JPH056572Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a focus servo circuit for an optical disc playback device, and particularly relates to the sharing of large capacity capacitors.

[Conventional technology]

Optical disc playback devices optically detect data such as video and audio recorded on optical discs such as compact discs (CDs) using laser light irradiation and its reflection, and play it back as video or audio. It is something. Therefore, an optical disc playback device has an optical system that focuses a laser beam on the recording track of the optical disc, and a focus servo that controls the position of the focal point by operating the objective lens of the optical system. It has a circuit.

[Problem that the invention attempts to solve]

By the way, this focus servo circuit includes a focus search circuit that operates only during focus search and a time constant circuit that operates after focus search, both of which require large capacitors. There is.

When converting a focus servo circuit into an IC, such a capacitor can be used by providing a terminal (pin) on the IC.
It must be connected to the outside of the IC, which, along with the installation of terminals, causes an increase in the number of parts.

This invention attempts to provide a focus servo circuit for an optical disc playback device in which the number of capacitors is reduced by sharing such a capacitor with a plurality of circuits.

(Means for Solving the Problems) As illustrated in FIG. 1, the focus servo circuit of the optical disc playback device of this invention searches for a focal point on the optical disc at the time of focus search. A focus search circuit 10 that generates a signal, and a hold circuit 12 that holds a detection signal indicating the presence or absence of a reflected signal from the optical disk.
A focus servo circuit for an optical disc playback device comprising: Detection circuit (AND circuit 3
0), a control circuit 16 that receives the output of this focus point detection circuit and generates a switching signal indicating the end of the focus search, a single external terminal formed on the IC, and a control circuit 16 connected to this external terminal. A single capacitor 2 is installed between the external terminal and the focus search circuit or the hold circuit, and is used for the focus search circuit or the hold circuit. The present invention is characterized by comprising a switch 8 which switches the connection to the focus search circuit side and switches the connection of the capacitor to the hold circuit side by a switching signal from the control circuit.

[Effect]

According to the focus servo circuit of the optical disk playback device of this invention, a focus search circuit that is in an operating state during a focus search and a hold circuit that is in an operating state at times other than a focus search can be integrated into a single IC. The capacitors that require a focus search circuit and a hold circuit are connected to a single external terminal, and a switch is interposed between this external terminal and each circuit to selectively change the connection relationship of the capacitors. It was made possible to do so.
Then, the switch is switched by the control circuit,
Switching by this control circuit is performed depending on the presence or absence of a switching signal indicating completion of focus search by the focus point detection circuit.

〔Example〕

FIG. 1 shows an embodiment of a focus servo circuit of an optical disc reproducing apparatus of this invention, and this embodiment represents a part of a focus servo IC in the focus servo circuit.

The capacitor 2 is connected to the terminal 6 of the focus servo IC 4, and is shared by the focus search circuit 10 and the hold circuit 12 via the switch 8. It is connected to the circuit 10, and also connected to the hold circuit 12 at times other than focus search. The focus search circuit 10 is a ramp function generator that includes the capacitor 2 as a component, and the hold circuit 12 is a circuit that includes the capacitor 2 as a component, and both have a time constant circuit that includes the capacitor 2 as a component. ing.

The switch 8 instantly switches contact a during a focus search by a switching signal generated by a control circuit 16 according to the operating conditions of a focus search circuit 10 and a hold circuit 12 of the capacitor 2.
side, the contact can be selectively switched to the b side at times other than focus search.

The switch 18 is closed as shown by a broken line by a switching signal generated by the control circuit 16 during a focus search, and is opened at other times.

Therefore, during focus search, the switch 8 is activated by the switching signal generated by the control circuit 16.
is instantaneously closed to the contact a side, and the switch 18 is closed as shown by the broken line, the focus search signal FS generated by the focus search circuit 10 using the capacitor 2 is transmitted from the output terminal 20 to the main circuit of the servo loop. The optical system is operated based on the signal FS. At this time, the laser beam reflected from the optical disk is detected by a sensor such as a light receiving diode, and the detection signal is amplified by an amplifier 22 as a focus error signal FE. By the way, since the focus search is performed by stopping the operation of the servo loop, the control circuit 16
The switch 24 is activated by a switching signal from the switch 24.
will be opened. For this reason, the focus error signal
FE is applied only to the comparator 26, and the comparator 26 detects its zero-crossing point and outputs a zero-crossing signal FZC representing the zero-crossing point of the focus error signal FE.

Further, the presence or absence of a reflected signal from the optical disk is detected by a comparator 28, and a detection signal FOK representing the reflected signal is held in a hold circuit 12 and used as a focus point detection circuit.
It is added to the AND circuit 30. The AND circuit 30 receives the zero cross signal FZC and the hold circuit 1.
The logical AND output representing the focus point is applied to the control circuit 16. The control circuit 16 generates a switching signal indicating the end of the focus search in response to the AND output indicating the focus point of the AND circuit 30. This switching signal closes the switch 24 as shown by the dashed line and activates the servo loop.

By the way, the detection signal FOK generated by the comparator 28 is a signal indicating that there is a reflected signal from the disk, so if the reflected signal is missing due to a scratch on the disk, the detection signal FOK will be instantaneously reflected by the missing signal. Move to a lower level. If such a detection signal FOK is applied directly to the AND circuit 30, an L output will be generated in the AND circuit 30 due to a missing part such as a scratch, which will open the switch 24 and stop the operation of the servo loop. . Therefore, the hold circuit 12 is used to hold the momentary intermittent detection signal FOK using the capacitor 2, and as shown in A in FIG. 2, when a hold input (detection signal FOK) is applied, As shown in FIG. 2B, a hold output with a hold time th is generated to compensate for signal loss caused by scratches on the disk, thereby preventing the servo loop from stopping.

[Effect of idea]

As explained above, according to this invention, the capacitors required by the focus search circuit and hold circuit installed on a single IC are connected to the external terminals of the IC via a switch, and the focus point is Since a single capacitor is selectively connected to the focus search circuit or the hold circuit by switching the switch based on detection,
By unifying the large capacity capacitors that were previously required individually, the number of parts can be omitted and the number of external terminals of the IC can be reduced, making it possible to save space and reduce the cost of the device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the focus servo circuit of the optical disk reproducing apparatus of this invention, and FIG. 2 is a diagram showing the operating waveforms of the hold circuit. 2...Capacitor, 8...Switch, 10...
Focus search circuit, 12... hold circuit,
16...control circuit, 30...AND circuit (focus point detection circuit).

Claims (1)

[Claims for Utility Model Registration] A focus search circuit that searches for a focal point on an optical disk and generates a focus search signal during a focus search, and a detection signal that indicates the presence or absence of a reflected signal from the optical disk. A focus servo circuit for an optical disc playback device comprising a hold circuit and a hold circuit for detecting a focus point on a single IC, the focus servo circuit detecting a focus point from a zero cross signal of a focus error signal and the detection signal of the hold circuit. a control circuit that receives the output of the focus point detection circuit and generates a switching signal indicating the end of the focus search; a single external terminal formed on the IC; a single capacitor connected to the terminal and used in the focus search circuit or the hold circuit; and a single capacitor installed between the external terminal and the focus search circuit or the hold circuit, and connected to the A focus optical disc playback device comprising: a switch for switching the connection of a capacitor to a focus search circuit side, and switching the connection of the capacitor to the hold circuit side according to a switching signal of the control circuit; servo circuit.