JPH0624011Y2 - Focus servo control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a focus servo control circuit for focusing an objective lens on a disk surface.

(B) Conventional Technology This type of focus servo control circuit is disclosed in Japanese Patent Laid-Open No.
As can be seen in JP-A-0-629, R from the disk surface
Whether or not the F signal is being reproduced is detected, and when the RF signal is detected, the focus servo loop is closed.

Further, it is determined whether or not the state of focus matching continues even after the focus matching is once performed.

(C) Problems to be solved by the invention By the way, when the focus is out of focus due to shock or vibration, the focus is matched again. Whether the focus is matched or not is determined by the RF from the disk surface.
Since it is performed depending on whether or not the signal is reproduced, it is determined that the focus is out of focus when the RF signal is not reproduced from the disk surface. Therefore, even if the objective lens is located at the focus matching point, if there is a mirror surface defect due to scratches on the disk surface, it is judged that the focus signal is out of focus because the RF signal is not reproduced from the disk surface, and the focus servo is meaningless Is performed, which adversely affects other operations.

(D) Means for Solving the Problems The focus servo control circuit of the present invention receives an RF signal and compares the DC component of the RF signal with a predetermined level to collect the light beam from the light source on the disk surface. A focus match detection circuit that generates a focus match detection signal indicating that the illuminating objective lens is located near the focus match point with respect to the disk surface, and an RF signal is input, and a mirror surface defect of the disk surface in the RF signal. A first hold circuit for holding a component due to a short time constant with a second time hold circuit for holding a component due to a mirror surface defect of the disk surface in the RF signal with a long time constant, and a first hold circuit. Circuit and second
The output signal of the hold circuit is compared with each other, and in response to the inversion of the levels of both signals, a defect detection circuit for generating a mirror surface defect detection signal indicating the presence of a mirror surface defect of the disk surface and the focus matching described above. And a logical sum signal of the detection signal and the defect detection signal to form a focus matching judgment signal.

(E) Operation According to the present invention, even if the RF signal is not reproduced, if the presence of the mirror surface defect is detected at that time, it is not judged that the focus is out of focus.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram of its essential part.

In FIG. 1, a focus match detection circuit (1) includes a focus amplifier (10) for extracting a DC component from an RF signal (a) and a comparator (11 for comparing the extracted DC signal (f) with a signal of a predetermined level. ).

Further, the defect detection circuit (2) includes an inverting amplifier (20) that inverts the RF signal (a), a first hold circuit (21) that bottom-holds the inversion RF signal (b) with a short time constant, and an inversion RF signal (b). ) Is bottom-held with a long time constant, the output signals of the second hold circuit (22) and these hold circuits (21) and (22) are c-coupled, and further differentiated and level-shifted, then both signals (c) (d ) Is compared.

The outputs (g) and (e) of both comparators (11) and (23) are logically ORed by an OR circuit composed of two diodes (3) and (4), and then the RC low pass filter (5). Is output as a focus matching determination signal (h).

The operation of such a circuit will be described in detail with reference to FIG.
RF signal (a) reproduced from the disc surface (not shown)
Is input to the focus amplifier (10). In the present embodiment, the RF signal (a) has a signal form having a component due to the mirror surface defect of the disk at the two arrows in the figure.

Thus, the RF signal input to the focus amplifier (10)
In (a), the DC component is extracted by the amplifier. Then, the DC signal (f) is compared with a signal of a predetermined level by the comparator (11), and the output of the comparator (11) becomes high level when the DC signal (f) is larger than the signal of the predetermined level. . As a result, the comparator (11) outputs the focus match detection signal that becomes high level when the focus is matched.
(g) will be output.

On the other hand, the RF signal (a) is inverted by the inverting amplifier (20) to be the inverted RF signal (b), and then bottom-held by the first hold circuit (21) and the second hold circuit (22). . First
The hold circuit (21) responds to the component due to the mirror surface defect of the disk in the inverted RF signal (b), and the second hold circuit (22)
Holds the level immediately before the component due to the mirror surface defect of the disk in the inverted RF signal (b). Then, the hold signals of these hold circuits (21) and (22) are c-coupled, and both hold signals (c) and (d) after further differentiation and level shift are performed.
Is compared by the comparator (23), the high level mirror surface defect detection signal (e) is generated when the mirror surface defect exists.

Then, the focus match detection circuit (1) and the defect detection circuit
The focus match detection signal (g) and the mirror surface defect detection signal (e), which are the output signals of (2), are logical sum signals by the logical sum circuit composed of the diodes (3) and (4), and then the focus match determination is made. It is output as signal (h).

Here, in the present embodiment, due to the presence of the two mirror surface defects, the focus match detection signal (g) is in the same state as the out-of-focus state at two places, but it is determined whether or not the focus is matched. Since the focus match determination signal (h) obtained by the logical sum of the focus match detection signal (g) and the mirror surface defect detection signal (e) is used, the determination of out-of-focus due to the mirror defect is prevented.

Note that when the focus is actually defocused, the mirror surface defect detection signal (e) becomes low level, so the result of the out-of-focus determination by the focus match detection signal (g) is output as the focus match determination signal. It

(G) Effect of the Invention According to the present invention, it is possible to determine whether or not the focus is in focus without being affected by the mirror surface defect of the disk, and thus it is possible to perform the focus servo stably. Become.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram of essential parts in the circuit diagram. (1) …… Focus matching detection circuit, (2) …… Defect detection circuit, (3) (4) …… Diode.

Claims (1)

[Scope of utility model registration request] 1. An objective lens for inputting an RF signal and comparing a DC component of the RF signal with a predetermined level to condense a light beam from a light source on a disk surface. A focus match detection circuit that generates a focus match detection signal indicating that the RF match signal is located in the vicinity of the first hold circuit; and a first hold circuit that receives an RF signal and holds a component of the RF signal due to a mirror surface defect with a short time constant. Comparing a level of each output signal of the first hold circuit and the second hold circuit with a second hold circuit that receives an RF signal and holds a component of the RF signal due to a mirror surface defect of the disk with a long time constant Then, in response to the reversal of the levels of both signals, a mirror surface defect detection signal indicating the presence of a mirror surface defect on the disk surface is generated. Focus servo control circuit, wherein the defect detection circuit, that with a logical OR signal of the focus match detection signal and the defect detection signal and a logic OR circuit which forms a decision signal of the focus match.