JPH0361254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention focuses a beam emitted from a radiation source, irradiates it onto a recording medium having a track on which information is recorded, and adjusts the track so that it receives a radiation flux modulated by the recorded information. The present invention relates to a tracking signal detection device for an optical information reproducing device in which four radiation detectors are arranged in a front field, centered around a radiation axis, and divided into the tracking direction and a direction perpendicular thereto.

Such a tracking signal detection device is disclosed in, for example, Japanese Patent Laid-Open No. 52-93222. 1 to 3 show the structure and operation of a tracking signal detection device disclosed in Japanese Patent Application Laid-Open No. 52-93222. In Figure 1, disk 1
is rotated by the spindle 2 at a speed of, for example, 1800 revolutions per minute. Concentric or spiral tracks 3 are recorded on the disk 1. Light emitted from a light source 4 such as a laser is focused by a lens 5, a half mirror 6, a reflecting mirror 7, and an objective lens 8 and projected onto a track 3 of a disk 1 as a spot. The light reflected by the disk 1 is collected by an objective lens 8, and the light reflected by a reflecting mirror 7 and a half mirror 6 is made to enter a light receiving device 10 via a lens 9. As shown in FIG. 2, this light receiving device has four detectors 11 to 14 divided into a track direction (Y-axis direction) and a direction perpendicular thereto (X-axis direction). located within the field. That is, these detectors 11 to 14 are equipped with an objective lens 8 so as to be able to separate and detect diffraction beams of various orders formed by the pit structure of the information track.
It is placed on a plane sufficiently far away from the image of the pit structure formed by.

As shown in FIG. 2, four detectors 11 to 14
Among the outputs S ₁ to S ₄ , sum circuits 15 and 16 calculate the sum of the outputs of the detectors 11 and 13 and 12 and 14 that are arranged diagonally. That is, sum circuit 1
5 outputs the sum S ₅ =S ₁ +S ₃ , and the sum circuit 16 outputs the sum S ₆ =S ₂
Output +S ₄ . Furthermore, the sum signal of these sums S ₅ and S ₆
S ₇ =S ₅ +S ₆ is determined by the sum circuit 17, and the difference signal S ₈ =S ₅ -
S ₆ is determined by the difference circuit 18. This sum signal _S7 is shown in FIG. 3A, is an information signal modulated by an information structure, and has a pit frequency.
Further, the difference signal _S8 , which is the output of the difference circuit 18, has opposite polarity depending on the direction of shift, as shown in B and C of FIG. 3, and has a phase of π/2 with respect to the sum signal _S7 . is out of alignment. Therefore, the phase of the sum signal S ₇ is delayed by π/2 by a π/2 phase shifter 19, and the phase-delayed sum signal S ₇ ' and the difference signal S ₈ are sent to a multiplier 20.
The frequency component that is twice the frequency of the resulting information signal is cut out by a low-pass filter (LPF) 21.
2, a tracking signal indicating the direction and magnitude of tracking deviation is obtained. The background of the method of obtaining a tracking signal by phase shifting and multiplication is described in the above-mentioned Japanese Patent Application Laid-Open No. 52-93222.
It is described in detail in the publication, but to briefly explain, tracking deviation, sum signal S ₇ and difference signal
The basic principle is that _S8 has the following relationship. In other words, as shown in Fig. 3, the difference signal _S8 is out of phase with the sum signal _S7 by ±π/2, and whether it is +π/2 or -π/2 is a matter of concern. It depends on whether the beam is shifted to the right or to the left with respect to the track. Therefore, the tracking signal can be obtained by delaying the phase of the sum signal S ₇ by π/2 to obtain the sum signal S ₇ ', and calculating this and the difference signal S ₈ .

In this way, the conventional tracking signal detection device uses the π/2 phase shifter 19 to delay the phase of the sum signal _S7 by π/2.
It is desirable to use a phase lock loop so that the phase delay is exactly π/2 for all frequencies of _S7 . However, this type of phase-lock loop has a significantly complicated circuit configuration.
It has the disadvantage of being expensive.

The present invention aims to eliminate these conventional drawbacks and provide a tracking signal detection device suitably configured to detect a desired tracking signal with an extremely simple configuration.

The present invention focuses a beam emitted from a radiation source and irradiates it onto a recording medium having a track on which information is recorded, and emits radiation into the front of the track so as to receive a radiation flux modulated by the recording medium. Four radiation detectors are arranged centered on the axis, each divided in the track direction and a direction perpendicular thereto, and based on the outputs of these radiation detectors, the direction perpendicular to the track direction of the radiation flux and the information track is arranged. In a tracking signal detecting device for an optical information reproducing device, which detects a tracking signal representing the amount and direction of deviation in the optical information reproducing device, a first detecting device that calculates the sum of the outputs of each of the four detectors arranged in a diagonal direction. and a second adder, a third adder that calculates the sum of the outputs of the first and second adders, and a third adder that calculates the sum of the outputs of the first and second adders;
a subtracter for calculating the difference between the outputs of the adders;
The output of the adder is input to the clock input terminal, and the output of the subtracter is input to the data input terminal.
The differential amplifier comprises a type flip-flop, a low-pass filter that integrates the output of the D-type flip-flop, and a differential amplifier that calculates the difference between the output of the low-pass filter and a predetermined reference value. The apparatus is characterized in that the tracking signal is obtained from the output of the apparatus.

The present invention will be described in detail below with reference to the drawings.

FIG. 4 is a block diagram showing the configuration of an example of a tracking signal detection device in an optical information reproducing device of the present invention. This tracking signal detection device supplies the output S7 of the sum circuit ₁₇ to the clock input terminal (CK) of the D-type flip-flop 31,
The output _S8 of the difference circuit 18 is supplied to the data input terminal (D) of the D-type flip-flop 31, the difference signal _S8 is sampled by the sum signal _S7 , and the output is integrated by the low-pass filter 32. The second point is that the required tracking signal is obtained at the output terminal 34 by calculating the difference from the reference value using the differential amplifier 33.
The elements are different from those shown in the figure, and the same reference numerals as those shown in FIG. 2 represent elements having the same function.

In FIGS. 1 and 4, when the center of the light beam projected onto the disk 1 coincides with the center of the track 3 of the disk 1, that is, when there is no track deviation, the output S ₈ of the difference circuit 18 is The level remains constant. In this example, this level is set as the threshold level (THR). In this way, at the rise of the output _S7 of the summation circuit 17, when the center of the light beam shifts to the right from the center of the track, the level of the difference signal _S8 will be above THR, and if the center of the light beam shifts to the left. Assuming that the time is on the lower side, if it is shifted to the right, the D type flip-flop 31
The output will be high level (H), and if it shifts to the left, it will be low level (L). On the other hand, the difference signal S ₈ generally contains random noise, and the sum signal S ₇
The band (around 8MHz) is sufficiently high compared to the highest band (20KHz) of the tracking signal you want to obtain. In this way, if noise is mixed in the difference signal _S8 , it will not be a value that reliably indicates the state of track deviation at that time when _the sum signal _S7 rises; The level of the difference signal _S8 at , has a probability distribution as shown in FIG. 5, with the highest frequency being the level when there is no noise (true level). That is,
The true level is the threshold level (THR)
The output of the D-type flip-flop 31 becomes H or L with a probability that is either negative or positive. Therefore, the output of the D-type flip-flop 31 is integrated by the low-pass filter 32 over a period that does not attenuate the highest frequency band of 20 KHz of the tracking signal to be obtained, and the output is integrated by the differential amplifier 33.
If the reference value of is set to a level between H and L of the D-type flip-flop 31 and the difference between the integrated output of the low-pass filter 32 and the reference value is found,
A tracking signal representing the direction and amount of track deviation can be obtained at the output terminal 34.
In other words, when the true level of the difference signal _S8 moves away from THR below or above, the frequency of H or L being repeated as the output of the D-type flip-flop 31 decreases, so the output is integrated. By calculating the difference from the reference value, a tracking signal representing the direction and amount of deviation according to the difference signal _S8 can be obtained.

The above noise is not always constant, and if the S/N ratio is good, the probability distribution mentioned above cannot be obtained, and even if the direction of track deviation can be detected, the amount of the deviation may not be detected. . In such a case, as shown in FIG. 6, noise is forcibly mixed into the output S8 of the difference circuit ₁₈ from the random noise generator 35. In this way, a probability distribution similar to that shown in FIG. 5 can be obtained, so that a required tracking signal representing the direction and amount of track deviation can be obtained.

As described above, in the present invention, the circuit portion that conventionally performed analog calculations using a π/2 phase shifter and multiplier is replaced with one D-type flip-flop to obtain the required tracking signal. , the circuit configuration can be made extremely simple.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an example of the optical system of a tracking signal detection device of a conventional optical information reproducing device, FIG. 2 is a circuit diagram showing the configuration of the signal processing section, and FIG. 3 is the same. FIG. 4 is a circuit diagram showing the configuration of an example of the tracking signal detection device of the present invention, FIG. 5 is a diagram showing the same operation, and FIG. FIG. 3 is a circuit diagram showing the configuration of another example of the tracking signal detection device of the invention. 10... Light receiving device, 11-14... Detector, 1
5 to 17...sum circuit, 18...difference circuit, 31...
D type flip-flop, 32...Low pass filter, 33...Differential amplifier, 34...Output terminal, 35...Random noise generator.

Claims (1)

[Scope of Claims] 1. A beam emitted from a radiation source is focused and irradiated onto a recording medium having a track on which information is recorded, and the beam is focused in the front of the track so as to receive the radiation flux modulated by the recording medium. With the radiation axis as the center, four radiation detectors divided in the track direction and a direction perpendicular thereto are placed, and based on the outputs of these radiation detectors, the radiation flux and the information track are divided perpendicularly to the track direction. In a tracking signal detection device for an optical information reproducing device configured to detect a tracking signal representing the amount and direction of deviation in a direction, the sum of the outputs of each of the four detectors arranged diagonally is determined. a first and second adder; a third adder that calculates the sum of the outputs of the first and second adders;
a subtracter for calculating the difference between the outputs of the adders;
The output of the adder is input to the clock input terminal, and the output of the subtracter is input to the data input terminal.
The differential amplifier comprises a type flip-flop, a low-pass filter that integrates the output of the D-type flip-flop, and a differential amplifier that calculates the difference between the output of the low-pass filter and a predetermined reference value. A tracking signal detection device in an optical information reproducing device, characterized in that the tracking signal is obtained from the output of the tracking signal.