JPS6344324A - Focus servo gain adjusting circuit for optical disk reproducing device - Google Patents

Abstract

PURPOSE:To execute the correct focus servo gain adjustment for a short time by oscillating an objective lens near a focus point position. CONSTITUTION:A focus error signal FE from a subtracter circuit 12 is supplied to a lens driving signal generating circuit 15. The generating circuit 15 inverts the polarity of a lens driving signal each time of a focus error signal is supplied. Thus, in one cycle period of a lens driving signal, since the objective lens passes through a focus point position plural times, plural focus error signals FE can be obtained, the level detection of the focus error signals FE can be correctly executed by an FE level detecting circuit 19 and consequently, the correct focus servo gain adjustment can be performed for a short time.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical disc playback device such as a compact disc player, and particularly to a focus servo gain adjustment that automatically adjusts the focus servo gain of the optical disc playback device, such as a compact disc player. Regarding circuit improvement.

(Prior Art) As is well known, in the fields of sound equipment and image production equipment, information signals are converted to digital data and recorded on discs in order to record and reproduce data with as high density and high fidelity as possible. recorded in
Optical disc playback devices that read digital data from the disc using an optical pickup are becoming popular. This divine optical disc playback device is
When playing a disc, the objective lens of the optical pickup is first moved to the vicinity of the focused position by the focus search means, and then the objective lens is held at the focused position by the focus servo means.

By the way, in practice, before performing a focus search,
The gain of the focus servo 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 a conventional focus servo gain adjustment means. That is, 11 in the figure is a photodetector installed in the optical pickup,
The reflected light of the laser beam irradiated onto the disk is received through an objective lens (not shown). This photodetector 11 is configured in a so-called 4-division type having four light-receiving areas a to d.
Currents are added to the signals output from , d, and d, respectively. These added signals are subtracted by a subtraction circuit 12 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 second fixed contact 14b of the switch circuit 14 includes a lens drive signal generation circuit 15.
A lens drive signal output from the lens drive signal is supplied. The focus error signal FE and lens drive signal are selectively supplied by a switch circuit 14 via a phase compensation circuit 16 and a drive circuit 17 to a focus actuator coil 18 that moves the objective lens in the focus direction. It is done like this.

Further, the focus error signal FE is supplied to an FE level detection circuit 19, and its level is detected. The FE level detection circuit 19 has the function of adjusting the focus servo gain by increasing the gain of the variable gain amplifier circuit 13 by 1ilIIl[l according to the level of the detected focus error signal FE. Further, the switch circuit 14 and the lens drive signal generation circuit 15 are
By the focus control circuit 20! controlled.

Here, when reproduction of the disc is requested, the focus control circuit 20 controls the switch circuit 14 to the switching state shown, and also drives the lens drive signal generation circuit 15, as shown in FIG. 5(a). A low-frequency lens drive signal is generated. Then, this lens drive signal is supplied to the focus actuator coil 18 via the switch circuit 141, phase compensation circuit 16, and drive circuit 17, and as shown in FIG. 5(b), the position of the objective lens is adjusted according to the lens drive signal. It is moved largely in the focus direction in response to the signal.

Then, when the objective lens passes through the focal point position F,
A focus error signal FE can be obtained from the subtraction circuit 12 as shown in FIG. 5(C). and,
By detecting the level of the focus error signal @FE obtained at this time by the FE level detection circuit 19,
The gain of the variable gain amplifier circuit 13 is now set.

Thereafter, when a focus search is performed by a focus search means not shown in FIG. Stop the signal generation. Then, from then on,
The objective lens is controlled based on the focus error signal FE output from the subtraction circuit 12, and focus servo is performed using the gain of the variable gain amplifier circuit 13, so that the disc is reproduced.

However, with the conventional focus servo gain adjusting means as described above, the following problems occur. That is, since the lens drive signal must have an amplitude that can move the objective lens over its entire movable range, its period is long, 0.5 to 1 sec. Furthermore, since the focus error signal FE is generated only when the objective lens reaches the vicinity of the in-focus position, the focus error signal is generated only twice in one period of the lens drive signal. Become.

Therefore, when the FE level detection circuit 19 detects the level of the focus error signal FE, only a few focus error signals can be taken in, making it impossible to accurately detect the level, which in turn makes it impossible to perform accurate focus servo gain adjustment. occurs. In particular, because the focus error signal FE may not be generated accurately due to the effects of scratches on the disc, etc., this problem is even worse. It has become serious.

Therefore, in an attempt to solve the above problem, if a large number of focus error signals FE are input to the FE level detection circuit 19 to perform accurate level detection, several periods of lens drive signals are required, and only one cycle is required for focus servo gain adjustment. This results in a problem in that l[tl becomes distorted between the request for disc playback and the actual sound output.

(Problems to be Solved by the Invention) As described above, the conventional focus servo gain adjustment means requires accurate gain adjustment, and also has the problem of requiring a long adjustment time. .

Therefore, the present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an extremely good focus servo gain adjustment circuit for an optical disc playback device that can perform accurate focus servo gain adjustment in a short time. .

[Structure of the Invention] (Measures for Solving Problems Q) That is, the focus servo gain adjustment circuit of the optical disc playback device according to the present invention adjusts the focus of the objective lens based on the signal read by the optical pickup. It is determined that the focus position has been delayed, and the polarity of the output of the lens drive signal generator is inverted, so that the objective lens is photographed near the focus position.

(Function) According to the above configuration, the objective lens passes through the in-focus position multiple times during one period of the lens drive signal, so it is possible to obtain multiple focus error signals FE. This makes it possible to perform accurate focus servo gain adjustment in a short time.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 4 are indicated by the same symbols, and only the different parts will be explained here. That is, the focus error signal FE is supplied to the lens drive signal generation circuit 15, and each time the focus error signal FE is supplied, the lens drive signal generation circuit 15
The difference from the conventional method is that the polarity of the output of a lens drive signal generating section (not shown) provided inside the lens drive signal is inverted.

Note that the added signals obtained by adding the currents of the signals output from the light receiving areas a, C, S, and d, respectively, are added in the adding circuit 21 to generate an RF multiplied signal. This RF multiplied signal is supplied to a signal processing circuit system (not shown) via the output terminal 22, and after being subjected to data generation and error correction processing, it is 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. 2(a), the position ML of the objective lens is changed as shown in FIG. be changed. Then, at time T2, the objective lens moves to the in-focus position F.
, the taper reduction circuit 12 generates a focus error signal FE as shown in FIG. 2(C). Further, at this time, the RF multiplied signal level generated from the adder circuit 21 is as high as the level of the eel, as shown in FIG. 2(d).

Then, at the timing when the focus error signal FE is no longer generated at time T2, the polarity of the output of the generating section of the lens drive signal generation circuit 15 is reversed, and the lens drive signal becomes as shown in FIG. 2(a). . Then, at time T3, the objective lens passes through the in-focus position F again,
A focus error signal FE can now be obtained. Then, the polarity of the output from the generating section of the lens drive signal generating circuit 15 is again inverted, and such an operation is repeated thereafter.

Therefore, the objective lens passes through the in-focus position F multiple times during one period of the lens drive signal, and multiple focus error signals FE can be obtained in a short period of 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, the polarity of the output of the generating section of the lens drive signal generating circuit 15 is inverted by the RF multiplied signal output from the adding circuit 21.

According to such a configuration, as shown in FIG.
Since it is generated at the same time as the double signal focus error signal FE, it is possible to obtain the same effect as in the above embodiment.

Further, the signal that serves as a trigger for inverting the polarity of the output of the generation section of the lens drive signal generation circuit 15 is not limited to the focus error signal FE or the RF multiplied signal, but is also used to determine that the objective lens has reached the in-focus position. Any signal that can be used can be used.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, it is possible to provide an extremely good focus servo gain adjustment circuit for an optical disc playback device that can perform accurate focus servo gain adjustment in a short time. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the focus servo gain adjustment circuit of an optical disc playback device according to the present invention, FIG. 2 is a timing diagram for explaining the operation of the embodiment, and FIG. FIGS. 4 and 5 are a block diagram showing a modification of the same embodiment, and FIGS. 4 and 5 are a block diagram showing a conventional focus servo gain adjusting means and a timing chart for explaining its operation, respectively. 11... Photodetector, 12... Subtraction circuit, 1
3... variable gain amplifier 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. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 5

Claims (1)

[Claims] A lens drive device that is installed in an optical disc playback device that reads signals from a disc via an optical pickup, and includes a generator that generates a lens drive signal of a predetermined frequency, and that moves the objective lens of the pickup in the focus direction. means, focus servo means for generating a focus error signal based on a signal read by the pickup and holding the objective lens at a focused position, and a state in which the objective lens is moved by the lens driving means. and a detection means for detecting the level of the focus error signal obtained by the focus servo gain adjustment circuit, which adjusts the gain of the focus servo means according to the output of the detection means, Means for determining that the objective lens has reached a focused position based on a signal read by the pickup while the objective lens is being moved, and reversing the polarity of the output of the lens drive signal generator. A focus servo gain adjustment circuit for an optical disc playback device, comprising: the objective lens being vibrated around a focal point position.