JPH01166369A - Reading signal amplifying circuit - Google Patents

Abstract

PURPOSE:To read information without error and amplifying a noise by amplifying the output signal of a direct current component removing means with a variable gain amplifier, outputting it as a reading signal and controlling a gain with the output signal of a direct current component extracting means. CONSTITUTION:For the output signal (a) of a pre-amplifier 4, a direct current component is removed by a high-pass filter 5 and the signal (a) is amplified by an automatic gain control (AGC) amplifier 7 and goes to a reading signal (d). For the output signal (a) of the pre-amplifier 4, the direct current component is extracted by a low-pass filter 9 and the reference voltage of a reference voltage source 10 is biased. Then, the signal (a) is added to the AGC amplifier 7 as a control signal VAGC2. This AGC amplifier 7 has a gain characteristic and the gain is controlled by the control signal VAGC2. Thus, the noise is suppressed and the reading error of the information is eliminated.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an optical disk device (including a magneto-optical disk device)
The present invention relates to a read signal amplification circuit.

(Conventional technology) FIG. 3 shows an example of a conventional optical disc device.

The optical disc 1 has information recorded as a pit train and is rotationally driven by a motor.The optical disc 1 is irradiated with light from a light source 2, and the reflected light is photoelectrically converted by a light receiving element 3. In this case, the amount of light reflected from the optical disc 1 becomes smaller at the pits on the optical disc 1 due to diffraction. The signal obtained from the light receiving element 3 is amplified by a preamplifier 4, and the DC component is removed by a high pass filter 5. The signal obtained from this high-pass filter 5 is controlled by automatic gain control ( AG
C) Controlled by circuit 6 to a substantially constant amplitude.

FIG. 4 shows the AGC circuit 6 mentioned above.

The AGC amplifier 7 amplifies the signal S from the high-pass filter 5 and outputs it as a read signal C, and the rectifier and smoothing circuit 8 consisting of a diode D, a resistor R, and a capacitor
The output signal C of the amplifier 7 is converted to DC to obtain the AGC reference voltage vA.
, cl to the AGC amplifier 7. AGC amplifier 7
has a gain characteristic as shown in Fig. 5, and the rectifying and smoothing circuit 8
The gain is controlled by the AGC reference voltage V A 6 C□ from V A 6 C□, and the larger the AGC reference voltage V AGCI, the lower the gain. This AGC circuit 6 is a kind of servo circuit.

The output signal C is controlled to have a substantially constant amplitude regardless of the amplitude of the input signal C.

However, in an optical disk device having such an AGC circuit 6, the gain of the AGC amplifier 7 becomes extremely high in the unrecorded portion of the optical disk 1, amplifying noise as shown in FIG. 2C. This noise also includes crosstalk from tracks adjacent to the track from which information is being read on the optical disc 1, so even if the part of the optical disc 1 from which information is being read is an unrecorded part, the information may be incorrectly recorded. This is inconvenient because the track may be read from the adjacent track.

(Objective) It is an object of the present invention to provide a read signal amplification circuit that eliminates the above-mentioned drawbacks and enables stable and error-free reading of information without amplifying noise in an optical disc device.

(Structure) The present invention provides an optical disc device that reads information recorded on a medium by irradiating light onto the medium from a light source and receiving the reflected light with a light receiving element, comprising: a preamplifier;
It includes a DC component extraction means, a DC component removal means, and a variable gain amplifier.

The preamplifier amplifies the output signal of the light receiving element, and the DC component extraction means extracts the DC component from the output signal of the preamplifier. The DC component removing means removes the DC component from the output signal of the preamplifier. The variable gain amplifier amplifies the output signal of the DC component removal means and outputs it as a read signal, and the gain becomes low when this output signal is large depending on the output signal of the DC component extraction means, and increases when the output signal of the DC component extraction means is small. controlled to be high.

FIG. 1 shows an embodiment of the invention.

In this embodiment, the signal from the light receiving element 3 is amplified into a readout signal d in the optical disc device,
The output side of the preamplifier 4 is branched into two, one of which is connected to the HPF 5, and the other is a low pass filter (LPF).
Connect to 9. The DC component of the output signal a of the preamplifier 4 is removed by the HPF 5, and the output signal a is amplified by the AGC amplifier 7 to become a readout signal d. Further, the DC component of the output signal a of the preamplifier 4 is extracted by the LPF 9, the reference voltage of the reference voltage source 10 is biased (added), and the AGC
It is applied to the amplifier 7 as a control signal V A G C □. The AGC amplifier 7 has a gain characteristic as shown in FIG. 5, and the gain is controlled by the control signal VAGCI.

Next, the present embodiment will be explained with reference to FIG.

The output signal a of the preamplifier 4 is generally as shown in FIG. 2a. In other words, the output signal a of the preamplifier 4 becomes a large voltage v0 in the unrecorded portion of the optical disk 1 because the amount of reflected light from the optical disk 1 increases, and in the recorded portion of the optical disk 1, the amount of reflected light decreases at the pit portion. , the voltage V2 becomes small and the amount of reflected light becomes small due to mutual interference even in the pit-free area, so the voltage V1 (V□≦v
0). ■Yo-v2 is the AC component in the output signal a of the preamplifier 4, the so-called RF multiplied signal amplitude (p-p value)
In preparation for the readout signal d being binarized by the subsequent binarization means, the output signal a of the preamplifier 4 is passed through the HPF 5.
It is extracted by removing the DC component. Conventionally, as shown in FIGS. 3 and 4, for the output signal as shown in FIG. 5 obtained from the HPF 5, the rectifying and smoothing circuit 8 in the AGC circuit generates an AG signal corresponding to the signal amplitude.
A C reference voltage V A 6 C was created, and the gain of the AGC amplifier 7 was controlled by this AGC reference voltage V A G e□. However, in the unrecorded part of the optical disc, AGC
Since the reference voltage V A G C becomes almost Ov, the gain of the AGC amplifier 7 becomes very large, and as a result, A
The output signal C of the GC amplifier 7 becomes as shown in FIG. 2C, and the noise in the unrecorded portion is amplified. In this embodiment, the output signal a of the preamplifier 4 is passed through the LPF 9, biased with a reference voltage, and the AGC reference voltage V is set as AGC2.
The gain of the GC amplifier 7 is controlled. The output signal e of the LPF 9 is as shown in FIG. 2e, and the reference voltage is a bias for determining the operating point of the AGC amplifier 7. LPF
According to the output signal e of 9 and FIG. 5, the gain of the AGC amplifier 7 is low in the unrecorded portion and high in the recorded portion. Generally, when the reflectance of the optical disk 1 decreases due to variations or deterioration and v2 approaches Ov, v2 cannot decrease further, so the gain of the AGC amplifier 7 increases and the amplitude of the read signal increases by 4% v z - v t becomes smaller. At this time, as a matter of course, the output signal (V + vz) /2 of the LPF 9 also decreases, so the gain of the AGC amplifier 7 increases, making it possible to compensate for the decrease in the amplitudes V and -V of the read signal. Furthermore, since the AGC amplifier 7 has a low gain in the unrecorded portion, it is possible to suppress noise components and eliminate misreading of information.

(Effects) As described above, according to the present invention, in an optical disc device that reads information recorded on the medium by irradiating light from a light source onto the medium and receiving the reflected light with the light receiving element, the light receiving element a preamplifier for amplifying the output signal of the
DC component extraction means for extracting a DC component from the output signal of the preamplifier, DC component removal means for removing the DC component from the output signal of the preamplifier, and amplifying the output signal of the DC component removal means. and a variable gain amplifier that outputs a readout signal and whose gain is controlled by the output signal of the DC component extraction means such that it becomes low when the output signal is large and becomes high when the output signal of the DC component extraction means is small. Therefore, the gain can be increased to cope with a decrease in the amplitude of the readout signal due to variations in the optical disc or changes over time, and stable information readout becomes possible. Furthermore, the gain is reduced in unrecorded areas on the optical disc, making it possible to suppress noise and eliminate misreading of information.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the same embodiment and a conventional example, FIG. 3 is a schematic diagram showing a conventional cutting disc device, and FIG. 4 is a circuit diagram showing the AGC circuit in the same optical disk device, and FIG.
FIG. 3 is a characteristic diagram showing the gain characteristics of a GC amplifier. 4... Preamplifier, 5... High pass filter, 7.
...AGC amplifier, 9...Low pass filter.

Claims (1)

[Claims] In an optical disc device that reads information recorded on the medium by irradiating light from a light source onto the medium and receiving the reflected light by a light receiving element, the preamplifier includes a preamplifier that amplifies the output signal of the light receiving element; a DC component extraction means for extracting a DC component from the output signal of the preamplifier; a DC component removal means for removing the DC component from the output signal of the preamplifier; and a readout signal by amplifying the output signal of the DC component removal means. and a variable gain amplifier whose gain is controlled by the output signal of the DC component extraction means such that it becomes low when the output signal is large and becomes high when the output signal of the DC component extraction means is small. Features a read signal amplification circuit.