JP2935930B2 - Focus servo balance adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo balance adjusting device, and more particularly to a CD, MD, LD, and CD-R.
In a device for reproducing or recording on an optical disk such as an OM or a magneto-optical disk, the balance of the focus servo can be automatically adjusted within the set without using a special jig. Related to the device.

[0002]

2. Description of the Related Art For example, in a CD player, information recorded on a disc can be read only when a beam spot of a laser beam emitted from an optical pickup is focused on a disc signal surface. Since the position of the signal surface of the disk constantly changes due to the runout of the disk, the focus servo is applied to the CD player so that the beam spot can always maintain the focused state with respect to the disk signal surface regardless of the fluctuation. Have been.

FIG. 11 is a configuration diagram of a conventional general focus servo system. 10 is a compact disk, 12 is a spindle motor for rotating the disk at a constant linear speed, 1
4 is an optical pickup for detecting the reflected beam irradiates the laser beam on the disk, 16 is a quadrant photodiode provided in the optical pickup, D _A to D
_{Consists of D.} D _A and D _C is connected in parallel, (A + C)
Outputs a signal, D _B and D _D are connected in parallel, (B +
D) A signal is output.

FIG. 12 shows a method of detecting a focus error.
FIG. . When the camera is in focus,
As described above, the reflected beam is reflected by the D of the four-division photodiode 16._A
~ D _DAnd the beam spot moves away from the signal plane.
When the distance is too high, as shown in FIG._AAnd D_cTo
Hit, D_BAnd D_DHit less. Beam spot
When the signal is too close to the signal surface, as shown in FIG.
D_BAnd D_DHit many, D_AAnd D_CHit less
You. Therefore, (A + C)-(B + D) is the beam spot
Is zero when is focused on the signal plane, and the beam spot
Becomes + if it is too far from the signal plane, and becomes-if it is too close
Therefore, (A + C)-(B + D) is the beam spot.
And the error between the focal point and the signal plane.

Reference numeral 18 denotes (A) of the four-division photodiode 16.
+ C) signal-to-current conversion of the signal (photocurrent signal) (A +
C) 'current-voltage converter (I-
V converter), 20 is the (B) of the four-division photodiode 16
+ D) signal (photocurrent signal) is subjected to current-current conversion to obtain (B +
D) 'current-voltage converter (I-
V converter).

Reference numeral 22 denotes a subtractor, which is k · ｛(A + C) ′ −
The calculation of (B + D) ′｝ is performed to create a focus error signal. The subtracter 22 includes an operational amplifier 22a and resistors R ₁ to R ₁ .
R ₃ and a feedback resistor R _f , and (B + D) ′
Inverting input terminal of the operational amplifier 20a signals through a resistor R ₁ (-), is input to the (A + C) 'signal via a resistor R ₂ non-inverting input terminal (+). Output feedback resistance R _f of the via and the inverting input terminal of the operational amplifier 22a (-) and are connected, the non-inverting input terminal (+) is grounded through a resistor R _3. According to the subtracter 22, the focus error signal FE is generally expressed as FE = {R ₄ (R ₁ + R _f ) / R ₁ (R ₂ + R ₃ )} · (A + C) ′ − (R ₁ / R _f ) · (B + D) ′ (1) Here, if R ₁ = R ₂ and R _f = R ₃ , then FE = (R _f / R ₁ ) · {(A + C) ′ − (B + D) ′}. The current-voltage converters 18 and 20 and the subtractor 2
2 constitutes a focus error detection circuit.

Reference numeral 24 denotes a servo amplifier for performing phase compensation and low-frequency boost on the focus error signal FE, 26 a focus driver for amplifying the output of the servo amplifier, and 28 provided in the optical pickup 14 and driven by the output of the focus driver. The focus actuator moves the objective lens 30 in the vertical direction with respect to the compact disk 10 while being operated. When the beam spot is too far from the disk signal surface due to the surface deflection of the compact disk 10, the focus error signal FE becomes negative, and the focus driver 26 brings the objective lens 30 closer to the disk signal surface. On the other hand, when the beam spot is too close to the disc signal surface due to the runout of the compact disc 10,
The focus error signal FE becomes positive, and the focus driver 26 moves the objective lens 30 away from the disk signal surface. In this manner, the beam spot can maintain a focused state with respect to the disk signal surface while following the surface deflection of the compact disk 10.

The adder 32 calculates (A + C) '+ (B +
D) 'is performed to generate an RF signal, and after the waveform equalization and shaping circuit 34 performs waveform equalization and waveform shaping,
It is output as a binary RF signal (EFM signal). The E
The FM signal is sent to the digital signal processing circuit 36,
Audio data and subcodes are read.

It is good if the optical system of the optical pickup 14 and the four-division photodiode 16 have ideal characteristics. However, in practice, there are variations in the characteristics of the elements themselves and mechanical arrangements in the optical pickup 14. From variations etc.,
Even when the beam spot is accurately focused on the disc signal surface, the beam spot is output from the optical pickup 14 (A +
Normally, the C) signal and the (B + D) signal are not completely balanced and the difference does not become zero. If the (A + D) signal and the (B + D) signal are kept in such an unbalanced state, a steady deviation remains between the beam spot controlled by the focus servo system and the disk signal surface, and the disk spot moves from the focal point of the beam spot to the disk. When the signal surface is deflected too far or too close, the function of the focus servo for returning to the in-focus state becomes dull, and the servo is likely to deviate.

For this reason, conventionally, after the set is assembled, the balance of the focus servo system is adjusted, and when the beam spot is accurately focused on the disk signal surface, the focus error signal FE becomes completely zero. And then ship it. Specifically, FIG.
As shown in 1, and the resistance R ₃ of the subtractor 22a in the semi-fixed resistor, keep the adjustable level As is clear from equation (1) (A + D) signal component. Then, the jitter of the binary RF signal increases in proportion to the poor balance between the (A + C) signal and the (B + D) signal in the focus servo system. A jitter meter 38 is connected to the output side and, for example, the shortest period pulse (3
Focusing on T), while the measurement of the jitter, the jitter to adjust the semi-fixed resistor R ₃ so as to minimize. If the jitter is minimized, the (A + C) signal and the (B + D) signal are balanced, and the focus servo system oscillates in either the direction where the disk signal surface is too far away or too close from the focus of the beam spot. Even in such a case, an optimum focus servo operation can be performed.

[0011]

However, in the above-mentioned prior art, a special jig such as a jitter meter must be prepared, and after the set is assembled, the operator must manually adjust the focus balance. In addition, there is a problem that it takes time and effort. In view of the above, it is an object of the present invention to provide a focus servo balance adjusting device capable of automatically adjusting a focus balance without using a special jig.

[0012]

According to the present invention, a disturbance signal applying means for generating a disturbance signal of a sine wave at a predetermined time and applying the signal to a focus servo system, and an RF generated from a detection output of a pickup. Detection means for detecting the envelope of the signal, peak detection means for detecting the lower peak level and upper peak level of the envelope determined by the detection means, and the center level between the two peak levels detected by the peak detection means. Waveform shaping means for shaping the envelope obtained by the detection means, using the center level as a threshold level, and a waveform shaping means.
Means for measuring the duty of the output signal;
Balun so that the duty of the output signal of the stage becomes 50%
This is achieved by providing control means for controlling the power adjustment circuit .

[0013]

[0014]

According to the present invention, at a predetermined time, a sine wave disturbance signal is generated and applied to the focus servo system. At this time, the envelope detection of the RF signal created from the detection output of the pickup is performed, and the envelope detection is performed. The lower peak level and the upper peak level are detected, the center level of the two detected peak levels is determined, and the duty is 50% when the envelope is waveform-shaped using the center level as a threshold level. The balance adjustment control is performed. Thus, it is not necessary to prepare a special jig such as a jitter meter at the time of balance adjustment, and it is also possible to automatically perform focus balance adjustment within the set, thereby eliminating the need for manual adjustment work.

[0015]

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure,
The same components as those in FIG. 11 are denoted by the same reference numerals. 10 is a compact disk, 12 is a spindle motor for rotating the disk at a constant linear speed, 14 is an optical pickup for irradiating the disk with a laser beam and detecting a reflected beam, and 16 is a four-division photodiode provided on the optical pickup. , (A + C) signal and (B
+ D) signal (both are photocurrent signals).

Reference numeral 18 denotes (A) of the four-division photodiode 16
+ C) current-voltage converter (IV converter) which converts the signal into a voltage (A + C) ′ signal (voltage signal), 2
Reference numeral 0 denotes a current-voltage converter (IV converter) that converts the (B + D) signal of the four-division photodiode 16 into a (B + D) ′ signal (voltage signal) by current-voltage conversion.

Reference numeral 220 denotes a subtractor, which is k ｛(A + C) '-
(B + D) ′｝ to calculate the focus error signal
create. As shown in FIG. 2, the subtractor 220 is an operational amplifier.
22a, resistance R₁, R_Two, R₃₁~ R₃₅, Switch SW₁
~ SW_Five, Feedback resistance R_fAnd (B +
D) 'signal is resistance R₁Of the operational amplifier 22a via the
Input terminal (-), (A + C) 'signal is a resistor R_TwoThrough
Input to the non-inverting input terminal (+). Operational amplifier 2
2a is a feedback resistor R_fFlip through
Connected to input terminal (-). Resistance R₃₁~ R₃₅Is each
Switch SW₁~ SW_FiveAnd were connected in series individually
That is, connect in parallel between the non-inverting input terminal (+) and ground.
Has been continued. Each switch SW₁~ SW_FiveIs an external control
It can be opened and closed individually. Resistance R₃₁~ R₃₅Is the resistance value
Are gradually different values (R ₃₁<R₃₂<R₃₃<
R₃₄<R₃₅). These resistors R₃₁~ R₃₅And switch SW₁
~ SW _FiveConstitutes the balance adjustment circuit 22b
I have. In this embodiment, the switch SW₁~ SW_FiveAfter
One is closed alternatively by the balance controller described
It is assumed that it is in a state of being broken.

According to the subtractor 220, the focus error
The error signal FE is generally given by FE = ｛R_Four(R₁+ R_f) / R₁(R_Two+ R_3i)｝ · (A + C) ′ − (R₁/ R_f) · (B + D) ′ (2) (where i = 1 to 5). Where R₁= R_Two , R
_f= R₃₃Then, switch SW_ThreeFE = (R_f/ R₁) · {(A + C) ′ − (B + D) ′}. Set the switch to close to SW_TwoOr SW₁To
The level of the (A + C) signal system increases step by step.
Set the switch to close to SW_FourOr SW _FiveWest
The level of the (A + C) signal system decreases step by step
I do. Therefore, the (A + C) signal system is
When the (B + D) signal system is balanced,
Switch_ThreeShould be closed, and the level of the (A + C) signal system
Is smaller than the (B + D) signal system,
Switch_TwoClose or switch₁Or (A +
C) The level of the signal system becomes larger than that of the (B + D) signal system.
The switch SW_FourClose or switch_FiveClose
Focus balance can be adjusted
Become. The current-voltage converters 18 and 20 and the subtractor 22
0 constitutes a focus error detection circuit.

Reference numeral 24 denotes a servo amplifier for performing phase compensation and low-frequency boost on the focus error signal FE; 26, a focus driver for amplifying the output of the servo amplifier; and 28, which is provided in the optical pickup 14 and is driven by the output of the focus driver. The focus actuator moves the objective lens 30 in the vertical direction with respect to the compact disk 10 while being operated. When the beam spot is too far from the disk signal surface due to the surface deflection of the compact disk 10, the focus error signal FE becomes negative, and the focus driver 26 brings the objective lens 30 closer to the disk signal surface. On the other hand, when the beam spot is too close to the disc signal surface due to the runout of the compact disc 10,
The focus error signal FE becomes positive, and the focus driver 26 moves the objective lens 30 away from the disk signal surface. In this manner, the beam spot can maintain a focused state with respect to the disk signal surface while following the surface deflection of the compact disk 10.

The adder 32 calculates (A + C) '+ (B +
D) 'is performed to generate an RF signal, and after the waveform equalization and shaping circuit 34 performs waveform equalization and waveform shaping,
It is output as a binary RF signal (EFM signal). The E
The FM signal is input to the digital signal processing circuit 36,
Audio data and subcodes are read.

Reference numeral 40 denotes a servo amplifier and a focus driver.
The adder 42 has a constant amplitude and a constant frequency f.
A disturbance signal AN consisting of a sine wave is generated and output to the adder 40.
Oscillator that operates according to the instructions of the balance controller.
Start or stop the oscillation operation. Note that oscillation
The device 42 changes at a frequency of 2f in synchronization with the disturbance signal AN.
Square wave signal MN₁And the frequency of f in synchronization with the disturbance signal AN.
Square wave signal MN changing with wave number_Two(See Figure 6)
See). 44 is for the RF signal output from the adder 32
Performs envelope detection, and detects the lower envelope of the RF signal.
, A detection circuit 46 for detecting a square wave signal NM₁Fall of
A pulse generator that generates a pulse SP at the timing
48 and 50 are AND circuits; 52 is an inverting circuit;
D circuit 48 is a square wave signal MN_TwoAND the pulse SP
To the upper peak timing of the disturbance signal AN.
Sampling pulse SP₁Is output, and an AND circuit 50 is output.
Is a square wave signal MN_TwoSquare wave signal obtained by inverting the
AND the pulse SP and the lower side of the disturbance signal AN
Sampling pulse SP corresponding to peak timing _Two
Is output.

S / H circuits (sampling &
Hold circuit), and the RF detected by the detection circuit 44
To lower envelope of the signal, to sample and hold the S / H circuit 54 with a sampling pulse SP _1, S / H circuit 56 performs sampling and hold with SP _2. 58 is a subtractor for calculating the difference between the output of the S / H circuit 54 and the output of the S / H circuit 56. Reference numeral 60 denotes a microcomputer-structured balance controller which generates a disturbance signal AN from the oscillator 42 at the time of predetermined balance adjustment, determines an optimum resistance value in the balance adjustment circuit 22b based on the output of the subtractor 58, and sets a switch. SW _{1 to} SW
The opening / closing control of ₅ is performed to perform balance adjustment control. Reference numeral 62 denotes a focus balance adjustment instruction key used by an operator or the like to instruct focus balance adjustment at an arbitrary time such as when assembling a set. A system controller 64 outputs a focus balance adjustment command to the balance controller 60 when reading the TOC information of the compact disc 10 loaded in the set.

FIG. 3 is a flow chart showing the processing of the balance controller 64, FIG. 4 is a diagram showing the relationship between the defocus amount and the amplitude of the RF signal, and FIGS. 5 and 6 are operation waveform diagrams of each part at the time of focus balance adjustment. There will be described with reference to these figures. The balance controller 60 by a power-on the other switches is closed by the switch SW ₃ of the balance adjustment circuit 22b is opened (step 101 in FIG. 3). When the compact disk 10 is already loaded in the set at power-on or when the compact disk 10 is loaded in the set after power-on, the system controller 64 reads various servos including the focus servo to read TOC information. Is turned on, but after the various servos have started up normally, a balance adjustment command is output to the balance controller 60.

When various servos are turned on, the rotation of the compact disk 10 is controlled at a specified linear velocity, and the optical pickup 1
4 detects a disk recording signal and outputs an (A + C) signal and a (B + D) signal (both current signals) from the four-division photodiode 16. Then, the current-to-voltage converters 18 and 20 individually perform current-to-voltage conversion and output the (A + C) 'signal and the (B + D)' signal (both are voltage signals).
A predetermined subtraction is performed by the subtractor 220 to generate the focus error signal FE. This focus error signal FE
Is output to the adder 40 after phase compensation and low-frequency boosting are performed by the servo amplifier 24. Initially, the oscillator 42 is in a non-operation state, and the disturbance signal AN output from the oscillator 42 to the adder 40 is in a non-signal state. Therefore, the output of the servo amplifier 24 is directly input to the focus driver 26. After the amplification, the focus actuator 28 is driven. As a result, the objective lens 30 moves in a direction perpendicular to the compact disk 10, and the laser beam follows the disk signal surface in accordance with the surface shake, so that the focused state is maintained.

However, when the (A + C) signal and the (B + D) signal are unbalanced due to variations in the optical system of the optical pickup 14 or the four-division photodiode 16, the focal point of the laser beam is accurate with respect to the disk signal surface. The in-focus state is not obtained, and a steady deviation remains. On the other hand, after the (A + C) 'signal and the (B + D)' signal are added by the adder 32 to generate an RF signal, the waveform equalizing / shaping circuit 34
Are subjected to waveform equalization and waveform shaping, and output as a binary RF signal. The binary RF signal is input to the digital signal processing circuit 36 to read a subcode (TOC) and audio data, and the subcode is output to the system controller 64. The RF signal output from the adder 32 is subjected to envelope detection by a detection circuit 44 and output to S / H circuits 54 and 56.

When the balance controller 60 receives a balance adjustment command from the system controller 64 (step 102), the balance controller 60 first activates the oscillator 42, generates a disturbance signal AN, inputs the disturbance signal AN to the adder 40, and sets a square wave signal. generating a signal MN ₁ and MN ₂ (step 103, see FIG. 6). Here, when the disturbance signal AN is applied to the focus servo system, the focal point of the laser beam periodically periodically approaches or goes far from the disk signal surface. At this time, the amplitude of the RF signal Decreases as the absolute value of the defocus amount increases, as shown in FIG. Therefore, the lower envelope of the RF signal output from the adder 32 changes at a frequency of 2f with respect to the frequency f of the disturbance signal AN, as shown in FIG. Each time the light passes through the in-focus position, it becomes the lower peak. on the other hand,
Of the lower envelope of the RF signal, the upper peak timing that changes at a frequency of 2f corresponds to the upper peak timing and the lower peak timing of the disturbance signal AN, but the (A + C) signal system of the optical pickup 14 and ( B +
D) If the signal system is originally in a balanced state, as shown in the upper part of FIG. 5, all the upper peaks of the envelope waveform of the RF signal have the same level.
As shown below, adjacent upper peaks have different levels (the greater the degree of imbalance, the greater the level difference).

If the disturbance signal AN has an upper peak,
Signal envelope when the signal is at the lower peak
The upper peak level of the loop waveform is S / H times with the S / H circuit 54.
Sampled and held individually in the path 56, and the subtractor 5
After the level difference ΔL is obtained in step 8, the balance control
Input to the controller 60. Balance controller 60
Shape signal MN_TwoAt the falling timing of
The output ΔL is input and built into the balance controller 60.
Switch SW currently closed in the memory _ThreeCompatible with
And register (step 104). Then, switch S
W_TwoAnd switch SW_ThreeAnd open the subtractor 220
The resistance connected between the non-inverting input terminal (+) and ground is R
₃₂, And after a certain time, the square wave signal MN_Twoof
Output ΔL of subtractor 58 is input at falling timing
Switch SW_Two(Step 105
NO, 106, 104) Similarly, switch SW
₁, SW_Four, SW_FiveSubtractor 58 when is alternatively closed
Are input and registered.

When these processes are completed, the balance controller 60 searches for the switch having the smallest absolute value of the input level from the subtractor 58 among the registers registered in the memory, closes the switch, and closes the other switch. After performing focus balance adjustment control by opening the switch (Step 1)
07), the operation of the oscillator 42 is stopped, and the focus balance adjustment processing ends (step 108).

When the focus balance adjustment is completed in this way, the focus servo system can optimize the focus servo even if the disk signal surface fluctuates too far or too far from the focus of the beam spot. The operation can be performed, so that not only the reading of the TOC information but also the subsequent reading of the audio data can be performed accurately. In addition, since the focus balance adjustment is performed completely automatically using only the circuit built into the set, there is no need for special jigs such as a jitter meter as in the past, and there is a need for manual adjustment by workers etc. Is also gone.

In contrast, after assembling the set,
If the operator wants to adjust the focus balance at any time during the reproduction of the compact disc 10 and presses the focus balance adjustment instruction key 62, the balance controller 60 determines YES in step 109 and the system controller 64 The focus balance automatic adjustment process is performed in exactly the same manner as when the balance adjustment command is received (the process after step 103).

In the above embodiment, the balance adjustment
The resistance value can be switched in five stages by the adjusting circuit 22b.
But it can be switched in less than 4 steps or more than 6 steps
You may be able to. For example, in FIG.
In the same configuration as the road 22b, of the five switches,
So that any one or more switches are closed at the same time
Then, five resistors R₃₁~ R₃₅Set the value of
By doing so, switching in six or more stages becomes possible. Also,
The resistance value of each stage is switched once,
Although the one with the smallest absolute value of the force was determined to be the optimum resistance value,
First switch SW _ThreeIs closed, the subtractor 58
As soon as the absolute value of the output is zero or within a certain range,
After completing the balance adjustment process, switch SW_ThreeClose
The absolute value of the output of the subtractor 58 exceeds a certain range.
If it is obtained, it is closed according to the sign of the output of the subtractor 58.
Switch SW next to switch_TwoOr SW_FourCut into pieces
Instead, the output of the subtractor 58 is checked again,
Is within a certain range, then terminate the balance adjustment process.
Still, the absolute value of the subtractor 58 remains the same while the output is the same.
If it exceeds the fixed range, set the switch to close to SW
₁Or SW_FiveSwitch to balance adjustment
Can also be performed.

FIG. 7 is a partially omitted configuration diagram showing a modification of the above embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals. Reference numeral 420 denotes an oscillator which generates a disturbance signal AN having a constant amplitude and a constant frequency f and outputs the same to the adder 40 when the balance signal is put into an operating state under the control of the balance controller. A waveform shaping circuit for shaping the waveform as a shoulder level and outputting a reference pulse NP that is H level while the disturbance signal AN is positive and L level when the disturbance signal AN is negative, and 68 is a reference pulse NP that is H level. Timer for counting time, 7
0 and 72 are an upper peak hold circuit and a lower peak hold circuit for detecting an upper peak level and a lower peak level of the lower envelope waveform of the RF signal output from the detection circuit 44, respectively. UL
And an average value circuit for calculating an average level of the lower peak level DU, a waveform shaping circuit for shaping the lower envelope waveform of the RF signal into a threshold level with the average level AL obtained by the average value circuit, and a waveform shaping circuit 78. The logical product of the output of the waveform shaping circuit and the reference pulse NP is calculated and the comparison pulse CP
, A timer 80 for measuring a period during which the comparison pulse CP is at the H level, and 600 a balance controller of a microcomputer configuration, which generates a disturbance signal AN from the oscillator 420 during predetermined balance adjustment. Thereafter, based on the output of the timer 68 and 80, determine the optimum resistance value at balance adjustment circuit 22b, the switch SW ₁ ~
Adjust the balance control performs closing control of the SW _5. The other components are configured exactly the same as in FIG.

FIG. 8 is a flow chart showing the processing of the balance controller 600, and FIG. 9 is an operation waveform diagram of each part at the time of focus balance adjustment, which will be described below with reference to these figures. The balance controller 600 by a power-on the other switch is closed only switch SW ₃ of the balance adjustment circuit 22b is opened (step 201 in FIG. 8). When the compact disk 10 is already loaded in the set at power-on or when the compact disk 10 is loaded in the set after power-on, the system controller 64 reads various servos including the focus servo to read TOC information. Is turned on, but after the various servos have started up normally, a balance adjustment command is output to the balance controller 600.

When various servos are turned on, the compact disk 10 is controlled to rotate at a specified linear velocity, and the optical pickup 1 is turned on.
4 detects a disk recording signal and outputs an (A + C) signal and a (B + D) signal (both current signals) from the four-division photodiode 16. Then, the current-to-voltage converters 18 and 20 individually perform current-to-voltage conversion and output the (A + C) 'signal and the (B + D)' signal (both are voltage signals).
A predetermined subtraction is performed by the subtractor 220 to generate the focus error signal FE. This focus error signal FE
Is output to the adder 40 after phase compensation and low-frequency boosting are performed by the servo amplifier 24. First, the oscillator 420
Is in a non-operating state, and the adder 4
Since the disturbance signal AN output to 0 is in a non-signal state, the output of the servo amplifier 24 is directly input to the focus driver 26 and amplified, and then the focus actuator 28 is driven. As a result, the objective lens 30 moves in a direction perpendicular to the compact disk 10, and the laser beam maintains a focused state with respect to the disk signal surface regardless of surface deflection.

However, when the (A + C) signal and the (B + D) signal are unbalanced due to variations in the optical system of the optical pickup 14 or the four-division photodiode 16, the focal point of the laser beam is accurate with respect to the disk signal surface. The in-focus state is not obtained, and a steady deviation remains. On the other hand, after the (A + C) 'signal and the (B + D)' signal are added by the adder 32 to generate an RF signal, the waveform equalizing / shaping circuit 34
Are subjected to waveform equalization and waveform shaping, and output as a binary RF signal. The binary RF signal is input to the digital signal processing circuit 36 to read a subcode (TOC) and audio data, and the subcode is output to the system controller 64. The RF signal output from the adder 32 is subjected to envelope detection by a detection circuit 44 and output to a waveform shaping circuit 76.

When the balance controller 640 receives the balance adjustment command from the system controller 68 (step 202), the balance controller 640 first activates the oscillator 420, generates a disturbance signal AN, and inputs the disturbance signal AN to the adder 40 (step 203, (See FIG. 9). When the disturbance signal AN is applied to the focus servo system, the focal point of the laser beam periodically periodically approaches or separates too far from the disc signal surface. As shown in FIG. 9, the lower envelope of the RF signal changes at a frequency 2f with respect to the frequency f of the disturbance signal AN, and each time the focal point of the laser beam passes through a perfect focus position with respect to the disk signal surface. , And the lower peak (see FIGS. 4 and 5). The lower envelope waveform of the RF signal corresponds to the (A + C) signal system of the optical pickup 14 and the (B +
D) If the signal system is originally in a balanced state, it changes sinusoidally at a frequency of 2f, and each cycle has the same waveform, and the pulse after waveform shaping at the center level has a duty ratio of 50%. In other words, the period during which the pulse is at the H level is half of the period during which the pulse obtained by shaping the waveform of the disturbance signal AN at the center level is at the H level. However, when the (A + C) signal system and the (B + D) signal system of the optical pickup 14 are unbalanced, as shown in FIG. 9, the pulse after the RF signal lower envelope waveform shaping has a duty ratio of 50%. (The greater the degree of imbalance, the greater the difference).

The disturbance signal AN is shaped by the waveform shaping circuit 66 at its center level and output as a reference pulse NP. A period during which the reference pulse NP is at the H level is measured by a timer 68. The lower envelope waveform of the RF signal is waveform-shaped at its center level by the waveform shaping circuit 76, and the positive half cycle of the disturbance signal AN is A
The pulse is extracted as a comparison pulse CP by the ND circuit 78, and a period during which the comparison pulse CP is at the H level is measured by the timer 80. The time measured by the timers 68 and 80 is input to the balance controller 600. The balance controller 600 inputs the measured time data T ₀ of the timer 68, and registers in the memory incorporated in the balance controller 600 as the reference time data to calculate the time T _0/2 of the half (step 204). Then, enter the measured time data T ₁ of the timer 80, switch SW is closed the current
_It is registered as comparison time data corresponding to ₃ (step 205). Incidentally, T ₁ / T ₀ is the duty of the comparison pulse CP
, And the duty if T ₁ = T _0/2 50% der
You. That is, the comparison time data T ₁ corresponds to the duty.
Is what you do. Then, closing the switch SW _2, by opening the switch SW _3, a resistor connected between the non-inverting input terminal of the subtracter 220 (+) Ground switched to R _32, after a predetermined time, again, counting of the timer 80 enter the data T _2, is registered as a comparison time data corresponding to the switch SW ₂ (step 206, 207), in a similar manner, the timer 80 when closing the switch SW _1, SW _4, SW ₅ alternatively Enter the timekeeping data in and register it as comparison time data.

When these processes are completed, the balance controller 600 determines that the difference from the reference time data among the comparison time data registered in the memory is the smallest ( data).
After the switch is closed, the switch is closed and the other switches are opened to perform focus balance adjustment control (step 208).
The operation of Step 20 is stopped, and the focus balance adjustment processing ends (Step 209).

When the focus balance adjustment is completed in this way, the focus servo system can optimize the focus servo even if the disk signal surface fluctuates too far or too far from the focus of the beam spot. The operation can be performed, so that not only the reading of the TOC information but also the subsequent reading of the audio data can be performed accurately. In addition, since the focus balance adjustment is performed completely automatically using only the circuit built into the set, there is no need for special jigs such as a jitter meter as in the past, and there is a need for manual adjustment by workers etc. Disappears.

In contrast, after assembling the set,
If the operator wants to adjust the focus balance at any time during the reproduction of the compact disc 10 and presses the focus balance adjustment instruction key 62, the balance controller 600 determines YES in step 210,
The focus balance automatic adjustment process is performed in exactly the same manner as when the balance adjustment command is received from the system controller 64 (the process after step 203). In the above modification, the resistance adjustment may be switched in four or less steps or in six or more steps by the balance adjustment circuit.

In the above-described embodiments and modifications, even when reproduction of the compact disk is stopped, when the focus balance adjustment instruction key is pressed, the balance controller gives a servo-on command to the system controller to temporarily stop the operation. After the various servos are started, the balance adjustment processing may be executed.
In addition, a temperature sensor is provided in the set, and the balance controller constantly monitors the output of the temperature sensor during the reproduction of the compact disc, and automatically operates when the temperature reaches or exceeds a certain value. In particular, the balance adjustment processing may be executed. Further, even when the reproduction of the compact disc is stopped, when the temperature becomes equal to or higher than a certain value or when the temperature becomes equal to or less than the certain value, the system controller is notified. The balance adjustment process may be executed after a servo-on command is given and various servos are started up temporarily.

In the above-described embodiment and the modification, the balance is adjusted by switching the resistance of the subtractor that outputs the focus error signal. However, as shown in FIG. 10, the resistance of the subtractor 22A is fixed. While VCA
(Voltage-controlled amplifier) current-voltage converter 18
At 0, current-to-voltage conversion is performed on the (A + C) signal (photocurrent signal) (the current-to-voltage converter 20 has a fixed gain). The balance of the (A + C) 'signal may be changed by changing the gain of the voltage converter 180, thereby performing the balance adjustment.
In this case, the balance controller 60A may change the gain of the current-voltage converter 180 in a stepwise manner, and in the case of FIG. 1, fix the gain at a point where the absolute value of the output ΔL of the subtractor 58 is minimized. In the case of FIG. 7, the gain may be fixed at a position where the difference between the half of the time measured by the timer 68 and the time measured by the timer 80 is minimized. As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[0044]

As described above, according to the present invention , the sine wave
Generates a disturbance signal and applies it to the focus servo system.
RF signal created from the detection output of the pickup
Of the envelope and the lower peak of the envelope
The upper and lower peak levels, and
Find the middle level of the peak level,
Waveform the envelope as a threshold level
The difference between the duty when shaping and 50% will be the minimum
Since the balance adjustment control is performed as
When adjusting the impedance, prepare a special jig such as a jitter meter.
And focus balun automatically within the set
Can be adjusted, eliminating the need for manual adjustment work.
No.

[0045]

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a specific configuration diagram of a subtractor including a balance adjustment circuit.

FIG. 3 is a flowchart showing processing of a balance controller.

FIG. 4 is a diagram showing the relationship between the amount of defocus and the amplitude of an RF signal.

FIG. 5 is a waveform diagram showing a relationship between a disturbance signal and an RF signal.

FIG. 6 is an operation waveform diagram at the time of focus balance adjustment.

FIG. 7 is a partially omitted configuration diagram according to a modification of the present invention.

FIG. 8 is a flowchart showing processing of a balance controller.

FIG. 9 is an operation waveform diagram at the time of focus balance adjustment.

FIG. 10 is a partially omitted configuration diagram according to another modification of the present invention.

FIG. 11 is a configuration diagram of a conventional focus servo system.

FIG. 12 is an explanatory diagram showing a focus error detection method.

[Explanation of symbols]

 14 Optical Pickup 18, 20, 180 Current-Voltage Converter 22b Balance Adjustment Circuit 220, 22A Subtractor 40 Adder 42, 420 Oscillator 44 Detector 54, 56 S / H Circuit 58 Subtractor 60, 600, 60A Balance Controller 66 , 76 Waveform shaping circuit 68, 80 Timer

Claims (1)

(57) [Claims] 1. A focus error signal is generated by a focus error detection circuit from a detection output of a pickup, a phase error of the focus error signal is compensated, and the focus error signal is output to a focus driver. The focus driver drives a focus actuator. A focus servo system having a focus servo system and a balance adjustment circuit for performing focus balance adjustment, wherein at a predetermined time, a disturbance signal applying means for generating a sine wave disturbance signal and applying the signal to the focus servo system; Detecting means for detecting the envelope of the RF signal generated from the detection output of the above; detecting means for detecting the lower peak level and upper peak level of the envelope obtained by the detecting means; The middle of the two peak levels Seeking bell, the central level as the threshold level, a waveform shaping means for shaping the waveform of the envelope which has been determined by the detecting means, means for measuring the duty cycle of the output signal of the waveform shaping means
And the duty of the output signal of the waveform shaping means becomes 50%
And a control means for controlling the balance adjustment circuit as described above .