JPH0248981Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to an optical disk player using a single beam type optical head, and particularly to a track skip prevention circuit thereof.

Prior Art and Problems Figure 1 is a diagram showing the principle of an optical DAD (Digital Audio Disk) player, in which 1 is an optical disk, 2 is a laser, and 3 is a light receiving element. The light beam L ₁ from the laser 2 is reflected by the prism 4 and reaches the prism 5 , where it changes its course and enters the disk 1 . 6 is the incident position on disk 1
The lens is moved in the radial direction of the lens, and is displaced in the direction of arrow A. The reflected light _L2 from the disk 1 enters the light receiving element 3 through the lens 6 and the prisms 5, 4, and 7. The optical system except for the disk 1 is integrated as an optical head.

FIG. 2 is an explanatory diagram of the optical disc 1, and a is a sectional view of a disc surface protrusion 11 called a pit. The thickness of the pit 11 is 1/4 of the wavelength λ of the light used, and there are few reflected components in that part. The pits 11 are arranged along the track 12 as shown in FIG. The photoreceptor 3 is divided into four parts as shown in FIG. Therefore, if a change (decrease) in the amount of light received by the pit 11 occurs at the A and C sections at the same time as shown in c, it can be determined that the track 12 is aligned with the center of the light receiving element 3 and there is no track deviation. If a track deviation (positional deviation between the track 12 and the center of the light-receiving element 3) occurs as shown in d, this can be detected since the same changes will not occur in portions A and C. Sections B and D form diagonal pairs with sections A and C, respectively, and detect a time difference, which will be described later.

3 and 4 show examples of conventional circuits that process the output of the four-division light-receiving element 3 to detect tracking errors. FIG. 3 shows a light-receiving element output circuit, and FIG. 4 shows a time difference detection circuit. In Figure 3, 20A
20D are IV amplifiers that convert the output currents of each part A to D of the light receiving element 3 into voltages, 21 is an adder that adds the outputs of the amplifiers 20A and 20D, and 2
2 is an adder that adds the outputs of the amplifiers 20B and 20C, 23 and 24 are circuits that waveform shape the outputs of the adders 21 and 22, and 25 and 26 are waveform shaping circuits 23,
This is an inverter that inverts the output of 24. The output ₁ ⁺ obtained from this light receiving element output circuit corresponds to the sum of the outputs of parts A and D of the light receiving element 3, and the output ₂ ⁺ corresponds to the sum of the outputs of parts B and C. It is. Furthermore, ₁ ^- and ₂ ^- are respectively ₁ ⁺ and
It is a signal with ^the opposite phase of ₂₊ .

The time difference detection circuit in Fig. 4 is ₁ ^- , ₁ ⁺ , ₂ ⁺ ,
₂ ^- as input, output Q _{A ~} from four flip-flops (hereinafter abbreviated as FF) 27A ~ 27D.
This is what gives rise to Q _D. D of each FF is a data terminal,
CK is a clock terminal, CLR is a clear terminal, and data terminals D are all connected to the power supply +Vcc. On the other hand, inputs ₁ ^- , ₁ ⁺ , ²⁺ , ₂ ^- are FF27A~2
7D is supplied to each clock terminal CK, and ₁ ^-
is to the clear terminal CLR of FF27C, ₁ ⁺ is to FF27
₂₊ is also supplied to the clear terminal CLR of FF27A, and ₂ ^is also supplied to the clear terminal CLR of FF27B. This results in
The relationship between the outputs Q _A to Q _D of the FFs 27A to 27D and the inputs is as shown in FIG. The figure shows an example in which the phase relationship is different between the first half and the second half. The first half is ₂ (B+C
Since the phase of ₁ (component of A+D) is leading with respect to the component (component), pulses are generated at the outputs Q _A and Q _B. On the other hand, in the second half, the phase of ₁ is delayed compared to ₂ , so pulses are generated at the outputs Q _C and Q _D. The reason why two types of outputs are generated with the same phase relationship is that one (Q _A , Q _D ) is related to falling, while the other (Q _B , Q _C ) is related to rising.

By the way, the above-mentioned tracking error detection circuit obtains two pulse-like signals by adding analog outputs of the portions located on the diagonal lines of the quadrant light receiving element 3, and calculates the time difference (phase difference) between the rise or fall of these signals. ) is proportional to the track deviation, but the problem is that it focuses only on time information, so if the above signal is dropped (dropout) due to scratches or dust on the disk, an abnormality may occur. This is because an error signal is generated, which disturbs the servo system and causes track skipping.

Purpose of the invention The present invention uses a time filter to prevent the output of a time difference detection circuit from becoming abnormally long due to a drop in an input signal, thereby preventing track jumps.

Structure of the invention The invention consists of an optical head that irradiates a rotating optical disk surface with a light beam and receives the reflected light with a light-receiving element, and divides the light-receiving element into four parts to calculate the time difference between the light reception output of each part with respect to the same pit. A time difference detection circuit detects a positional deviation between the optical axis of the optical head and the track of the disk, and the optical axis of the light receiving head is corrected to the center of the track based on an output pulse corresponding to the time difference of the detection circuit. An optical disc player having a servo system is characterized in that a time filter is provided at a subsequent stage of the time difference detection circuit to regulate the upper limit of the pulse width of the detection circuit output to a constant value. This will be explained in detail with reference to an example.

Embodiment of the invention FIG. 6 is a schematic block diagram showing an embodiment of the invention, in which 30 is an optical head, 31 is a light receiving element output circuit in FIG. 3, 32 is a time difference detection circuit in FIG.
3 is a time filter added according to the present invention, 34
is a phase compensation circuit, and 35 is an actuator driver. In addition to the four-part light receiving element 3, the optical head 30 houses a tracking and actuator coil 36 for finely moving the lens 6 shown in FIG. is adjusted.

FIG. 7 shows a specific example of the time filter 33, with 41,
42 is an OR circuit, 51 and 52 are the outputs of time τ
61, 62 are inverters that invert the output, 71 is an AND gate,
72 is a NAND gate. This time filter 3
Function 3 attempts to limit the upper limit of the pulse width to the delay time τ for each of the inputs Q _A to Q _D. The OR circuit 41 has two inputs with a time difference.
Q _A and Q _B share the delay circuit 51 and the like, and the OR circuit 42 also shares the delay circuit 52 and the like between two inputs Q _C and Q _D with a time difference. Developing this idea, Q _A , Q _B and
Since Q _C and Q _D exclusively generate pulses, if the outputs of the OR circuits 41 and 42 are further combined with another 2-input OR circuit, only one set of delay circuits is required.

The operation will be explained below with reference to the time chart shown in FIG. Output of light receiving element output circuit 31
₁ and ₂ as shown in the figure, some of the flip-flops 27A to 27D of the time difference detection circuit 32 will not be cleared.
The output Q _B of 7B is fixed at H (high). If this output Q _B is input directly to the phase compensation circuit 34 as in the conventional case, the position of the lens 6 will shift too much, causing track jumps, but in this example, the upper limit of the time width is set by the time filter 33 shown in FIG. Since τ is limited to τ, the influence of dropouts due to scratches, dust, etc. can be avoided or reduced. In other words, the input Q _A ,
If the OR output X ₁ of Q _B is delayed by the delay circuit 51 and then inverted by the inverter 61, it becomes X ₂ , so if this is ANDed with X ₁ , the final output is
For X ₀ , Q _A and Q _B that are less than the time width τ are output as they are, and those that exceed τ are outputted while being limited to τ.
Q _B ' of X ₀ has a pulse width limited to τ by a time filter.

Assuming that the output of the AND circuit 72 is X ₀ ', the two outputs of the time filter 33 are X ₀ ,
X ₀ ' is combined and input to the phase compensation circuit 34.
The actuator driver 35 is a phase compensation circuit 34
The coil 36 is driven based on the output of the time filter 33, and indirectly the output of the time filter 33. Therefore, if the output X ₀ (same as X ₀ ') of the time filter 33 is only Q _A and Q _B indicating the original phase difference, the center of the light receiving element 3 is tracked as explained in FIG. A position correction is made such that it corresponds to 12. On the other hand, applying a time width τ that is not based on the actual phase difference does not correct the track deviation in a strict sense. However, this is an emergency measure to solve the problem of abnormal situations such as dropouts, which would cause track jumps if a time limit of τ was not added. Next, pits will begin to be detected, allowing correction within the same track. Therefore, the delay time τ is determined from such a point of view. For example, when the laser beam diameter is 1.6 μm and the tangential speed of the disk is 1.25 m/s, τ=600 μm is a tentative standard. This value has also been confirmed to be satisfactory through experiments.

Incidentally, the above-described time filter 33 can also be applied to other parts of the DAD player, such as a disk rotation speed error detection circuit using a phase comparator.

Effects of the invention As described above, according to the invention, the optical
In a DAD player, there is an advantage that track skipping caused by scratches or dust on the disk surface can be prevented by simply adding a simple circuit.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the principle of an optical DAD player.
Fig. 2 is an explanatory diagram of track deviation, Fig. 3 is a block diagram of the light receiving element output circuit, Fig. 4 is a block diagram of the time difference detection circuit, Fig. 5 is a time chart thereof, and Fig. 6 is an implementation of the present invention. A block diagram showing an example, FIG. 7 is a detailed diagram of a time filter, and FIG. 8 is a time chart of the embodiment. In the figure, 1 is a disk, 2 is a laser, 3 is a 4-split light receiving element, 6 is a lens, 11 is a pit, 12 is a track, 30 is an optical head, 32 is a time difference detection circuit, 33 is a time filter, and 34 is a phase compensation circuit,
35 is an actuator driver, and 36 is a tracking actuator coil.

Claims (1)

[Scope of utility model registration request] an optical head that irradiates a rotating optical disk surface with a light beam and receives the reflected light with a light receiving element;
a time difference detection circuit that divides the light receiving element into four parts and detects a positional deviation between the optical axis of the optical head and the track of the disk from the time difference between the light reception outputs of each part for the same pit; and an output corresponding to the time difference of the detection circuit. In an optical disk player having a servo system that corrects the optical axis of the optical head to the center of the track based on pulses, the upper limit of the pulse width of the output of the detection circuit is set to a constant value at a stage subsequent to the time difference detection circuit. An optical disc player characterized by being provided with a time filter for regulating time.