential amplifier 48, Vs = Vt, and ■- is determined as follows.

= ”” (4a+ L+ is+ io) + 2
V5t4V.

(13) That is, the voltage v6 becomes a signal proportional to the total amount of light received by the optical sensor.

In the circuit of the invention, if an input offset voltage exists in each differential amplifier, the voltage offset appearing at each converter output is controlled to be equal to this input offset voltage. Therefore, the offset voltage does not change due to fluctuations in the amount of light received by the optical sensor. Therefore,
If a means for compensating the input offset voltage is provided in advance, an accurate error signal can always be detected without being affected even if the amount of light received by the optical sensor fluctuates.

In the embodiments described above, each transducer is preferably formed on the same chip and is thermally coupled. This is to compensate for errors that occur and perform more accurate signal detection.

The present invention can be applied in various ways in addition to the embodiments described above. For example, although the so-called astigmatism method and the bush pull method have been described as methods for detecting error signals, the present invention can also be applied to cases where error signals are detected by 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 the optical information processing device of the present invention include a current-voltage conversion circuit that includes a current mirror, a current switch, and a current-voltage converter. Since the shunt ratio of the current switch is controlled so that the sum of the output voltages is constant, it becomes possible to detect focusing and/or tracking error signals with constant sensitivity.

[Brief explanation of drawings]

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. FIG. 4 is a diagram showing an example of a conventional signal processing circuit, and FIG. 5 is a diagram showing an example of the configuration of a circuit for detecting an error signal from the output of the signal processing circuit. 1, 2, 3, 4.5... Current-voltage conversion circuit 6,
7.8.9... Optical sensor 41.42...
... Constant current source 43 ... Current mirror 44 ... Current switch 45, 47.48 ... Differential amplifier 46 , 49.50.51.52.53...
Resistance V r1;;;])

Claims (8)

[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 into an output voltage for generating a tracking and/or focusing error signal includes a plurality of current mirrors into which each output current of the optical sensor is input, and an output current of each of the current mirrors. a plurality of current switches that shunt current at a shunting ratio that varies according to the same control signal; a plurality of current-to-voltage converters that convert the current shunted by each of the current switches into voltage; and outputs of the plurality of converters. and a circuit that generates the control signal based on a signal obtained by adding up the converters, and feeds back the control signal to each of the current switches so that the sum of the outputs of the plurality of converters is constant. signal processing circuit. (2) The signal processing circuit according to claim 1, wherein each of the current mirrors amplifies the current input from the optical sensor and outputs the amplified current to each of the current switches. (3) An offset current is applied to the input terminal of each of the current mirrors, and a current equal to the offset current multiplied by the current amplification factor of the mirror is subtracted from the output of the current mirror. The signal processing circuit according to scope 2. (4) a second current mirror that is not connected to the optical sensor; a second current switch that shunts the output current of the second current mirror at a shunt ratio that changes according to the control signal; a second current-to-voltage converter that converts the current shunted by the second current switch into a voltage, and a difference between the output voltage of the second converter and a reference voltage to calculate the total amount of light received by the optical sensor. 2. The signal processing circuit according to claim 1, further comprising a differential circuit that outputs a proportional voltage, and a circuit that feeds back the output of the differential circuit to the input terminal of the second converter. (5) 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 the signal 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 current mirrors into which each output current of the optical sensor is input; a plurality of current switches that shunt the output current of each of the current mirrors at a shunting ratio that changes according to the same control signal; a plurality of current-to-voltage converters that convert current shunted by a switch into voltage; and generating the control signal based on a signal obtained by adding the outputs of the plurality of converters; 1. An optical information processing device comprising: a circuit that feeds back this control signal to each of the current switches so that the current switch is constant. (6) The optical information processing device according to claim 5, wherein each of the current mirrors amplifies the current input from the optical sensor and outputs the amplified current to each of the current switches. (7) An offset current is applied to the input terminal of each of the current mirrors, and a current equal to the offset current multiplied by the current amplification factor of the mirror is subtracted from the output of the current mirror. The optical information processing device according to scope 6. (8) a second current mirror that is not connected to the optical sensor; a second current switch that shunts the output current of the second current mirror at a shunting ratio that changes according to the control signal; a second current-to-voltage converter that converts the current shunted by the second current switch into a voltage, and a difference between the output voltage of the second converter and a reference voltage to calculate the total amount of light received by the optical sensor. 6. The optical information processing device according to claim 5, further comprising a differential circuit that outputs a proportional voltage, and a circuit that feeds back the output of the differential circuit to the input terminal of the second converter.