JPH0510247Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention moves the objective lens of the optical pick-up in the optical axis direction in order to draw the focal point of the optical pick-up into the operating area of the focus servo system circuit. , relates to a focus search circuit for generally focusing the pickup on the signal surface of the disk.

(b) Prior Art A CD player is known that uses an optical pickup to read out signals from a compact disc (CD) on which concavities and convexities corresponding to digital signals are engraved. In the CD player, it is necessary to perform focusing control in order to properly focus the optical beam of the pickup onto the signal surface on the disc. When performing the focusing control, first, the objective lens of the pick-up is moved in the optical axis direction, and a focus search is performed to approximately bring the focus of the pick-up onto the signal surface of the disk. The light beam from the pick-up is drawn into the operating area of a focus servo system circuit for correcting the focal deviation between the beam and the signal surface of the disk, and then the light beam of the pick-up is always aligned with the signal surface by the focus servo system circuit. I'm doing it like that. This is described, for example, in Japanese Patent Publication No. 58-38855.

By the way, as a focus search circuit for performing the focus search, for example,
There is a publication No. 17041. The focus search circuit disclosed in the above publication includes an operational amplifier, a time constant circuit that is charged and discharged by a feedback resistor connected between the output of the operational amplifier and one input terminal, and the other input terminal of the operational amplifier. It is equipped with a resistor circuit that divides and applies the output voltage of the operational amplifier, and a switching element connected between a part of the resistor circuit and a predetermined level of potential, and which connects the focal point of the optical pickup and the signal surface of the disk. The switching element is turned on by a signal indicating that the two match with each other, and oscillation is made while the switching element was previously turned off, making it possible to perform a focus search with a simple circuit configuration. has been completed.

(c) Problems to be solved by the invention However, in the above device, the direction in which the objective lens of the pick-up is driven is determined by the terminal voltage of the capacitor included in the time constant circuit, and the terminal electrons of the capacitor are Since the switching elements other than the middle ones are not set to a predetermined level when they are in the ON state, the driving direction of the objective lens cannot be determined at the start of the focus search. As a result, the reliability of the focus search sometimes deteriorates, and the time required for the focus search sometimes increases. In other words, when performing a focus search, if the objective lens of the pick-up is moved close to the disk and then moved away from the disk, the amount of reflected light will first increase when the focus of the light beam of the pick-up is on the disk. This is the position where the signal surface is reached, so when the first increase in the amount of reflected light is detected, it is pulled into the operating area of the focus servo system circuit, thereby protecting the signal surface. It is possible to prevent false detection from occurring due to an increase in the amount of reflected light. Therefore, the objective lens of the pick-up is designed so that it is pulled into the operating area of the focus servo system circuit when it is being driven away from the disk, but the objective lens is first driven. If the direction is not determined, the driving of the objective lens will start from a direction in which the focus servo system circuit is not pulled into the operating area, and the focus servo system will be activated within the determined focus search operation time. This reduces the chance of drawing the light beam into the active area of the circuit, or increases the time it takes for the pickup's light beam to reach the signal surface of the disk when the objective lens is driven away from the disk. will be done.

(d) Means for solving the problem The present invention has been made in view of the above points, and includes an operational amplifier, a feedback resistor connected between the output terminal and one input terminal of the operational amplifier, and the feedback resistor. a time constant circuit configured with a capacitor connected to a resistor; and a voltage divider circuit that divides and applies the output voltage of the operational amplifier to the other input terminal of the operational amplifier;
a voltage generation circuit that generates a voltage at a predetermined level when a focus servo system circuit is operating; a switching element that is connected between the time constant circuit and the voltage generation circuit and turns off during focus search; It is characterized by being composed of.

(E) Effect The present invention charges a capacitor of a time constant circuit with a voltage of a predetermined level generated from a voltage generation circuit when a focus search is not in progress, and at the start of a focus search, charges the terminal voltage of the capacitor. It is set at a predetermined level so that the objective lens of the optical pickup always starts moving in the same direction.

(F) Embodiment FIG. 2 is a block diagram showing the focusing control system of a DAD player, in which 1 is a disk, 2 is a motor that drives the disk 1, and 3 is a light beam that is projected and reflected from the disk 1. an optical pickup having a light sensor that receives a light beam; 4
5 is a preamplifier for amplifying the signal generated from the optical sensor of the optical pickup 1, and 5 is an output signal generated from the preamplifier 4 to correct the focal error between the light beam of the optical pickup 3 and the signal surface of the disk. 6 is a line amplifier that amplifies the output signal generated from the focus error detection circuit 5; 7 is a line amplifier that amplifies the output signal generated from the preamplifier 4, and the output signal is received by the optical sensor of the optical pickup 3; A reflected light amount detection circuit 8 generates an "H" signal when the power is turned on, generates an "L" signal after a predetermined time, and responds to the output signal generated from the reflected light amount detection circuit 7. 9 is an oscillation circuit that oscillates when the "H" signal is generated from the control signal generation circuit 8; 10 is an oscillation circuit from the line amplifier 6 and the oscillation circuit 9; A focus coil drive circuit drives the objective lens of the optical pickup 3 in the optical axis direction (direction of arrow A) according to the generated output signal, and 11 connects the oscillation circuit 9 to the objective lens of the optical pickup 3. This is a prohibition circuit that prohibits the operation of the reflected light amount detection circuit 7 when a signal for bringing the lens closer to the disk 1 is generated. The preamplifier 4, focus error detection circuit 5, and line amplifier 6 constitute a focus servo system circuit, and the reflected light amount detection circuit 7, control signal generation circuit 8, oscillation circuit 9, and inhibition circuit 11 constitute a focus search circuit. Configure the system circuit.

In the above device, when the power is turned on, a positive voltage is applied to the terminal 12, the muting transistor 13 is turned on, the focus servo system circuit is muted, and the control signal generation circuit 8 outputs "H". ” signal is generated and the oscillation circuit 9
Preparations for oscillation are made. After a predetermined time has elapsed, when the control signal generation circuit 8 generates an "L" signal, the oscillation circuit 9 starts oscillating. At this time, if power muting is completed and the muting transistor 13 is off, the focus coil drive circuit 10 generates an output signal in response to the oscillation output generated from the oscillation circuit 9, and the optical pickup The objective lens No. 3 is driven in the optical axis direction. If the disk 1 is attached, the amount of the light beam received by the optical sensor of the optical pickup 3 changes as the objective lens is driven in the optical axis direction, so the amount of the light beam is detected by the reflected light amount detection circuit. 7, the pickup 3 is focused on the signal surface of the disk 1. In that case, when a signal is generated that causes the oscillation circuit 9 to bring the objective lens of the optical pickup 3 closer to the disk 1, the prohibition circuit 11 is activated to stop the operation of the reflected light amount detection circuit 7. Therefore, there will be no malfunction due to reflection on the plastic surface for protecting the signal surface of the disk 1.

When the reflected light amount detection circuit 7 determines that the light beam of the optical pickup 3 and the disk 1 are focused, an output signal is generated from the reflected light amount detection circuit 7, and this signal causes the control signal generation circuit to 8, the "H" signal is again generated, and the oscillation of the oscillation circuit 9 is stopped. Thereafter, the focus servo system circuit starts operating, and the objective lens of the optical pickup 3 is driven in accordance with the error signal obtained by the focus error detection circuit 5, so that the optical pickup 3's light beam is always and the signal surface of disk 1 come into focus.

FIG. 1 shows an embodiment of the present invention, which corresponds to the oscillation circuit 9 and inhibition circuit 11 provided in the focus search circuit shown in FIG.
an operational amplifier whose power source is Vcc, 15 a time constant circuit consisting of a first feedback resistor 16 connected between the output terminal and the negative input terminal of the operational amplifier 14 and a capacitor 17 connected to the feedback resistor 16;
21 is a voltage dividing circuit consisting of a second feedback resistor 19 connected between the output terminal and the positive input terminal of the operational amplifier 14 and a resistor 20 connected to the feedback resistor 19, and 21 is a voltage dividing circuit between the power supply (+Vcc) and the ground. a voltage generating circuit consisting of resistors 22 and 23 connected to 24;
25 is a transistor whose base is connected to the output terminal of the operational amplifier 14 via a diode 26 and a resistor 27. be. A diode 28 is connected to the gate of the FET 24, and a self-biasing resistor 29 is connected between the gate and source.

An output signal generated from the control signal generation circuit 8 shown in FIG. 2 is applied to an input terminal 30 connected to the cathode of the diode 28, and the output signal generated from the control signal generation circuit 8 shown in FIG. A positive voltage is applied when the surfaces of the disks coincide with each other and signals can be read from the disk, and a negative voltage is applied when the disk is out of focus and signals cannot be read. An output terminal 31 connected to the capacitor 17 of the time constant circuit 15
The focus coil drive circuit 10 in FIG. 2 is connected to the signal path 32 connected to the collector of the transistor 25, which is a signal path connecting the preamplifier 4 and the reflected light amount detection circuit 7 in FIG.

Now, when the power supply is turned on and a positive voltage (+Vcc) is applied to the input terminal 30 as shown in FIG.
Diode 28 is reverse biased, so that FET
The gate of the FET 24 is at approximately the same voltage as the connection point B of the resistors 22 and 23 of the voltage generating circuit 21.
Therefore, the terminal voltage of the capacitor 17 of the time constant circuit 15 is the voltage of the connection point B +
If the output voltage is set to Vo, it is fixed to +Vo as shown in Fig. 3B. At this time, the output voltage of the operational amplifier 14 is not fed back, so there is no oscillation.

When the predetermined time _t1 elapses and a negative voltage (-Vcc) is applied to the input terminal 30, the diode 28 becomes forward biased, and the gate of the FET 24 becomes lower than the voltage applied to the input terminal 30. Since the rising voltage of the diode 28 is lowered to a higher voltage, the FET 24 is turned off. When the FET 24 is turned off, the terminal voltage of the capacitor 17 starts to change, and oscillation starts. Here, since the terminal voltage of the capacitor 17 is fixed to +Vo before oscillation starts, the operational amplifier 1
A negative output signal (-Vcc) is always generated from the output terminal 4 at the start of oscillation. When a negative output signal is generated at the output terminal of the operational amplifier 14, discharge of the capacitor 17 is started according to the time constant of the time constant circuit 15, and the terminal voltage of the capacitor 17 gradually decreases. Then, due to the discharge, the terminal voltage of the capacitor 17 becomes the voltage -V ₂ at the connection point C between the resistors 19 and 20 of the voltage divider circuit 18 when the operational amplifier 14 is generating a negative output signal.
When it tries to become smaller at time _t2 , a positive output signal (+
Vcc) occurs. Then, time constant circuit 1
Charging of the capacitor 17 is started according to a time constant of 5, and the terminal voltage of the capacitor 17 gradually increases. Then, due to charging, the capacitor 1
7 is the voltage at the connection point C when the operational amplifier 14 is generating a positive output signal +V ₂
When the voltage is about to increase at time _t3 , a negative output signal is generated again at the output terminal of the operational amplifier 14, and the capacitor 17 starts discharging, and thereafter, as described above, the capacitor 17 is repeatedly charged and discharged for a predetermined period of time. A triangular wave signal having a peak at ±V ₂ as shown in FIG. 3B is generated from the output terminal 31. The triangular wave signal is supplied to a focus coil drive circuit, and when the voltage of the triangular wave signal decreases, the objective lens of the optical pickup is driven away from the disk, and when the voltage increases, the objective lens approaches the disk. The objective lens is driven to reciprocate between operating limit positions in both directions of the optical axis. Therefore, when the objective lens is driven with the disk attached, when the objective lens reaches a certain position, the focus of the optical pickup will be on the signal surface of the disk.

By the way, the output signal of the operational amplifier 14 is passed through a diode 26 and a resistor 27 to a transistor 25.
When a positive output signal is generated from the operational amplifier 14, the transistor 25 turns on. Therefore, when a triangular wave signal is generated in the direction of driving the objective lens of the optical pickup closer to the disk, the reflected light amount detection circuit 7 in FIG. 2 does not operate. Therefore, at that time, the reflected light amount detection circuit 7 does not generate an output signal, and the focus servo system circuit does not become operational.

When the focus of the optical pickup is aligned with the signal surface of the disk at time _t4 in FIG. voltage is applied. Therefore, the FET 24 is turned on, the terminal voltage of the capacitor 17 is fixed at +Vo, the oscillation operation is stopped, the focus search operation is completed, and the focus servo system circuit becomes operational.

In addition, in the above-mentioned circuit, since the terminal voltage of the capacitor 17 of the time constant circuit 15 is fixed to +Vo even during disk replacement, even immediately after disk replacement,
A focus search operation similar to that described above is performed.

Furthermore, in the above circuit, the voltage generation circuit 21
A negative power supply is applied to the point B of the voltage generating circuit 21.
By generating a negative voltage at , it is possible to reverse the direction in which the objective lens of the optical pickup starts moving.

(g) Effects of the invention As described above, the present invention enables the optical Since the pick-up objective lens always starts moving in the same direction, it has the advantage of improving the reliability of focus search and shortening the time required for focus search without increasing costs.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a block diagram showing a focusing control system of an optical pickup, and FIG. 3 is a waveform diagram for explaining FIG. 1. Explanation of main figure numbers, 14... operational amplifier, 15...
...Time constant circuit, 16...Feedback resistor, 17...Capacitor, 18...Voltage divider circuit, 21...Voltage generation circuit, 24...FET.

Claims (1)

[Scope of utility model registration request] In a focus search circuit that moves the objective lens of the optical pickup used for reading out signals from a disk in the optical axis direction in order to focus the optical pickup on the signal surface of the disk, an operational amplifier and an output terminal of the operational amplifier are connected to each other. a time constant circuit comprising a feedback resistor connected between one input terminal of the operational amplifier and a capacitor connected between one input terminal of the operational amplifier and a reference voltage; A voltage divider circuit that divides and applies the output voltage of the operational amplifier, and a voltage generator circuit that generates a voltage at a predetermined level when the focus servo system circuit that corrects the focus shift with the disk signal surface is operating. and a switching element connected between the time constant circuit and the voltage generation circuit and turned off during a focus search, the terminal voltage of the capacitor being controlled by the voltage generation circuit when the switching element is turned on. When the switching element is off, the voltage is determined by the output voltage of the operational amplifier, and the objective lens of the pickup is driven in accordance with the terminal voltage of the capacitor. A focus search circuit for an optical pick-up, characterized in that an objective lens is driven from a predetermined direction.