JPS6349292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reproducing apparatus that scans an information track and reproduces a signal, and particularly relates to a reproducing apparatus that reproduces signals while vibrating (meandering) with a constant amplitude in a direction orthogonal to the scanning direction of an information track. Regarding the wobbling method or the recording wobbling method that scans and reproduces an information track recorded by vibrating (meandering) in advance, its purpose is to detect that the reproduced signal has undergone amplitude modulation due to the vibration (meandering). An object of the present invention is to stabilize the loop gain of a servo loop system in the above-mentioned reproducing apparatus which reproduces information while tracking it.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the main structure of a reproducing apparatus according to the present invention. Reference numeral 1 denotes an optical reflective disk having a known structure, on which information tracks are recorded as shown in FIG. In FIG. 2, 31 is the center line of the information track, and 32 is the recorded information track, which meanderes at a constant frequency in a direction perpendicular to the scanning direction 37 with respect to the center line 31. 33, 34, and 35 are recorded synchronization signals, and the meandering phase is set to be a constant phase with respect to the synchronization signal. 3
Reference numeral 6 denotes a reading spot, which is shown, for example, as a beam spot focused by the reading lens 7 in FIG. Further, in FIG. 1, reference numeral 2 denotes a motor for rotationally driving the disk 1, and 3 a laser device.The light beam passes through a half mirror 4, is reflected by a tracking mirror 6, and is focused onto the disk 1 by a reading lens 7. In this way, disk 1
The read spot 36 illuminated by the disk 1
It is further reflected by the half mirror 4 via the reading lens 7 and the tracking mirror 6,
The optical detector 5 converts the signal into an electrical signal. The output signal of the optical detector 5 is amplified by a preamplifier 8 and demodulated into an information signal by a demodulator 9.

As mentioned above, the information signal includes the synchronization signal 33,
34 and 35, and this synchronization signal is separated by a synchronization separator 10. This separated synchronization signal is input to the phase comparator 11, and the phase comparator 1
1, LPF [low pass filter] 12, and VCO [voltage controlled oscillator] 13, PLL loop [phase lock loop] A is converted into a continuous signal synchronized with the synchronization signal, and generated at the output of VCO 13. do.

On the other hand, since the output signal of the preamplifier 8 is amplitude-modulated at the frequency of the meandering component due to the information track, by inputting the output of the preamplifier 8 to the envelope detector 14, the meandering signal is superimposed on the detected output. There is. This envelope detector 14 output is
The signal is input to a phase detector 16 via a BPF (band pass filter) 15. The output of the VCO 13 is simultaneously input to the phase detector 16, and a tracking error signal is obtained at the output of the phase detector 16. This tracking error signal is transmitted to the phase compensation circuit 1.
7 and is amplified by a DC amplifier 18, which drives the tracking mirror 6 and reads the reading spot 36.
Follow-up control is performed so that the information track 32 is scanned. The above system is called a tracking servo system,
By the way, before this tracking servo system operates, the reading spot 36 is located on the information track 3.
2, the envelope detector 14 input becomes as shown in FIG. 3a, and the envelope detector 14 at this time
The output will be as shown in Figure 3b. That is, the above-mentioned meandering signal (referred to as a wobbling signal) appears superimposed on the signal caused by the reading of the information track 32 and the crossing of the spot 36. Furthermore, since the size of the wobbling is generally about 0.1 micron, the amplitude of the wobbling signal is relatively small.
S/N does not become large. Therefore, in the embodiment shown in FIG. 1, a BRF 15 is provided, and by tuning the center frequency of this BPF 15 to the frequency of the wobbling signal, only the meandering component is extracted and the S/N is increased.

However, if you increase the Q of BPF15,
It was found that the phase characteristics of the tracking servo system deteriorated, making it impossible to increase the loop gain.

FIG. 4 shows a specific example of the EPF 15 used in this embodiment. The BPF 15 in FIG. 4 is a type of BPF amplifier, which matches the resonant frequency determined by L and C with the wobbling frequency, and changes Q by R.

Figure 5 shows the phase and gain frequency characteristics of BPF15 in Figure 4, where characteristic A is for a resistance value of R = R ₁ , and characteristic B is for a resistance value of R = R ₂ [however, R ₂ > R ₁ ]. shows. Here, R ₁ is 1KΩ and R ₂ is 5KΩ. When the center frequency is f ₀ and the bandwidth of the tracking servo system is f, the phase characteristics of the BPF 15 are set to be at least within ±60° at f ₀ ±f.

FIG. 6 shows the frequency characteristics of the output gain and phase of the phase detector 16, where characteristic A is when R of the BPF 15 is set to _R1 , and characteristic B is when R is set to _R2 .

It can thus be seen that the detection characteristics of the tracking servo system change depending on the characteristics of the BPF 15. In order to obtain good tracking servo characteristics, it is desirable that the phase delay is small and the gain frequency characteristics extend to a high frequency range, as shown in characteristic A in FIG. This standard is based on the phase delay at the upper limit frequency of the required bandwidth of the tracking servo system.
Must be within 60°.

Next, it was found that since the phase detector 16 is a type of multiplier, frequencies that are twice or more the wobbling frequency appear as so-called harmonic components. Therefore, in order to operate the tracking servo system more stably, it is desirable to provide a filter or trap that blocks only the harmonic components from the detected output.

Further, in the above embodiment, the synchronization signal was stabilized by the PLL loop and then input to the phase detector 16. The purpose of this is, as shown in FIG. 3, since the reading spot 36 does not follow the information track 32 before the tracking servo system operates, the preamplifier 8
The output does not have a constant amplitude, and the synchronous separator 10
The output becomes intermittent and an accurate synchronization signal cannot be obtained. Therefore, in the embodiment of FIG. 1, a continuous synchronization signal is obtained by setting the response characteristic of the PLL loop system A to an appropriate value, thereby allowing the tracking servo system to operate accurately.

In this way, the BPF15 is used to extract the wobbling signal, and a PLL loop system A is provided to prevent discontinuity of the synchronization signal.
Since the output and the PLL loop system A output are phase-detected and harmonic components are removed from the detected output, an extremely stable tracking servo system can be realized.

The above explanation takes as an example the case of recording wobbling, in which an information track that has been recorded in advance by meandering in a direction perpendicular to the information track scanning direction at a constant phase with respect to the synchronization signal of the information track is scanned and reproduced. However, in the case of playback wobbling in which playback is performed while making the playback pickup meander in a direction perpendicular to the information track scanning direction with a constant amplitude, the phase detector 16 receives the BPF 15 output signal and a signal that causes the playback pickup to meander. is input.

As explained above, according to the present invention, the amplitude variation of the reproduced signal due to the meandering component is detected using a bandpass filter having a predetermined phase characteristic before phase detection. The S/N ratio is improved and a stable loop gain can be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a block diagram of the main parts of a playback device according to the present invention, FIG. 2 is an explanatory diagram schematically representing an information track on a disk, and FIG. 3 is an envelope detection diagram. Figure 4 shows the input and output waveforms of the device.
A specific circuit diagram of the BPF, FIG. 5 is a frequency characteristic diagram of the phase and gain of the BPF, and FIG. 6 is a frequency characteristic diagram of the gain and phase of the tracking signal detection system corresponding to FIG. 1...Disk, 9...Demodulator, 10...Synchronization separator, 14...Envelope detector, 15...Band pass filter, 16...Phase detector, A...PLL
Loop type.

Claims (1)

[Scope of Claims] 1. The reproduction pickup is reproduced while meandering at a constant amplitude in a direction perpendicular to the scanning direction of the information track, or recorded by meandering at a constant phase with respect to the synchronization signal of the information track in advance. The information track is scanned and reproduced, it is detected that the reproduced signal has undergone amplitude modulation by the meandering component, and the amplitude fluctuation of the reproduced signal is converted into a meandering signal for the reproduction pickup or a constant frequency signal synchronized with the synchronization signal. In a tracking servo system of a playback device that performs phase detection and tracks an information track, a bandpass filter is provided upstream of the phase detector for extracting amplitude fluctuations of the playback signal received by the meandering component, The phase characteristic of the band-pass filter is set within ±60° at f ₀ ±f, where the center frequency of the band-pass filter is f ₀ and the bandwidth of the tracking servo system is f. playback device. 2. Separate the constant frequency signal input to the phase detector from the synchronization signal from the information track reproduction signal output,
2. The playback device according to claim 1, wherein the playback device is configured to obtain a continuous signal by converting the separated synchronization signal into a continuous signal using a PLL loop system. 3. The reproducing device according to claim 1, wherein the phase detector is configured to remove harmonic components of the meandering signal after phase detection.