JP2542463Y2 - Disk scratch detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a scratch detection circuit for an optical disc, which is suitable for use in a reproducing apparatus such as a compact disc.

(Prior Art) As shown in FIG. 3, a conventional flaw detection circuit for a disk has an output A from a four-division photodiode which converts reflected light from an optical disk into an electric signal in an optical pickup.
B, C, upon and supplied to the inverting amplifier of the same gain respectively D inverting input terminal A of the adder E consisting of the operational amplifier _{U 1 ', B', C} ', D' summing is applied to each another in and it is supplied to the integration circuit composed of the addition output from the resistor R ₁ and capacitor C ₁ Prefecture, the output of the integrating circuit operational amplifier U ₂ and the reference voltage source P
Is applied to the comparator F, which is compared with the voltage level of the reference voltage source P, and the comparator F detects that the output of the integrating circuit has dropped below the voltage level of the reference voltage source P. That had been detected.

In this way, the focus output by the focus servo circuit is relaxed by the detection output that detects the presence of a flaw.

(Problem to be solved by the invention) However, when using the conventional flaw detection circuit as described above,
For wounds that are long in time, after reaching a state without scratches,
There is a problem in that the period until the flaw detection output disappears, that is, the recovery time becomes long.

Will be described with reference to this drawing, when there is a scratch time t ₀ ~t ₁ period and the time t ₂ period ~t ₃ as shown in FIG. 2 (a), the output of the adder E Chapter 2 As shown in FIG. Here at time t ₀ ~t ₁ period short, the time t ₂ ~t ₃
Is long.

When the flaw detection for a minor wound as the wound for a period of time t ₀ ~t _1, since the focus is loosened even during this short period, not detected as wound against scratches such minor For this purpose, the time constant of the integrating circuit must be set to a considerably large value. FIG. 2 (b) shows the output of the integrator circuit in a state where the time constant of the integrator circuit is increased. In FIG. 2, the dashed line indicates the voltage level of the reference voltage source P. As apparent from FIG. 2 (b), is not flaw detection for a short period of scratches period t ₀ ~t _1, period t ₂
It will be flaw detection for wounds ~t _3. However, since the time constant of the integrating circuit is set to be large as described above, the recovery time at the time of flaw detection is not longer than the period shown in FIG.
Long become a problem as shown in T ₁ so that occurs.

An object of the present invention is to provide a flaw detection circuit which has a short recovery time for a long flaw or a large flaw, and has a low sensitivity to flaw detection.

(Means for Solving the Problems) According to the present invention, a disc flaw detection circuit includes an adder for receiving reflected light from an optical disc by a four-division photodiode and adding each output converted into an electric signal; When the output is input, the peak hold means and the charge time constant of the peak hold means are set sufficiently smaller than the discharge time constant,
And a time constant setting means for setting the discharge time constant of the peak hold means to a time constant sufficiently larger than the charge time constant, and a comparison means for detecting that the hold output of the peak hold means has become equal to or lower than the reference voltage level, The detection output from the comparing means is a flaw detection output.

(Operation) When the optical disk is damaged, the level of the output of the adding means decreases during the period of the damage. Therefore, the output level of the peak holding means for peak holding the output of the adding means also decreases. At the time of this decrease, the discharge time constant of the peak hold means is set to be sufficiently larger than the charge time constant by the time constant setting means. It will fall below the reference voltage level with a longer delay. On the other hand, the output of the addition circuit increases from the position where the scratch disappears, and the charge time constant of the peak hold means is set sufficiently smaller than the discharge time constant, so that the hold output of the peak hold means is rapidly increased. In this case, the reference voltage level exceeds the reference voltage level with a slight delay from the position where the scratch disappears.

Therefore, in the case of a minor flaw, the hold output of the peak hold means decreases, but recovers rapidly and does not decrease below the reference voltage level, and no minor flaw is detected. Even when the flaw is not insignificant, the hold output of the peak hold means increases rapidly from the disappearance of the flaw, and the recovery time at the time of flaw detection can be short.

(Example) Hereinafter, this invention is demonstrated with an Example.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The outputs A, B, C, and D from the four-division photodiode are supplied to inverting amplifiers having the same gain, and are inverted.
Input terminal A of the adder E consisting of the operational amplifier U ₁ ', B',
C 'and D' are separately applied and added. Addition output diode D from the adder E, the resistance R ₂ and applied to the peak hold circuit comprising a capacitor C _2, the capacitor C ₂ and a resistor R ₃ in parallel, with a capacitor C ₂ and a resistor R ₃ A discharge circuit having a large time constant is formed. Here, the resistors R ₂ and R ₃ set the charging time constant of the peak hold circuit to a time constant sufficiently smaller than the discharge time constant so that the hold output of the peak hold circuit recovers promptly after the end of the damage, and the discharge time constant is negligible. The time constant setting means is configured to set a time constant sufficiently larger than the charging time constant so as not to detect a flaw. The hold voltage held by the peak hold circuit, that is, the terminal voltage of the capacitor C ₂ is applied to the comparator F,
The terminal voltage level of the C ₂ is compared with the voltage level of the reference voltage source P, there is a flaw by detecting the terminal voltage level of the capacitor C ₂ is lowered below the voltage level of the reference voltage source P by the comparator F Detect that.

The operation of this embodiment configured as described above will be described.
The outputs A, B, C, and D obtained by converting the reflected light from the optical disk into electric signals by a four-division photodiode are inverted and amplified, and the outputs added by an adder E are as shown in FIG. 2 (a). And That period t ₀ ~t ₁ of period length of the temporally short minor scratches and duration t ₂ ~t ₃ of period length of the temporally long scratches assumed to be on the optical disk.

The output of the adder E is at a predetermined potential in a portion having no flaw, and is held by a peak hold circuit.
That the terminal voltage of the capacitor C ₂ is maintained at a predetermined voltage level. Period t ₀ ~t charging the capacitor C ₂ in temporally short there is a slight crack portion ₁ is stopped during the period t ₀ ~t _1, charge of the capacitor C ₂ is connected through a resistor R ₃ discharge Is done. But the resistance of the resistor R ₃ is set larger, the terminal voltage of the capacitor C ₂ for constant is set to be larger when the by the capacitor C ₂ and the resistor R ₃ is not throat no changes殆, comparison of the comparator F The output remains at high potential. That is, no minor flaw is detected.

In a portion where there is a period t ₂ ~t ₃ of period length of the temporally long scratches, charging of the capacitor C ₂ is stopped during the period t ₂ ~t _3, the charge of capacitor C ₂ is through a resistor R ₃ Is discharged.
But the time constant due to the capacitor C ₂ and the resistor R ₃ as described above is set large, the terminal voltage of the capacitor C ₂ with the discharge time constant decreases. The terminal voltage level of the capacitor C ₂ in the middle of decrease becomes below the voltage level indicated by a one-dot chain line in FIG. 2 of the reference voltage source P (c), the output of the comparator F becomes a high potential and low potential, scratches Is detected. This state continues until a time t _3, the output voltage of the adder E at time t ₃ is returned to a predetermined voltage level, the capacitor C ₃ from time t ₃ is charged. However, since the diode D is present, the charging time constant of the peak hold circuit by a resistor R ₂ and capacitor C ₂ is not permissible be set small, the charging time constant is set small. Thus the charging of the capacitor C ₂ is being rapidly carried out, the terminal voltage of the capacitor C ₂ is going to rise rapidly. During this rise, the capacitor C ₂
Terminal voltage level exceeds the voltage level of the reference voltage source P,
At this time, the comparison output of the comparator F changes from the low potential to the high potential, and it is detected that the flaw is no longer present.

This state is a is as shown in FIG. 2 (c), the period of the output becomes the low potential of the comparator F is a period shown in T _3, the output of the comparator F from gone scratches high potential recovery time to return has become a as listed in T ₂ in FIG. 2 (c), in a very short time from the return period T ₁ of the conventional example. Further, the time when the output of the comparator F changes from the high potential to the low potential is later than in the case of the conventional example, and the sensitivity to the detection of the flaw is reduced.

(Effect of the invention) As described above, according to the invention, the peak hold means to which the addition output of the addition means is input, and the charge time constant of the peak hold means are set sufficiently smaller than the discharge time constant.
And a time constant setting means for setting the discharge time constant of the peak hold means to a time constant sufficiently larger than the charge time constant, so that a scratch detection output can be provided for a long scratch or a large scratch on the optical disc. Return time is shorter,
Even if there is no flaw, the period in which the focus is loosened almost disappears.

In addition, when each electric signal is output from the four-division photodiode at the time of starting the disk, there is also an effect that the normal operation state can be entered, for example, focusing is performed early because the return time is short as described above. .

Furthermore, since the discharge time constant is set to a large time constant, the sensitivity for flaw detection is reduced, and no flaw detection is performed for minor flaws.

In addition, since the output of the four-division photodiode is added to perform flaw detection, the output level is large and erroneous detection hardly occurs. The tracking servo circuit is turned off, and the focus servo circuit is operated. This has the effect that the detection of scratches does not become impossible even during the operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a timing chart for explaining the operation of the embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a conventional example. D ...... diode, C ₂ ...... capacitor, E ...... adder,
F ...... comparator, P ...... reference voltage source, R ₂ and R ₃ ...... resistance, U ₁ and U ₃ ...... operational amplifier.

Claims (1)

(57) [Scope of request for utility model registration] 1. An adder for receiving reflected light from an optical disk by a four-division photodiode and converting each output converted into an electric signal, a peak hold unit receiving an output of the adder as an input, and charging the peak hold unit. Time constant setting means for setting the time constant sufficiently smaller than the discharge time constant and setting the discharge time constant of the peak hold means to a time constant sufficiently larger than the charge time constant, and the hold output of the peak hold means being equal to or lower than the reference voltage level. And a comparing means for detecting that the disc has been reduced, and wherein a detection output from the comparing means is used as a flaw detection output.