JPH0449531A - Optical disk servo system - Google Patents

Abstract

PURPOSE:To keep the input level of an AD converter proper even for optical disks different in reflection factor and to prevent an influence of quantization error by providing a variable gain amplifier and a gain controller. CONSTITUTION:The light of a laser diode is reflected by an optical disk and is returned to an optical pickup 1 and is thrown to a photodetector to generate an error signal. A variable gain amplifier 2 amplifies this error signal with the gain determined by the output of a gain controller 9, and the signal is quantized to N bits by an AD converter 3, and an adder 4 adds a wobbling signal for loop gain adjustment, and a coefficient multiplier 5 multiplies a coefficient with which the loop gain is one in the gain crossing frequency by the output of a loop gain discriminator 10, and an equalizer 6 suppresses the steady- state deviation and improves the responsiveness by accumulating the difference filters, and an adder 11 adds a disturbance signal for the purpose of observing a maximum amplitude of the error signal, and a DA converter 7 converts it to an analog signal, and the actuator of an optical pickup 1 is driven through a drive signal amplifier 8 to move an objective lens, thus making the error signal of 0.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital servo system compatible with optical discs having different reflectances.

BACKGROUND OF THE INVENTION In recent years, there has been a need for drive devices that can handle not only read-only optical discs but also rewritable optical discs. In these devices, it is important to digitize the processing in order to achieve high-speed access by devising a servo processing method or to rationalize the number of parts.

FIG. 8 shows a block diagram of a conventional digital servo system for a drive device. 1 is an optical pickup, 12 is an amplifier with a constant gain G1, 3 is an AD converter, 4 is an adder that adds wobbling signals, 5 is a coefficient multiplier,
6 is an equalizer, 7 is a DA converter that converts a digital signal into an analog signal, 8 is a drive signal amplifier, 10
is a loop gain judger.

Next, this operation will be explained. In the optical pickup 1, light emitted from a laser diode is reflected back from an optical disk, hits a photodetector, and generates an error signal. The amplifier 12 converts this error signal into a constant gain G1
The AD converter 3 quantizes the input signal with N bits, the adder 4 adds the wobbling signal used for loop gain adjustment, and the coefficient multiplier 5 uses the output of the loop gain determiner 10 to amplify the loop at the gain intersection frequency. The product is multiplied by the gain G2 determined so that the gain is 1, the equalizer 6 uses a cumulative filter and a differential filter to suppress steady-state deviations and improves responsiveness, the DA converter 7 converts it into an analog signal, and the drive signal amplifier The actuator of the optical pickup 1 is driven through 8 to move the objective lens so that the error signal becomes zero.

Next, the loop gain determiner 10 will be explained. Now, with the servo applied, the input signal of adder 4 is a, the output signal is C, the wobbling signal is C, and the loop gain is g.
shall be. Here, it is assumed that the frequency of the wobbling signal C is made to match the gain intersection frequency. Further, it is assumed that the disturbance input level in the optical pickup 1 is small. Then, the following formula holds.

b=a+c a=b・g,', a ten b=c fist (1+
g) / (1-g) where g=reexp(-j
θ), when r=1, (a+b) has a phase delay of 90 degrees with respect to C, when r>1, it is greater than 90 degrees, and when r<1, it is less than 90 degrees (however, - 180 degrees θ<-9
0 degrees).

FIG. 9 shows a block diagram of the configuration of the loop gain determiner 10 according to this principle. 61 is an adder, 62 is a phase detector, and 63 is a coefficient ROM. In the adder 61 (a + b)
The phase detector 62 detects the phase lag, and the coefficient ROM 63 calculates a value smaller than the currently used coefficient when the phase lag is greater than 90 degrees, and a value smaller than the currently used coefficient when the phase lag is less than 90 degrees. It outputs a large value. Then, the coefficient multiplier 5 multiplies the input signal by this coefficient. In this way, loop gain adjustment is performed.

Problems to be Solved by the Invention However, with the above-mentioned conventional configuration, when dealing with a magneto-optical recording disk, especially a disk with a low light reflectance, such as the green portion mentioned above, or a disk with a high reflectance, such as a compact disk, the amplifier At the output of 12, the former has a small amplitude, and A
Only a part of the number of quantization pits in D converter 3 can be used,
As a result, the servo becomes unstable due to the quantization error, and the latter has a large amplitude, exceeding the input dynamic range of the AD converter 3, resulting in a problem that the effective range of the servo becomes narrow.

The present invention solves the above-mentioned conventional problems, and aims to provide an optical disk servo system that provides stable servo for both disks with low reflectance and disks with high reflectance.

Means for Solving the Problems To achieve this object, the optical disk servo system of the present invention drives an actuator with a disturbance signal, inputs an error signal to a variable gain amplifier, and inputs the output of the variable gain amplifier to an AD converter. The output of the AD converter is input to a gain controller, and the output of the gain controller is used as the gain control input of the variable gain amplifier.

Effect of the present invention With the above-described configuration, a large disturbance signal is applied to the servo loop to cause the error signal to swing to the maximum possible amplitude.
The gain of the amplifier in the stage preceding the AD converter is controlled so that this amplitude becomes an appropriate input level for the AD converter.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an optical disc servo system in a first embodiment of the present invention. 1 is an optical pickup, 2 is a variable gain amplifier with variable gain, and 3 is an AD
Converter, 4 is an adder, 5 is a coefficient multiplier, 6 is an equalizer, 7 is a DA that converts a digital signal into an analog signal
8 is a drive signal amplifier, 9 is a gain controller, 10 is a loop gain determiner, and 11 is an adder.

Next, this operation will be explained. In the optical pickup 1, light emitted from a laser diode is reflected back from an optical disk, hits a photodetector, and generates an error signal. The variable gain amplifier 2 amplifies this error signal with a gain determined by the output of the gain controller 9, the AD converter 3 quantizes the amplified signal with N bits, and the adder 4
adds the wobbling signal used for loop gain adjustment, the coefficient multiplier 5 multiplies the output of the loop gain determiner 10 by a coefficient determined so that the loop gain becomes 1 at the gain intersection frequency, and the equalizer 6 adds the additive filter and the difference A filter is used to suppress steady-state deviations and improve responsiveness, and an adder 11 adds a disturbance signal to observe the maximum amplitude of the error signal.The DA converter 7 converts it into an analog signal, and the optical signal is transmitted through a drive signal amplifier 8. Drive the actuator of pickup 1 to move the objective lens so that the error signal becomes zero.

Note that a pulse width modulator may be used instead of the DA converter 7.

First, the input/output characteristics of the optical pickup 1 will be explained using FIG. 2. The optical pickup 1 has a monotonically increasing characteristic in which when the drive input magnitude is smaller than Dt, the error output magnitude is smaller than Et, and when the drive input magnitude is greater than Dt, the error output magnitude increases. is E again
t, resulting in a figure-8 curve characteristic. When a disturbance signal is input to the adder 11 and a drive input larger than Dt is applied to the optical pickup 1, the error signal is changed from Et to -
It can swing up to Et. This signal is input to the AD converter 3.

Next, FIG. 3 shows the input/output characteristics of the AD converter 3.

In the AD converter 3, when the analog input level is small, the digital output level is proportional to the input level, but when the input dynamic range is exceeded, the output becomes constant at 2 to 1. Here, the target output level is set to a value To slightly smaller than 211 so that the quantization error does not affect it. Assuming that the input level at this time is Ti, the role of the gain controller 9 is to set the gain of the variable gain amplifier 2 so that Et and Ti match. An embodiment of a block diagram of the gain controller 9 is shown in FIG. 41 is the amplitude memo 1
42 is a comparator, and 43 is an up/down counter. Next, this operation will be explained. The disturbance signal is sent to the adder 11
While the amplitude memory 41 is connected to the AD converter 3
Read the maximum amplitude of the output. Let this value be Ao. A comparator 42 compares the sizes of Ao and To. When AO is smaller than TO, the up/down counter 43 is incremented, and a control output for increasing the gain of the variable gain amplifier 2 is output. When AO is greater than TO, the up/down counter 43 is decremented and a control output is output that reduces the gain of the variable gain amplifier 2. An example of the configuration of the variable gain amplifier 2 is shown in FIG.

It is assumed that R+ < Re < . . . R1, and the switch connects R1 to the operational amplifier output when the control output is 1, and connects RM to the operational amplifier output when it is M.

When adjusting the gain, perform it in the order described below. Initially, a disturbance signal is added to adjust the gain of the variable gain amplifier 2 so that the magnitude of the output of the AD converter 3 becomes close to To. Next, a wobbling signal is added to change the coefficient of the coefficient multiplier 5, and the loop gain is adjusted.

FIG. 6 is a block diagram showing the configuration of an optical disk servo system in a second embodiment of the present invention. In this example, the output of the variable gain amplifier 2 is input as an analog signal to the gain controller 89, and the gain of the variable gain amplifier 2 is set using the output. A block diagram of the gain controller 89 is shown in FIG. 91 is an analog amplitude memory, and 92 is a comparator. The analog amplitude memory 91 stores the maximum amplitude Ai of the output of the variable gain amplifier 2, and the comparator 92 compares the magnitudes of At and Ti. When At is smaller than Ti, the up/down counter 43 is increased;
A control output is issued to increase the gain of the variable gain amplifier 2.

If At is larger than Ti, up/down counter 4
3 and outputs a control output that reduces the gain of the variable gain amplifier 2.

In the embodiment described above, a configuration has been shown in which the value of the feedback resistance of the operational amplifier is switched as the variable gain amplifier 2, but this can also be realized by switching the value of the input resistance. It can also be realized with a variable gain amplifier that changes the gain by controlling the current flowing through the differential amplifier using a DC voltage value as a control input.

With the above configuration, it is possible to maintain an appropriate AD converter input level even for optical discs with different reflectances, and it is possible to realize a digital servo system that is less susceptible to quantization errors.

Effects of the Invention As described above, the present invention is equipped with a variable gain amplifier and a gain controller, so that the input level of the AD converter can be maintained appropriately even for optical discs with different reflectances, and the quantization error can be reduced. It is possible to realize a digital servo system that is less susceptible to the effects of

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an optical disk servo system in the first embodiment of the present invention, Fig. 2 is a characteristic diagram showing the input/output characteristics of the optical pickup, and Fig. 3 shows the input/output characteristics of the AD converter. 4 is a block diagram showing the =12- configuration of the gain controller in the first embodiment. FIG. 5 is a circuit diagram showing a specific example of the configuration of the variable gain amplifier in the first embodiment. The figure is a block diagram showing the configuration of an optical disk servo system in a second embodiment of the present invention, FIG. 7 is a block diagram showing the configuration of a gain controller in the second embodiment, and FIG. 8 is a conventional optical disk servo system. FIG. 9 is a block diagram showing the structure of a loop gain determiner in the conventional example. 1... Optical pickup, 2... Variable gain amplifier, 3... AD converter, 4... Adder,
5...Coefficient multiplier, 6...Equalizer, 7
DA converter, 8 Drive signal amplifier, 9 Gain controller, 10 Loop gain determiner, 11 Adder, 89 Gain controller.

Claims (4)

[Claims] (1) A variable gain amplifier that can vary the amplification gain and an AD converter that converts the output of the amplifier from analog to digital are provided in the servo loop, and when a disturbance signal of a predetermined magnitude is applied to the servo loop, An optical disc servo system comprising a gain controller that controls the gain of the variable gain amplifier so that the output value of the AD converter becomes a predetermined value. (2) The gain controller includes an amplitude memory that stores the maximum amplitude of the output of the AD converter, a comparator that compares the output of the memory with the target amplitude, and a count increase or decrease depending on the output of the memory. The count decreased,
2. The optical disk servo system according to claim 1, further comprising an up/down counter for obtaining a control signal for controlling the gain of the variable gain amplifier. (3) A variable gain amplifier capable of varying amplification gain is provided in the servo loop, so that when a disturbance signal of a predetermined magnitude is applied to the servo loop, the output value of the variable gain amplifier becomes a predetermined value. Optical disk servo system equipped with a gain controller to control gain. (4) The gain controller includes an analog amplitude memory that stores the maximum amplitude of the output of the variable gain controller, a comparator that compares the output of the memory with the target amplitude, and an analog amplitude memory that stores the maximum amplitude of the output of the variable gain controller. The count increases or the count decreases,
4. The optical disk servo system according to claim 3, further comprising an up/down counter for obtaining a control signal for controlling the gain of the variable gain amplifier.