JP2703198B2 - Optical disc player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus, and more particularly to an optical disk reproducing apparatus capable of ensuring reading accuracy even when a so-called eye pattern is deteriorated.

[0002]

2. Description of the Related Art Optical discs represented by compact discs (CDs) are widely used as randomly accessible audio, navigation systems or mass storage devices for computers. The so-called eye pattern is the most important item when reading an optical disc in an optically non-contact manner.

FIG. 7 shows an example of a good eye pattern and a binarized signal. The read signal (a) has the same magnitude in the positive and negative directions about a reference value. Therefore, since the angle at which the read signal crosses the reference value is constant, the binary signal (b)
Has no jitter. However, the read signal drifts due to defocusing of the optical system, circumferential inclination of the optical disc, coma of the objective lens, astigmatism of the laser or optical components, or spherical aberration of the lens, and the eye pattern is degraded.

FIG. 8 shows an example of an eye pattern having a drift and a binarized signal. The read signal (c) has a small amplitude in the positive direction and a large amplitude in the negative direction with respect to the reference value. For this reason, jitter occurs in the binary signal (d). The deterioration of the eye pattern appears as jitter when the read signal is binarized, and a read error occurs when the jitter exceeds a predetermined threshold.

An optical disk reproducing apparatus using a time average value of a read signal as a threshold for binarization in order to suppress the occurrence of jitter due to the drift of the read signal has been conventionally used.

[0006]

However, the deterioration of the eye pattern is not only caused by DC drift,
It is also caused by a decrease in amplitude due to laser deterioration or an asymmetrical amplitude due to tilt of the optical axis. In particular, the decrease in amplitude not only occurs uniformly, but also decreases as the length of the pits formed on the optical disk becomes shorter.

FIG. 9 shows an eye pattern when the amplitude of a read signal having a short bit length is reduced. The amplitude of a 3T signal is the smallest, and the amplitude of a 4T signal is also slightly smaller. In this case as well, the occurrence of jitter cannot be avoided, and the occurrence of jitter is irregular and the rate of occurrence of read errors increases.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide an optical disc reproducing apparatus capable of ensuring reading accuracy even when a reading signal becomes abnormal.

[0009]

According to a first aspect of the present invention, there is provided an optical disk reproducing apparatus which limits an optical head to a predetermined limited amplitude if the amplitude of a read signal output from the optical head is equal to or greater than a predetermined limited amplitude. Amplitude limiting means, an amplitude adjusting means for adjusting the output of the amplitude limiting means to a predetermined amplitude, a comparing means for comparing the output of the amplitude adjusting means with a threshold value to binarize, and a signal outputted from the comparing means. Integrating means for integrating the binarized signal and feeding it back as a threshold value of the comparing means.

An optical disc reproducing apparatus according to a second aspect of the present invention is a reference value changing device for changing a reference value of an amplitude limit value of an amplitude limiter and a reference value of a predetermined amplitude of an amplitude adjuster in accordance with an integral value of an integrator. Means are further provided. An optical disc reproducing apparatus according to a third aspect of the present invention includes a DC cutoff unit between the optical head and the amplitude limiting unit.

According to a fourth aspect of the present invention, there is provided an optical disk reproducing apparatus, comprising: a DC component extracting means for extracting a DC component from an output signal of an optical head; and an amplitude limiting means based on the DC component extracted by the DC component extracting means. The apparatus further includes amplitude limit reference value changing means for determining a reference value of the limit value. An optical disc reproducing apparatus according to a fifth aspect of the present invention provides a minimum period inversion signal extracting unit that extracts a minimum period inversion signal from an output signal of an optical head, and a minimum period inversion signal extracted by the minimum period inversion signal extraction unit. The apparatus further includes amplitude limit value changing means for determining an amplitude limit value of the amplitude limit means.

[0012]

In the optical disk reproducing apparatus according to the first invention, a read signal having a certain amplitude or more is limited by a threshold value, and then amplified to be binarized. In the optical disc reproducing apparatus according to the second invention, the limit value of the amplitude is changed based on the average value of the binarized signal.

In the optical disk reproducing apparatus according to the third invention, the DC component included in the read signal is removed by the high-pass filter. In the optical disc reproducing apparatus according to the fourth invention, the limit value of the amplitude is changed based on the DC component included in the read signal. In the optical disk reproducing apparatus according to the fifth invention, the amplitude limit value is changed based on the minimum cycle amplitude in the read signal.

[0014]

FIG. 1 is a block diagram of a compact disk reproducing apparatus, which is a compact disk (hereinafter referred to as a CD) 1.
Numeral 01 is rotationally driven by a spindle motor 102. The information recorded on the CD is the optical head 103
The signal is amplified by the RF amplifier 104 and demodulated into a digital signal by the demodulator 105.

The output of the RF amplifier 104 is the RF PLL 10
The clock is also supplied to the spindle motor 107 and the clock is reproduced by the spindle motor 107 via the spindle servo 107.
2 is changed to control the linear velocity at the time of reading information constant. The output of the RF amplifier 104 is also supplied to a tracking / focus servo 108, which drives an actuator (not shown) incorporated in the optical head 103 to control tracking and focusing.

Further, the tracking signal drives a thread feed motor 110 via a slide drive circuit 109,
The optical head 103 is moved in the radial direction of the CD 10. The digital signal demodulated by the demodulator 105 performs error data detection and correction by an error detection and correction unit (hereinafter, referred to as ECC) 111, is converted into an analog signal by a D / A converter 112, and is amplified by an audio amplifier 113. Is output.

The operation of the compact disk reproducing apparatus is controlled by a control unit 12 composed of a microcomputer. The present invention is applied to circuits from the optical head 103 to the demodulator 105. FIG. 2 is a circuit diagram of the first reading circuit. A reading signal output from the optical head 103 is input to the amplitude limiting circuit 130.

The amplitude limiting circuit 130 is composed of zener diodes 130a and 130b which are connected in opposite directions to ground. That is, the amplitude of the read signal whose absolute amplitude is greater than or equal to the Zener voltage with respect to the ground is limited by the Zener voltage. The Zener voltages of the Zener diodes 130a and 130b are selected so that the amplitude of the read signal having a low frequency, that is, the amplitude of the read signal having a long pit length is limited.

Therefore, the amplitude of the read signal when the pit length is short, that is, the amplitude of the read signal having a high frequency is output without restriction. Subsequently, the read signal is input to the RF amplifier 104. The RF amplifier 104 is a circuit having an automatic gain adjustment function.
4b and a gain adjusting FET 104c.

That is, the output of the main amplifier 104a is compared with the set value in the error amplifier 104b, and the error signal is supplied to the gate of the gain adjusting FET 104c. Therefore, the feedback impedance of the main amplifier 104a is adjusted, and the output of the main amplifier 104a has a constant amplitude. The output of the RF amplifier 104 is supplied to a demodulator 105 and converted into a binary signal.

The demodulator 105 includes a DC component cutting capacitor 105a, a comparator 105b, and an integrating capacitor 10.
5c and a buffer amplifier 105d. The read signal has its DC component cut by the DC component cutting capacitor 105a and is compared with a threshold value. If the read signal from which the DC component has been cut is greater than the threshold value, the output of the comparator 105b is at "H" level, and if it is smaller, the output of the comparator 105b is at "L" level.

The output of the comparator 105b is integrated by the integration capacitor 105c, and the average value of the binary signal is calculated. This average value is supplied to the comparator 105b via the buffer amplifier 105d and functions as a threshold. That is, when the "H" level or the "L" level is continuously output, the read signal is considered to have drifted, and the threshold value for conversion to the binarized signal is changed to suppress further drift. .

FIG. 3 is a circuit diagram of the second reading circuit.
Output of buffer amplifier 105d of demodulator 105 and Zener diodes 130a and 130b of amplitude limiting circuit 130
The error amplifier 104b of the RF amplifier 104 and the gain adjustment FET 104c are connected by a wiring 131. As a result, the reference potentials of the Zener diodes 130a and 130b of the amplitude limiting circuit 130, the error amplifier 104b of the RF amplifier 104, and the gain adjustment FET 104c are changed by the average value of the binarized signal, and the occurrence of jitter during binarization is generated. It is suppressed more reliably.

FIG. 4 is a circuit diagram of a third reading circuit,
A high-pass filter 132 is arranged between the optical head 103 and the amplitude limiting circuit 130. The high-pass filter 132 includes a capacitor 132a, a resistor 132b, and a buffer amplifier 132c. Light that is directly reflected on the CD surface during reading by the optical head 103 appears as a DC component of the read signal. Cause.

Therefore, a high-pass filter 132 is provided to remove the DC component in the read signal. FIG. 5 is a circuit diagram of a fourth reading circuit, which is another configuration for removing a DC component of a reading signal. That is, the output of the optical head 103 is input to the low-pass filter 133, and the DC component in the read signal is extracted. The low-pass filter 133 includes a resistor 133a, a capacitor 133b, and a buffer amplifier 133c.

A wiring 133d is further provided to use the output of the low-pass filter 133 as the reference potential of the amplitude limiting circuit 130 and the RF amplifier 104. According to the present embodiment, the amplitude limiting circuit 1 is controlled by the DC component in the read signal.
30 and the reference potential of the RF amplifier 104 are changed.
FIG. 6 is a circuit diagram of the fifth reading circuit, which makes it possible to limit the amplitude more accurately.

The length of the pit formed on the CD surface is 3T.
To 11T, but the shorter the pit length, the smaller the amplitude. Therefore, in the fifth reading circuit, the reference potential of the amplitude limiting circuit is changed based on the amplitude of the read signal having a short pit length. That is, the amplitude limiting circuit 130 of the fifth reading circuit includes a band-pass filter 130c, a detecting diode 130d, adders 130e and 130f, and amplitude limiting diodes 130g and 130h.

That is, the output of the RF amplifier 104 is branched and input to the band-pass filter 130c to output 3T signals in the read signal.
The component is extracted, and 3T is detected by the detection diode 130d.
Extract the amplitude signal of the component. In the present embodiment, the threshold value of the comparator 105b is corrected with a 3T component amplitude signal and used as the reference potential of the amplitude limiting circuit 130.

That is, the threshold value of the comparator 105b and 3
The T component amplitude signals are added by adders 130e and 130f and applied to amplitude limiting diodes 130g and 130h. With this configuration, the amplitude of the read signal can be limited based on the minimum amplitude in the read signal, and the occurrence of jitter can be suppressed more reliably.

[0030]

According to the optical disk reproducing apparatus of the first invention, the occurrence of jitter is suppressed by limiting the read signal having a certain amplitude or more with a threshold value, and then amplifying and binarizing the read signal. Becomes possible. According to the optical disc reproducing apparatus of the second invention, it is possible to suppress the drift of the binarized signal by changing the limit value of the amplitude based on the average value of the binarized signal.

According to the optical disc reproducing apparatus of the third invention, it is possible to suppress the read signal from being asymmetrically limited in amplitude by removing the DC component included in the read signal by the high-pass filter. Become. 4th
According to the optical disk reproducing apparatus of the present invention, it is possible to suppress the read signal from being asymmetrically limited by changing the amplitude limit value based on the DC component included in the read signal.

According to the optical disk reproducing apparatus of the fifth aspect, it is possible to suppress the occurrence of jitter by changing the amplitude limit value based on the minimum cycle amplitude in the read signal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a compact disc reproducing apparatus.

FIG. 2 is a circuit diagram of a first reading circuit.

FIG. 3 is a circuit diagram of a second reading circuit.

FIG. 4 is a circuit diagram of a third reading circuit.

FIG. 5 is a circuit diagram of a fourth reading circuit.

FIG. 6 is a circuit diagram of a fifth reading circuit.

FIG. 7 shows a good eye pattern and a binarized signal.

FIG. 8 shows an eye pattern having a drift and a binarized signal.

FIG. 9 is an eye pattern when the amplitude of a read signal having a short bit length is reduced.

[Explanation of symbols]

 103 optical head 104 RF amplifier 105 demodulator 130 amplitude limiting circuit 131 wiring 132 high-pass filter 133 low-pass filter

Claims (5)

(57) [Claims] An optical head; amplitude limiting means for limiting the amplitude of a read signal output from the optical head to a predetermined limit amplitude if the amplitude is equal to or greater than a predetermined limit amplitude; Amplitude adjusting means for making the amplitude uniform, comparing means for comparing the output of the amplitude adjusting means with a threshold to binarize, and integrating the binarized signal output from the comparing means with the comparing means And an integrating means for feeding back as a threshold value. 2. The apparatus according to claim 1, further comprising a reference value changing means for changing a reference value of the amplitude limit value of said amplitude limiting means and a reference value of a predetermined amplitude of said amplitude adjusting means in accordance with an integrated value of said integrating means. 2. The optical disc reproducing apparatus according to 1. 3. The optical disk reproducing apparatus according to claim 1, wherein a DC cutoff means is provided between said optical head and said amplitude limiting means. 4. A DC component extracting unit for extracting a DC component from an output signal of the optical head, and a reference value of an amplitude limit value of the amplitude limiting unit is determined based on the DC component extracted by the DC component extracting unit. 4. The optical disk reproducing apparatus according to claim 1, further comprising an amplitude limit reference value changing unit. 5. A minimum-period inversion signal extracting means for extracting a minimum-period inversion signal from an output signal of said optical head, and said amplitude limiting means based on the minimum-period inversion signal extracted by said minimum-period inversion signal extraction means. 5. An apparatus according to claim 1, further comprising an amplitude limit value changing unit for determining an amplitude limit value.
The optical disc reproducing apparatus according to any one of claims 1 to 7.