JPS6248299B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operation determination circuit for a focus servo device in an information reading device such as a digital audio disk playback device or a video disk playback device.

The information recording carrier from which the information recorded by the information reading device is read is made of, for example, a disc, and recesses (hereinafter referred to as pits) are arranged on the information recording surface of the disc to form concentric or spiral tracks. Information is recorded by the length and spacing of these pits. The optical system of an information reading device for reading information from a rotationally driven information recording carrier is constructed as shown in FIG. 1, for example. That is, for example, a light beam from a H _e -N _e laser light source is incident on a tangential mirror 2 via a beam splitter 1 and is reflected by the tangential mirror 2 . The light beam reflected by the tangential mirror 2 is sent to the tracking mirror 3
The light beam reflected by the tracking mirror 3 is focused on the information recording surface of the information recording carrier 5 through the objective lens 4 and irradiated as a light spot. The light spot irradiated onto the information recording surface is modulated and reflected by the information recording surface. This reflected beam passes through the opposite path to the above and is irradiated to the photoelectric conversion element 6 via the beam splitter 1, and the information recorded on the information recording carrier 5 is converted from the output of the photoelectric conversion element 6 into an electrical signal. is being detected.

Further, when reading the above-mentioned information, it is necessary to make the light spot follow the center of a track consisting of a row of pits, and it is also necessary to focus the light beam on the information recording surface of the information recording carrier 5. For the former purpose, a tracking servo device detects a tracking error corresponding to the distance that the optical spot is away from the track center from amplitude information in the output signal of the photoelectric conversion element 6, and rotates the tracking mirror 3. The rotation angle of the tracking mirror 3 is controlled so that the tracking error becomes zero. For the latter purpose, a focus error signal corresponding to the shape of the spot image of the reflected light on the photoelectric conversion element 6 is detected from the output signal of the photoelectric conversion element 6, and the movement of the objective lens 4 is controlled to transfer it to the information recording surface. The irradiation light beam is applied to a focus servo device that focuses it on the information recording surface, and is controlled so that the focus error signal becomes zero.

However, when operating the tracking servo device, it is necessary to determine the operating state of the focus servo device, such as that the focus servo device must already be operating stably.

The present invention has been made in view of the above, and an object of the present invention is to provide an operation determination circuit for a focus servo device that determines the operating state of the focus servo device.

According to the present invention, this object is achieved by rectifying the positive and negative signals of the focus error signal and detecting whether the rectified focus error signal is below a predetermined level.

The present invention will be explained below with reference to Examples.

FIG. 2 is a block diagram of a focus error signal detection circuit, and FIG. 3 is a block diagram of an embodiment of the present invention. An embodiment of the present invention will be explained by taking as an example a case where the operation and non-operation of a tracking servo device are controlled by the output according to an embodiment of the present invention.

The photoelectric conversion element 6 that receives the reflected beam from the information recording carrier 5 is a photoelectric conversion element 6 divided into four parts.
It consists of ₁ , _6-2 , _6-3 and _6-4 . As is well known, the focus error detection circuit adds the output of the photoelectric conversion element _6-1 and the output of the photoelectric conversion element 6-4 located on the diagonal line of the photoelectric conversion element _{6 divided into four} , using an adder 7. Photoelectric conversion element 6-
The output of ₂ and the output of photoelectric conversion element _6-3 are added in an adder 8, and the output of the adder 7 and the output of the adder 8 are input to a differential amplifier 9, and the output of the adder 7 is added. The focus error signal is obtained by subtracting the output of the device 8.

On the other hand, the operation determination circuit in one embodiment of the present invention includes a preamplifier A consisting of a non-inverting amplifier 10 for amplifying the focus error signal, as shown in FIG.
A diode 11 that rectifies the positive output signal of the preamplifier A, a low-pass filter that includes a capacitor 13 and a resistor 14 and receives the output of the diode 11, a diode 12 that rectifies the negative output signal of the preamplifier A, and a capacitor. 15 and a resistor 16, and a rectifier circuit B consisting of a low-pass filter that receives the output signal of the diode 12, and an inverting amplifier 1.
an inverting buffer C that inverts the output signal of a low-pass filter consisting of a capacitor 15 and a resistor 16 consisting of a capacitor 15 and a resistor 16; a signal selection circuit D that selects and outputs the output signal with a higher level of both output signals, a non-inverting amplifier 20, and a reference voltage source 21. It consists of a comparator E which compares the voltage with the voltage of .

Further, in this embodiment, the output of the comparator E is supplied to the switch circuit 22 to control the driving of the switch circuit 22 and control the operation of the tracking servo circuit.
It is configured to control inactivity.

Note that the voltage of the reference voltage source 21 is set to a voltage that does not exceed the focus error signal when the focus servo device is operating stably.

Prior to explaining the operation of this embodiment constructed as above, the operation of the focus error signal detection circuit shown in FIG. 2 will be explained.

When the objective lens 4 and the information recording carrier 5 are in proper positions, a light spot is focused on the information recording surface of the information recording carrier 5, and the image of the reflected beam on the photoelectric conversion element 6 becomes a circle in FIG. If the objective lens 4 comes too close to the information recording carrier 5 than the appropriate position, the photoelectric conversion element 6
The image of the reflected beam on the photoelectric conversion element 6 looks like an ellipse indicated by the broken line in FIG. In FIG. 2, it looks like an ellipse indicated by a chain line. Therefore, as shown in FIG. 4, the output signal of the differential amplifier 9, that is, the focus error signal, is 0 (V) when the focus is in focus, and becomes a signal shifted in the positive or negative direction when the focus is out of focus, which is the so-called S. This indicates the characteristics of the character. Therefore, when the focus servo rotation is operating stably, the focus error signal has a DC component of 0 (V), and the amplitude of the reduction component is also suppressed to a small value. However, when the servo of the focus servo circuit is off, the DC component of the focus error signal has a large value in the positive or negative direction, or the amplitude of the component is reduced due to surface vibration of the information recording carrier 5, etc. becomes larger.

Such a focus error signal is applied to preamplifier A and amplified by preamplifier A. The focus error signal amplified by the preamplifier A is separated into positive and negative signal voltages by diodes 11 and 12 and rectified. A reduced component of the rectified output of the diode 11 is outputted through a low-pass filter connected to the diode 11, and a reduced component of the rectified output of the diode 12 is outputted through the low-pass filter connected to the diode 12. The output of the low pass filter consisting of capacitor 15 and resistor 16 is inverted by inverting buffer C. Therefore, the polarity of the output of the low-pass filter consisting of the capacitor 13 and resistor 14 of the rectifier circuit B and the polarity of the output of the inverting buffer C are positively aligned, and the level of each output is equal to the DC component of the focus error and the reduction. It corresponds to the amplitude level of the sexual component. Both output levels are diode 1
The signal selection circuit D consisting of 8 and 19 selects the one with the higher level.
will be output from. The output voltage of the signal selection circuit D is input to the comparator E and compared with the voltage of the reference voltage source 21. If the focus servo device is not operating stably, the signal selection circuit D
The output voltage exceeds the voltage of the reference voltage source 21, the comparator E generates a high potential output, and the switch circuit 22 is controlled to be off. Therefore, the tracking servo device becomes inactive. When the focus servo device is operating stably, the output voltage of the signal selection circuit D is lower than the voltage of the reference voltage source 21, the comparator E generates a low voltage output, and the switch circuit 22 is controlled to be in the on state. be done. Therefore, the tracking servo device becomes operational.

Furthermore, it can be determined whether the focus servo device is operating stably based on the output level of the comparator E.

In the embodiment of the present invention described above, the inverting buffer C is connected to the output terminal of the low-pass filter of the rectifier circuit B consisting of the capacitor 15 and the resistor 16, and the input of the signal selection circuit D is aligned with the positive polarity. Although the larger of both inputs was selected, the inverting buffer C is replaced by a rectifier circuit B consisting of a capacitor 13 and a resistor 14.
The same configuration can be achieved by connecting the signal selection circuit D to the output terminal of the low-pass filter and aligning the input of the signal selection circuit D with negative polarity.

As explained above, according to the present invention, the operating state of the focus servo circuit can be determined, and the operation or non-operation of the tracking servo circuit can also be controlled based on the operating state of the focus servo circuit.

Additionally, since it uses a much lower frequency component than the HF signal detected from the information reading device, it has the effect of making the circuit more stable. Furthermore, since the focus servo circuit is not controlled by the HF signal that is the sum of the four-divided photoelectric conversion elements, it is also resistant to dropouts.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the optical system of the information reading device. Second
The figure is a block diagram of the focus error signal detection circuit. FIG. 3 is a block diagram showing one embodiment of the present invention. FIG. 4 is a characteristic diagram of the focus error signal detection circuit shown in FIG. 2. A... Preamplifier, B... Rectifier circuit, C... Inverting buffer, D... Signal selection circuit, E... Comparator, 5... Information recording carrier, 6, 6- ₁ , 6- ₂ , 6- ₃ and 4
- ₄ ...Photoelectric conversion element, 7 and 8...Adder, 9...
Differential amplifier.

Claims (1)

[Claims] 1. A focus error signal exhibiting S-shaped characteristics with respect to the relative distance between the information recording surface of the information recording carrier and the objective lens is input, and the movement of the objective lens is controlled to focus the irradiated light beam on the information recording surface. an information reading device equipped with a focus servo device, comprising: first and second rectifying means for separately rectifying one polarity signal and the other polarity signal of the focus error signal; first and second low-pass filters each inputting the output signal of the rectifying means separately; an inverting buffer for inverting the output signal of the second low-pass filter; and an output signal of the first low-pass filter. comprising a signal selection circuit that selects and outputs the output signal having a higher level from the output signal of the inversion buffer; and a comparator that compares the output signal of the signal selection circuit with a reference voltage; An operation determination circuit for a focus servo device, characterized in that the operation state of the focus servo device is determined based on the output level of a comparator.