JPH03272025A - Error signal detecting circuit for optical disk device - Google Patents

Abstract

PURPOSE:To accurately acquire the servo leading-in timing by providing a means which binarizes an original error signal without passing a divider. CONSTITUTION:Output current iA and iB of photo diodes 1A and 1B which receive the reflected light from an optical disk are differentially amplified, and the gain of an original error signal 3a as the differentially amplified signal is normalized to obtain a signal 7, and this normalized error signal 7 is used as a positioning servo error signal. A binarizing amplifier 6 is provided which binarizes the original error signal without passing a divider. That is, the original error signal 3a before input to a divider is binarized and the positioning servo leading-in timing is discriminated by the edge of this binarized signal when the normalized error signal 7 is used to perform the positioning servo of an optical head, and the binarized signal is counted to find a target track at the time of seek of the tracking servo. Thus, the focus servo is normally led in.

Description

[Detailed description of the invention] [Industrial application field]

This invention relates to an error signal detection circuit for detecting focus errors and tracking errors in an optical disk device, and in particular, an optical disk device having a function of accurately detecting the point of servo pull-in while using a divider to stabilize the gain of the error signal. The present invention relates to an error signal detection circuit for an apparatus. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Conventional technology]

An optical disc device focuses a light spot on an optical disc (therefore, an optical head).
Focus servo as positioning control in the optical axis direction,
Tracking servo is also performed to position the optical head in the cross-track direction to position the optical spot at the center of the track on which data is to be recorded. These servos generate focus error signals that indicate the amount of positional deviation of the focus in the optical axis direction and the direction of the positional deviation.
This is performed using a tracking error signal that indicates the amount of positional deviation of the light spot (center) from the track center in the cross-track direction and the direction of the positional deviation. The method for detecting these error signals is to process the laser beam reflected by the optical disk and returned to the optical head using a polarizing plate or lens in the optical system, and then to process the laser beam by using multiple (usually two) photodiodes (hereinafter also abbreviated as PD). ) is used to detect that the balance of the laser beam that hits the target changes with the amount of positional deviation.As a method for detecting the focus error signal, for example, there is an astigmatism method using a cylindrical lens.
As a method for detecting a tracking error signal, for example, there is a method called a push-pull method. In these methods, an error signal can be obtained by finding a differential signal between the output currents of two PDs in the optical head. However, if the amount of light emitted by the laser diode or the reflectance of the optical disk changes, the gain of the error signal changes. For example, the output currents of two PDs IA and IB are iA and iB, respectively, and the difference current 1A-iB is 1
Assume that an error signal is obtained using Kl (iAiB) which has been amplified twice. At this time, if the signal returned from the optical disk to the optical head changes and becomes KO times as described above, then PD
IA. The amount of light hitting each IB is also multiplied by KO, and the output current is also multiplied by KO.
1AKo-iB, so the error signal is 1(KO-iB).
iA −KO−1B)=KO・(Kl(iA −
1B)), and the error signal obtained for the same amount of positional deviation becomes KO times as large. In an optical disk device, since the optical disk as a medium is convertible, its reflectance may change. Furthermore, in a data write operation or a data erase operation in a magneto-optical disk device, the amount of light emitted by the laser diode changes. In such a case, the gain of the error signal changes and the oven loop gain of the servo system changes accordingly, resulting in poor servo stability and possible out-of-focus and tracking errors. In order to prevent such a situation, a circuit shown in FIG. 3 has conventionally been used. That is, in the figure, 1 (IA, IB) is a photodiode (PD) that receives reflected light from an optical disk not shown, and 2 (2^, 2B) is this PD.
A current/voltage conversion amplifier converts the currents of IA and IB into voltage, 3 is a differential amplifier that amplifies the difference between the two output voltages of amplifiers 2A and 2B, and 4 is a differential amplifier between amplifiers 2A and 2B.
A summing amplifier 5 amplifies the sum of two output voltages, and 5 divides the output (also called a differential signal) 3a of the differential amplifier 3 by the output 4a of the summing amplifier 4 (referred to as a reflected light amount sum signal). This is a divider that outputs the result as a normalized error signal 7. In this circuit, the error signal (
In other words, the difference between the output currents iA and iB of PDIA and IB (in other words, the difference in the amount of light received by these two PDs) is proportional to the amount of total reflected light (that is, the sum of the amounts of light received by PDIA and 1B) using the divider 5. By dividing by the reflected light quantity sum signal 4a as a signal obtained by dividing the normalized error signal 7 by the reflected light quantity sum signal 4a, the error signal gain is kept constant regardless of the magnitude of the reflected light quantity. For example, when iA and iB are output from the two PDIA and IB in FIG. 3 as described above, the differential signal 3a is
(iA - iB), and the reflected light amount sum signal 4a is 2 (
i^+iB), the divider 5 obtains a - signal 7. If the optical spot is misaligned here, the PD
Although the amount of light hitting each of IA and IB changes, the total amount of light hitting the two PDs is constant. The amount of reflected light from the optical disk changes and PDIA. Assuming that the amount of light hitting each IB is multiplied by KO,
The differential signal 3a is KHKO・iA −KO−1B)=KO・Kl(iA
-1B), and the reflected light amount sum signal 4a is 2(KO-iA +KO・1B) = KO- is 2(iA
+ iB), so the divider 5 divides the signal 3a into 4
The result of division by 8 is X(iAt-3B), and a normalized error signal 7 with a constant gain can be obtained regardless of changes in the amount of reflected light. This normalized error signal 7 is then used to perform the aforementioned focus servo and tracking servo. In the following, for convenience, the error signal (differential signal) 3a before manual input of the divider 5 will be referred to as a family error signal to distinguish it from the normalized error signal 7.

[Question B that the invention attempts to solve]

Consider a case where a circuit as shown in FIG. 3 is used as a focus error detection circuit. When the objective lens is moved from the farthest position to the closest position to the disk by the focus actuator, the ring focus error signal (differential output, before division) 3a becomes as shown in FIG. That is, the detection range of the ring focus error signal 3a is very narrow compared to the movable range of the objective lens. For this reason, when trying to start focus servo, the objective lens is usually not within the detection range of the ring focus error signal 3a, so the objective lens is slowly brought closer to the disk until it enters the detection range of the ring focus error signal 3a. By the way, the servo loop is closed and pulled into the focus servo. In order to find the detection range of the ring focus error signal 3a, for example, the ring focus error signal 3a is binarized at the binarization level L1 as shown in FIG. All you have to do is find the edge of the conversion signal DZ. However, as mentioned above, the divider 5 generates the group error signal 3a.
When normalized, the amount of light returning to the head becomes very small when the focus is shifted, and the denominator K of the division mentioned above becomes
Since 2(i^+iB) becomes close to 0 at O-, the slight offset of the differential output 3a is greatly amplified, and the divider 5
The focus error signal 7 and its binarized signal DZI as an output may end up as shown in FIG. At this time, the focus servo is attempted to be pulled in at the falling edge of the binary signal DZI, but the binary signal DZI
Since the first falling edge of is outside the detection range of the focus error signal 7, there is a problem in that it cannot be drawn into the focus servo. Also, consider a case where the error signal detection circuit using the divider 5 shown in FIG. 3 is used for tracking error signal detection. When performing a seek operation to move a light spot to an arbitrary trunk in an optical disk device, in order to detect the number of tracks moved, the tracking error signal outputs a signal of one cycle each time it crosses a track. Then, the tracking error signal 7 is binarized at the center level, and the number of moving tracks is obtained by counting the number of pulses of the binarized signal. However, the problem is that it is difficult to obtain a divider 5 with good frequency characteristics, and as the track crossing speed increases and the frequency of the tracking error signal increases, the signal attenuates and binarization becomes difficult. For example, the frequency band required for tracking servo is about 3 to 6 Hlz, but a band of several 100 KIIz is required for track counting. SUMMARY OF THE INVENTION An object of the present invention is to provide an error signal detection circuit for an optical disc device that can solve the above-mentioned problems.

[Means to solve the problem]

In order to solve the above problems, the circuit of the first invention includes a pair of photodiodes which are provided within the optical head to detect an error signal for positioning servo of the optical head and which receive reflected light from an optical disk. CIA, IB, etc.> output current (iA, iB, etc.) is differentially amplified (via differential amplifier 3, etc.), and the ring error signal (3a, etc.) as this differentially amplified signal is divided. A signal (manato) is obtained by normalizing the gain of the ring error signal by dividing it by a signal (such as 4a) proportional to the amount of light reflected from the optical disk to the optical head through a device (such as 5); In the error signal detection circuit of the optical disk device which provides the error signal for the positioning servo, the ring error signal is converted to 24M without passing through the divider.
It is assumed that one device is equipped with a means for converting into digital data (a binarizing amplifier 6, a comparator located outside the park). Further, the circuit of the second invention is provided in the optical head to detect an error signal for focus servo of the r-optical head, and includes a pair of photodiodes (IA, 1B, etc.) that receive reflected light from the optical disk. The output current (iA, in, etc.) is differentially amplified (via differential amplifier 3, etc.), and the ring error signal (3a, etc.) as the differentially amplified signal is sent to a divider (5, etc.). A signal (such as 7) is obtained by normalizing the gain of the ring error signal by dividing it by a signal (such as 4a, hereinafter referred to as reflected light amount sum signal) proportional to the amount of light reflected from the optical disk to the optical head. , in the optical disk device error signal detection circuit that provides the error signal for the focus servo, the signal at a fixed level (such as the partial voltage value of the DC power supply VCC) is divided by the signal in place of the reflected light amount sum signal until the focus servo is pulled in. Means for inputting to the device (analog switch 9, voltage dividing resistor 10, 11
, control microcomputer 12, etc.).

[For use]

l) Regarding the first invention: When performing positioning servo of the optical head using the normalized error signal 7, the ring error signal 3a before input to the divider is binarized, and the edge of the binary signal is used to perform the positioning servo. The target track is found by counting this binary signal when the tracking servo is seeking. 2> Regarding the second invention: When performing focus servo of the optical head (optical spot) using the normalized error signal 7, the input potential of the divisor (denominator) of the divider 5 is clamped to a constant potential until the servo is pulled in. , so that the divider output signal 7 has a similar waveform to the ring error signal 3a. As a result, this divider output is binarized to determine the focus servo pull-in point, and after that, the manual clamping of the divider of the divider is stopped and the normal circuit is restored, and the output of the divider 5 is normalized. Focus servo is performed so that it becomes an error signal.

【Example】

FIG. 1 shows an embodiment of the first invention. In FIG. 1, the circuit of FIG. 3 is further provided with a path for amplifying the differential signal (ring error signal) 3a through a binarization amplifier 6 without passing through the divider 5, and the output 8 is Binarize using a comparator not shown. Then, as in FIG. 4, the edge of this binary signal is detected and determined as the servo pull-in point. Note that as the error signal for servo, the regular error signal 7 passed through the divider 5 is used as before. When this circuit is used for focus error detection, the laser diode emits light with the specified laser power during read when the focus is pulled in, so the only factor that changes the amount of reflected light is the reflectance of the disk. The fluctuation is not extremely large, and even if the magnitude of the ring error signal 3a or 8 changes depending on the reflectance, it is sufficient that the normalized focus error signal 7 can be normally binarized to indicate the detection range. Also, when the present invention is used for tracking error signal detection, the output 8 of the path that does not pass through the divider 5 is similarly binarized,
Used for trunk count during seek. However, in this case, the current-voltage conversion amplifier 2 in the first stage, the differential amplifier 3 in the second stage, and the binarization amplifier 6 in the third stage should have good frequency characteristics, so that the signal can be maintained even at the highest seek speed. There should be almost no attenuation. During seek, the laser power is at the specified speed value, so the only factor that changes the amount of reflected light is the reflectance of the media, and even if the magnitude of the differential signal 3a changes, it will not be converted into a binary signal. Good if possible. In this method, the paths for error signals for servo and for binarization are separate, and there is no need to switch signal lines. FIG. 2 shows an embodiment of the second invention. In the same figure, unlike FIG. 3, an analog switch (or FET
) 9 is attached, and the divider 5 of this switch 9 is added.
A high resistance 10.11 is added to the side terminal section to divide the voltage between the positive DC power supply VCC and the ground GND. Then, the analog switch 9 is opened and closed by a control microcomputer. In FIG. 2, by turning off the analog switch 9 according to a command from the control microcomputer 12 until the focus servo is pulled in, the value of the denominator manually input to the divider 5 becomes the voltage value determined by the two voltage dividing resistors 10 and 11. Fixed. If this voltage value is made almost equal to the value when the laser power is in focus during reading, the normalized focus error signal 7 up to servo pull-in will have a waveform like the same signal 7 in Figure 5. First, the waveform becomes as shown in the ring focus error signal 3a in Fig. 4, and by binarizing this normalized focus error signal as shown in Fig. 4, the edges of this binarized signal are detected and a normal signal is detected. Servo pull-in operation can be performed. In this case, it goes without saying that the analog switch 9 is turned on after the servo is pulled in, and at this time, the voltage dividing resistor 10.
Since 11 has a high resistance, the value manually input to the divider 7 (as a denominator for division) is almost completely lost to the output value (reflected light quantity sum signal) 4a of the adding amplifier 4. In addition, in FIG. 2, the normalized focus error signal 7 when the analog switch 9 is in the OFF state is determined by the reflectance of the disc.
The size of the image changes, but as long as the binarization can be performed normally, some fluctuation is not a problem. However, although this method can solve the problem regarding focus servo pull-in by adding a simple component, it cannot improve the frequency characteristics of the divider 5, so it is not effective against the problem of tracking error signals during seek.

【Effect of the invention】

According to the present invention, in addition to giving a differential amplification signal (ring error signal) 3a of the current of two PDs in the optical head to the divider 5, it is also converted into a binary signal for track counting during servo pull-in and seek. In order to obtain a signal for use, it is necessary to provide a path for the differential amplified signal 3a that does not pass through the divider, or to fix the potential of the denominator (divisor) of the divider until the focus servo is pulled in. Therefore, it is possible to configure a focus error detection circuit that can perform normal focus servo pull-in, and it is also possible to use an amplifier with good frequency characteristics in the signal amplification path for binarization that does not pass through a divider. Therefore, it is possible to construct a tracking error detection circuit that can correctly count tracks even at the highest seek speed.

[Brief explanation of drawings]

Figure 1 is a block circuit diagram showing the configuration of an embodiment of the first invention, Figure 2 is a block circuit diagram showing the configuration of an embodiment of the second invention, and Figure 3 is similar to Figures 1 and 2. A corresponding conventional block circuit diagram, FIG. 4 is a waveform diagram of the ring focus error signal and its binarized signal, and FIG. 5 is a waveform diagram of the normalized focus error signal and its binarized signal. 1 (18, I B) Niphotodiode, 2 (2A
. 2B): Current/voltage conversion amplifier, 3: Differential amplifier, 3a
: Differential signal (ring error signal), 4: Adding amplifier, 4a
: Reflected light amount sum signal, 5: Divider, 6: Binarization amplifier, 7: Normalization error signal, 8: 2(I!! conversion error signal, 9: Analog switch, 10.11 = partial pressure resistance, 1
2: Control microcomputer. Heat 3 Diagram E Outer Area 4th Ward Diagnostic Map

Claims (1)

[Scope of Claims] 1) Differential amplification of the output current of a pair of photodiodes that are provided in the optical head to detect an error signal for positioning servo of the optical head and that receive reflected light from an optical disk. Then, the original error signal as a differentially amplified signal is divided by a signal proportional to the amount of light reflected from the optical disk to the optical head through a divider to normalize the gain of the original error signal. An optical disc characterized in that the error signal detection circuit of an optical disc device obtains a converted signal and provides it as an error signal for the positioning servo, comprising means for binarizing the original error signal without passing through the divider. Equipment error signal detection circuit. 2) Differentially amplify the output current of a pair of photodiodes that are provided in the optical head to detect the error signal for focus servo of the optical head and receive reflected light from the optical disk. The gain of the original error signal is determined by dividing the original error signal as a widened signal by a signal proportional to the amount of light reflected from the optical disk to the optical head (hereinafter referred to as reflected light amount sum signal) through a divider. In the error signal detection circuit of the optical disk device, which obtains a normalized signal and provides it as the error signal for the focus servo, a fixed level signal is sent to the divider instead of the reflected light amount sum signal until the focus servo is pulled in. An error signal detection circuit for an optical disc device, characterized in that it is provided with means for inputting.