JPH01169603A - Automatic loop gain control circuit - Google Patents

Abstract

PURPOSE:To constantly operate a circuit in an optimum condition even when the sensitivity of respective elements is fluctuated by adding the reference signal of a prescribed frequency from an adding point in the closed loop of an automatic control circuit, comparing the amplitude of the reference signal before and after the adding point and controlling to make the amplitude ratio constant. CONSTITUTION:When a loop gain is increased, for example, like C2 due to some reason, the gain for an angle frequency omegac is increased more than the set value, and therefore, the amplitude level of a reference signal Sa is increased to a reference signal Sb and an amplitude level ratio ¦Sa¦/¦Sb¦ is larger than '1'. When the loop gain becomes two times as much as the set value, a dividing circuit 17 supplies a gain control voltage, which is '2', to a variable gain amplifier circuit 5, and therefore, the gain of the variable gain amplifier circuit 5 descends so as to become 1/2 of the initial set value, in short, G/2. Thus, the fluctuation of the servo system loop gain is automatically suppressed, the loop gain is always kept to the set value and the stability of the system is not damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic loop gain control circuit for keeping the loop gain of an automatic control circuit having a closed loop constant.

(Prior Art) Conventionally, in optical disk devices or magneto-optical disk devices (hereinafter collectively referred to as optical disk devices), tracking in focus servo and track servo is required to accurately record and reproduce information. Since the errors must be suppressed to about ±1 μm and ±0.1 μm, respectively, these servo systems practically require an open loop gain of 60 dB or more in the low frequency range (for example, 15H2 or 30H7). Furthermore, due to its structure, the objective lens drive device (hereinafter referred to as actuator) exhibits a gain peaking phenomenon due to secondary resonance in a band of several KH7 or more, causing rapid phase deterioration. In a track servo system, it is difficult to ensure sufficient phase margin and gain margin.

Therefore, in a servo system with such high gain and insufficient phase margin and gain margin, an automatic loop gain control circuit is installed to prevent fluctuations in the open loop gain, which significantly impairs the stability of the system. This is intended to suppress fluctuations in open loop gain.

Conventionally, this type of automatic loop gain control circuit has been described in Japanese Patent Laid-Open No. 60-22746. The configuration will be explained below using figures.

FIG. 2 is a block diagram showing an example of a conventional automatic loop gain control circuit.

An actuator 2 is provided below the optical disk or magneto-optical disk (hereinafter simply referred to as disk) to drive the objective lens in the vertical and horizontal directions in response to the surface runout and eccentricity of the disk 1. A four-segment type photodetector 3 known from the cylindrical lens method is connected to. This photodetector 3 has a function of receiving reflected light from the disk 1 and outputting an electric signal proportional to the amount of received light to a focus servo system A and a total reflected light amount signal processing system (hereinafter referred to as ΣPD processing system) B. have. In addition, in an actual optical disk device,
A track servo system is also provided, but it is omitted in FIG.

The focus servo system A has a differential amplifier 4 not connected to the photodetector 3, and the differential amplifier 4 includes a variable gain amplifier 5, a phase compensation circuit 6 including a phase shifter, etc., and an actuator drive. The drive circuits 7 for the actuator 2 are connected in cascade, and the drive circuits 7 are further connected to the actuator 2 to form a servo loop.

It has an inverting summing amplifier 8 connected to the ΣPD processing system photodetector 3, and the output of the amplifier 8 is sent to the variable gain amplifier 5 as a gain control signal 9S via a low-pass filter 9.
It is connected to the.

In the above configuration, each output signal from the four-part photodetector 3 is first summed with the signals from the light receiving portions of the photodetector 3 located diagonally, and then each added signal is converted into a differential signal. The variable gain amplifier 5 outputs a focus error signal 4s that is differentially amplified by the amplifier 4 and represents the direction and magnitude of the focus shift.
and is input to the drive circuit 7 via the phase compensation circuit 6.

The drive circuit 7 amplifies the power of this input signal and supplies it to the actuator 2 that drives the objective lens so as to correct the focus shift. Each output signal from the four-part photodetector 3 is fully summed by an inverting summing amplifier 8 and amplified so that the output has negative polarity, and after noise components are removed by a low-pass filter 9 in the next stage, It is supplied to the variable gain amplifier 5 as a gain control signal 9S.

In the optical disk servo system in this type of automatic loop gain control circuit, the loop gain is set to an optimum value based on the amount of light received by the four-segment detector 3 when the medium reflectance and laser power are at a certain value. , the gains of electric circuit sections such as the amplifier 4.5 and the phase compensation circuit 6 are adjusted. However, during actual operation, the loop gain fluctuates due to variations in reflectance due to non-uniformity of the medium and changes in light amount due to changes in laser power, etc., making the servo operation unstable.

For this reason, the outputs of the respective light receiving sections of the quadripartite photodetector 3 are completely summed by the inverting summing amplifier 8 to measure the amount of received light, and the change in the amount of received light is detected to change the gain of the variable gain amplifier 5. This is done to keep the loop gain constant. In other words, the gain of the variable gain amplifier 5 is adjusted to optimize the loop gain based on the gain control signal 9S that has passed through the inverting amplifier 8 and the low-pass filter 9 when the amount of received light is as the reference value. When the amount of received light increases and the level of the gain control signal 9s increases, the gain of the variable gain amplifier 5 decreases, and conversely, the amount of received light decreases and the level of the gain control signal 9s increases.
By increasing the gain of the variable gain amplifier 5 when the level of S decreases, fluctuations in the loop gain due to changes in the amount of light are absorbed.

(Problem to be Solved by the Invention) However, the automatic loop gain control circuit with the above configuration cannot absorb fluctuations in the loop gain caused by changes in the light amount due to changes in the reflectance of the medium, changes in the laser power, etc. However, these factors have no effect on loop gain fluctuations caused by changes in the force constant of the actuator 2, changes in the sensitivity of the error detector, changes in gain due to circuit elements, etc. Not only does this make the servo system unstable, but since the loop gain is controlled by the gain control signal 9S from outside the servo system, there is a problem that if there is an abnormality in this gain control signal 9S, the servo system malfunctions. .

The present invention solves the problems that the prior art had, in that the servo system becomes unstable due to fluctuations in the loop gain due to changes in sensitivity of each element making up the closed loop, and that if there is an abnormality in the gain control signal, the servo system The present invention provides an automatic loop gain control circuit that solves the problem of system malfunction.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an automatic loop gain control circuit that maintains the loop gain of an automatic control circuit having a closed loop of control signals at a constant value. At least, an addition means for adding a reference signal during the closed loop, a first signal extraction means for selectively extracting only the reference signal component from the control signal immediately before the addition means, and a first signal extraction means for selectively extracting only the reference signal component from the control signal immediately before the addition means; a second signal extraction means for selectively extracting only the reference signal component from the control signal; an amplitude ratio detection means for detecting the amplitude ratio of the signals from the first and second signal extraction means; and the control signal. and a loop gain variable means for changing the loop gain in inverse proportion to the output of the amplitude ratio detecting means.

(Function) According to the present invention, since the automatic loop gain control circuit is configured as described above, the addition means adds a reference signal of a predetermined frequency to the closed roof of the automatic control circuit, and the reference signal before and after this addition point A signal is extracted by a first signal extraction means and a second signal extraction means, an amplitude ratio of the two extracted reference signals is detected by an amplitude ratio detection means, and the amplitude ratio is made constant by a loop gain variable means. Change the loop gain. In this way, changes in the loop gain of the servo system can be directly measured,
Based on this, the loop gain variable means is controlled to change the loop gain, so not only the loop gain fluctuation due to changes in the amount of light but also the fluctuations in the loop gain due to sensitivity changes of each element constituting the closed loop are controlled. It also absorbs energy and enables stable servo operation. Therefore, the above-mentioned problem can be eliminated.

(Embodiment) FIG. 1 is a block diagram of an automatic loop gain control circuit in an optical disk device showing an embodiment of the present invention.
Elements that are the same as those in the conventional FIG. 2 are given the same reference numerals. Note that in FIG. 1, only the focus servo system is shown, and the track servo system is omitted and not shown as in FIG. 2.

This automatic loop gain control circuit is equipped with a disk 1 and an actuator 3 as in the conventional case, and the actuator 3 includes a four-part photodetector 3 forming a closed loop, a differential amplifier 4, and a variable loop gain variable means. A gain amplifier 5, a phase compensation circuit 6, and a drive circuit 7 are connected, and a gain control signal generation circuit for controlling the gain of the variable gain amplifier 5 is provided between the phase compensation circuit 6 and the drive circuit 7. It differs from conventional circuits in the way it is connected.

This gain control signal generation circuit includes a reference signal generation circuit 10 that generates a reference signal Sc, and a differential circuit 11 that functions as an adding means, and (+) input terminals of the first differential circuit 11. is the output side of the phase compensation circuit 6, its (-) input terminals are the output side of the reference signal generation circuit 10,
and their output terminals are respectively connected to the input side of the drive circuit 7. This differential circuit 11 calculates the difference between the control signal outputted from the phase compensation circuit 6, that is, the servo signal 6S, and the reference signal Sc outputted from the reference signal generation circuit 10, and converts it into a servo signal 11s. This circuit supplies the drive circuit 7 and is composed of an operational amplifier and the like.

Further, on the output side of the differential circuit 11, an inverting amplifier 12, a band pass filter 13b serving as a second signal extraction means, an absolute value circuit 15b, and a low pass filter 16b are connected in cascade, and the differential circuit On the input side of 11, there is a band pass filter 13a which is a first signal extraction means, a phase adjustment circuit 14, an absolute value circuit 15a, and a low pass filter 16a.
are connected in cascade. Furthermore, the output side of one low-pass filter 16b is a division circuit 17 which is an amplitude ratio detection means.
is connected to the input terminal X of the other low-pass filter 16a, and the output side of the other low-pass filter 16a is connected to the input terminal Y of the division circuit 17,
An output terminal Z of the division circuit 17 is connected to the variable gain amplifier 5.

Here, the band pass filters 13a and 1:3b have the same characteristics, one of which is a circuit that extracts only the reference signal Sa from the servo signal 6s, and the other band pass filter 13b is a circuit that extracts only the reference signal Sa from the servo signal 6s. This circuit extracts only the reference signal sb inside. Phase adjustment circuit 1
Reference numeral 4 is for aligning the phases of the reference signals Sa and Sb, and is composed of a phase shifter or the like that does not affect the amplitude characteristics. The absolute value circuits 15a and 15b have the same characteristics, and one of the absolute value circuits 15a is a phase adjustment circuit].The other absolute value circuit 15b is a circuit that performs full-wave rectification on the output of [4] to obtain its absolute value. Bandpass filter 13b
This is a circuit that, for example, performs full-wave rectification on the output of the circuit and calculates its absolute value. The low-pass filters 16a and 16b are circuits that have the same characteristics and average the outputs of the absolute value circuits 15a and 15b, respectively, and supply them to the input terminals Y and X of the division circuit 17. Further, the division circuit 17 divides the signal amplitude level of the input terminal Y by the signal amplitude level of the input terminal This is a circuit that supplies the amplifier 5.

Before explaining the operation of the automatic loop gain control circuit configured as described above, the transfer characteristics of the servo system will first be explained with reference to FIGS. 3 and 4.

FIG. 3 is a Bode diagram showing the open loop transfer characteristics of the servo system in the optical disk device. The upper part of Figure 3 is a gain diagram; C1 is the diagram when the loop gain is appropriate, C2 is the diagram when the gain increases, and C3 is the diagram when the gain is decreased. The lower part of the diagram is the phase diagram. be.

The angular frequency of the gain intersection when the appropriate gain C1 is ω. From the viewpoint of stability and coordination, the phase margin and gain margin are generally 40° to 60° and 10 to 20° in servo systems.
It is designed to be about dB. Furthermore, in a frequency band above ω, the open loop gain becomes below OdB and the servo is not sufficient. One boat fishing is to set the frequency band higher than the frequency band of the input signal to the servo system.

The actuator (2) used in optical disk devices, etc.
As mentioned above, due to its structure, it has gain peaking due to secondary resonance in the high frequency range, which causes rapid phase deterioration, so for some reason the loop gain increases to 02, and the gain intersection ω0 that does not correspond to this increases in the high frequency range. When moving to the side ωch,
The phase margin and gain margin decrease, and the system becomes oscillatory.
It becomes unstable. On the other hand, the loop gain decreases to 03 and does not correspond to ω. is ω on the low frequency side. , Il, the decrease in phase margin is small, but a problem arises in that the tracking error increases due to the overall lack of gain.

The factors that cause this open loop gain to vary are:
Changes in the light intensity due to changes in the reflectance of the medium, changes in the laser power, changes in the force constant of the actuator (2), changes in the gain of the circuit, and other changes in the sensitivity of each element that make up the closed loop. At the time of servo system design or initial gain adjustment, it is difficult to predict how it will change. Therefore, it is necessary to investigate the transfer characteristics of the servo system that is actually operating, but it is known that this can be measured by using a circuit as shown in FIG.

FIG. 4 shows a circuit used to measure loop characteristics in an automatic loop gain control circuit.

This circuit consists of resistors 20, 21°22 with the same resistance value.
．． 23, an operational amplifier 24, and a variable frequency oscillator 25, the node N1 is connected to the (+) input terminals of the operational amplifier 24 through the resistor 22, and the variable frequency oscillator 25 is connected to the operational amplifier 24 through the resistor 20. (-) input terminals.

Further, the (+) input terminals of the operational amplifier 24 are grounded via the resistor 23, and the (-) input terminals are connected to the resistor 21.
The output terminal and the sword N2 are connected through the terminal.

When examining the transfer characteristics, a part of the closed loop making up the servo system is cut and the circuit shown in FIG. 4 is inserted. At this time, a servo signal is input from node N1 and output from node N2, thereby forming a closed loop.
The operational amplifier 24 receives a comparison signal from the variable frequency oscillator 25 to the extent that it does not impair the stability of the automatic loop gain control circuit.
is applied to the (-) input terminals of the servo signal of the node N2, and the comparison signal in the servo signal of the node N2 is used as a reference, and the signal is passed through the loop to the node N1.
By measuring the amplitude level and phase of the comparison signal among the servo signals appearing in the servo signal, a Bode diagram as shown in FIG. 3 showing the characteristics of the servo system can be obtained. However, the phase diagram of the measurement results is
The phase diagram shown in FIG. 3 is output with a 180° offset.

Next, the operation of the circuit shown in FIG. 1 will be explained.

The reference signal generating circuit 10 shown in FIG. A sine wave reference signal Sc of an angular frequency is generated. This reference signal Sc is used as a servo signal 6s in the differential circuit 11.
(or added with negative polarity to the servo signal 6s), and its output is supplied to the drive circuit 7 and the inverting amplifier 12 in a closed loop in the form of servo signals 1-18.

The output of the inverting amplifier 12 has a center angular frequency of ω. Only the reference signal sb in the servo signal 11s is taken out by the bandpass filter 13b set to It is applied to input terminal X.

On the other hand, the servo signal 11s output from the differential circuit 11 goes around the closed loop and is output to the (+) input terminals of the differential circuit 11 and the off-center angular frequency as the output servo signal 6s of the phase compensation circuit #I6. of. bandpass filter 13 set to
supplied to a. The band pass filter 13a extracts only the reference signal Sa from the servo signal 6s and supplies it to the phase adjustment circuit 14 at the next stage. The reference signal Sa is supplied to the phase adjustment circuit 14.
is adjusted so that there is no phase shift with respect to the reference signal sb, full-wave rectified by the absolute value circuit 15a, and further averaged by the low-pass filter 16a.
is supplied to Then, the division circuit 17 divides the signal amplitude level of the input terminal Y/the signal amplitude level of the input terminal X, outputs the division result from the output terminal Z as a gain control signal 17s, and sends it to the variable gain amplifier 5. supply

FIG. 5 shows an example of the characteristics of the variable gain amplifier 5 suitable for use here. In this variable gain amplifier 5, when normalized by the initial setting gain control voltage, when the control voltage is 1, the gain is constant G, and for example, when the control voltage is doubled to 2, the gain is halved to G/2. On the other hand, when the control voltage is halved to 0.5, the gain doubles to 2G, so it has a variable gain characteristic that is inversely proportional to the gain control voltage.

In the automatic loop gain control circuit of this embodiment, if the open loop gain of the servo system is as set as 01 in FIG. 3, the gain intersection point is ω. Because of the angular frequency.

The amplitude levels of the reference signals Sa and Sb are equal, and the phases of the reference signals Sa and Sb are matched by a phase adjustment circuit 14, full-wave rectified by absolute value circuits 1.5a and 15b, respectively, and further low-pass filters 16a, If the signal amplitude level after being averaged by 16b is divided by the division circuit 17, the result of the division will be 1. Therefore, the gain of the variable gain amplifier circuit 5 remains at G at the initial setting. However, if the loop gain does not increase as shown in 02 in Figure 3 due to some reason, such as a change in the amount of light due to a change in the reflectance of the medium or the power, or a change in the force constant of the actuator 2, then the angular frequency of. Since the gain for the reference signal Sa increases from the set value, the amplitude level of the reference signal Sa increases with respect to the reference signal sb, and the amplitude level ratio I 5a-1/l Sb l
becomes larger than 1-.

If the loop gain becomes twice the set value,
Division circuit] 97 applies a gain control voltage of "2" to the variable gain amplifier Fl! In order to supply the signal to I5, the gain of this variable gain amplifier circuit 5 is reduced to 1/2 of the initial setting value, that is, G/2. Conversely, the loop gain is C3 in Figure 3.
If the angular frequency is decreased as shown in . Since the gain for the reference signal Sa decreases from the time of setting, the amplitude level of the reference signal Sa decreases with respect to the reference signal sb, and the amplitude level ratio becomes 1.
sal/1sbl becomes 1 or less. Therefore, the divider circuit 17 outputs a gain control voltage so as to increase the gain of the variable gain amplifier circuit 5 from the set value G. In other words, if the loop gain becomes half of the set value,
The divider circuit 17 outputs a gain control voltage of rO,5J, which makes the gain of the variable gain amplifier circuit 5 twice the initial setting value (2G). Therefore, by such an operation, the loop gain of the servo system is constantly kept constant.

As described above, in the automatic loop gain control circuit of this embodiment, the amount of light changes due to changes in the reflectance of the medium and the laser power.
Automatically suppresses fluctuations in the loop gain of the servo system caused by changes in the force constant of the actuator 2 or variations in circuit elements, ensuring that the loop gain is always maintained at the set value and reducing the stability of the system. You can avoid it.

Moreover, since the gain control signal]-78 is fed back from the loop to be controlled, rather than from the outside as in the conventional case, reliability is high.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of such modifications include the following.

(i) In FIG. 1, the variable gain amplifier circuit 5 is used as the loop gain variable means, but if the loop gain can be varied, other means such as making the sensitivity of the photodetector 3 variable may also be used. good.

(ii) The reference signal Sc may be applied at any position within the loop. Further, either the addition means for adding the reference signal Sc or the loop gain variable means may be installed first in the loop.

(iii) Although the amplitude ratio detection means is configured by the division circuit 17, it is also possible to configure it by other circuits. For example, the circuit may be configured to differentially amplify a logarithmically amplified signal and further perform antilogarithmically amplifying the signal.

(IV) In the above embodiment, the servo system of an optical disk device was explained as an example, but the present invention is not limited to this, but can be widely applied to automatic control circuits having a generally closed loop.

(Effects of the Invention) As described above in detail, according to the present invention, reference signals of a predetermined frequency are added from a summing point during the closed loop of an automatic control circuit, and the amplitudes of the reference signals before and after the summing point are compared. death,
Since the amplitude ratio is controlled to be constant, even if the sensitivity of each element making up the loop fluctuates for some reason, the automatic control circuit is constantly optimized by keeping the loop gain constant. It can be operated under normal conditions. Furthermore, since the gain control signal that controls the gain of the loop gain variable means to keep the loop gain constant is fed back from the loop to be controlled, rather than from the outside, it is highly reliable and extremely useful in practice. It is.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of an automatic loop gain control circuit showing an embodiment of the present invention, FIG. 2 is a configuration block diagram of a conventional automatic loop gain control circuit, and FIG. 3 is a Bode diagram of open loop transfer characteristics. FIG. 4 is a circuit diagram of the loop characteristic measuring circuit, and FIG. 5 is a characteristic diagram of the variable gain amplifier shown in FIG. 1...Disc, 2...Actuator, 3...Photodetector, 4...Differential amplifier, 5...Variable gain amplifier , 6... phase compensation circuit, 7... drive circuit, ]0...
・Reference signal generation circuit, 11...Differential circuit, 13
a, 13b...Band pass filter, 17...
...Division circuit. Applicant's agent Yasushi Kakimoto (1) cc
1JJc ωcft 1) (r(ld/3) Bode diagram of open loop transfer characteristics Fig. 3 Circuit for measuring loop characteristics Fig. 4 Gain control voltage movable 1] Characteristic diagram of gain amplifier development Fig. 3 Procedure correction band August 26, 1988 Patent Application No. 329153 2 Name of the invention Automatic loop gain control circuit Representative Nobumitsu Kosugi's "Detailed Description of the Invention" column and drawings. 6 Contents of the Amendment <1-) In the specification, "to cause" on page 3, line 8 is corrected to "often occurs," and "open loop" on lines 14 and 166 of the same page is corrected to "loop." (2) Same, page 4, line 19, “Composed of a phase shifter, etc.”
Delete. (3) Same, on page 5, line 17, "fourth division" is amended to "further four divisions." (4) Same, page 6, lines 8 to 9, ``.However, during actual operation,'' is replaced with ``but,'' and page 6, lines 11 to 12, ``but, servo operation.'' becomes unstable.For this reason, we correct ``to'' to ``to''. (5) Same, ] - Correct "Actuator 3" in the 7th and 8th lines of page 0 to "Actuator 2". (6) Same, page 8 and 9 “Inverting amplifier 1
-2," is deleted. (7) Same, on page 13, line 5, "transfer characteristics" is corrected to "relationship between transfer characteristics and stability." (8) Same, page 14, line 3, [(2) ] is r2°,
``Arise'' in line 5 of the same page is changed to ``often occurs,'' and ``open loop'' in line 144 of the same page is changed to ``loop.'' 166 of the same page.
Line ' (2) J to r2. and correct them respectively. (9) Same, change "Auto loop gain" on the 5th line of page 1-5 to "Auto j with closed loop" and "N2" on the 1-5 line of the same page.
to rN2," respectively. (10) Same,] “Circuit 7” on page 6, lines 18 to 20
and ... Signal 1] - 8 medium'', 3
b. The band-pass filter 13b corrects the servo signal to "-18". (11) Correct the "absolute value" in the first line of page 17 to "absolute value of the next stage". (12) Correct Figure 1 as shown in the attached sheet.

Claims (1)

[Claims] 1. Adding means for adding a reference signal into the closed loop of an automatic control circuit having a closed loop of control signals, and selectively adding only the reference signal component from the control signal immediately before the adding means. a first signal extracting means for extracting; a second signal extracting means for selectively extracting only the reference signal component from the control signal immediately after the adding means; and from the first and second signal extracting means. and amplitude ratio detection means for detecting the amplitude ratio of the signal; and loop gain variable means for inputting the control signal and changing the loop gain so as to be inversely proportional to the output of the amplitude ratio detection means. Automatic loop gain control circuit. 2. The automatic loop gain control circuit according to claim 1, wherein the angular frequency of the reference signal is made the same as the angular frequency of the gain intersection when the loop gain of the automatic control circuit is maintained optimally. 3. The addition means is a reference signal generation circuit and a differential circuit,
Claim 1 or 2, wherein the first and second signal extraction means are band-pass filters, the amplitude ratio detection means is a division circuit, and the loop gain variable means is a variable gain amplifier, respectively. Automatic loop gain control circuit as described.