JPS6159626A - Mark detection system of optical disc - Google Patents

Abstract

PURPOSE:To eliminate the variance of waveform and prevent erroneous detection of sector marks due to the degradation of resolution to improve the read reliability by reproducing a low frequency component by a DC circuit on a basis of the signal level of total reflected just before the sector mark. CONSTITUTION:An amplified read signal 1 is applied to a DC reproducing circuit 29 and has a DC component restored, and a DC reproduced output waveform 30 is uniformed to the total reflection signal level and is inputted to a peak holding circuit 31. The circuit 31 holds a peak voltage 32 of the sector mark and divides this voltage to output a reference voltage 33. The waveform 30 is compared with the voltage 33 by a comparator 34 to output a pulse output 35. The output 35 is a pulse shorter than the sector mark independently of resolution, thus preventing erroneous detection of sector marks.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for detecting a special mark composed of a long hole on an optical disc.

[Background of the invention]

When recording information on an optical disc, for example,
As described in the specification of No. 51230, it is common to attach a mark to each recording unit to indicate its starting point. Here, the recording unit is called a sector, and the mark mentioned above is called a sector mark. The sector mark is another isolated 'KP (first sector mark) recorded as data on the track TR.
It is composed of a combination of lengths 'F: and Q as shown in Fig. 1 (B) so that it can be distinguished from Fig. 1 (A)).

Therefore, when the optical head scans a track in which the sector mark part M consisting of the long KQ and the data part consisting of the vertical hole P are continuous as shown in FIG. 2(A), the sector mark waveform output from the optical head is It will look like figure (B). In this case, since DC amplifiers with good high frequency characteristics are expensive, AC
When amplification is performed using a coupled high-frequency amplifier, the waveform after amplification will have components that fluctuate over time, as shown in FIG. 2(C). For this reason, conventionally, a circuit as shown in FIG. 3 has been used to remove this variation before detecting a sector mark.

In FIG. 3, the amplified read signal 1 is shaped into a pulse by the pulse forming circuit 2, and is input to the pulse width/position detection circuit 3, where the sector mark is recognized from the width and positional relationship. A sector mark detection signal 4 is output.

In the pulsing circuit 2, a differentiating circuit 5 removes from the read signal 1 the low frequency component of the signal which is a factor causing temporal fluctuations, and generates a differentiated waveform 6 shown in FIG. The differential waveform 6 is input to comparators 9 and 10, and compared with the positive reference voltage and the negative reference voltage generated from the reference voltage and pressure generators 7 and 8, respectively, to set and reset the S flip-flop 11. As a result, a pulsed output waveform 14 is obtained from the flip-flop 11. The sector mark is made up of four combinations of two types of long holes, TI and T2, and the T1 width long hole detector 15 detects a T1 width pulse, and the T2 width long hole detector 16 detects a 12 width pulse. It is detected that there was a pulse. These detection signals are appropriately delayed by the delay circuit 17 or 18, and
When detecting a normal sector mark, a plurality of long detection signals are all input to the determination circuit 19, and a sector mark detection signal 4 is output based on the determination result of the positional relationship to the length.

In FIG. 4, the plus side reference voltage 12 and the minus side reference voltage 13 must each be sufficiently larger than the noise 21 on the differential waveform 6 caused by the disk noise 20.

The problem with the conventional method is that sector marks are erroneously detected even in the data section when the resolution is reduced. That is, the data portion under normal conditions has a sufficient imaging width, as shown by waveform 1' in FIG. In this case, the differential waveform 6' also exceeds the plus side reference voltage 12 and the minus side reference voltage 13, and the pulsed output waveform 14' becomes a series of short pulse widths, so that it will not be erroneously detected as a sector mark. However, when the resolution decreases, the amplitude of the data section waveform 1' becomes smaller as shown in FIG. 6, so the differential waveform 6'' also becomes smaller.
The voltage is almost the same as the positive reference voltage 12 and the negative reference voltage 13. For this reason, when the pulsed output 14' generates a part with a long pulse width, as in the case of a long pulse, and the pulse width and positional relationship are the same as a sector mark, it is incorrectly detected as a sector mark. Sometimes. Due to this, there is a possibility that the reading reliability of the low-resolution portion may be lowered.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a mark detection method that eliminates waveform fluctuations caused by the use of an AC-coupled high-frequency amplifier, and that makes it possible to extract digitized signal pulses of sector marks without being affected by resolution degradation. .

[Summary of the invention]

Since the sector mark is located at the beginning of each sector, an unwritten area called a gap continues for a certain length immediately before the sector mark. This part is at the signal level of total reflection, so
Using this level as a reference, it is possible to reproduce the low frequency components lost in the AC coupled high frequency amplifier using a DC regeneration circuit used in television receivers and the like.

In the conventional method, a differentiating circuit was used to further remove low frequency components, which also removed the low frequency components of the sector marks themselves, and as a result, it was no longer possible to distinguish between sector marks and other signals. , regeneration of low frequency components using a DC regeneration circuit is effective in solving this problem.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 7 and 8.

FIG. 7 shows a configuration diagram of a pulsing circuit according to the present invention, which replaces the pulsing circuit 2 of FIG. 3, which has been explained and illustrated as a conventional example.

The amplified face-picking signal 1 is applied to a DC regeneration circuit 29, and the DC signal is recovered. As a result, the DC reproduction output waveform is adjusted to the total reflection signal level and input to the peak hold circuit 31, as shown in FIG. The peak hold circuit 31 holds the peak voltage 32 of the sector mark, divides it at an appropriate voltage division ratio, and outputs a reference voltage 33. [Theta flow reproduced output waveform 30 is determined by the comparator 34 when the base thread voltage 3
3, resulting in a pulsed output 35. According to this method, the data part pulsed output 36 is
, the pulse is sufficiently smaller than the sector mark, and erroneous detection of the sector mark in the data area can be prevented.

〔Effect of the invention〕

According to the present invention, waveform fluctuations caused by the use of an AC-coupled high-frequency amplifier can be removed, and erroneous sector mark detection due to a decrease in resolution can be prevented, thereby providing a highly reliable and low-cost sector mark detection circuit.

[Brief explanation of the drawing]

Figures 1 (A) and (B) are diagrams for explaining the relationship between data and marks on an optical disk, respectively, and Figure 2 (A)
, CB), (C) is an explanatory diagram of the length of a sector mark and a read waveform, FIG. 3 is an explanatory diagram of a conventional sector mark detection circuit, and FIGS. 4 to 6 are explanatory diagrams of signal waveforms in the above conventional circuit. FIG. 7 is a circuit diagram showing an embodiment of the present invention, and FIG. 8 is a waveform explanatory diagram thereof. 1st concave θ 0100f σ θ θ l0t)z2
figure

Claims (1)

[Claims] 1. In a signal reproducing system from an optical disc where mark information is recorded on the track through elongated holes, data information is recorded through vertical holes, and the unrecorded area has a total reflection surface, the output signal from the optical head is input to perform total reflection. A DC regeneration circuit that outputs a signal with a uniform level on the side, a peak hold circuit that holds the output signal peak voltage of the DC regeneration circuit, divides it, and outputs it as a reference voltage, and a peak hold circuit that outputs the output signal as a reference voltage. A mark detection method comprising a voltage comparator that binarizes the output of the DC reproduction circuit as a reference, and the mark information is identified from a pulse pattern obtained from the voltage comparator.