KR960006096B1 - Signal circuit at optical pick-up using doppler effect - Google Patents

Abstract

a lasing part, an optical pick-up which has an optical detection part which induces the reference beam from the lasing part and the reflection beam from the recoding medium; a focusing servo part which conducts focusing servo accepted from the focusing error signal; a RF signal processing part which processes the accepted RF signal; a filter part which filters the focusing error signal component and the RF signal component according to the frequency of the accepted signal.

Description

Signal Processing Circuit in Optical Pickup Device Using Doppler Effect

1 is a view showing an optical pickup device using the Doppler effect to explain the present invention,

2 is a block diagram of a signal processing circuit in the optical pickup apparatus using the Doppler effect according to the present invention;

3 is a diagram showing the output characteristics of each part shown in FIG.

* Explanation of symbols for main parts of the drawings

10 optical disc 20 light emitting unit

30 beam splitter 40 objective lens

50: light detector 60: concave mirror

80: filter unit 90: focusing servo unit

100: RF signal processing unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit in an optical pickup apparatus using the Doppler effect. In particular, the Doppler effect is used to superimpose a reflected beam from a reference beam and a recording medium. The present invention relates to a signal processing circuit in an optical pickup apparatus using a Doppler effect in which a focusing error signal and an RF signal are separated from a detection signal in the optical pickup apparatus to be detected.

Conventionally, optical discs have grooves called pits, which are generally 0.4-0.5 μm wide, with a length of one pit and an interval of pit from 3T (where T is the length of one clock pulse) to 1 lT. The tracks of the pits are arranged side by side in the circumferential direction at intervals (track pitch) of about 1.6 μm.

Specifically, for example, a compact disc has a clock frequency of 4.3218 MHz, so a disc recorded with a linear speed of 1.25 m / s has a T = 1.25 / 4.3218 = 0.2892 μm and a pit length of at least 0.8677 μm (= 1 lT). The method calculates the minimum pit length of 0.8330 μm and the maximum pit length of 3.0543 μm for discs recorded with a linear velocity of 1.2 m / s. The maximum pit length is 3.5633 μm.

Here, from the incident side of the lazy beam, the reflecting surface of the disk is flat and there is a long circular protrusion called a pit on it. Digital signals are recorded on the discs in different lengths.

In addition, the conventional optical pickup device discriminates the presence or absence of the pit of the disk reflecting surface by the amount of the reflected beam (i.e. the brightness of the reflecting beam). A bright beam spot is incident on the photodetector, and a spot of a slightly dark beam is incident because the beam is scattered by light diffraction and returns only about 30% at the pit.

For example, the mechanical height of a pit formed on a compact disc is about 0.111 μm, but the optical height is 0.65 μm multiplied by the refractive index of the transparent plastic. Eventually, this value is very close to 1/4 wavelength (= 0.195 μm) of the laser wavelength of 0.78 μm, and the beam reaching the end of the pit is about half the round trip compared to the light reaching the flat part around it. It becomes a wavelength, and about 180 degrees is delayed as a phase (half wavelength becomes 180 degrees because 360 degrees is 1 wavelength). Since the 180 ° phase difference is the same as the inverse phase, the beam reflected at the flat portion around the pit and the beam reflected at the tip of the pit disappear. On the other hand, among the beams reflected at the end of the pit, the beams are amplified in a multiple of 360 °, i.e., in phase, with the reflected light in the flat part by the angle. As a result, when looking at the intensity distribution of the beam, it becomes bright in the part without the pit and dark in the part with the pit, so that the shape of the source pit can be read on the disk by this contrast.

However, in the conventional method, the optical disc has a limitation in miniaturization due to the high density of the recording data, and the optical pickup apparatus has a limitation in the simplification and miniaturization of components, which is an obstacle to the miniaturization of the optical disc player.

Therefore, in order to achieve miniaturization of a recording medium such as an optical disc, a method of recording data by changing the shape of an inclined surface of a pit, for example, has been proposed, and an optical pickup device for reading data from such a recording medium has also been proposed. There is a demand for development of an apparatus for effectively processing a signal detected by the system.

Accordingly, the present invention has been made in view of the above circumstances, and in the optical pickup apparatus which overlaps the reflected beam from the reference beam and the recording medium using the Doppler effect, and detects the beat wave due to the interference between the reference beam and the reflected beam. It is an object of the present invention to provide a signal processing circuit in an optical pickup apparatus using a Doppler effect to effectively separate a focusing error signal and an RF signal from a detection signal.

According to a preferred embodiment of the signal processing circuit of the present invention for achieving the above object, there is provided a light emitting portion for generating a beam, a light detecting portion for receiving the reflected beam from the recording medium and the reference beam scanned by the light emitting portion In the optical pickup apparatus comprising an optical pickup, a focusing servo unit receiving a focusing error signal among the signals from the photodetector unit and performing a focusing servo; and an RF signal processing unit receiving and processing an RF signal among the signals from the photodetector unit. The signal processing circuit may further include a filter unit for extracting a focusing error signal component and an RF signal component according to a frequency from a signal applied by the photodetector.

The filter unit receives a signal from the photodetector and detects only a frequency component below a predetermined frequency and outputs this component to the focusing servo unit as a focusing error signal, and receives a signal from the photodetector to a predetermined frequency. And a second filter which detects only the above frequency components and outputs the components as RF signals to the RF signal processing unit.

In the case where the recording medium is a compact disc, the predetermined frequency is preferably selected from 70 kHz to 3 MHz. In the case where the recording medium is a laser disc, the predetermined frequency is preferably selected from 140 kHz to 12 MHz.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing an optical pickup apparatus using the Doppler effect to explain the present invention, and includes a light emitting unit 20 made of a light emitting element such as a laser diode for generating a laser beam, and A beam splitter 30 which separates an incident beam and a reflected beam from a recording medium 10 such as an optical disk having irregularities such as a feed, and the laser beam incident through the beam splitter 30 as the recording medium ( 10 and the reflected light from the recording medium 10 is applied through the objective lens 40 and the objective lens 40 and the beam splitter 30 to detect a focusing state and a tracking state. A photodetector 50 having a light receiving element such as a photodiode for reading data recorded on the recording medium 10 is provided, and the side of the beam splitter 30 reflects the incident beam. Further, a concave mirror 60 is provided only as reflection water. In addition, the beam splitter 30 is specially coated to be divided into two beams incident to the light emitting part 20 and applied to the objective lens 40 and the concave mirror 60. The photodetector 50 is also adapted to receive a reference beam from the concave mirror 60.

In the above configuration, as the recording medium 10 rotates (or moves), the laser beam scanned by the light emitting unit 20 of the optical pickup device passes through the pit where the signal is recorded, where the pit is uneven. Because of the inclination and inclination, the reflecting surface of the beam is moved forward and backward in the scanning direction of the beam to oscillate in the vertical direction. As a result, the reflected beam reflected from the recording medium 10 changes according to the Doppler effect as follows.

In other words,

Where v is the frequency of the incident beam, u is the moving speed by the pit of the recording medium, and c is the speed of light.

Thereafter, the reflected beam having the changed frequency is incident to the photodetector 50 through the objective lens 40 and the beam splitter 30. Accordingly, the reference beam and the reflected beam are combined with the photodetector 50 to be incident in the form of a composite beam. This composite beam is represented by a beat wave having a frequency of v ₁ = (v'-v) / 2. The frequency details of the beat wave are as follows.

That is, in general, the beat frequency corresponding to the focusing error of the compact disc is about 70 kHz and the beat frequency of the RF signal is about 3 to 8 MHz. The beat frequency corresponding to the focusing error of the laser disc is about 140 kHz, and the beat frequency of the RF signal is about 12 to 35 MHz.

2 is a block diagram of a signal processing circuit in the optical pickup apparatus using the Doppler effect according to the present invention, for example, a focusing error signal component according to frequency in the beat wave of the composite beam incident on the photodetector 50 made of photodiode; A filter unit 80 for extracting an RF signal component, a focusing servo unit 90 for performing a focusing servo by receiving a focusing error signal among the signals from the filter unit 80, and an RF in the signal from the filter unit 80 An RF signal processor 100 for receiving a signal and processing the signal is provided.

The filter unit 80 receives a signal from the photodetector 50 and detects only a frequency component below a predetermined frequency and outputs the component to the focusing servo unit 90 as a focusing error signal. And a second filter 80B which receives a signal from the photodetector 50 and detects only a frequency component equal to or greater than the predetermined frequency and outputs the component to the RF signal processing unit 100 as an RF signal.

Here, when the recording medium 10 is a compact disc, it is preferable that the predetermined frequency is selected from 70 kHz to 3 MHz. When the recording medium is a laser disc, the predetermined frequency is preferably selected from 140 kHz to 1 2 MHz.

FIG. 3A shows the pit shape of the optical disk as a recording medium, and FIGS. 3B to 3D show the RF signal waveforms, focusing error signal waveforms, and combinations thereof corresponding to FIG. 3A. Signal waveform is shown. As described above, since the frequency range of the focusing error signal of the general recording medium and the frequency band of the RF signal show a certain difference, the combined signal of the focusing error signal and the RF signal output from the photodetector 50 [the third signal] (D)] by appropriately setting the reference filtering frequencies of the first filter (80A) and the second filter (80B), respectively, the focusing error signal [FIG. 3C] and the RF signal [FIG. 3B]. ] Can be separated.

As described above, according to the signal processing circuit in the optical pickup apparatus using the Doppler effect of the present invention, the focusing error signal component and the RF signal component can be extracted simply and effectively from the beat wave detected by the photodetector according to the frequency. .

Claims (4)

An optical pickup having a light emitting unit 20 for generating a beam, a light detecting unit 50 for receiving a reflected beam from the recording medium 10 and a reference beam scanned by the light emitting unit 20; A focusing servo unit 90 which receives a focusing error signal among the signals from the photodetector 50 and performs a focusing servo, and an RF signal processing unit 100 which receives an RF signal among the signals from the photodetector 50 and processes the signal. In the signal processing circuit in the optical pickup device having a further comprising: a filter unit 80 for extracting a focusing error signal component and an RF signal component according to the frequency from the signal applied by the photodetector 50 A signal processing circuit in an optical pickup apparatus using the Doppler effect. The method of claim 1, wherein the filter unit 80 receives a signal from the photodetector unit 50 and detects only a frequency component below a predetermined frequency, and outputs the component to the focusing servo unit 90 as a focusing error signal. A second filter that receives a signal from the first filter 80A and the photodetector 50, detects only a frequency component equal to or greater than the predetermined frequency, and outputs the component to the RF signal processor 100 as an RF signal ( 80B), the signal processing circuit in the optical pickup device using the Doppler effect. 3. The signal processing circuit according to claim 2, wherein said conventional medium (10) is a compact disc and said predetermined frequency is selected from 70 kHz to 3 MHz. 3. The signal processing circuit according to claim 2, wherein the recording medium (10) is a laser disc and the predetermined frequency is selected from 140 kHz to 12 MHz.