JPH0770064B2 - Recording medium drive - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium drive device such as an optical disk or a magneto-optical disk, and particularly to a drive of a tracking servo mechanism and a focusing servo mechanism. The present invention relates to a recording medium driving device focusing on an amplifier of an output current of a detector that detects an error signal.

2. Description of the Related Art In recent years, the amount of information processed by computers has been increasing, and attention has been paid to optical disk devices that record a large amount of information in order to record and reproduce the increased information, and there is a remarkable improvement in the technology. Since the information recorded on or recorded on the recording medium in the optical disc device is a minute bit of 1 μm or less, the laser beam is focused on the minute spot light having a diameter of about 1 μm to prevent surface wobbling or track wobbling of the recording medium. Regardless, a focusing servo mechanism and a tracking servo mechanism that constantly irradiate the medium surface are indispensable, and development of a highly accurate servo function is desired.

[Conventional technology]

Conventionally, in an optical disc device or a magneto-optical disc device, when recording information, there is a difference in relative peripheral speed between the optical head and the disc on the inner or outer circumference of the disc. It is necessary to increase the intensity of the recording laser light. In this control, the track number information previously recorded on the disk is demodulated and the D / A
It is converted to control the laser power.

On the other hand, a servo system such as a track servo or a focus servo that drives an optical head uses reflected or transmitted light, so that if the laser power changes or the reflectance of the disk changes, the servo drive signal also changes. Therefore, in order to obtain a stable servo drive signal, it is necessary to automatically change the servo gain so that an averaged servo drive signal can be obtained regardless of changes in the laser power and changes in the reflectance of the disk.

Next, a specific example of the amplifier that automatically changes the servo gain will be described with reference to the one disclosed in Japanese Patent Laid-Open No. 60-22746.

FIG. 8 shows a conventional servo gain control circuit.

In the figure, (117) is a four-division photodetector known by the cylindrical lens method, which outputs three types of systems of a track shift signal, a focus shift signal and a total reflection light amount signal from the upper stage of the figure. Track shift signal system (118)
Is a differential amplifier, and (119) and (121) are amplifiers connected in series to output a track servo drive signal to an output terminal (122). In the system of the focus shift signal (12
3) is a differential amplifier, and (124) and (126) are amplifiers, respectively, which output a focus servo drive signal to an output terminal (127) connected in series. In the total reflection light quantity system, an inverting amplifier (128) and a filter (129) are connected in series, and the output of the filter (129) has a negative polarity and is of a field effect transistor (hereinafter abbreviated as FET) (120) and (125). A circuit in which the gate terminals G are connected in parallel, the source terminals S of the FETs (120) and (125) are grounded, and the drain terminals D are connected to one input terminals of the amplifiers (119) and (124), respectively. It is configured.

FIG. 9 shows an example of the characteristic curve of the gate voltage V _{GS of the} FET vs. the equivalent drain / source resistance value R _DS.
It has the characteristics of the following curve. Here, the center point of the linear region is P.

Next, the operation of the servo gain control circuit shown in FIG. 8 will be described.

The output of the amplifier (128) is a total reflection light amount signal, and the noise component is removed by the filter (129), and then the FET (120) and (1
Connected in parallel to each gate terminal G of 25), the level variation of the total reflection light amount signal is applied as the gate voltage V _GS, the resistance between the equivalent drain / source corresponding to the gate voltage V _GS of the characteristic curve of Figure 9 The value R _DS changes. FET (12
The resistance value of 0) is R _DS4 , the resistance value of FET (125) is R _DS9 , the resistance between one input terminal and the output terminal of the amplifier (119) is R ₃ , the same resistance of the amplifier (124) is R ₈ , the amplifier If the amplification gains of (119) and (124) are A ₃ and A ₈ , The amplification gain is automatically controlled according to the change of the resistance value R _DS of each FET. That is, if the value of the total reflected light amount decreases, the gate voltage V _GS decreases in proportion to this, the resistance value R _DS also decreases, and conversely the amplification gain increases, which is used to average the servo drive signal output. Is measuring.

By the way, since the intensity ratio of the laser light is large at the time of recording and reproducing the information, the output of the total reflected light amount, that is, the output of the amplifier (128) is small at the time of reproducing the information.
Since there is no choice but to use a region where the linearity of the characteristic is poor, a sufficient amplification gain cannot be obtained and a stable servo circuit cannot be realized.

As a remedy for the drawbacks of the above conventional example, the servo gain is increased at the time of reproduction, the servo gain is changed in response to the output of the total reflection light amount of the optical head at the time of recording, and total reflection during reproduction and recording is performed. It is conceivable to use an automatic servo gain adjustment circuit that can obtain a stable optical head drive output regardless of changes in the light amount.

As an improvement measure, an amplifier for amplifying the track shift signal and the focus shift signal from the optical head respectively is provided, and the servo gain is adjusted to perform the track servo and the focus servo respectively at the output of each amplifier. In the disk device to be performed, a switching switch for switching the gain of the both amplifiers by a switching signal at the time of recording and reproducing is provided, and the outputs of both amplifiers are stabilized at substantially the same level regardless of the classification at the time of recording and reproducing. It is conceivable to provide a control means for performing

FIG. 10 shows a configuration example of an automatic servo gain adjusting circuit according to the above-mentioned improvement measure, and shows only a changed portion from the conventional example of FIG.

In FIG. 10, (130) and (131) are contact points (13
An analog switch having 6), (137), (138), and (139), which is driven by a disk recording / reproducing gate signal input to a terminal (133). (132)
Is an amplifier, and the total reflection light amount signal that has passed through the filter (129) is input, and its output is an analog switch (131).
Is connected to the gate terminal G of the FET (120) via the contact (138) of the. In addition, the output of the filter (129) is branched to connect to the contact (139).
Is connected to the gate terminal G of the FET (120) via. FET (1
The source terminal S of 20) is grounded, the drain terminal D is connected to one input terminal of the amplifier (119), and the contact (136) and the resistor (R134) of the analog switch (130) and the contact (137) and the resistor (137) are connected. It has a circuit configuration in which it is commonly connected to the output terminal of the amplifier (119) via R135).

Next, the operation of the circuit shown in FIG. 10 will be described. The analog switch (130) and the contact (136) of (131) (138) close the input signal of the terminal (133) at the time of reproduction, and the contacts (137) and (139) open and the input signal is recorded. It is set to perform the opposite actions.

The total reflection light amount signal obtained by combining all the outputs of the four-division photodetector (117) shown in FIG.
At the time of inputting the output as the gate voltage of the FET (120) through the filter (129) of the next stage, the average value of the input gate voltage is recorded when the information is recorded. In, the gain of the amplifier (128) is set so that it is at the position where the linearity is good in FIG. Then, the laser power is lowered at the time of reproducing information, but the gain of the amplifier (132) is set so that the input gate voltage of the FET (120) at that time becomes about the same as the average value at the time of recording. In this state, input the record / playback gate signal to the terminal (13
When applied to 3), the input gate voltage of the FET (120) fluctuates up and down within a range of good linearity around the point P of the characteristic curve in Fig. 9 at the time of recording, and at the time of reproduction, at the functional limit of the amplifier (132). A gate voltage that does not fluctuate much can be obtained centering on a fixed output (a gate voltage that can approach the operating point P).

Next, set the servo gain. For example, photodetector (11
When the track shift signal of 7) is amplified by the differential amplifier (118), this output shows the direction and magnitude of the track shift, and the track shift is corrected through the amplifiers (119) and (121). It is connected to a coil that moves the objective lens. Here the servo gain is set by amplifiers (118) and (119), but the gain of amplifier (119) is FET (1
20) Equivalent drain-source resistance value R _DS4 and resistance (R13
4), determined by (R135). If the gain of the amplifier (119) is A _3W at the time of recording and A _3R at the time of reproduction, It is represented by.

If the gain of the amplifier (128) is set on the basis of the average value of the laser power at the time of recording, the gain of the amplifier (132) is set because the laser power is low at the time of reproduction, and the servo gain is insufficient. There is a tendency. Therefore, the analog switch (130) is controlled by the recording / playback gate,
The resistance (R134) and (R1
Optimum servo gain can be set by selecting the value of 35).

Although the circuit of FIG. 10 has been described with respect to the system of the track servo drive signal, it can be applied to the system of the focus shift signal in exactly the same manner. In the circuit of FIG. 10, the differential amplifier (118) ( A stable focus servo drive signal can be obtained by replacing the amplifiers (119) and (121) with (124) and (126), respectively.

As described above, the automatic servo gain adjustment circuit according to this improvement has a simple structure and provides a stable servo drive signal even if the output of the total reflected light amount fluctuates regardless of whether information is recorded or reproduced. It is easy to obtain.

[Problems to be solved by the invention]

The conventional optical disk drive device and its improvement are constructed as described above. That is, by dividing the servo drive signal by the amount of total reflected light, the servo drive signal is averaged to maintain a constant servo loop gain regardless of the laser power or the disk reflectance (hereinafter referred to as A
uto G ain abbreviated as AGC from initials C on-tvol) has a, also Beku is Nau complement the narrowest point dynamic range of the AGC, for varying cut gain stairs playback / recording A gain switching stage is provided before the AGC.

By the way, the characteristics of such an AGC include the accuracy (about ± 1 μm for focusing servo and ± 0.1 μm for tracking servo) required for the servo of the optical disc and the band (gain crossover frequency of 3 KHz). Considering that, the dynamic range is limited to 5 to 10 times.

However, there are various optical disk recording media having various characteristics. Considering the reflectivity after recording, the change in the reflectivity of the optical disk is about 10 times.

In addition, the reproducing power also needs to be changed according to the sensitivity of the recording medium so as not to destroy the recorded data, and the recording power also varies depending on the type of the recording medium. is there. Furthermore, considering even a device such as a magneto-optical disk which is designed to erase recorded data by continuously illuminating a semiconductor laser with a power equal to or higher than the recording power, an average laser power change But it will be about 10 times.

Therefore, for optical discs or magneto-optical discs as recording media with various characteristics, AGC
However, there is a problem that the conventional example in which the dynamic range of (1) is expanded only by the gain switching of reproduction / recording in the preceding stage is insufficient.

The present invention has been made in order to solve the above problems, and supplements the dynamic range of AGC to an optical disk or a magneto-optical disk as a recording medium having various characteristics. It is an object of the present invention to provide a recording medium drive device which includes a gain switching means capable of controlling the gain and an amplifier which can obtain a servo drive signal with high precision and in a wide band.

[Means for solving problems]

In the recording medium drive device according to the present invention, the amplifier for amplifying the output current of the detector for obtaining the required servo drive signal includes the required number of current mirrors, and the current mirror outputs the output current of the detector. Means are provided for directly supplying and amplifying and for performing the required current calculation on this amplified output current.

[Work]

According to the present invention, the output current of the detector for detecting the required servo drive signal is subjected to the required amplification by the amplification function unit including at least one current mirror.

〔Example〕

FIG. 1 is a configuration diagram of a photodetector and an amplifier portion in a recording medium driving device as one embodiment of the present invention.

In FIG. 1, the output current (I
_PD ) is a current mirror circuit (15) consisting of transistors (2) to (8) and resistors (9) to (14) with uniform characteristics.
The output current (I _out ) of a predetermined multiple (for example, five times) is obtained by being amplified by.

Next, the operation will be described.

When light is input to the photodetector (1) composed of a PIN photodiode, an output current (I _PD ) proportional to the energy of the input light is obtained. Now, assuming that the emitter-base voltage of the transistors (2) and (3) is V _BE and the resistance value of the resistor (9) is R ₉ , PIN
The reverse bias voltage (E _PD ) required for the photo diode is as follows.

E _PD ≈ V _CC −2V _BE −I _PD · R ₉ − (1) Here, by selecting R ₉ corresponding to the maximum value of I _PD ,
A sufficiently large E without sacrificing its frequency characteristics
_The fact that _PD can be obtained is recognized from the above equation (1). That is, for example, by selecting I _PD · R ₉ to be approximately equal to V _BE , it is possible to add E _PD ≈V _CC −3 V _BE ≈V _CC −2.1 V and a reverse bypass close to the power supply voltage.

As can be seen from this FIG. 1, the transistor (3)
Since the base potentials of ~ (8) always match each other,
Emitter-base voltages (V _BE (3) to V _BE (8)) of these transistors (3) to (8) and resistance values (R ₉ to R 14) of the corresponding resistors (9) to (14). If R ₁₄ ) is adjusted according to the required accuracy of the amplifier, the relationship between the emitter currents (I _{9 to} I ₁₄ ) flowing through the resistors (9) to (14) can be obtained by the following equation.

I ₉ · R ₉ + V _BE (3) = I ₁₀ · R ₁₀ + V _BE (4) = ………… = I ₁₄ · R ₁₄ + V _BE (8)-(2) And within the range of desired accuracy, The relation of formula is materialized.

I ₉ = I ₁₀ = ... I ₁₄ − (3) Doing this makes transistors (3) to (8),
Further, the resistors (9) to (14) corresponding to them can be easily realized by closely integrating them on the same wafer.

On the other hand, the collector current of the transistor (3) is obtained by subtracting the base current of the transistor (2) from the output current ( _IPD ) of the photodetector (1). Here, the base current for the transistor (2) is given by the following equation, assuming that hfe of the transistors (2) to (8) are equal to each other.

Now, assuming that hfe is made large and, for example, that all the transistors are set to be 78 or more, the collector current of the transistor (3) has an accuracy of 0.1% or less and the photodetector (1 It can be seen from the equation (4) that the output current (I _PD ) of) matches.

Therefore, the emitter current (I ₉ ) of the transistor (3)
Is the sum of the base current and collector current of the transistor, so that within the range of accuracy determined by hfe of the transistor,

I ₉ = (collector current of transistor (3)) + (base current of transistor (3)) = I _PD + (base current of transistor (3))-(5) Also, for transistors (4) to (8) Emitter current (I
The relation between _{10 to} I ₁₄ ) and collector current (I _{4 to} I ₈ ) is as follows.

As can be seen from the equation (3), since the emitter currents (I ₉ ) to (I ₁₄ ) of the transistors (3) to (8) are equal to each other, hre of these transistors is within a predetermined range. Sometimes, the transistor (3)
The base current for (8) will also fall within a certain predetermined range. Therefore, the following equation is obtained from the above equations (3), (5) and (6).

I _PD = ₄ = I ₅ = ……… ＝ I ₈ − (7) As can be seen from this equation (7), the output current (I ₄ ) to (I ₈ ) equal to the input current (current) I _PD. Appearing as reflected by a mirror, the transistors (2)-(8) and their corresponding resistors (9)-
The circuit (15) composed of (14) is called a current mirror circuit.

And the output current I _OUT of the current mirror circuit (15) is
Collector current (I ₄ ) of transistors (4) to (8)
The sum of (I ₈ ) is as follows.

I _OUT = I ₄ + I ₅ + ... …… + I ₈ = 5 · I _PD − (8) Thus, the current mirror circuit (15) operates as an amplifier having a current amplification factor of 5 times. It is recognized from the equation (8).

Such a current mirror circuit can easily be made highly accurate, especially when it is made into an IC.

FIG. 2 is a configuration diagram of a photodetector and an amplifier portion in a recording medium driving device as another embodiment of the present invention.

In FIG. 2, the output current (I
_PD ) is a transistor with uniform characteristics (2), (3),
The current mirror circuit (36) composed of (16) to (22) and resistors (9) and (23) to (29) steps (eg, 1
(2 times, 2 times, 4 times) is amplified. The stepwise amplified current is switched by the switches (37), (38) and (39) formed by the transistors (30) to (35), and the I _PD is appropriately amplified. Output current I
_OUT is designed to be obtained.

Next, the operation will be described.

The operations of the photodetector (1) and the current mirror circuit (36) are the same as those in the case of FIG. 1 described above, and accordingly, the collector current I of the transistors (16) to (22).
_{16 to} I ₂₂ will be equal to I _PD .

On the other hand, the transistors (30) and (31), (32) and (33), and (34) and (35) respectively constitute a switch, and the current amplified by the current mirror circuit (36) is , V _CC side or output side. For example, in the switch (37) consisting of the transistors (30) and (31), when the base potential of the transistor (30)> the base potential of the transistor (31) + V0.7V- (9), the transistor (30) Is turned on between the base and the emitter, and the base of the transistor (31)
Since it is turned off between the emitters, the collector current I ₁₆ of the transistor (16) is
Connected to the V _CC side through the emitters. On the other hand, when the base potential of the transistor (31)> the base potential of the transistor (30) + V0.7V- (9) ', the collector current I of the transistor (16) is
₁₆ is output through the collector of the transistor (31) and the emitter.

Here, when the transistors (30), (32), (34) of the switches (37), (38), (39) on the V _CC side are turned on, it is "O", while the output Side transistor (3
1), (33), (the 35) may be ON is assumed to be "1", as shown in FIG. 2, I _OUT is I from O
₁₆ + I ₁₇ + I ₁₈ + I ₁₉ + I ₂₀ + I ₂₁ + I ₂₂ will be changed stepwise. As described above, since the condition of I _PD = I ₁₆ = I ₁₇ = I ₁₈ = ... = I ₂₂ − (10) is satisfied, I _OUT is from O to 1 · I _PD , 2
・ I _PD , ……, 7 ・ I _PD will change.

Thus, the current mirror circuit (36) and switch (3
7), (38), and (39) depend on the states of the switches (37), (38), and (39), and are 0 to 7 times.
It will operate as an amplifier having a current amplification factor of eight stages up to double.

The current mirror circuit (36) described above may be configured as shown in FIGS. 3 and 4 described later, though there is a problem in accuracy.

Now, referring to FIG. 3, the two transistors (17) and (18) in FIG.
7), and similarly, the four transistors (19), (20), (21), (22) are replaced by one transistor (19). In the case of FIG. 3, since the collector currents flowing through the transistors (16), (17), and (19) are different from each other, when the characteristics of these transistors are the same, those emitters have the same characteristics. The voltages between the bases are different from each other, and the accuracy of the current mirror circuit is deteriorated accordingly. Therefore, when the current mirror circuit as shown in FIG. 3 is adopted, the transistors (17) and (1
By making the emitter area of 9) a proper multiple of the emitter area of the transistor (16) and aligning the emitter-base voltages thereof, it is possible to prevent the aforementioned deterioration of accuracy to some extent.

Next, referring to FIG. 4, in the current mirror circuit (36) in FIG. 4, the emitter areas of the transistors (40) and (41) are twice as large as the emitter area of the transistor (16), respectively. It has been quadrupled.
However, in FIG. 4, the indication of various resistors is omitted.

Here, transistors (3), (16), (40), (41)
Assuming that the hfe can be aligned with the required accuracy, these transistors (3), (16), (40),
Since the base potentials of (41) are all equal to each other, the emitter currents of the transistors (3) and (16) are equal to each other, and the emitter current of the transistor (40) is twice that of the transistor (16). In addition, the emitter current of the transistor (41) is four times that of the transistor (16). The corresponding base current is also doubled and quadrupled in the same manner.

Therefore, the collector current of the transistor (16) becomes equal to the input current _IPD to the current mirror circuit (36),
The collector current of the transistor (40) is equal to 2 · I _PD , and the collector current of the transistor (41) is 4 · I _PD.
It is equal to I _PD .

In addition, in the circuit shown in FIG. 2, FIG. 3, and FIG. 4, the current amplification factor of the multistage current mirror circuit is 2 ^R.
(R is an integer, 0, 1, 2 in the above example), and by switching these with an appropriate current switch, the overall gain is 2 ^m (m is the current mirror circuit). Although the number of stages, in the above example, can be changed to m = 3) stages, the weight is changed so that the dynamic range can be expanded by a current mirror circuit with a small number of stages, and the gain is changed nonlinearly. May be.

FIG. 5 shows a recording medium driving device according to the present invention.
It is a block diagram centering on a photodetector, a current-voltage conversion circuit, a voltage-current conversion circuit, and an amplifier part.

In FIG. 5, the output current of the photodetector (1) is
It is converted into a corresponding voltage signal by a current-voltage conversion circuit (45) including a resistor (43), an operational amplifier (42) and a power supply (44). Then, this voltage signal is transmitted through the transmission line (46), and then the operational amplifier (47) and the transistor (4
8), the voltage-current conversion circuit (51) composed of the resistors (49) and (50) again converts the corresponding current signal. The current signal thus converted is transferred to the transistor (5
2) to (54) and resistors (55) to (57) are added to a constant current circuit (58). The collector currents output by the transistors (52) to (54) are of the same magnitude as the reconverted current signal due to the property of the current mirror circuit. The collector current output in this way is applied to the switches (63) and (64) formed by the transistors (59) to (62).
Output current (I _OUT ) of 0 times, 1 times, 2 times, 3 times (where the resistance values of the resistors (43) and (50) are made equal to each other) of I _{PD is} switched by It is designed to be obtained.

Next, the operation will be described.

The output current _IPD of the photodetector (1) flows through the resistor (43), and the potential at point a is set to the voltage E _O of the power supply (44) by the operation of the operational amplifier (42). Now, assuming that the resistance value of the resistor (43) is R ₄₃ , the output of the operational amplifier (42) is made into a voltage signal of E _O −I _PD · R ₄₃ .
Then, after the voltage signal and the power supply voltage E _O are transmitted through the transmission line (46) composed of, for example, a two-core shielded cable, the potential at the point b is E _O −I _{PD. Made} to be R ₄₃ . Where the resistance (5
Assuming that the resistance value of 0) is R ₅₀ , it will be converted into the following current signal.

Note that when R ₄₃ = R ₅₀ , the original I _PD is restored.

This I _PD becomes the collector current of the transistor (48),
It flows through the resistor (49) with the base current. This fifth
Transistors (48), (52) as shown
The base potentials of ~ (54) always match each other, and the characteristics and resistances of these transistors (49), (55) ~ (5).
By aligning it in 7), the function as the current mirror circuit described above is fulfilled. Therefore, the collector currents of the transistors (52) to (54) are
With a certain accuracy, it will match I _PD ,
The constant current circuit (58) including the transistors (52) to (54) and the resistors (55) to (57) operates similarly to the current mirror circuit. Thus, the constant current circuit (58) outputs a current I _{1 that} is 1 times that of I _PD and a current I ₂ that is twice that of I _PD . Then, depending on the switching operation by the switches (63) and (64) composed of the transistors (59) to (62) and the input code to the switch, the gain is increased in four stages from 0 times to 3 times. Can be changed.

FIG. 6 shows a recording medium driving device according to the present invention.
It is a block diagram centering on a photodetector, an amplifier, and a postcurrent calculator part.

In FIG. 6, two photodetectors (1a), (1b)
The output currents I _PD (a) and I _PD (b) of each are amplified by the current amplifiers (36a) and (36b) according to a predetermined input code (SW input), respectively. The amplified currents I _OUT (a) and I _OUT (b) are supplied to the current mirror circuit (86) including the transistors (66) and (67) and the resistors (68) and (69) and the transistor, respectively. (70), (7
1), (72), current mirror circuit (87) consisting of resistors (73), (74), (75), and transistor (7)
6), (77), (78), resistors (79), (80), (81) current mirror circuit (88) and transistor (8)
2), (83), resistors (84), (85) current mirror circuit (89), + I _OUT (a), + I _OUT (a),
-I _OUT (b) and + I _OUT (b) are generated, and a required current calculation is performed by passing these through resistors (90) and (91). Then, as the calculation result, V _DEF and V _ADD
Is obtained as follows.

V _DEF = V _ref- {I _OUT (a) -I _OUT (b)}-R ₉₀ V _ADD = V _ref- {I _OUT (a) + I _OUT (b)}-R ₉₁ However, resistance (90), The resistance value of (91) is R
₉₀ and R ₉₁ .

Next, the operation will be described.

The internal operation of the current mirror circuits (86), (87), (88), (89) is the same as that described so far, and the description thereof is omitted. The output current I _PD (a) of the photodetector (1a) is amplified by the current amplifier (36a) and is I
It becomes _OUT (a). This amplified output current is finally output by the operation of the current mirror circuits (86) (87).
It becomes equal to the collector current of the transistors (71) and (72). On the other hand, the output current I _PD (b) of the photodetector (1b) is amplified by the current amplifier (36b) and becomes I _OUT (b).
This amplified output current is transferred to the current mirror circuit (8
The operations of 8) and (89) finally become equal to the collector currents of the transistors (78) and (83). here,
Since the transistor (71) is of the NPN type and the transistor (78) is of the PNP type, the directions of the collector currents of the two are different from each other. Therefore, if these collector currents are added and wired so as to flow through the resistor (90), the added collector current is converted into a voltage signal as a voltage drop from the V _rex potential. Then, this converted output V _DEF becomes V _DEF = V _ref − (I _OUT (a) −I _OUT (b)) · R ₉₀ , and the difference signal between I _OUT (a) and I _OUT (b) Will be obtained. Further, since the transistors (72) and (83) are both of the NPN type and the directions of the collector currents of the both are the same, the collector currents of these transistors are added so that they flow through the resistor (91). When the wiring is made, the added collector current is converted into a voltage signal as a voltage drop from the V _ref potential. And this converted output V _ADD
Becomes V _ADD = V _ref − (I _OUT (a) + I _OUT (b)) · R ₉₁ , and a sum signal of I _OUT (a) and I _OUT (b) is obtained.

The difference signal thus obtained is the photodetector (1a),
When (1b) is for detecting a tracking error signal, it is used as a tracking error signal for driving the tracking servo mechanism, and when it is for detecting a focusing error signal, it is used as a focusing error signal. Used as a focusing error signal to drive a single servo mechanism.

On the other hand, for the sum signal, the photodetector (1
When a) and (1b) are for detecting tracking error signals, they are used as control signals for automatic adjustment (AGC) of the tracking servo loop gain, and for detecting focusing error signals. When used, it is used as a control signal for automatic adjustment (AGC) of the focusing servo loop gain.

In FIG. 6, the current mirror circuit (8
6), (87), (88), and (89) are shown as having a theoretical configuration, but as a practical circuit configuration, the characteristics of the transistor used and the circuit itself are required. In consideration of the accuracy and response characteristics,
A circuit configured as shown is used.

In FIG. 7, transistors (92), (93), (94) included in the current mirror circuit (86) are for speeding up the operation as a current mirror circuit. Here, the collector-emitter voltage of the transistors (92) and (93) is used so that the collector potentials of the transistors (66) and (67) forming the current mirror circuit are the same as those of the amplifier (36a) as a current source. It is prevented from changing due to fluctuations in the output potential. In this case, the collector potential becomes almost equal to the base potential. By doing so, it is possible to use a transistor having a low withstand voltage but a high speed as a transistor forming the current mirror circuit. Further, even if the impedance of the current mirror circuit is high, the collector impedance of the current mirror transistor is high. Since it can be lowered, the speed of the circuit can be increased. Similarly, transistors (97), (98), included in the current mirror circuit (87),
(99) and (100) are transistors (10) included in the current mirror circuit (88) with respect to the transistors (70), (71) and (72) which form the current mirror circuit.
4), (105), (106) and (107) are included in the transistors (76), (77) and (78) forming the current mirror circuit and in the current mirror circuit (89). The transistors (111), (112), and (113) are for speeding up the operation of the current mirror circuit with respect to the transistors (82) and (83) forming the current mirror circuit, respectively. .

In the current mirror circuit (86), the transistor (11
6) and the resistor (95) are for speeding up the operation of the current mirror circuit, and function to reduce the impedance of the bases of the transistors (66) and (67) that form the current mirror circuit. ing. Similarly, the transistor (102) and the resistor (101) in the current mirror circuit (87) are different from the transistors (70), (71) and (72) forming the current mirror circuit in that
Transistor (10 in current mirror circuit (88)
9) and the resistor (108) are for the transistors (79), (80), (81) which form the current mirror circuit, and the transistor (115) and the resistor (114) in the current mirror circuit (89) are , To speed up the operation of the transistors (82) and (83) forming the current mirror circuit as a current mirror circuit.

The transistor (96) included in the current mirror circuit (86) is for improving the accuracy of the current mirror circuit. Here, the input current to the current mirror circuit (86) is the collector current of the transistor (66) and the transistors (66), (67), (92), (96).
It is shunted to the base current of. Then, when hfe of these transistors is small and the magnitude of the base current with respect to the collector current cannot be ignored, the accuracy of the current mirror circuit deteriorates. Therefore, by inserting a transistor (96) between the bases of the transistors (66), (67), (92), and (93) and the input current terminal, the ratio of the base current to the collector current is further reduced by ▲ hf.
By setting ² _e , the accuracy as a current mirror circuit is improved. Similarly, the transistor (103) is different from the current mirror circuit (87) in the transistor (110).
Is for the current mirror circuit (88), and the transistor (116) is for the current mirror circuit (89).
It is provided to improve the accuracy of each.

Although not described in the above embodiment, the recording medium requiring the tracking servo or the focusing servo is not limited to the optical disk or the magneto-optical disk, and for example, an optical card, an optical sheet, or the like. Various types such as an optical drum can be considered.

The recording medium itself to be used may have various constitutions including metals, oxides, various inorganic compounds and organic compounds.

Also, the condenser lens included in the device is not limited to a spherical lens, and any desired condenser lens such as an aspherical lens, a hologram lens, a diffraction grating, and a Fresnel lens can be used. Can be used.

Furthermore, the photodetector used is not limited to PIN photodiodes, but PN photodiodes and avalanche
Any format may be used as long as a signal from a photodiode, a PSD, a solar cell or the like can be obtained as current information.

〔The invention's effect〕

As described above, in the recording medium drive device according to the present invention, the output current of the detector that detects the error signal necessary for driving the tracking servo mechanism or the focusing servo mechanism is directly applied to the required current mirror. Since it is designed to supply and amplify a number of signals, it is possible to broaden the bandwidth of the signal processing system, lower offset and lower noise, and improve the reliability of the entire recording medium drive device with a small number of parts. It is also advantageous in that it can be obtained, and the device can be miniaturized and integrated into an IC.

[Brief description of drawings]

FIG. 1 is a circuit exemplification diagram of one embodiment of the present invention, FIGS. 2 to 6 are circuit exemplification diagrams of a part of the above embodiment modified, and FIG. 7 is a part of a modification of the above embodiment. FIG. 8 is a circuit example diagram of a post-current calculator in the example, FIG. 8 is a circuit example diagram of a conventional example, FIG. 9 is an operation explanatory diagram of the conventional example, and FIG. 10 is a circuit example diagram of another conventional example. Is. In the figure, (1) is a photodetector, (15), (36) and (58) are current mirrors (for current amplification), (37), (38), (39) and (6
3) and (64) are switch circuits, (45) is a current-voltage conversion circuit, (51) is a voltage-current conversion circuit, and (86) and (8
7), (88) and (89) are current mirrors (for current calculation), and (90) and (91) are resistors for voltage signal conversion of calculation results. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (4)

[Claims] 1. A recording spot is irradiated with a light spot on a recording medium surface through a condenser lens to perform recording / reproduction and / or erasing, and from the reflected light, a tracking error signal and / or a tracking error signal necessary for driving a tracking servo mechanism. A recording medium driving device comprising a detector for detecting a focusing error signal necessary for driving a focusing servo mechanism of the condenser lens, and an amplifier for amplifying an output of the detector, wherein the amplifier has an amplification factor. Of a plurality of current mirrors different from each other, the output current of the detector is directly supplied to the current mirror for amplification, and the outputs of the plurality of current mirrors are switched by a predetermined switching circuit. A recording medium drive device having a variable amplification factor. 2. The amplification factor of each of the plurality of (m) current mirrors is set to 2 ^{n + 1} , 2 ^{n + 2} , ..., 2 ^{n + m} (n is an integer). From 2 ^{n + 1} gain The recording medium drive device according to claim 1, wherein the recording medium drive device is variable in stages. 3. A recording spot is irradiated with a light spot on a recording medium surface through a condenser lens to perform recording / reproduction and / or erasing, and from the reflected light, a tracking error signal and / or a tracking error signal necessary for driving a tracking servo mechanism. In a recording medium driving device comprising a detector for detecting a focusing error signal necessary for driving a focusing servo mechanism of the condenser lens, and an amplifier for amplifying an output of the detector, the amplifier supplies a current to a voltage. A first converter for converting into a voltage, a second converter for converting a voltage into a current, and a current mirror, and the output current of the detector is converted into a voltage by the first converter and then transmitted. A recording medium driving device, characterized in that it is transmitted to the second converter via a path to be converted back into a current, and thereafter amplified by the current mirror. 4. A recording spot is irradiated with a light spot on a recording medium surface through a condenser lens to perform recording / reproduction and / or erasing, and from the reflected light, a tracking error signal and / or a tracking error signal necessary for driving a tracking servo mechanism. First and second detectors for detecting a focusing error signal necessary for driving a focusing servo mechanism of the condenser lens, and first and second detectors for amplifying outputs of the first and second detectors, respectively.
And a second medium amplifier, wherein the first and second amplifiers include a front stage current mirror and a rear stage current mirror, respectively, and output currents of the first and second detectors, respectively. After being amplified by the pre-stage current mirrors of the first and second amplifiers, required current addition and / or subtraction is performed by the post-current calculator composed of the post-stage current mirrors of the first and second amplifiers, respectively. A recording medium drive device characterized by the above.