JP2733965B2 - Focus control circuit and optical disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial application field B Outline of the invention C Conventional technology (FIGS. 3 and 4) D Problems to be solved by the invention (FIGS. 3 and 4) E Means for solving the problems (FIGS. 1 and 2) F function (FIGS. 1 and 2) G embodiment (FIGS. 1 and 2) Effect of H invention A Industrial application field The present invention relates to a focus control circuit and light. The disk device is suitable for application to an optical disk device such as a compact disk (CD) player and a focus control circuit built in the optical disk device.

B. Outline of the Invention According to the present invention, in a focus control circuit and an optical disc device for adding a focus bias signal so that a reproduced RF signal is optimized with respect to a focus error signal, the focus RF signal is input in a state before focusing is performed. The focus error signal is converted into focus error data having a digital value, the average value data during the predetermined period is calculated, and then the focus zero detection signal is generated at the timing when the focus error data becomes equal to the average value data. With the transmission, it is possible to always shift to the focus pull-in state at an optimal timing regardless of the value of the focus bias signal added to the focus error signal.

C Conventional Technology Conventionally, in a conventional CD player, a biaxial device that holds an objective lens of an optical head is driven by using a focus control circuit based on, for example, an astigmatism method, whereby a laser beam is always just-formed on a compact disc. Some control is performed so that irradiation can be performed in a scum state.

Further, in the focus control circuit, prior to the focus servo operation, the objective lens is held.
The axis device is driven by a focus search signal having an arbitrary ramp function to execute a focus search operation, and a zero cross point of a focus error signal having an S-shaped curve obtained by this operation (hereinafter referred to as a focus zero cross point). (Referred to as (FZC)), the focus servo operation is shifted to the focus servo operation, so that the optical head objective lens can execute the focus servo operation from a state as close as possible to the just focus state. It has been made like that.

That is, as shown in FIG. 3, in the focus control circuit 1, a laser beam emitted from a semiconductor laser (not shown) is irradiated onto a compact disc (not shown), and its return light is reflected and Light is incident on the light receiving section 2 which is a divided light receiving element.

Thereby, the four light receiving elements 2A, 2B, 2C,
First, second, third and fourth light receiving outputs S obtained from 2D
_PDA, S _PDB, S _PDC and S _PDD, the first and third light receiving output S _PDA and S _PDC respectively, receiving the output of the second and 4 S _PDB and S _PDD are summed, the first and second Addition signals S _IN1 and S _IN
It is input to the focus error amplifier circuit 3 as _IN2 .

In the focus error amplifier circuit 3, the first and second
Signals S _IN1 and S _IN2 are converted from a current value to a voltage value through first and second buffer circuits 3A and 3B, respectively, and are converted by an operational amplifier through first and second input resistors R1 and R2, respectively. Is input to the inversion input terminal and the display inversion input terminal of the subtraction circuit 3C.

In the subtraction circuit 3C, an inverting input terminal is connected to a predetermined negative feedback resistor R3, also with a non-inverting input terminal is grounded through a predetermined resistance R4, the positive and between a negative power supply V _A and V _B connect a variable resistor VR1, the bias voltage V _BS obtained from made bias circuit 3D to obtain an arbitrary voltage is supplied from any contact.

The bias voltage _VBS is applied to each light receiving element 2 of the light receiving section 2.
It corrects the adjustment error in the characteristics on the variation or the optical system of A～2D, for example, first to fourth sum signal of the light receiving output S _PDA to S _PDD of the manufacturing process, i.e. monitoring the eye pattern of the reproduced RF signal The voltage value is adjusted to optimize this eye pattern.

Thus, the focus error amplifying circuit 3 converts the focus error signal S _FE by the astigmatism method using the four-division light receiving elements 2A to 2D as the output signal of the subtraction circuit 3C into the phase compensation circuit 4 and the operational amplifier. The signal is sent to the FZC detection circuit 5 comprising the comparison circuit 5A.

The FZC detection circuit 5 receives the focus error signal S
The _FE is compared with a predetermined reference voltage V _REF, while the voltage level of the Fuo Kas error signal S _FE is the reference voltage V _REF higher period,
An FZC detection signal S _FZC having a theoretical “H” level is sent to a servo control circuit 6 having a microcomputer configuration.

The phase compensating circuit 4, the phase of the input Fuo Kas error signal S _FE compensated in accordance with the servo characteristics, which as Fuo scum servo signal S _SB, Fuokasu switching circuit 7
To the first input terminal a.

A focus search signal S _FS given from a focus search circuit 8 under the control of the servo control circuit 6 is input to a second input terminal b of the focus switching circuit 7.

In addition, a switching control signal CNT _SW is input from the servo control circuit 6 to the focus switching circuit 7,
Thus, the output signal transmitted from the output terminal c of the focus switching circuit 7 is
Supplied to the focus coil 10A of the axis device 10, the two-axis device 10, that is, the objective lens
It is adapted to control the drive in response to S _SB or Fuo debris search signal S _FS.

In this focus control circuit 1, when a compact disc is mounted on a CD player, for example, the servo control circuit 6 first detects this based on a CD control signal CNT _CD obtained from a system control circuit (not shown). A switching control signal CNT _SW for selecting the second input terminal b is sent to the focus switching circuit 7, and a focus search control signal CNT _FS for instructing the focus search circuit 8 to start a focus search operation. Is sent.

Accordingly, the focus search circuit 8 supplies the focus search signal S _FS having a predetermined ramp function waveform to the focus coil 10A of the two-axis device 10 via the focus switching circuit 7 and the focus coil drive circuit 9. Then, the objective lens is gradually brought closer to the disc surface side of the compact disc from the reference position when the compact disc is not mounted.

At this time, the system control circuit emits a laser beam from a semiconductor laser, by receiving the reflected light by the light receiving section 2, Fuo Kas error signal S _FE obtained from Fuo Kas error amplifier circuit 3 is input to the FZC detecting circuit 5 Is done.

In practice, the focus error signal S _FE obtained at this time is
As shown in FIG. 4 (A), as shown in FIG. 4 (A), corresponding to the search time according to the distance between the objective lens and the disk surface, the level sequentially rises from the 0 level to the maximum value, and then crosses the 0 level to the minimum. falling to a value, further followed it in the S-shaped curve to rise to 0 level, FZC detecting circuit 5 Fuo scum error signal S _FE is the reference voltage V _REF (in this case, the reference voltage V
_REF is, FZC detection signal S _FZC (Fourth having from time t ₀ to be higher than become a voltage value 0 [V]), during the period until time t ₁ that crosses the reference voltage V _REF, a logic "H" level (B) is sent to the servo control circuit 6.

As a result, the servo control circuit 6 detects the falling timing of the FZC detection signal S _FZC and sends a switching control signal CNT _SW for selecting the first input terminal a to the focus switching circuit 7 at this timing, A focus search control signal CNT _FS for instructing the focus search circuit 8 to end the focus search operation is transmitted.

Thus Fuokasu control circuit 1, the compact disc is attached to the CD player, the Fuo Kas coil 10A of the biaxial device 10 for holding the objective lens, perform a Fuo Kas search operation by driving in Fuo Kas search signal S _FS Then, the focus search operation is terminated at the timing when the focus zero cross point of the focus error signal S _{FE having} the S-shaped curve obtained is detected, and the focus servo signal S _SB obtained from the phase compensation circuit 4 is changed. By driving the focus coil 10A of the two-axis device 10 using this, the operation shifts to a focus servo operation.

In will to problems way Fuokasu control circuit 1 of this configuration Solved D invention, the bias voltage V _BS is added to the subtraction circuit 3C of Fuo Kas error amplifier circuit 3, the first to fourth light receiving output S _PDA to S By optimizing the eye pattern of the sum signal of the _PDD , that is, the reproduced RF signal, the dispersion of the four-divided light receiving elements 2A to 2D of the light receiving unit 2 and the adjustment error of the optical system are corrected.

However, in the focus control circuit 1, the open loop control is actually performed during the focus search operation, and the focus search signal S _FS generated by the focus search circuit 8 is transmitted to the focus switching circuit 7 and the focus coil drive circuit 9 To the focusing coil 10A of the two-axis device 10 via the.

Therefore, in the Fuo Kas search In operation, Fuo Kas error signal S _FE obtained from Fuo Kas error amplifier circuit 3, the offset voltage V _OFF corresponding to the bias voltage V _BS
Occurs.

As shown in FIG. 4C, in the case of the focus error signal S _{FE1 having} the positive offset voltage V _OFF1 as the focus error signal S _FE having the offset voltage V _OFF , for example, as shown in FIG. from a positive offset voltage level of the voltage V _OFF1, after One rising to FIG. 4 (a) that is, the voltage level obtained by adding the offset voltage V _OFF1 to the maximum value of the standard Fuo Kas error signal S _FE, offset voltage V _OFF1 A standard focus error signal S
_Fall to the voltage level obtained by subtracting the offset voltage V _OFF1 from the minimum value of _FE , and then reset to the voltage level
It has an S-shaped curve that rises to the voltage level of V _OFF1 .

Therefore, the FZC detection signal S obtained from the FZC detection circuit 5
_FZC1 has a standard _focus error signal S _FE equal to the reference voltage V
Time point t ₁₁ delayed by a predetermined time τ ₀ from time point t ₁ crossing _REF
Falls to the logical “L” level at the timing of
(D).

Conversely, in the case of the _focus error signal S _FE2 in which the negative _offset voltage V _OFF2 is generated, as shown in FIG. 4 (E), the standard focus voltage is _{shifted from} the voltage level of the negative _offset voltage V OFF2. After the voltage _rises to a voltage level _obtained by adding the _offset voltage V _OFF2 to the maximum value of the error signal S _FE , and _crosses the voltage level of the _offset voltage V _OFF2 , the _offset voltage decreases from the minimum value of the standard _focus error signal S _FE. V _OFF2
, And then falls to a voltage level obtained by subtracting, and then rises to the voltage level of the _offset voltage V _OFF2 .

Therefore, the FZC detection signal S obtained from the FZC detection circuit 5
_FZC2 the standard Fuo Kas error signal S _FE is 0 from the time t ₂₁ which is delayed from the time t ₀ for a predetermined time tau ₁ across the rising reference voltage V _REF from the level, the standard Fuo Kas error signal S _FE is the reference voltage Predetermined time τ ₂ from time t ₁ crossing V _REF
For only a period of earlier time t _22, it has a logic "H" level (FIG. 4 (F)).

When the offset voltage V _OFF occurs in the focus error signal S _FE as described above, an error occurs at the time when the FZC detection signal S _FZC obtained from the FZC detection circuit 5 falls. When the lens is not in the just-focused state, there is a possibility that the lens shifts to the focus servo operation. As a result, the lens cannot be shifted to the focus servo operation once, and the focus search operation is performed many times. There is a problem that fluttering occurs in the two-axis device 10.

In order to solve this problem, the focus control circuit 1 described above is used.
In the voltage value of the reference voltage V _REF applied to the comparator circuit 5A for FZC detecting circuit 5, which was made to be equal to the offset voltage V _OFF which occurs in Fuo Kas error signal S _FE is proposed.

However, in this case, as shown in FIG. 4 (G), if the _focus error signal _SFE3 obtained during the focus search operation contains many noise components, the FZC detection is performed according to the noise components. The logic level of the signal S _FZC3 changes frequently, so that in the servo control circuit, for example,
When the FZC detection signal S _FZC3 has a logic “H” level for a predetermined time or more, a complex judgment circuit is required to use this as a correct FZC detection signal S _FZC , which eventually _{results in a} complicated and large circuit configuration as a whole. However, the solution was still insufficient.

The present invention has been made in view of the above points, and has a focus control circuit and a focus control circuit which can always shift from a focus search operation to a focus servo operation at an optimal timing regardless of an offset voltage generated in a focus error signal. An optical disk device is proposed.

Means for Solving E Problem In order to solve such a problem, the present invention provides focus control in which a focus bias signal V _BS is added to a focus error signal S _{FE so} that a reproduced RF signal is optimized. In the circuit 10, analog digital conversion means 21 for converting the focus error signal S _FE into focus error data DT _FE having a digital value, and calculating and averaging an average value of the focus error data DT _{FE for} a predetermined period. An average value calculating means 25 for obtaining the value data DT _REF2 is provided.

F operation In a state before focusing, the average value data DT _REF2 of the focus error data DT _{FE for} a predetermined period is calculated, and then the focus error data DT _FE is converted to the average value data.
By sending the _focus zero detection signal DT _FZC at a timing equal to DT _REF2 , the focus bias signal V _BS added to the _focus error signal S _FE
As a result, even when the offset voltage V _OFF occurs, it is possible to always shift to the focus pull-in state at an optimal timing.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1 in which parts corresponding to those in FIG. 3 are assigned the same reference numerals, reference numeral 20 denotes a focus control circuit according to the present invention as a whole, and a focus error signal S _FE obtained from the focus error amplifier 3 is The signal is input to an analog-to-digital conversion circuit 21, whereby a timing control circuit 2 is provided based on a clock signal CLK obtained from a system control circuit 22.
At the timing of the timing clock CLK _GEN generated in 3 it is converted to Fuo Kas error data DT _FE consisting of digital data.

The focus error data DT _FE is a digital signal processing processor having a microcomputer configuration, and performs a digital processing at a timing of a timing clock CLK _GEN obtained from a timing control circuit 23 and an FZC detection circuit 25. Is input to

The phase compensating circuit 24 digitally compensates the phase of the input focus error data DT _FE according to the focus servo characteristics, and uses this as the focus servo data DT _SB to output the first input of the focus switching circuit 7. Input to terminal a. Further, the FZC detection circuit 25, based on the FZC control signal CNT _FZC obtained from the system control circuit 22,
The ZC detection processing program SP1 is executed, and FZC detection data DT _FZC corresponding to the FZC detection result obtained thereby is sent to the servo control circuit 26.

The servo control circuit 26 _{creates a focus} search control signal CNT _FS1 based on the servo control signal CNT _SB input from the system control circuit 22 and the FZC detection data DT _FZC obtained from the FZC detection circuit 25, and performs a focus search. In addition to controlling the circuit 27, the switching control signal CNT _SW1 is generated to selectively control the input terminal of the focus switching circuit 7.

The focus search circuit 27 generates, based on the focus search control signal CNT _FS1 , focus search data DT _FS whose value gradually increases in accordance with a predetermined ramp function. 2 to the input terminal b.

Output data transmitted from the output terminal c of the focus switching circuit 7 is input to a PWM (pulse width modulation) decoding circuit 28, and is decoded by, for example, a PWM modulation method.
Thus the Fuo Kas coil driving circuit 9 that follows the decoding signal obtained is sent as Fuo scum coil drive signals S _DV.

Thus, the focus coil drive signal S _DV is supplied to the focus coil 10A of the two-axis device 10 via the focus coil drive circuit 9, and the two-axis device 10, ie, the objective lens, is moved to the focus servo data DT _SB or the focus servo data DT _SB . It is adapted to drive in accordance with the search data DT _FS.

In the above configuration, for example, when a compact disc is mounted on a CD player, the system control circuit 22 sends a servo control signal CNT _SB to the servo control circuit 26, and the servo control circuit 26 is obtained from the FZC detection circuit 25. Control to wait for FZC detection data DT _FZC input.

In addition, the system control circuit 22
FZC control signal CNT _FZC to execute FZC detection operation for 5
, And the FZC detection circuit 25 starts executing the FZC detection processing program SP1 (FIG. 2).

That is, the FZC detection circuit 25 executes the FZC detection processing program SP
In step 1, the internal counter X is set to a value "0" in the next step SP2, and the internal maximum value data DT _MAX and the minimum value data DT _MIN are set to a value "0" in a subsequent step SP3 for initialization. Then, in the subsequent step SP4, the value "64" is set in the internal counter N, and the process proceeds to the next step SP5.

In step SP5, the FZC detection circuit 25 outputs the focus error data obtained from the analog digital conversion circuit 21.
DT _FE is input, the focus error data DT _FE and the maximum value data DT _MAX input in the next step SP6 are compared, the maximum value data DT _MAX is updated using data having a large value, and the next step is performed. In SP7, the focus error data DT _FE and the minimum value data DT _MIN input are compared, and the minimum value data DT _MIN is updated using data having a small value.

Subsequently, the FZC detection circuit 25 decrements the internal counter N in step SP8, determines whether or not the internal counter N is equal to or less than the value "0" in the next step SP9, and if a negative result is obtained here, proceeds to step SP5. back, running step SP5-SP6-SP7-SP8 described above to enter a new Fuo Kas error data DT _FE, the maximum value data DT _MAX and minimum value data DT for the Fuo Kas error data DT _FE
Perform _MIN update processing.

Eventually (in the case of this embodiment, the above-mentioned steps SP5-SP6
-Execute the processing loop of -SP7-SP8 64 times) Step SP9
If an affirmative result is obtained in step (2), in the next step SP10, the FZC detection circuit 25 performs the above-described steps SP5-SP6-SP7-SP8.
Using the maximum value data DT _MAX and the minimum value data DT _MIN of the 64 focus error data DT _FE obtained by repeating the processing loop of 64 times, the following equation: After calculating the primary average value data DT _REF1 expressed by
Next, the procedure moves to step SP11.

In step SP11, the FZC detection circuit 25 outputs the primary average value data DT obtained in step SP10.
_REF1 is stored in an internal register MX in which the value of the internal counter X is used as an argument.

Subsequently, in step SP12, the FZC detection circuit 25 increments the internal counter X, and then proceeds to the next step SP12.
In step 13, it is determined whether or not the internal counter X is greater than the value "3". If a negative result is obtained here, the process returns to step SP3, where steps SP3-SP4 and steps SP5-SP6-SP7 described above are performed.
The primary loop obtained by using the maximum value data DT _MAX and the minimum value data DT _MIN of the new 64 focus error data DT _FE by executing the processing loop of SP 8 and the steps SP 10 -SP 11 -SP 12 The value data DT _REF1 is stored in the internal register MX.

When the FZC detection circuit 25 obtains an affirmative result in step SP13, in the next step SP14, the four 1s stored in the internal registers M0 to M3 as described above.
Using the next average value data DT _REF1 , To obtain the secondary average value data DT _REF2 represented by

The secondary average value data DT _REF2 is an average value of the focus error data DT _FE when neither the focus search operation nor the focus servo operation is performed,
The bias voltage V applied to the focus servo amplifier circuit 3 after eliminating the influence of the noise component as much as possible.
Indicates _BS .

Subsequently, in step SP14, the FZC detection circuit 25 sends FZC detection data _DTFZC indicating the start of the focus search operation to the servo control circuit 26.

As a result, the servo control circuit 26 sends out the focus search control signal CNT _FS1 for instructing the focus search operation to start the focus search operation to the focus search circuit 27 and the second input to the focus switching circuit 7. The switching control signal CNT _SW1 for selecting the end b is transmitted.

Thus Fuo Kas search circuit 27 generates a Fuo Kas search data DT _FS, which Fuokasu switching circuit 7
Then, the signal is decoded via the PWM decode circuit 28 and sent to the subsequent focus coil drive circuit 9, thereby controlling the focus coil 10A of the biaxial device 10 to start the focus search operation.

Subsequently FZC detecting circuit 25, the next step SP16, type the Fuo Kas error data DT _FE obtained Te cowpea to Fuo Kas search operation continues Fuo Kas error data DT _FE inputted in step SP17 is, the above-mentioned step SP2~ step equal whether the determined to the value of the average secondary value data DT _REF2 or bias voltage V _BS was collected using SP14 Niyotsu, connexion returns to step SP16 to obtain a negative result, new Fuo Kas error data The above processing is repeated for DT _FE .

Eventually, when the FZC detection circuit 25 obtains an affirmative result in step SP17 (that is, this means that the bias voltage V _BS
Indicates that a focus zero crossing point of the focus error signal S _FE having an S-shaped curve including the SZ curve has been detected.) In the next step SP18, servo control is _performed on the FZC detection data DT _FZC indicating the end of the focus search operation. Circuit 26
And in the following step SP19, the FZC detection processing program SP1 ends.

As a result, the servo control circuit 26 sends out the focus search control signal CNT _FS1 for instructing the focus search operation to end the focus search operation to the focus search circuit 27 and the first input to the focus switching circuit 7. The switching control signal CNT _SW1 for selecting the terminal a is transmitted.

Thus, the focus servo data DT _SB obtained from the phase compensating circuit 24 via the focus switching circuit 7 is input to the PWM decoding circuit 28, which decodes the data and sends it out to the subsequent focus coil driving circuit 9, and Axis device 10
The focus servo operation is started by controlling the focus coil 10A.

In this way, when the compact disk is mounted, the focus control circuit 20 first digitizes the focus error signal S _FE obtained from the focus amplifying circuit 3 and averages the focus error data DT _{FE for} a predetermined period. From the data DT _REF2 , the bias voltage V _BS applied to the focus amplification circuit 3 is obtained.

Subsequently Fuokasu control circuit 20, a Fuo Kas coil 10A of the biaxial device 10 for holding the objective lens, running Fuo Kas search operation by driving with Fuo Kas search data DT _FS, S-shaped thereby obtained the equal timing to the average value data DT _REF2 which Fuo Kas error data DT _FE comprising a curve is at a bias voltage V _BS, detects a Fuo scum zero crossing point, and ends the Fuo Kas search operation at this timing, a phase compensation circuit by driving the Fuo Kas coil 10 of the biaxial device 10 using Fuo Kas servo data DT _SB obtained from 24, it is adapted to shift to Fuo Kas servo operation.

According to the above configuration, the average value data DT _REF2 of the focus error data DT _FE obtained by digitizing the focus error signal S _FE obtained from the focus amplifying circuit 3 is given to the focus amplifying circuit 3. The bias voltage V _BS is obtained, and the timing at which the focus error data DT _FE formed of an S-shaped curve obtained by the focus search operation becomes equal to the average value data DT _{REF2 formed of the} bias voltage V _BS is defined as a focus zero cross point. The focus search operation is terminated at this timing, and the focus coil 10 of the two-axis device 10 is used using the focus servo data DT _SB obtained from the phase compensation circuit 24.
Migration by which is adapted to start driving the A to Fuo Kas servo operation, regardless of the offset voltage V _OFF which occurs in Fuo Kas error signal S _FE, always at the right time from Fuo Kas search operation in Fuo Kas servo operation The focus control circuit 20 can be realized. According to a further configuration described above, when a noise component is often generated Fuo scum error signal S _FE obtained during Fuo Kas search operation, by modifying the calculation equation described above for (2),
The following formula, Using, in obtaining the second average value data DT _REF2, the if to apply the off-excisional data DT _OFFSET corresponding to the level of the noise component, effectively preventing the Fuo Kas zero-crossing point of the erroneous detection due to noise The obtained focus control circuit 20 can be realized.

In the above embodiment, the average value data DT of the focus error data DT _FE is included in the FZC detection processing program.
_REF2, i.e. has been to determine the bias voltage V _BS is found given to Fuo Kas servo amplifier circuit 3, instead of this, for example, using a low-pass filter of the digital signal processing processor configuration, predetermined Fuo Kas error data DT _FE The average value of the period may be obtained.

Further, in the above-described embodiment, the focus search data DT obtained from the output terminal c of the focus switching circuit 7 is used.
_{The FS} or the focus servo data DT _SB is PWM-modulated and used as the focus coil drive signal S _DV. Alternatively, for example, the focus coil drive signal is converted into an analog signal via a digital-to-analog conversion circuit.
Even when the S _DV is obtained, the same effect as in the above embodiment can be obtained.

Further, in the above-described embodiment, the case where the present invention is applied to the focus control circuit that performs focus control by the astigmatism method has been described. However, the present invention is not limited to this, and may be applied to a focus control circuit that performs other focus control. Widely applicable.

Further, in the above-described embodiment, a case has been described in which the present invention is applied to a focus control circuit of an optical disc device such as a CD player. However, the present invention is not limited to this, and for example, a magneto-optical disc device, an optical tape device, etc. It is suitable for being widely applied to a focus control circuit of an optical recording / reproducing apparatus.

H Advantageous Effects of the Invention As described above, according to the present invention, in a focus control circuit that adds a focus bias signal to a focus error signal so as to optimize a reproduction RF signal, an input before focus pull-in is performed. The converted focus error signal is converted into focus error data consisting of digital values, average value data during the predetermined period is calculated, and then focus zero detection is performed at a timing when the focus error data becomes equal to the average value data. By transmitting the signal, it is possible to realize a focus control circuit and an optical disk device that can shift to the focus pull-in state at an optimum timing regardless of the value of the focus bias signal added to the focus error signal. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a flowchart for explaining the operation of the FZC detection circuit, FIG. 3 is a block diagram showing a conventional focus control circuit, and FIG. FIG. 4 is a signal waveform diagram for explaining the operation. 1, 20: Focus control circuit, 5, 25: FZC detection circuit, 21: Analog digital conversion circuit, S _FE: Focus error signal, DT _FE: Focus error data,
DT _REF2 …… Average value data, V _BS …… Offset voltage.

Claims (2)

(57) [Claims] 1. A focus control circuit for adding a focus bias signal to a focus error signal so as to optimize a reproduced RF signal, wherein the focus error signal is converted into focus error data having a digital value. Analog digital conversion means; and average value calculating means for calculating an average value of the focus error data during a predetermined period to obtain average value data, wherein a predetermined value of the focus error data is obtained before focusing. A focus control circuit for calculating average value data during a period, and subsequently transmitting a focus zero detection signal at a timing when the focus error data becomes equal to the average value data. 2. A means for generating a focus error signal and a reproduction signal based on light reflected from an optical disk; and an analog / digital conversion means for converting the focus air signal into focus error data having a digital value. Opening and closing means for opening and closing the focus servo loop; measuring means for measuring the maximum value and the minimum value of the focus error data in a state where the focus servo loop is open; Average value calculating means for calculating the average value of the focus error data based on the maximum value and the minimum value; and comparing the average value calculated by the average value calculating means with the focus error data to form the focus error data. A focus zero-cross signal generating means for generating a cas zero-cross signal, and a focus zero-cross signal generating means. That it comprises a control means for controlling the opening and closing means to close the Fuo Kas servo loop based on Fuo Kas zero cross signal generated of the light-disc device according to claim.