JPH0253224A - Waveform shaping circuit - Google Patents

Abstract

PURPOSE:To obtain a digital signal always having an approximately 50% duty ratio by holding reference voltage immediately before a transition from an interval in which a signal corresponding to a pit in an analog regenerative signal exists to another interval in which the above-mentioned signal does not exist when the signal corresponding to the pit does not exist in the analog regenerative signal. CONSTITUTION:The analog regenerative signal from a pickup is compared with the reference voltage and waveform-shaped into a digital signal by a comparator 1, and control means 2 and 3 detect the time mean value of the digital signal from the comparator 1 and control the reference voltage so that the time mean value can be equal to the intermediate voltage between the high level and the low level of the digital signal. Further, a holding circuit 4 holds the reference voltage immediately before the transition from the interval in which the signal corresponding to the pit in the analog regenerative signal exists to the interval in which the signal corresponding to the pit does not exist when the signal corresponding to the pit does not exist in the analog regenerative signal. Thus, the digital signal always having the approximately 50% duty ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveform shaping circuit in a disk device that uses a pickup to read information recorded on a disk as a pit string.

[Conventional technology]

The modulated data recorded on the disc, such as the EFM code used in compact disc devices, has an average duty ratio of 5C% (the average length of each high-level and low-level section of the modulated data is 5C%). A waveform shaping circuit utilizing this fact (1:1 ratio) was published in Japanese Patent Application Laid-Open No. 59-7763.
It is known from Publication No. 4. In this waveform shaping circuit, as shown in FIG. 7, an analog playback signal S read from a disk by a pickup in a disk device is compared with a reference voltage E2 by a comparator 1 and waveform-shaped into a digital signal S2. Signal S2
is output to the demodulation circuit and simultaneously integrated by the integrating circuit 2 to obtain the average voltage (time average value) E of the digital signal S2.
l is found. The output voltage E of the integrating circuit 2 is converted to the high level of the digital signal S2 by the subtracter 3. It is compared with a reference voltage E set to an intermediate voltage (V, +VL)/2 between the low level vL and the low level vL, and the reference voltage E is subtracted, and the output voltage of the subtracter 3 is set as the reference voltage E2.

According to this waveform shaping circuit, the comparison is performed so that the average voltage of the digital signal S□ after waveform shaping is equal to the intermediate value between the high level and the low level, that is, the duty ratio of the digital signal S2 is 50%. The reference voltage (slice level) E to the device 1 is controlled to prevent recording power fluctuations in the disk device.

Even if the analog reproduced signal S becomes asymmetrical as shown in FIG. 8 due to variations in characteristics of the disk medium, waveform shaping can be performed at the optimum slice level E□.

[Problem to be solved by the invention]

The above-mentioned waveform shaping circuit is effective when reproducing data continuously recorded on a disk medium such as in a compact disk device, but general optical disk devices that can record new data on a disk, etc. Magneto-optical disk devices have the following drawbacks.

Usually, in a disk device, recording and reproduction are performed by dividing the track of the disk medium into sectors.

Information indicating a sector address called an ID is recorded at the beginning of each sector on a disk medium, and actual data is recorded between the IDs of each sector. Of course, before data is recorded on a disk medium, there is no data between the IDs of each sector, and when data is recorded on the disk medium, the portion between the IDs of each sector may be lost due to changes in the rotation speed of the disk medium. To prevent data from being accidentally overwritten on the ID section of the disk medium due to changes in the time it takes to pass through the recording position, a sufficient gap must be created in advance between the ID on the disk medium and the data recording section. provided.

When a signal is reproduced from such a disk by a disk device, an analog reproduced signal S shown in FIG. 9 is obtained from the pickup. This analog playback signal S work is ID
There is a mixture of signal sections where signals such as and data exist, and no-signal sections such as gaps and unrecorded areas. Here, it is assumed that the signal section includes an asymmetric signal as shown in FIG. At this time, when the waveform shaping circuit of FIG. 7 performs waveform shaping on the analog reproduction signal S, the slice level E2 changes relatively slowly as shown in FIG. 9, and as a result, the duty ratio of the output signal s2 From the time you enter the part where ID and data exist, it slowly decreases to 50%.
Set to . If this settling time is too short, the instantaneous change in the duty ratio of the output signal S due to the data modulation pattern will cause the slide level E2 to change and become unstable, so the output signal S will be inverted. It needs to be sufficiently longer than the cycle. As a result, the duty ratio of the output signal S□ does not reach 50% for a while after entering the portion where the ID and data exist, and there is a risk that the data may be erroneously reproduced due to a data demodulation error or a synchronization error.

The present invention solves the above-mentioned drawbacks, and the duty ratio is always approximately 50.
% of the digital signal.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a disk device that uses a pickup to read information recorded as a bit string on a disk. control means for detecting a time average value of the digital signal from the comparator and controlling the reference voltage so that the time average value is equal to an intermediate voltage between a high level and a low level of the digital signal; When a signal corresponding to the pit does not exist in the analog playback signal, the criterion immediately before transitioning from a section in the analog playback signal where the signal corresponding to the pit record exists to a section in which the signal corresponding to the pit does not exist. It is equipped with a hold circuit that holds the voltage.

[For production]

The analog playback signal from the pickup is compared with a reference voltage by a comparator and waveform-shaped into a digital signal.The control means detects the time average value of the digital signal from the comparator, and this time average value is used as the digital signal. The reference voltage is controlled to be equal to an intermediate voltage between high level and low level. Then, when a signal corresponding to a pit does not exist in the analog playback signal, the hold circuit detects the reference voltage immediately before transition from a section in which a signal corresponding to a pit exists in the analog playback signal to a section in which a signal corresponding to a pit does not exist. hold.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and the same parts as FIG. 7,
Identical signals are given the same reference numerals.

In this embodiment, the output voltage E2 of the subtraction a3 is inputted to the comparator 1 via the hold circuit 4 as a reference voltage (slice level) E3'. The hold circuit 4 outputs the input voltage E2 from the subtracter 3 as it is as a reference voltage E2' to the comparator 1 in a signal section where an information signal exists in the analog reproduction signal S8 from the pickup, and outputs the input voltage E2 from the subtracter 3 as it is as a reference voltage E2', In the no-signal section where there is no information signal, the input voltage E immediately before that period is held as the hold signal Ho1d.
is held and output to the comparator 1 as a reference voltage E,'. The digital signal S2 from comparator 1 is returned.

It is demodulated by the open circuit 5 and output to the host device, and the address (ID) is detected by the address detection circuit 6 and a signal synchronized with the address part (ID part) and data part is output to the host device. It is output to the hold circuit 4 as a hold signal Ho1d.

Since this address detection circuit 6 is generally provided in a disk device to record and reproduce data in units of sectors, it is possible to obtain the hold signal Ho1d without newly providing special hardware.

FIG. 2 shows the operation of this embodiment.

The analog reproduction signal S from the pickup has an ID section and a data section intermittently. Now, it is assumed that in this analog reproduction signal S, the signals of the ID part and the data part are asymmetrical as shown in FIG. When the analog reproduction signal S1 enters the first signal section (ID section in FIG. 2), the hold circuit 4 receives the hold signal Ho1d from the address detection circuit 7.
The circuit becomes conductive (through) and outputs the output voltage E2 of the subtracter 3 as it is to the comparator 1 as the reference voltage E2', so that the duty ratio of the digital signal S2 from the comparator 1 becomes 50% on average. controlled by. When the signal section of the analog playback signal S1 ends and becomes a no-signal section, the hold circuit 4 enters a hold state by the hold signal Ho1d from the address detection circuit 7, and immediately before the analog playback signal S1 transitions from the signal section to the no-signal section. input voltage E
□ is held and outputted as the reference voltage E2' of the comparator 18.

As described above, the reference voltage E2' to the comparator 1 would return to O during the no-signal period as shown by the dotted line in FIG. 2 if the hold circuit 4 were not provided.

When the analog 4 playback signal S0 enters the next signal section,
The hold circuit 4 becomes conductive due to the hold signal (told) from the address detection circuit 7, outputs the output voltage E of the subtracter 3 as it is to the comparator 1 as the reference voltage E2', and again calculates the duty ratio of the digital signal S3. Control begins. However, this time, control of the duty ratio of the digital signal S2 is resumed from the final value controlled in the previous signal section, so the settling time is almost zero, and the digital signal S with a duty ratio of approximately 50% is controlled from the beginning of the signal section. can get.

In the above embodiment, the hold signal Ho1d was obtained from the address detection circuit 7, but it may also be obtained by a circuit as shown in FIG. 3. This circuit operates as shown in FIG. The signal S is envelope-detected by the envelope detection circuit 8, and the output voltage 82' of the envelope detection circuit 8 is compared with the constant voltage E' of the constant voltage source 10 by the comparator 9 to generate a hold signal)tol.
d is obtained.

Further, as the hold circuit 4, a circuit as shown in FIG. 5 or 6 is used.

The circuit shown in FIG. 5 is a so-called sample and hold circuit. The switch 11 is used to apply the above-mentioned hold signal) fold as a sample signal, and when the hold signal Ho1d is at a low level, the switch 11 is turned on and the input voltage E2 from the subtracter 3 is applied to the capacitor 12 and compared via the buffer 13. The reference voltage E2' is input to the device 1 as a reference voltage E2'. When the hold signal Ho1d becomes high level, the switch 11 is turned off, and the voltage E2 inputted from the subtracter 3 just before is held by the capacitor 12 and inputted to the comparator 1 as the reference voltage E2' via the buffer 13. be done. In this case, it is difficult to hold for several seconds or more because the capacitor 12 will be discharged due to leakage current or the like.

The circuit shown in FIG. 6 is a so-called tracking A/D (analog/digital) converter. The up/down counter 14 becomes disabled and holds the count value when the hold signal Ho1d becomes high level, and becomes enabled and counts the clock when the hold signal Ho1d becomes low level. The count value of the up/down counter 14 is digital/analog converted by a D/A (digital/analog) converter 15 and compared with the output voltage E2 of the subtracter 3 by a comparator 16, and the output signal of this comparator 16 is increased. /down signal is input to the up/down counter 14. Therefore, in the enabled state, the up/down counter 14 has a count value corresponding to the output voltage E2 of the subtracter 3, and in the disable state, it holds the count value immediately before the transition from the enabled state. The count value of this up/down counter 14 is transferred to the D/A converter 15.
The signal is digital/analog converted and input to the comparator 1 as a reference voltage E2'.

〔Effect of the invention〕

As described above, according to the present invention, in a disk device that uses a pickup to read information recorded on a disk as a pit string, there is provided a comparator that compares an analog playback signal from the pickup with a reference voltage and shapes the waveform into a digital signal; a control means for detecting a time average value of the digital signal from the comparator and controlling the reference voltage so that the time average value is equal to a voltage intermediate between the high level and the low level of the digital signal; When a signal corresponding to the pit does not exist in the reproduced signal, the base voltage immediately before transition from a section in the analog reproduction signal in which the signal corresponding to the pit exists to a section in which the signal corresponding to the pit does not exist. Since it is equipped with a hold circuit that holds the
% digital signal can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a timing chart showing the operation of the same embodiment, Fig. 3 is a block diagram showing an example of a hold signal generation circuit, and Fig. 4 is the same circuit. Timing charts showing the operation of FIGS. 5 and 6
The figure is a block diagram showing each side of the hold circuit, Figure 7 is a block diagram showing a conventional waveform shaping circuit, Figure 8 is a timing chart showing the operation of the circuit, and Figure 9 is a diagram for explaining the circuit. This is a timing chart. 1... Comparator, 2, 3... Control means, 4... Hold circuit. Bird b Figure Horse 6 Figure Clock Lua Figure

Claims (1)

[Claims] A disk device that uses a pickup to read information recorded as a pit string on a disk includes a comparator that compares an analog playback signal from the pickup with a reference voltage and shapes the waveform into a digital signal, and a time average of the digital signal from the comparator. control means for detecting the reference voltage and controlling the reference voltage so that the time average value is equal to a voltage intermediate between the high level and the low level of the digital signal; and a signal corresponding to the pit in the analog playback signal. a hold circuit that holds the reference voltage immediately before transition from a section in the analog playback signal in which a signal corresponding to the pit exists to a section in which a signal corresponding to the pit does not exist when the signal corresponding to the pit does not exist. A waveform shaping circuit featuring: