JPS61230637A - Tracking error detecting device - Google Patents

Abstract

PURPOSE:To obtain accurately a tracking error signal regardless of the fluctuation of a carrier frequency and with a simple constitution, by transmitting the result of multiplication of a signal obtained by giving the 1/4 minimum cycle delay to a reproduction signal and a diagonal difference signal through an LPF. CONSTITUTION:A delay circuit 21 delays a sum signal of detection outputs of photodetectors 1-4 by 1/4 minimum cycle of said sum signal. A multiplier 12 multiplies the difference signal of the sum signal of detection outputs of photodetectors 1 and 3 as well as 2 and 4 set on the diagonal lines by the delay signal delivered from the circuit 21. Then the output of the multiplier 12 is transmitted through an LPF 13, and the low band component of said output is defined as a tracking error signal. Thus an accurate tracking error signal is obtained regardless of the fluctuation of the carrier frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a trunking error detection device used for tracking a recording trunk of an optical recording medium.

[Summary of the invention]

The present invention provides a tracking error detection device as described above, in which the reproduction signal is approximately 1/1/1 of the minimum period of the reproduction signal.
By multiplying the delayed signal delayed by 4 periods by the diagonal difference signal and using the low frequency component of this multiplication result as the tracking error signal, an accurate tracking error signal can be obtained no matter how the carrier frequency changes. can be obtained using low-cost equipment.

[Conventional technology]

FIG. 11 shows the first conventional example of the present invention, JP-A-51-9.
This figure shows the tracking error detection device of No. 3223 (Japanese Patent Publication No. 1983-306, October).

In this first conventional example, the direction (y-axis direction) of a recording track of an optical recording medium (not shown) and the direction (X-axis direction) orthogonal thereto are
It has four photodetectors 1 to 4 which are respectively divided in the axial direction), and adders 5 to 7 add the 12th photodetector at point A.
A reproduced signal with a waveform as shown in FIG. A is obtained. and 90
Since the reproduced signal is input to the phase shifter 8 which delays the phase by .degree., a signal having a waveform as shown in FIG. 12B is obtained at point B.

On the other hand, the subtracter 11 subtracts the output signals from the adders 5 and 6, and the signal at point C, which is the output signal (diagonal difference signal) from the subtracter 11, is shown in FIG. Similarly, if the beam deviates to the right for one recording hour, the phase is delayed by 90° compared to the reproduced signal, and if the beam deviates to the left, the phase is advanced by 90°.

Since the signals at points B and C are multiplied by the multiplier 12, a signal having a waveform as shown in Figure 12 is obtained at point D. At point E after passing through the low-pass filter 13, as shown in FIG. 12E, if the beam deviates to the right with respect to the recording track, a positive DC signal is obtained; Then a negative DC signal can be obtained. Moreover, if the beam is on the recording track, the DC signal shown in FIG. 12E will not appear.

Therefore, the signal at point E indicates the tracking error, and tracking servo can be performed based on this tracking error signal.

Further, as a second conventional example of the present invention, Japanese Patent Application Laid-Open No. 57-7483
As in No. 7, the signal at point C is sampled separately at the zero cross points of both the rising and falling edges of the signal at point A in Figure 11, and the sampled signals are subtracted from each other, and the result of this subtraction is There is a method in which the signal is used as a trunking error signal.

Furthermore, as a third conventional example of the present invention, Japanese Patent Application Laid-Open No. 57-18
There is also a method, as in No. 1433, in which only the phase information of the respective output signals of adders 5 and 6 in FIG. 11 is used as the tracking error signal.

[Problem that the invention seeks to solve]

However, in the first conventional method described above, the reproduced signal is
Since the phase is shifted by 1, it is effective only in the case of a single carrier. In other words, in cases where the carrier frequency fluctuates significantly or in the case of the EFM format, which is the NRZ format used in compact discs, it is difficult to perform a 90° phase shift over a wide band, and accurate tracking is difficult. There is a problem that an error signal cannot be obtained.

Further, the above-mentioned second conventional method requires high-speed switching elements, has a complicated structure, and cannot be easily integrated into an IC, resulting in a high cost.

Furthermore, the method of the third conventional example described above uses only phase information and does not use amplitude information, so it is vulnerable to noise etc.
(poor playability), that is, it is impossible to obtain an accurate tracking error signal.

[Means for solving problems]

The tracking error detection device according to the present invention is arranged in the direction of the recording track of the optical recording medium (y-axis direction) with the optical axis as the center.
The light 23 from the recording track is divided into a direction perpendicular to the direction of the recording track (X-axis direction).
first to fourth photodetectors 1 to 4 that detect the first to fourth photodetectors 1 to 4;
The delay circuit 21 obtains a delayed signal that is delayed by approximately 1/4 period of the minimum period of the sum signal with respect to the sum signal of the detection outputs of the fourth photodetectors 1 to 4. The sum signal of the detection outputs of the first and third photodetectors 1.3 and the second
and a multiplier 12.41 which multiplies the difference signal between the detection output of the fourth photodetector 2.4 and the sum signal by the delayed signal, and a low frequency multiplier 12.41 which receives the output of the multiplier 1'2.41. They are each equipped with a filter 13.

[Effect]

According to the trunking error detection device according to the present invention, a reproduced signal is multiplied by a diagonal difference signal and a delayed signal delayed by approximately 1/4 cycle of the minimum cycle of the reproduced signal, and the result of this multiplication is Since the low frequency component is used as the trunking error signal, an accurate tracking error signal can be obtained no matter how the carrier frequency changes.

〔Example〕

Hereinafter, first to fourth embodiments of the present invention will be described with reference to FIGS. 1 to 10.

1 to 3 show a first embodiment.

As shown in FIG. 1, this first embodiment has substantially the same configuration as the first conventional example described above, except that a delay circuit 2] is used in place of the phase shifter 8. It's good.

When the carrier frequency of the reproduced signal is single, setting the delay time τ by the delay circuit 21 to 1/4 of the gear period is equivalent to having a phase delay of 90°. Therefore, in this case, the tracking error signal can be obtained using the same principle as the first conventional example described above.

When the reproduced signal is in the NRZ format, for example, the BFM format, the delay time τ is set to approximately 1/2 of the shortest pit length, that is, approximately 1/4 of the minimum period. Therefore, in the case of a compact disc, since the shortest pit length is about 700 ns, the delay time is set to τ-350 ns.

As a result, the reproduced signal at point A in FIG. 1 as shown in FIG. 2A is delayed by the time τ by the delay circuit 21, and the reproduced signal at point B in FIG. Become.

On the other hand, the signals at the zero point are generated inverted from each other around the zero-crossing points of the rising and falling edges of the reproduced signal. In this case, as shown in Figure 2C, if the beam deviates to the right with respect to the recording trunk, it will be negative at the rising edge and positive at the falling edge, and if it deviated to the left, it will be positive at the rising edge and negative at the falling edge. becomes.

As a result, a signal with a waveform as shown in the second diagram is obtained at point D. At point E, as shown in FIG. 2, if the beam deviates to the right with respect to the recording trunk, a positive DC signal will be obtained, and if it deviates to the left, a negative DC signal will be obtained. If the beam is on the recording track, then E
The DC signal shown in does not appear.

In other words, as in the first conventional example described above, the signal at point E indicates a tracking error.

FIG. 3 shows the optical system of this first embodiment. A beam 23 emitted from the light ri, 22 of a semiconductor laser or the like enters an optical recording medium (not shown) via a beam splinter 24, a collimator lens 25, and an objective lens 26. Also, the beam 2 reflected from this optical recording medium
Third, the light enters the photodetectors 1 to 4 described above via the objective lens 26, collimator lens 25, and beam splitter 24.

4 and 5 show a second embodiment.

This second embodiment is a system that binarizes a reproduced signal as digital data, such as in the case of Combat 1 to Disc.

Therefore, in this second embodiment, as shown in FIG. 4, a binarization circuit 27 is provided before the point A from which the reproduced signal is obtained.
Further, in front of the multiplier 12, there is provided a bipolarization circuit 28, that is, a circuit that outputs a signal of 10 when the input signal is 1, and outputs a signal of - when the input signal is 0.

The bipolarization circuit 28 may be of a type that applies a bias to the digital signal, a type of AC coupling, or a type of level conversion as shown in FIG. 5.

The level conversion type bipolarization circuit 28 shown in FIG.
T circuit 31, resistor 32, transistor 33 and resistor 34
It consists of And ten. When a signal of 0 is inputted, a signal of +Vcc is outputted, and when a signal of 0 is inputted, a signal of -Vcc is outputted.

The signal obtained from the bipolarization circuit 28 has sharp rising and falling edges, but is substantially the same as the signal shown in FIG. 2B. Therefore, in this second embodiment as well, a tracking error signal can be obtained using the same principle as in the first embodiment described above.

Incidentally, although the multiplier 12 was used in both the first and second embodiments described above, in the actual multiplier 12, when the input signals are a and b, the output signal C is as follows: c=, ab It is expressed as 10 to 2 a+, , b kl >> k2, ks.

k2. 3 is a coefficient that determines the feedthrough amount, and is 0 if the multiplier 12 is ideal. However, if the multiplier 12 is inexpensive or if null adjustment etc. are omitted, k2 or 3
is relatively large and its influence cannot be ignored.

If k2 or ni3 is relatively large, the carrier will leak,
The S/N of the tracking error signal deteriorates. In particular, when the bit length is long, the spectrum of the leakage signal spreads to include low frequency components, so that the low-pass filter 13 may not be able to filter the signal sufficiently.

FIGS. 6 and 7 show a third embodiment that can cope with such a situation. FIG. 7 A-H shows the waveforms of the signals at points A-H in FIG. 6, respectively, and NO.
The output signals of the T circuit 35, the AND circuit 36, the NOR circuit 37, and the subtracter 38 have waveforms as shown in FIG. 7B, D, E, and F, respectively. Therefore, in this third embodiment, a tracking error signal can be obtained using the same principle as in the first embodiment described above.

However, in the signal at point F, which is the carrier input to the multiplier 12, as shown in FIG. 7F, the low frequency components of the spectrum have been removed. Therefore, deterioration of the S/H of the trunking error signal can be prevented.

8 to 10 show a fourth embodiment.

In this fourth embodiment, a phase switching amplifier 4 is used instead of the bipolarization circuit 28 and multiplier 12 of the second embodiment shown in FIG.
1 was used.

This phase switching amplifier 41 receives the input signal A of FIG.
When the logic of the signal at a point is 1, it becomes a non-inverting amplifier, and when it is 0, it becomes an inverting amplifier.

In other words, by turning on and off the signal at point A in FIG. 8 as shown in FIG. 10A, the signal at point B in FIG. 8 as shown in FIG. 10B is detected, and the signal at point B in FIG. Now, the first
A signal as shown in Figure 0C is obtained. Therefore, a smoothed tracking error signal is obtained from the low-pass filter 13.

FIG. 9 shows a specific circuit example of the phase switching amplifier 41, which includes an operational amplifier 42,
It consists of a switch 43 and resistors R1 to R3.

The switch 43 is configured to be turned off when the signal at point A is 1, and turned on when the signal is -0. Therefore, when the signal at point A is 1, the phase switching amplifier 4
The amplification degree A of 1 is R,R.

So, when the signal at point A is O, A--□--
1 (R,,=R2)I. In other words, the phase switching amplifier 41 can switch the phase by 180°.

i [Effects of the Invention] As described above, according to the tracking error detection device according to the present invention, an accurate tracking error signal can be generated no matter how the carrier frequency changes by using only a delay circuit, a multiplier, and a low-pass filter. is obtained.

Therefore, since the configuration is simple and it is easy to integrate into an IC, an accurate tracking error signal can be obtained with a low-cost device.

[Brief explanation of the drawing]

1 to 10 show embodiments of the present invention.
Figure 2 is a block diagram of the first embodiment, Figure 2 is a signal waveform diagram in the first embodiment, Figure 3 is a perspective view of the optical system of the first embodiment, and Figure 4 is a block diagram of the second embodiment. , Fig. 5 is a circuit diagram of the main part of the second embodiment, Fig. 6 is a block diagram of the third embodiment, Fig. 7 is a signal waveform diagram in the third embodiment, and Fig. 8 is a diagram of the fourth embodiment. FIG. 9 is a circuit diagram of the main part of the fourth embodiment, and FIG. 10 is a signal waveform diagram in the fourth embodiment. FIG. 11 is a block diagram of a first conventional example of the present invention, and FIG. 12 is a signal waveform diagram in the first conventional example. In addition, in the symbols used in the drawings, L2, 3.4-----1 photodetector 12----- Multiplier 13-----1-----Low pass filter 21--------One delay circuit 23----
------Beam 41----------- Phase switching amplifier.

Claims (1)

[Scope of Claims] First to fourth parts are divided in the direction of the recording track of the optical recording medium and in the direction perpendicular to the direction of the recording track, with the optical axis as the center, and detect light from the recording track. a photodetector, and a delay circuit that obtains a delayed signal that is delayed by approximately 1/4 period of the minimum period of the sum signal with respect to the sum signal of the detection outputs of the first to fourth photodetectors; Multiplication in which the difference signal between the sum signal of the detection outputs of the first and third photodetectors on the diagonal and the sum signal of the detection outputs of the second and fourth photodetectors is multiplied by the delay signal. A tracking error detection device comprising: a multiplier; and a low-pass filter into which the output of the multiplier is input, and the output of the low-pass filter is used as a tracking error signal.