JPS6220144A - Tracking controller - Google Patents

Abstract

PURPOSE:To prevent the noise of a tracking actuator due to the transmitting characteristic of a disk from arising by smoothing the reproduction signal frequency characteristic of a photoelectric transducer output through a waveform equalizing circuit correcting provisionally a disk transmission frequency characteristics. CONSTITUTION:The waveform equalizing circuits 8 and 9 act as to correct the frequency characteristic of the photoelectric transducer outputs (a) and (b), that is, the transmitting characteristic of the disk. By passing provisionally the photoelectric transducer output through the waveform equalizing circuits 8 and 9 correcting the disk transmitting characteristic, the frequency characteristic of the reproduction signal is smoothed, and therefore the amplitude of the reproduction signal can be unified irrespective of the frequency even if it lies between music on the disk. Moreover the occurrence of the noise dependent upon a conventional synchronizing signal period can be prevented from a tracking error signal obtained by envelope-detecting and comparing two subspots even if they have a signal detecting time difference.

Description

[Detailed Description of the Invention] [Utilization of the Invention] The present invention provides an optical digital audio disc (DA
D) It relates to players, video disc players, etc., and particularly relates to tracking control for faithfully tracking signal tracks on a disc.

[Background of the invention]

As a method for faithfully tracking the signal track of an optical disk, for example, as shown in Japanese Patent Application Laid-Open No. 56-41538, a pair of photoelectric converters that photoelectrically convert the reflected optical cover from the track and their outputs are used. It is equipped with a pair of band amplifiers that each pass only the frequency components of recorded information from the signal, and a pair of envelope line detectors that detect the respective envelopes of the output signal waveforms of the band amplifiers. It is known that by comparing the outputs, an error signal corresponding to the amount of track deviation is obtained, and this is used to perform the track tracking operation of the optical semi-semiconductor reader.

In this conventional method, only the signal components recorded on the disc are passed through a band-limiting amplifier, etc., and below that, harmful signal components such as scratches on the disc, or DC components generated by the optical reading device are removed. etc., so it is possible to accurately track the signal track on the disk without being affected by such harmful signal components. However, when applied to a 3-spot optical reader, However, no consideration was given to the noise generated by the tracking actuator due to the transfer characteristics of the disk.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks, and to accurately track the information recording track of one disk in a three-spot type optical reading device without generating noise of the one-tracking actuator caused by the transfer characteristics of the disk. The object of the present invention is to provide a suitable Trafkin control device that can perform the following operations.

[Summary of the invention]

To achieve this objective, the present invention first passes the outputs of a pair of photoelectric converters through a waveform equivalent circuit, corrects the transfer characteristics of the disk using the waveform equivalent circuit, and then passes the outputs of a pair of photoelectric converters through a bandpass amplifier (or high-pass filter). ), envelope 8! It is characterized in that a tracking error signal is obtained by performing detection and comparing both output signals.

[Embodiments of the invention]

FIG. 1 shows a block diagram of a tracking control device according to the present invention. In the figure, 1 is an optical disk, 2 is a disk motor 1) 3 is an optical pickup, and 4 is a disk on the pickup 3. A photoelectric converter consisting of a light receiving element 5 for photo-to-current conversion of the amount of reflected light from the signal track, and a pair of current-voltage converters 6 and 7 for converting the output current of the light receiving element into voltage; 9 is 1
A pair of waveform equivalent circuits, 10 and 11 are a pair of high-pass filters, 12 and 13 are a pair of envelope detectors, 14
1 is a comparator, and 15 is a tracking actuator for driving the optical pickup 3 to track the signal track of the disk.

In this embodiment, the outputs a and b of a pair of photoelectric converters are passed through waveform equivalent circuits 8 and 9, respectively, to correct the frequency transfer characteristics of the disk, and high-pass filters 10 and 1
1, extracts only the signal component of the recorded information on one disk, and outputs high-pass filters e and f.
g whose envelope is detected by envelope detectors 12 and 15, respectively.

The tracking error signal is obtained by comparing the h signal between comparators, and as with the conventional example, it is possible to cut signal components harmful to tracking due to scratches on the disk and DC offset voltage generated in the pickup optical system. Of course, by correcting the disk transfer characteristics using the waveform equivalent circuit, the tracking actuator 15 can perform stable and accurate tracking control operation with less noise.

In Fig. 1, the optical pickup 3 and photoelectric converter 4 are of a three-spot type that is widely used in digital audio disc players, etc., but since the principle of operation is well known, details will not be given here. Omitted,
Hereinafter, the operation of the tracking error signal detecting section, which has a particularly different configuration from the conventional one, will be explained while presenting operation waveform diagrams and the like.

FIG. 2 shows a specific circuit example based on the block diagram of FIG. 1. In the same figure, the waveform equivalent circuit 9I bypass filter 11 and envelope detector 13 are respectively 8,
Since it is the same as 10 and 12, the details are omitted.

The waveform equivalent circuit 8 functions to correct the frequency characteristics of the photoelectric converter output a, that is, the transfer characteristics of the disk. Figure 6 shows an example of the output signal amplitude characteristics of a digital audio disc (objective lens aperture ratio of the optical system NA - 0, 5, laser light wavelength λ - 780 μm, disc linear velocity - 1, 25 m/S).
(calculated value when
This corrects the amplitude difference of about 6 dB between the two and flattens the characteristics. The no-pass filter 10 works to pass only the signal component of the recorded information on the disk of the waveform equalizer output C. For example, the pass cutoff frequency is set to about several tens of KFiz in consideration of the lowest value of the signal component of the recorded information. . The envelope detector 12 is a well-known Emi-Holo detector using a constant current source as a load, and the peak value envelope signal of the input signal e is obtained as the output g.

In such a configuration, the optical pickup 3 in FIG.
FIG. 4 shows the operating waveforms of each part when the signal crosses the signal track on the disk. In the figure, 16 to 18 are the centers of signal tracks on the disk.

Waveform A shows a signal waveform obtained by photoelectrically converting the photocurrent of the main signal detection light receiving element 5-3 in the 5-spot system shown in FIG. The main signal output becomes a signal of maximum amplitude when the optical pickup is located at the center of the track and a signal of minimum amplitude when located between the tracks.

On the other hand, in the 3-spot method, the two trunk detection sub-spots that illuminate the disk are positioned equidistantly (±90° in electrical angle) to the left and right in the radial direction of the disk with respect to the main spot. Therefore, signals a and b obtained by photoelectrically converting the photocurrents of the light receiving elements 5-1 and 5-2 shown in FIG. 1 are as shown in FIG. 4 for the main signal output A, respectively.

The photoelectric conversion outputs of a and b are passed through a waveform equivalent circuit and a high-pass filter, and the outputs are e and f, respectively, and their envelope detection signals are gth, respectively.By comparing these, it can be obtained as shown in Figure 1, 5. Zero when the main spot is located at the center of the track, left from the center of the track.

If there is a shift to the right, a tracking error signal with a polarity corresponding to the direction and a level corresponding to the amount of shift is obtained.

According to this embodiment, if there is a scratch on the signal track of the disk, the incident light from the optical pickup to the disk signal surface and the reflected light from the disk signal surface are lost, so the signals shown in Fig. 4 e and f are lost. Missing. That is, since the high frequency signal component is missing, the envelope detection outputs of g and h also become zero, and the F racking error signal i also becomes zero, making it possible to prevent the generation of harmful signals. In addition, even if the outputs of the two photoelectric converters a and b become unbalanced due to the optical system unbalance of the optical bikuku acupuncture, etc., the AC signal component of the recorded information can be converted into a DC signal by passing both through a high-pass filter. It is possible to suppress the DC offset generated by the tracking error signal iK in order to compare the amplitude difference between the envelope detection outputs.

Next, in order to clarify the effectiveness and importance of the present invention, the reduction in trafking actuator noise by installing a waveform equivalent circuit that is particularly different from the conventional one will be explained below.

In a digital audio disc, the recording information signal on the disc is 3T to 11T (T is the transmission pic rate 4.32
18 MHz), it is approximately 20 MHz as mentioned above.
The frequency is 0KH2 to 720KHz. Among these, the information component as a music signal is 3T to 10T, and the 11T component is the disc C.
It is used as a synchronizing signal for both LV (constant linear velocity) rotation sides, and this signal is recorded at equal intervals of 588T (735KEIZ).

Furthermore, when looking at disc-recorded music signals, the signal components within a song are randomly distributed between 3T and 1oT, but between songs (
In general, a relatively high information component (close to the 3T component) is dominant in the song and track area of the song.

FIG. 5 shows this situation. This figure shows the photoelectric conversion of the reflected light from the sub-spot for tracking error detection when tracking between songs using a conventional device, and the output through a high-pass filter. Synchronization signal component 7 with low frequency due to disk transfer characteristics
, 35 KHz is large, and the amplitude of the high frequency signal component is small, and this amplitude generates actuator noise. In other words, in the 3-spot method, the two track detection sub-spots are not only positioned to the left and right in the disk radial direction with respect to the main spot, but also to the front and rear in the track scanning direction. Because they are located at the same distance apart, there is a time difference in signal detection depending on this separation distance, and both are covered! ! In the tracking error signal compared by line detection, noise with a synchronization signal period of 735 KHz occurs in which the amplitude of the detection signal suddenly changes, and the actuator is driven by this noise, causing noise. This phenomenon is noticeable not only during tracks on a disc, but also during tracking between tracks, where the recorded information components are concentrated in a high frequency region and the amplitude difference with the synchronization signal component is large.

On the other hand, it can be easily inferred that the above-mentioned noise is reduced according to the present invention. That is, in the present invention, since the frequency characteristics of the reproduced signal are flattened by using the photoelectric converter output through a waveform equivalent circuit that corrects the -H disk transfer characteristics, the frequency characteristics shown in FIG. This situation can be avoided and the amplitude of the reproduced signal can be made uniform regardless of the frequency. Therefore, even if there is a difference in signal detection time between the two sub-subjects, the tracking error signal that is compared by envelope detection of both is synchronized as in the conventional method. It is possible to suppress the occurrence of noise depending on the signal period.

Note that the present invention is not limited to the above embodiments,
Of course, various modifications can be made without departing from the gist of the invention, such as placing it after a high-pass filter, which is a waveform equivalent circuit.

〔Effect of the invention〕

As described above, according to the present invention, the above-described configuration flattens the reproduced signal frequency characteristics of the photoelectric converter output through the waveform equivalent circuit that corrects the -H disk transmission frequency characteristics. Even with the 3-spot optical PikkuApu, the synchronization signal period (7.35 KHz and It is possible to provide a tracking control device for an optical pickup that can suppress the noise of harmonics (integral multiples), so that the noise of the tracking actuator is small, and can perform tracking control of an information recording tractor stably and accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a specific embodiment of the invention, FIG. 3 is a diagram showing the transfer characteristics of a digital audio disc, and FIG. 4 is a diagram showing a specific embodiment of the invention. FIG. 5 is a waveform diagram for explaining the operation of the photoelectric converter for track detection, and FIG. 6 is a diagram showing the effects of the present invention. 6.7...Photoelectric converter, 8,9...Waveform equivalent circuit, 10.11...Bypass filter p-112,13.
・・Envelope wire detector, K・1,
-14... Comparator.

Claims (1)

[Claims] In an apparatus that reproduces signals recorded on a disk while performing optical tracking servo using a readout light spot and a plurality of tracking light spots correlated with the readout light spot, the radius of the disk is A pair of light receiving elements for detecting signals recorded in correspondence with directions, a pair of photoelectric converters for photoelectrically converting the outputs of these light receiving elements, and a pair of photoelectric converters for correcting the transfer characteristics of the disk. A waveform equivalent circuit, a pair of high-pass filters that respectively pass signals in the frequency domain of information recorded on the disk from the output signals of the pair of waveform equivalent circuits, and detecting the respective envelopes of the output signal waveforms of these high-pass filters. a pair of envelope detectors,
Equipped with a comparator that compares the outputs of these envelope detectors,
A tracking control device characterized in that a track tracking operation of the disc playback device is performed based on the output of the comparator.