JPH0318255B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking error signal detection method and detection method in an information reading device that optically detects and reads information from an information recording carrier used in a video disc playback device, a digital audio disk playback device, etc. Regarding equipment.

The information recording carrier is made of, for example, a transparent disk,
Concave portions (referred to as pits in this specification) are arranged in the information recording image of the disc body so as to form concentric or spiral tracks, and information is recorded depending on the length and spacing of these pits. There is. An information reading device for reading information from a rotationally driven information recording carrier is, for example, a He-Ne device as shown in FIG.
A light beam from a laser light source is reflected by a tangential mirror 2 via a polarizing beam splitter 1, the light reflected by the tangential mirror 2 is reflected by a tracking mirror 3, and an objective lens 4
is incident on the information recording carrier 5 by the objective lens 4.
The light is focused on the signal recording surface of the information recording carrier 5 and irradiated as a light spot, and is reflected on the information recording surface of the information recording carrier 5.
This reflected beam is projected onto the photoelectric conversion element 6 via the polarization splitter 1 through the opposite path to the above,
Information recorded on the information recording carrier 5 is converted into an electrical signal from the output of the photoelectric conversion element 6 and detected.

Further, when reading the above information, it is necessary to make the optical spot follow the center of the track consisting of a row of pits, and for this reason, it is necessary to make the optical spot follow the center of the track consisting of a row of pits. A tracking error signal corresponding to the distance is detected, the tracking error signal is applied to a servo amplifier, and the rotation angle of the tracking mirror 3 is controlled so that the tracking error becomes zero.

The photoelectric conversion element 6, which converts information into an electrical signal and reads it out, has an optical axis as the origin 0, an X-axis corresponding to the tangential direction of the track, and a Y-axis corresponding to the normal direction of the track, as shown in FIG. 2, for example. It is divided into each quadrant of the XY coordinates.

On the other hand, the tracking error signal is transmitted through four divided photoelectric conversion elements _6-11 , _6-12 , _6-21 and _6-22.
The sum signal H _F of the output signals of (photoelectric conversion elements _6-11 , 6
_-12 , _6-21 and _6-22 output signals as _S11 , _S12 ,
When S ₂₁ and S ₂₂ , H _F = S ₁₁ + S ₁₂ + S ₂₁ +
S ₂₂ ) or difference signal D _L {= (S ₁₂ + S ₂₁ ) − (S ₁₁ +
S ₂₂ )} was detected from the amplitude information.

However, since the reflected light from the information recording carrier 5 changes depending on the optical characteristics of the information reading device, the conventional method of detecting the tracking error signal from the amplitude information of the sum signal H _F or the difference signal D _L as described above This method has the disadvantage that the sensitivity of the tracking signal changes depending on the amplitude level of the sum signal H _F or the difference signal D _L , that is, the optical characteristics of the information reading device.

The present invention has been made in view of the above, and an object of the present invention is to provide a tracking error signal detection method and detection device for an information reading device that eliminates the above-mentioned drawbacks.

According to the present invention, this object is achieved by detecting a tracking error from phase information contained in the output signal of a photoelectric conversion element.

Hereinafter, the present invention will be explained using examples and in comparison with conventional examples.

FIG. 3 shows the diffraction pattern of the reflected beam with respect to the relative position of the optical spot of the projection beam focused on the information recording surface of the information recording carrier 5 and the track. The upper part of each column in Fig. 3 shows the relative position of the pit and the light spot, the circle at the top of each column in Fig. 3 shows the outer shape of the light spot, and the shaded part shows a part of the pit. There is.
The lower part of each column in FIG. 3 shows the diffraction pattern on the surface of the objective lens 4, the circle shows the cross-sectional outline of the objective lens 4, and the hatched part shows the diffraction pattern.
In FIG. 3, the state shown in column b shows the change in the diffraction pattern on the objective lens 4 from the time the pit enters the light spot until it exits when the center of the light spot is on the center line of the track. The state shown in column a shows a similar change when the light spot is located to the right of the track center line, and the state shown in column c shows the same change when the light spot is located to the left of the track center line. Similar changes are shown in each case.

Therefore, when the diffraction pattern on the surface of the objective lens 4 is mapped onto the photoelectric conversion element 6 and the output is calculated to obtain the sum signal H _F and the difference signal D _L , the sum signal H _F and the difference signal D The waveform of _L is as shown in FIGS. 4A and 4B corresponding to FIG. That is, in the case of column b in Fig. 3, the sum signal H _F is the fourth
The waveform is as shown by the solid line in Figure A, and in the case of columns a and c in Figure 3, the sum signal H _F is
The waveform is as shown by the broken line in Figure A. In FIG. 4A, the Roman numeral ~ corresponds to row 1~ in FIG. 3, and the state indicates that the light spot is halfway into the pit,
Contrary to the state shown in FIG. 2, the state shown in FIG.
The difference signal D _L is as shown in FIG. 4B, and in FIG. 4B, lines a, b and c are the third
Corresponding to columns a, b, and c in the figure, the Roman numerals are the same as in FIG. 4A. As is clear from FIGS. 3 and 4, the amplitude of the sum signal H _F is different between the state of column b in FIG. 3 and the state of columns a and c in FIG. In the case of column a in Fig. 3, the difference signal D _L has a phase lead of 90 degrees from the sum signal H _F , and in the case of column c in Fig. 3, the difference signal D _L has a phase of 90 degrees ahead of the sum signal H _F. I'll be late. Further, in the case of column b in FIG. 3, the difference signal D _L does not change. Further, although the amplitude of the sum signal H _F changes depending on the amount of deviation between the track center line and the optical spot, there is no change in phase during this time.

Therefore, conventionally, the tracking error signal has been detected using a circuit as shown in FIG. 5, for example. That is, the output signals of photoelectric conversion elements _6-11 and _6-22 are added by adder 7, the output signals of photoelectric conversion elements _6-12 and _6-21 are added by adder 8, and adder 7
The output signals of 8 and 8 are added together by adder 9 to produce a sum signal.
Get H _F. The waveform of the sum signal H _F is as shown in FIG. 6b. A subtracter 10 subtracts the output signal of the adder 7 from the output signal of the adder 8 to obtain a difference signal D _L. The waveform of the difference signal D _L is as shown in FIG. 6a. Also,
The output signal (D _L signal) of the subtracter 10 is applied to sample and hold circuits 11 and 12, respectively, and the output signal (H _F signal) of the adder 9 is applied to the zero cross detection circuit 13 to increase the H _F signal. 6th in
Obtain the sampling pulse shown in Figure c, use this sampling pulse to sample and hold the output signal of the subtracter 10, and generate the output signal of the adder 9 (H _F signal).
is applied to the zero cross detection circuit 14 to obtain the sampling pulse shown in FIG. 6d while the H _F signal is decreasing, and the output signal of the subtracter 10 is sampled and held using this sampling pulse. Therefore, the output signal of the sample and hold circuit 12 has a waveform as shown in FIG. 6e, and the sample and hold circuit 11
The output signal has a waveform as shown in FIG. 6f. Since the output signal waveforms of the sample and hold circuits 11 and 12 have opposite phases, by differentially amplifying these two signals by the differential amplifier 15, a tracking error signal free from disturbances such as offsets is obtained.

However, since the relationship between the optical spot and the length of the pit is such that as the spatial frequency of the pit decreases, the degree of modulation of the reflected light beam decreases, H _F with respect to the spatial frequency of the pit on the information recording carrier 5,
The amplitude level of the _DL signal gradually decreases as the spatial frequency increases, as shown in FIG. Therefore, when the spatial frequency of the pits on the information record carrier 5 is in a wide range, the amplitude levels of the _HF signal and the _DL signal change depending on the frequency of the recorded information on the information record carrier 5. For this purpose, as shown in Figure 5.
The method of obtaining a tracking error signal by sampling and holding the amplitude level of _{the DL signal} has the disadvantage that changes in the amplitude level of the DL signal cause disturbance to the tracking error signal. Furthermore, if the focus gain is insufficient, the amplitude levels of the H _F signal and the D _L signal change during one revolution of the information recording carrier 5, and this change causes a disturbance to the tracking error signal.

FIG. 8 is a block diagram of one embodiment of the present invention.

In one embodiment of the present invention, the photoelectric conversion element 6
- The output signal of photoelectric conversion element _6-11 and the output signal of photoelectric conversion element _6-22 are input to adder 7 and added.
- The output signal of ₁₂ and the output signal of the photoelectric conversion element _6-21 are input to the adder 8 and added, and the output signal T _S1 of the adder 7 and the output signal T _S2 of the adder 8 are added to the adder 9.
Enter and add. The output signal T _S1 of the adder 7 is applied to a voltage comparator 16 whose comparison potential is the ground potential, and the output signal T _S1 of the adder 7 is compared with the ground potential. Similarly, the output signal H _F of the adder 9 is applied to the voltage comparator 17 to compare the output signal H _F of the adder 9 with the ground potential. Output signal T _S2 of adder 8
is simultaneously applied to the voltage comparator 18 to compare the output signal T _S2 of the adder 8 with the ground potential. The output signals of voltage comparators 16 and 17 are each input to a phase comparator 19 for phase comparison. The output signals of voltage comparators 18 and 17 are also respectively input to phase comparator 20 for phase comparison. Phase comparators 19 and 2
The output signals of 0 are respectively input to low-pass filters 21 and 22 and filtered, and the output signals of low-pass filter 21 and low-pass filter 22 are filtered.
The output signal is input to a differential amplifier 23 and a tracking error signal is obtained from the output terminal of the differential amplifier 23.

In one embodiment of the present invention configured as described above, when the light spot is located on the track center, that is, at the position shown in column b in FIG. 3, the output signal H _F of the adder 9, Adder 7
The output signal T _S1 of the adder 8 and the output signal T _S2 of the adder 8 are in phase as shown by the solid line b in FIGS. 9A, B and C. Furthermore, when the light spot is located on the right side of the track, _that is, at the position shown in column a in _FIG . , and the output signal T _S2 of adder 8 is the output signal of adder 9.
The phase advances relative to H _F , as shown by the thick broken line a in FIGS. 9B and 9C. Furthermore, when the light spot is located on the left side of the track, _that is, at the position shown in column C in _FIG . , the output signal T _S2 of the adder 8 is delayed in phase with respect to the output signal H _F of the adder 9, as shown by the thin broken line C in FIGS. 9B and 9C. Further, the phase advance and lag angles of the output signals T _S1 of adders 7 and 8 with respect to the output signal H _F of adder 9 are proportional to the amount of deviation between the optical spot and the track.

Therefore, the output signals T _S1 of adder 7 and adder 9
A tracking error signal can be obtained from a signal obtained by comparing the phase with H _F or a signal obtained by comparing the phases of the output signals T _S2 of adder 8 and adder 9 with H _F. Also, a tracking signal can be obtained by combining the output signals of phase comparators 19 and 20.

The following will explain an embodiment of the present invention shown in FIG. 8 assuming that the light spot is located on the right side of the track, that is, in row a of FIG. 3.

In this state, the output signal H _F of the adder 9 has a waveform as shown in the curve of FIG. 10A, and the output signal V ₃ of the voltage comparator 17 has a pulse waveform as shown in FIG. 10A. Furthermore, since the output signal T _S1 of the adder 7 is delayed in phase from the output signal H _F of the adder 9 as described above, it has a waveform as shown in the curve in FIG. 10B, and the output signal V ₁ of the voltage comparator 16 is The pulse waveform is shown in Figure 10B. Therefore, the output signal of the phase comparator 19
V ₄ is connected to voltage comparators 16 and 1 as shown in FIG. 10D.
This becomes a negative pulse with a pulse width corresponding to the phase difference between the output pulse and the output pulse. On the other hand, since the output signal T _S2 of the adder 8 leads the output signal H _F of the adder 9 in phase as described above, the output signal T _S2 of the adder 8
has a waveform as shown in the curve of FIG. 10C, and the output signal V ₂ of the voltage comparator 18 has a pulse waveform as shown in FIG. 10C. Therefore, the output signal of the phase comparator 20
V ₅ is connected to voltage comparators 17 and 1 as shown in FIG. 10E.
It becomes a positive pulse with a pulse width corresponding to the phase difference of the output pulse with 8.

Therefore, the output signal of the low-pass filter 21 is at a lower level than the voltage during the state shown in column b of FIG. The voltage will be higher than the voltage at . Therefore, by differentially amplifying the output signals of the low-pass filters 21 and 22 by the differential amplifier 23, the optical spot is shifted to the right side of the track (Fig. 3a).
A tracking error signal for the column is obtained.

Conversely, when the light spot is shifted to the left side of the track, the levels of the output signals of the low-pass filters 21 and 22 change in the opposite direction to the level when the light spot is shifted to the right side of the track. , a tracking error signal for column C in FIG. 3, in which the optical spot is shifted to the left side of the track, is obtained from the output terminal of the differential amplifier 23.

In addition, in one embodiment of the present invention described above, the output signals of the phase comparators 19 and 20 are sent to the differential amplifier 23.
In this example, the tracking error signal is obtained by combining the phase comparator 19 or 20.
It is clear from the above description that a tracking error signal can be obtained by each output signal. A tracking error signal free from disturbances such as offset can be obtained by combining the signals using only the differential amplifier 23.

As explained above, according to the present invention, since the tracking error signal is obtained by detecting the phase information contained in the output signal of the photoelectric conversion element, the sensitivity of the tracking error signal is higher than that of the photoelectric conversion element. It no longer changes depending on the amplitude level of the output signal.

In addition, when the focus gain is insufficient, the amplitude level of the output signal of the photoelectric conversion element becomes partially low as in the conventional case, causing disturbance to the amplitude, but in the present invention, the phase information in the output of the photoelectric conversion element Since the tracking signal is obtained by detection, there is also the effect that the lack of focus gain does not affect the tracking error signal as a disturbance.

Furthermore, a tracking error signal is generated from the phase difference between the output of the first adder circuit and the output of the third adder circuit, and/or the phase difference between the output of the second adder circuit and the output of the third adder circuit. Therefore, the first addend input signal of the third adder circuit is
Alternatively, the output of the second adder circuit is included. As a result, compared to the case where a tracking error signal is obtained from the phase difference detection output of the summed output between different pairs of photoelectric conversion elements, there is an effect that the tracking error signal is not affected by variations in detection sensitivity of the phase difference detection circuit.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical system in an information reading device. FIG. 2 is a layout diagram of photoelectric conversion elements. FIG. 3 is an explanatory diagram showing the pattern of the reflected beam on the objective lens with respect to the relative positions of the light spot and the track. FIG. 4 is a waveform diagram of the output signal of the photoelectric conversion element.
FIG. 5 is a block diagram showing an example of a conventional tracking error detection device. FIG. 6 is a waveform diagram for explaining the operation of the tracking error detection device shown in FIG. 5. FIG. 7 is a characteristic diagram showing the relationship between the spatial frequency of pits and the output signal level of the photoelectric conversion element. 8th
The figure is a block diagram of one embodiment of the present invention. FIGS. 9 and 10 are waveform diagrams for explaining the operation of an embodiment of the present invention. 5... Information record carrier, _6-11 , _6-12 , _6-21
and _6-22 ...photoelectric conversion element, 7, 8 and 9
... Adder, 16 to 18 ... Voltage comparator, 19 and 20 ... Phase comparator, 21 and 22 ... Low pass filter.

Claims (1)

[Scope of Claims] 1. Four photoelectric converters arranged around the optical axis convert the reflected light of a light spot irradiated onto an information recording carrier on which information is recorded in information recording pits forming concentric or spiral tracks. In an information reading device that reads information by receiving light with an element, a first method for adding output signals of first and fourth photoelectric conversion elements facing each other across the optical axis among the four photoelectric conversion elements; an addition circuit; a second addition circuit that adds output signals of the second and third photoelectric conversion elements among the four photoelectric conversion elements; and the first, second, third, and fourth photoelectric conversion elements; a third addition circuit that adds the output signals of the conversion elements; and a phase difference between the output signal of the first addition circuit and the output signal of the third addition circuit, or the output signal of the second addition circuit and the A tracking error signal in an information reading device comprising: a phase difference detection circuit for detecting a phase difference with an output signal of a third adder circuit; and a tracking error signal is obtained from the output signal of the phase difference detection circuit. King error signal detection device. 2 The reflected light of the light spot irradiated onto the information recording carrier recording information in the information recording pits forming concentric or spiral tracks is received by four photoelectric conversion elements arranged around the optical axis, and information is generated. In the information reading device for reading information, a first adding circuit adds output signals of first and fourth photoelectric conversion elements facing each other across the optical axis among the four photoelectric conversion elements; a second addition circuit that adds the output signals of the second and third photoelectric conversion elements among the photoelectric conversion elements; a third addition circuit that performs addition; a first phase difference detection circuit that detects a phase difference between the output signal of the first addition circuit and the output signal of the third addition circuit; and the second addition circuit. a second phase difference detection circuit that detects the phase difference between the output signal of the first phase difference detection circuit and the output signal of the third addition circuit; and subtracting means for subtracting the output signal and outputting an output signal corresponding to a phase difference between the output signal of the first addition circuit and the output signal of the second addition circuit. A tracking error signal detection device in an information reading device.