JPH0724111B2 - Focus servo gain adjustment circuit for optical disc playback device - Google Patents

Description

The present invention relates to an optical disc reproducing device such as a compact disc player, and more particularly to a focus servo gain adjustment for automatically adjusting the focus servo gain thereof. Regarding circuit improvement.

(Prior Art) As is well known, in the field of audio equipment, image equipment, etc., an information signal is converted to digital data and recorded on a disc in order to achieve high density and high fidelity recording / reproduction. However, an optical disc reproducing apparatus that reads digital data from the disc by using an optical pickup is becoming widespread. When reproducing a disc, this type of optical disc reproducing apparatus first moves the objective lens of the optical pickup to the vicinity of the in-focus position by the focus search means, and then holds the objective lens at the in-focus position by the focus servo means. I am trying.

By the way, in practice, before doing a focus search,
The focus servo gain is adjusted by moving the objective lens of the optical pickup largely in the focus direction and determining the level of the focus error signal obtained when the objective lens passes near the in-focus position. There is.

FIG. 4 shows such conventional focus servo gain adjusting means. That is, reference numeral 11 in the drawing denotes a photodetector installed in the optical pickup, which receives the reflected light of the laser beam applied to the disc through an objective lens (not shown). This photodetector 11 has a so-called four-divisional type having four light receiving regions a to d, and has a light receiving region a, c and b, d.
The signals output from each are current-added.
The subtraction circuit 12 subtracts both of these addition signals to generate a focus error signal FE corresponding to the deviation of the objective lens from the in-focus position.

Here, the focus error signal FE is supplied to the first fixed contact 14a of the switch circuit 14 via the variable gain amplifier circuit 13. Further, the lens drive signal output from the lens drive signal generation circuit 15 is supplied to the second fixed contact 14b of the switch circuit 14. Then, the focus error signal FE and the lens drive signal are selectively supplied to the phase compensation circuit 16 by the switch circuit 14.
And a focus actuator coil for moving the objective lens in the focus direction via the drive circuit 17.
It is designed to be supplied to 18.

Further, the focus error signal FE is supplied to the FE level detection circuit 19 and its level is detected. The FE level detecting circuit 19 controls the gain of the variable gain amplifying circuit 13 according to the level of the detected focus error signal FE to adjust the focus servo gain. The switch circuit 14 and the lens drive signal generation circuit 15 are controlled by the focus control circuit 20.

When the reproduction of the disc is requested, the focus control circuit 20 controls the switch circuit 14 to the switching state shown in the figure and drives the lens drive signal generation circuit 15 to drive the lens drive signal generation circuit 15 as shown in FIG. It generates a low frequency lens drive signal. Then, this lens drive signal is supplied to the focus actuator coil 18 via the switch circuit 14, the phase compensation circuit 16, and the drive circuit 17, and the fifth
As shown in FIG. 6B, the position L of the objective lens is largely moved in the focus direction in response to the lens driving signal.

Then, when the objective lens passes the in-focus position F,
As shown in FIG. 5 (c), the focus error signal FE is obtained from the subtraction circuit 12. Then, the level of the focus error signal FE obtained at this time is
The gain of the variable gain amplifier circuit 13 is set by the detection by the FE level detection circuit 19.

After that, when a focus search is performed by a focus search means (not shown in FIG. 4), the focus control circuit 20 controls the switch circuit 14 to the switching state opposite to that shown in the drawing, and the lens drive signal generation circuit 15 drives the lens. Stop signal generation. Then, after that, the objective lens is controlled based on the focus error signal FE output from the subtraction circuit 12, and the focus servo is performed by the gain of the variable gain amplifier circuit 13 to reproduce the disc. Is.

However, the conventional focus servo gain adjusting means as described above has the following problems. That is, the lens drive signal must have an amplitude that allows the objective lens to be moved over the entire movable range thereof, so that its cycle becomes 0.5 to 1 sec. Further, the focus error signal FE is generated only when the objective lens reaches the vicinity of the in-focus position, so that the focus error signal is generated only twice in one cycle period of the lens drive signal. Become.

Therefore, the FE level detection circuit 19 causes the focus error signal
When detecting the FE level, since only a few focus error signals can be taken in, accurate level detection cannot be performed, which in turn makes it impossible to perform accurate focus servo gain adjustment. In particular, since the focus error signal FE may not be accurately generated due to the effect of scratches on the disc, this problem becomes more serious.

Therefore, in order to solve the above problem, if a large number of focus error signals FE are input to the FE level detection circuit 19 for accurate level detection, a lens drive signal for several cycles is required, and this is only for focus servo gain adjustment. Therefore, a lot of time is spent, and there is a problem that it takes time from when the disc is requested to be reproduced until the sound is actually produced.

(Problems to be Solved by the Invention) As described above, the conventional focus servo gain adjusting means has a problem that it is difficult to perform accurate gain adjustment, and the adjustment time is long.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an extremely good focus servo gain adjustment circuit for an optical disc reproducing apparatus capable of performing accurate focus servo gain adjustment in a short time. .

[Structure of the Invention] (Means for Solving Problems) That is, in the focus servo gain adjusting circuit of the optical disc reproducing apparatus according to the present invention, the objective lens is focused on the basis of the signal read by the optical pickup. When the position has been reached, the polarity of the output of the lens drive signal generator is inverted and the objective lens is vibrated in the vicinity of the in-focus position.

(Operation) According to the above configuration, the objective lens passes through the in-focus position a plurality of times in one cycle period of the lens drive signal.
FE can be obtained, and accurate focus servo gain adjustment can be performed in a short time.

(Embodiment) Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as those in FIG. 4 are designated by the same reference numerals, and only different parts will be described here. That is, the focus error signal FE is supplied to the lens drive signal generation circuit 15, and the focus error signal FE is supplied.
Is different from the conventional one in that the polarity of the output of the not-shown lens drive signal generating section provided in the lens drive signal generating circuit 15 is inverted every time the power is supplied.

It should be noted that an RF signal is generated by the addition circuit 21 adding together the two addition signals obtained by current addition of the signals output from the light receiving regions a, c and b, d. This RF signal is supplied to a signal processing circuit system (not shown) via the output terminal 22, undergoes data generation and error correction processing, and is then converted into an analog signal and reproduced.

According to the above configuration, if a lens drive signal is generated at time T1 in FIG. 2 as shown in FIG. 2A, the position L of the objective lens is changed as shown in FIG. Be changed. Then, when the objective lens passes the in-focus position F at time T2, the subtraction circuit 12 generates a focus error signal FE as shown in FIG. 2 (c). Further, at this time, the level of the RF signal generated from the adder circuit 21 becomes the maximum as shown in FIG.

Then, at the timing when the focus error signal FE is no longer generated at time T2, the polarity of the output of the generation unit of the lens drive signal generation circuit 15 is inverted, and the lens drive signal is changed to the second value.
As shown in FIG. Then, at time T3, the objective lens again passes through the in-focus position F, and the focus error signal FE is obtained. and again,
The polarity of the output of the generation section of the lens drive signal generation circuit 15 is inverted, and the above operation is repeated thereafter.

Therefore, the objective lens passes through the in-focus position F a plurality of times during one period of the lens drive signal, and a plurality of focus error signals FE can be obtained in a short time. Since the level of the focus error signal FE can be detected, accurate focus servo gain adjustment can be performed.

Next, FIG. 3 shows a modification of the above embodiment.
That is, by the RF signal output from the adder circuit 21,
The polarity of the output of the generation unit of the lens drive signal generation circuit 15 is inverted.

With such a configuration, as shown in FIG. 2, the RF signal is generated at the same time as the focus error signal FE, so that the same effect as that of the above embodiment can be obtained.

Further, the signal serving as a trigger for inverting the polarity of the output of the generation unit of the lens drive signal generation circuit 15 is not limited to the focus error signal FE, the RF signal, etc., but determines that the objective lens has reached the in-focus position. Any signal that can be used can be used.

The present invention is not limited to the above-described embodiment, and can be variously modified and implemented without departing from the scope of the invention.

[Effects of the Invention] Therefore, as described in detail above, according to the present invention, it is possible to provide a very good focus servo gain adjustment circuit for an optical disc reproducing apparatus, which can perform accurate focus servo gain adjustment in a short time. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a focus servo gain adjusting circuit of an optical disk reproducing apparatus according to the present invention, FIG. 2 is a timing diagram for explaining the operation of the embodiment, and FIG. FIG. 4 is a block diagram showing a modified example of the embodiment, and FIG. 4 and FIG. 5 are a block diagram showing a conventional focus servo gain adjusting means and a timing diagram for explaining the operation thereof. 11 ... Photo detector, 12 ... Subtraction circuit, 13 ... Variable gain amplification circuit, 14 ... Switch circuit, 15 ... Lens drive signal generation circuit, 16 ... Phase compensation circuit, 17 ... Drive circuit, 18 ... Focus actuator coil, 19 …… FE
Level detection circuit, 20 ... Focus control circuit, 21 ... Addition circuit, 22 ... Output terminal.

Claims (1)

[Claims] 1. An optical disc reproducing apparatus for reading a signal from a disc through an optical pickup, comprising a generator for generating a lens driving signal of a predetermined frequency, and an objective lens of the pickup in a focusing direction. Lens driving means for moving the objective lens to the focus position, focus servo means for generating a focus error signal based on the signal read by the pickup, and holding the objective lens at a focus position, and the objective lens is moved by the lens driving means. In the focus servo gain adjusting circuit for adjusting the gain of the focus servo means according to the output of the detecting means, the focus driving signal is detected by the lens driving means. With the objective lens being moved, The objective lens is provided with means for deciding that the objective lens has reached the in-focus position based on the signal read by the pickup and inverting the polarity of the output of the lens drive signal generating section. A focus servo gain adjusting circuit for an optical disc reproducing apparatus, wherein the focus servo gain adjusting circuit is configured to vibrate about a position.