JPH0624010Y2 - Focus search circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a focus search circuit for an optical disc player, and more particularly to a focus search circuit suitable for performing a stable focus search for a CD player. 2. Related Art The conventional focus search circuit operates according to the waveform diagrams and circuit diagrams shown in FIGS. 2 and 3.

The focus search circuit outputs S which is a focus error output.
The zero level of the curve is detected, the focus error output is input to a microcomputer (not shown) at the falling waveform of the FZC waveform, and the focus servo system is closed by the microcomputer control to set the focus point. It was working to tie.

Figure 2 shows the focus error output S curve 5 and FZC.
It is a waveform diagram showing the characteristics of (focus.zero.cross) waveform.

When the focus search is executed, the S curve 5 rises from 5a near the zero level. Then, a focus error output is generated on the plus side in a place where an objective lens (not shown) for focusing is separated, and approaches zero level when the objective lens approaches the in-focus point. Further, it has a characteristic of the S curve 5 such that the focus error output reaches the zero level 5b and exceeds the zero level and becomes large in the minus side.

The FZC waveform is a waveform in which the zero levels 5a and 5b of the S curve 5 are detected and the focus error output changes to L level on the minus side and H level on the plus side.

In the vicinity of the zero level 5a, the focus error output has a ringing phenomenon, and the FZC output waveform causes chattering as shown in FIG.

FIG. 3A is a circuit diagram in which a negative bias is applied to prevent chattering of the FZC waveform.

The focus error terminal 6 is biased to a negative voltage by the resistors R6, R7 and R8. The switch S2 is OFF.

In the figure, VR is a semi-fixed resistor for adjusting the loop gain of the focus system, and resistors R1 and R5 and a capacitor C1 are filter circuits for gain compensation at low frequencies when the focus servo is closed.

S2 is a switch that detects the falling waveform of the FZC waveform and turns on when the focus servo system is closed.

FIG. 3 (B) is an S curve and FZC waveform diagram showing the operating characteristics of the circuit diagram of FIG. 3 (A).

The S curve 8 is biased to the negative side by the above bias of the negative voltage (8a portion), and the FZC waveform is at the L level.

When the S curve 8 reaches the zero level (8b portion), the FZC waveform rises to the plus side and becomes the H level. This FZC waveform is applied to the FZC terminal 7, superimposed on the focus error terminal 6 via the resistor 9 and the capacitor C2, and the S curve 8 is suddenly raised to the plus side at that moment, and the S curve 8 rises as 8b. .

That is, the S curve 8 having the ringing phenomenon does not cross the zero level several times as shown in FIG. 2, but when the zero level is exceeded, the S curve 8 is lifted to the plus side as it is, and a plus focus error output is obtained.

When the focus search progresses, the objective lens reaches the focus pull-in range, and the S curve 8 reaches the zero level (8c portion), this zero level is detected, and the FZC waveform falls from the H level to the L level.

As described above, microcomputer control is performed by the falling waveform of the FZC waveform, the focus servo system is closed, and at the same time, the semiconductor switch S2 is turned on, and the bias of the negative voltage at the focus error terminal 6 disappears.

In this way, the focus search operation is completed, and the in-focus point can be focused by the control of the focus servo system.

(C) Problems to be solved by the device However, in the above-mentioned conventional example, in the example of FIG. 2, chattering of the FZC waveform occurs due to the ringing phenomenon of the S curve 5 of the focus error output. The falling waveform of chattering activates the microcomputer control to close the focus servo system, but the objective lens is still far away from the focus point and is not within the focus pull-in range. It had the drawback that the servo could not be closed.

Further, in FIG. 3 which is designed to prevent the chattering of the FZC waveform, since the negative side bias is applied, the ringing phenomenon of the focus error output is large or the ringing at the moment when the S curve reaches the zero level. Depending on the timing of the phenomenon, the focus servo system may malfunction as described above.

The present invention has been made in view of the above points, and its purpose is to solve the drawbacks of the conventional example and execute a stable focus search by the S curve of the focus error output biased to the positive side. It is to provide a focus search circuit for operating the focus servo system.

(D) Means for solving the problem The focus search circuit of the present invention is an optical disc
During the focus search in the focus search circuit that operates the focus servo system by detecting the zero level of the S curve which is the focus error output in the player,
A bias circuit for applying a positive DC bias voltage to the focus error output, a filter circuit for compensating for a low frequency of a reproduction signal, and a switching means for switching between the bias circuit and the filter circuit after the focus search is completed. Solves the above problems.

(E) Action In order to accurately detect the zero level of the S curve of the focus error output, when the objective lens of the focus is far away from the in-focus position and the focus error output is near the zero level, correct operation is avoided to avoid malfunction. Bias with the DC voltage of so that it does not cross the zero level.

When the objective lens is within the focus pull-in range, the zero level is properly detected, the FZC signal falls, and the falling waveform of this FZC signal controls the focus servo system and at the same time releases the bias. Is a focus search circuit.

(F) Embodiment An embodiment of the focus search circuit according to the present invention will be described with reference to FIGS. 1 (A) and 1 (B).

In the figure, 1 is an input terminal of the focus search circuit, 2 is a focus servo amplifier, and 3 is a focus coil. VR is a semi-fixed resistor, R1 to R5 are resistors, and C1 is a capacitor. S1 is a switch shown in a schematic diagram of a semiconductor switch, and + B and -B are positive and negative supply voltage sources for supplying a bias voltage.

The semi-fixed resistor VR is for adjusting the loop gain of the focus servo system, and the focus error signal adjusted by VR is amplified by the focus servo amplifier 2 to drive the focus coil and bring it to the in-focus point. Operate.
However, the focus error signal is biased or the like by the circuit of the switch S1.

FIG. 1B is a waveform diagram for explaining the operation of the focus servo circuit.

Reference numeral 4 indicates a focus error S curve waveform, 4b indicates the time when this S curve crosses the zero level, and ΔV is a bias voltage biased to the positive side. The FZC waveform is a square wave that changes from H level to L level at the point 4b.

When performing a focus search, switch S1 is connected to the NC contact. The NC contact is a bias circuit that connects resistors R2, R3, and R4 to + B and -B to bias the NC contact to the positive side.

+ B and -B of the supply voltage source are positive and negative tracking power supplies, and these positive and negative power supplies have the same absolute value. Therefore, the resistance value of the same constant is used for R2 on the + B side and R4 on the -B side, and the resistance value of the resistor R3 is set in order to determine the bias voltage ΔV on the positive side of the NC contact.

In this way, during focus search, the S curve 4 of focus error is biased to the positive side (4a portion),
The FZC waveform is at H level.

When the focus search progresses, the objective lens reaches the in-focus point, and the S curve 4 of the focus error reaches the zero level 4b, this zero level 4b is detected and the FZC waveform changes to the L level.

The falling signal of the FZC waveform is input to the microcomputer (not shown) as described above, and at the same time the focus servo system is closed, S1 is switched to the NO contact, the positive side bias of the focus search circuit is turned off, and the resistor R5 ,
Connected to the filter circuit consisting of capacitor C1.

The resistors R1 and R5 and the capacitor C1 are a filter circuit for gain compensation at low frequencies when the focus servo system is closed.

In this way, the focus search operation is performed, the objective lens sufficiently reaches the focus pull-in range, the focus servo system is closed, and stable focus is established.

As described above, the FZC waveform is at the H level until the zero level of the S curve 4 is detected. During the period when the FZC waveform is at the H level, the microcomputer does not accept the FZC signal. There is no stable operation.

(G) Effect of the Invention According to the focus search circuit of the present invention, since the S curve of the focus error signal is biased by the positive voltage during the focus search, the FZC signal causes chattering due to the ringing phenomenon of the focus error signal. The effect is that the focus servo system can be closed in a stable manner.

Further, since the ± B power supplies are tracking power supplies, the absolute values of the bias circuit resistors R2, R3, and R4 are not so important, and the mass production effect can be improved.

In addition, a low-frequency gain compensation resistor R5 and capacitor C1
The filter circuit of is switched by the switch S1 and is not connected during the focus search, so that the high-frequency gain of the focus error output is prevented from decreasing and the amplitude becoming small.

In addition, it has excellent features such as a simple structure and a low cost, which makes it easy to implement.

[Brief description of drawings]

1 (A) and 1 (B) show an embodiment of a focus search circuit according to the present invention, and FIG. 1 (A) is a circuit diagram,
Figure (B) is a waveform diagram. 2 and 3 (A) and (B) show a conventional example,
FIG. 3 is a waveform diagram, FIG. 3 (A) is a circuit diagram of another conventional example, and FIG.
FIG. 3B is a waveform diagram of FIG. Description of main numbers 2: Focus servo amplifier 3: Focus coil 4, 5, 8: S curve 6: Focus error output terminal 7: FZC input terminal S1, S2: Semiconductor switch

Claims (1)

[Scope of utility model registration request] 1. A zero level of an S curve which is a focus error output in an optical disc player is detected,
In the focus search circuit that operates the focus servo system, a bias circuit that applies a positive DC bias voltage to the focus error output during the focus search, a filter circuit that performs gain compensation of the low frequency of the reproduction signal, and A focus search circuit comprising a switching means for switching between a bias circuit and the filter circuit.