JPS61198437A - Circuit for generating tracking error signal of disc reproducing device - Google Patents

Abstract

PURPOSE:To attain stable and sure tracking servo operation by providing a means extracting an envelope component of a reproducing signal, a means generating a binary error signal, a means holding a level of the error signal and a means amplifying a signal component corresponding to the holding state. CONSTITUTION:An output summing signal (a+b) from photodetecting regions (a, b) of a photodetector 17 and an output summing signal (c+d) from photode tector regions (c, d) are added by an adder circuit 22 to generate an RF signal being a reproducing signal. The signal connects to a non-inverting input termi nal (+) of a comparator circuit 24 via an envelope detection circuit 23 and reference voltage Es outputted from a constant voltage source 25 is fed to an inverting input terminal (-) of the comparator circuit 24. On the other hand, an output terminal of the said subtraction circuit 18 connects to the inverting input terminal (-) of a subtraction circuit 26, connects to a non- inverting input terminal (+) of the subtraction circuit 26 via a sample-and-hold circuit 27 and an amplifier circuit 28, and an output terminal of the subtraction circuit 26 connects to an input terminal of a phase compensation circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a disc playback device such as an optical compact disc player, and particularly relates to an improvement of a tracking error signal generation circuit thereof.

[Technical Background of the Invention] As is well known, in the fields of audio equipment and image processing, for example, analog information signals are converted into digitized data in order to achieve high-density and high-fidelity recording and playback. Optical disc playback devices have become popular, which convert and record data in rows on a disc, and optically read digitized data from the disc to obtain the original analog information signal.

In such an optical disc playback device, the beam spot formed on the disc by the objective lens as a pickup element accurately traces the data row without deviation from the data row recorded on the disc. A tracking servo is provided to control the objective lens to follow. This tracking servo is performed by generating a tracking error signal corresponding to the deviation of the beam spot from the data sequence based on the reproduction signal of the disk, and controlling the objective lens in accordance with this tracking error signal.

FIG. 5 shows such conventional tracking servo means. That is, the laser light emitted from the laser diode 11 provided in the pickup is converted into parallel light by the first optical system 12, goes straight through the beam splitter 13, and is directed onto the signal recording surface of the disk 15 by the objective lens 14. The light is focused and a beam spot is formed on the disk 15 here. The laser beam reflected by the disk 15 travels backward through the objective lens 14 and is reflected at right angles by the beam splitter 13, and then passes through the second optical system 1.
The light is focused on a photodetector 11 via a photodetector 6.

Here, the photodetector 17 has four light receiving areas a to d. Of these, the output signals of the light receiving areas a and b and the output signals of the light receiving areas c and d are added together,
The subtracting circuit 18 consisting of resistors R1 to R4, capacitors CI and C2, and operational amplifier ○P1 performs the calculation (a+b)-(c+d), thereby producing a tracking error corresponding to the deviation of the beam spot from the data string. A signal is generated. Then, this tracking error signal is transmitted to the phase compensation circuit 19 and the drive amplifier circuit 20.
The signal is supplied to a tracking actuator coil 21 provided in the pickup for driving the objective lens 14 in the tracking direction.

In the above configuration, with reference to FIG.
The relationships between the data string, the beam spot, and the tracking error signal will be explained.

That is, in FIG. 6(a), Q1 to l indicate adjacent data strings (bit strings), and S indicates a beam spot. Moreover, what is shown by a solid line in FIG. 6(b) is a tracking error signal.

First, when the beam spot S is accurately located on the bit string β1, the tracking error signal is 0 [■]
level, that is, a value corresponding to no error.

Therefore, the tracking actuator coil 21
The voltage applied to the objective lens 14 is also O [V].
is made so that it cannot be moved.

In this state, assume that the beam spot S is moved in the direction of the bit string ρ2 due to eccentricity of the disk 15 or external vibration, for example. Then, the tracking error signal becomes a positive voltage, and this positive voltage is also supplied to the tracking actuator coil 21. Here, in a state where a positive voltage is applied to the tracking actuator coil 21,
It is set to act to draw the objective lens 14 in the direction of the bit row a1, and tracking servo is performed here.

[Problems with Background Art] However, the conventional tracking servo means as described above has the following problems. That is, as shown in FIG.
In a state where it is shifted within a certain range from the center of 23,
The beam spot S can be drawn into the bit string λ1 to λ23 based on the tracking error signal, but if the deviation of the beam spot S exceeds the above range, the level of the tracking error signal will drop and it will no longer be used for tracking servo, resulting in poor tracking. This makes servo operation impossible. In FIG. 6(b), a, c, and e are areas where the tracking error signal is used for tracking servo, and b, d, and f are areas where the tracking error signal is not used for tracking servo.

The sawtooth wave signal shown by the dotted line in FIG. 6(1) shows the waveform of an ideal tracking error signal free from the above-mentioned problems.

[Object of the Invention] The present invention has been made in consideration of the above circumstances, and provides an extremely good disk that reduces the area not used for tracking servo and generates a tracking error signal that enables stable and reliable tracking servo operation. An object of the present invention is to provide a tracking error signal generation circuit for a playback device.

[Summary of the Invention 111] That is, the tracking error signal generation circuit of the disc playback device according to the present invention reads an information signal by having a pickup element follow an information string recorded on the disc, and the read playback signal tracking servo means for generating an error signal corresponding to the deviation of the pickup element from the information sequence based on the error signal, and controlling the pickup element to follow the information sequence based on the error signal. In the disk playback device, envelope detection means extracts an envelope component of the playback signal, and a signal outputted from the envelope detection means is compared with a predetermined reference level to detect an area of the error signal to be used for the tracking servo. Comparing means for generating a binary signal having a corresponding first value and a second value corresponding to an area of the error signal that is not used for the tracking servo, and an output of the comparing means serving as the first value. a sample hold means for holding the level of the error signal in a state where the error signal becomes a sample state and the output of the comparison means becomes a second value; By including layer width means for amplifying at least the signal component corresponding to the hold state, the area not used for tracking servo is reduced, and a tracking error signal capable of performing stable and reliable tracking servo operation is generated. This is what I did.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the oral surface. In FIG. 1, the same parts as in FIG. 5 are indicated by the same symbols, and only the different parts will be explained here. That is, the output sum signal (a+b) from the light receiving areas a, b of the photodetector 17 and the output sum signal (c+d) from the light receiving areas c, d are added by the adder circuit 22, and are the reproduction signal of the disc 15. An RF multiplied signal is generated. The output terminal of this adder circuit 22 is connected to a non-inverting input terminal of a comparator circuit 24 via an envelope detection circuit 23. The reference voltage ES output from the constant voltage source 25 is connected to the inverting input terminal of the comparison circuit 24.
is applied.

On the other hand, the output terminal of the subtraction circuit 18 is connected to the inverting input terminal of the subtraction circuit 26 and also connected to the non-inverting input terminal of the subtraction circuit 26 via the sample hold circuit 21 and the amplifier circuit 28. There is. The output terminal of this subtraction circuit 2B is connected to the input terminal of the phase compensation circuit 19. Here, the sample hold circuit 27
is controlled into a sample state and a hold state according to the output of the comparator circuit 24. Further, the amplification circuit 28 functions to amplify the input signal level by two times.

In the above configuration, referring to FIG. 2 below,
Let's explain its operation. However, (b) to (h) in Figure 2
show the signal waveforms at points (b) to (h) in FIG. 1, respectively. That is, as shown in FIG. 2(a),
Assume that the beam spot S is moved as shown by the arrow in the figure with respect to adjacent bit strings 1 to 23. Then, the RF multiplied signal output from the adder circuit 22, FIG. 2(b)
As shown in FIG.
It has a ripple component every time it crosses.

Here, the ripple component of the RF multiplied signal is extracted by the envelope detection circuit 23 as shown in FIG. 2(C), and compared with the reference voltage ES by the comparison circuit 24.

As shown in FIG. 2(d), this comparison circuit 24 outputs a pulse-like control signal having an H level when the level of the ripple component is higher than the reference voltage ES, and an L level when it is lower.

By the way, as mentioned above, from the subtraction circuit 18,
A tracking error signal as shown in FIG. 2(e) is output. The relationship between the control signal and the tracking error signal is such that the H level period of the control signal corresponds to the area of the tracking error signal used for tracking servo, and the L level period of the control signal corresponds to the area of the tracking error signal used for tracking servo. It is designed to accommodate areas where it is not provided.

Here, the sample and hold circuit 27 is in a sample state for a period when the control signal is at an H level, and leads the tracking error signal as it is to the amplifier circuit 28, and is in a hold state for a period when the control signal is at an L level, holding the level of the tracking error signal. amplification circuit 2
It is operated to lead to 8. Therefore, the sample and hold circuit 27 outputs the signal shown in FIG. 2(f). And this sample hold circuit 27
The output signal is amplified by the amplifier circuit 28 so that its level is doubled, as shown in FIG.

Thereafter, the subtraction circuit 26 subtracts the tracking error signal shown in FIG. 2(e) from the signal shown in FIG. 2(Q), thereby producing a new tracking error signal as shown in FIG. 2(h). will be generated.

Here, when the control signal is at H level, that is, when the tracking error signal output from the subtraction circuit 18 corresponds to the area provided for tracking servo, the signal level of the tracking error signal is set to V.
1, the output signal level v2 of the subtraction circuit 26 becomes V2-2V1-Vl-Vl, and the tracking error signal shown in FIG. 2(e) is supplied as is to the phase compensation circuit 19. Furthermore, during the period when the control signal is at L level, that is, when the tracking error signal output from the subtraction circuit 18 corresponds to an area not used for tracking servo, the output signal level (2) of the subtraction circuit 26 is further increased. becomes high, and a state is established in which tracking servo can be performed.

The new tracking error signal generated as described above is transmitted to the phase compensation circuit 19 and the drive amplifier circuit 20.
The signal is supplied to the tracking actuator coil 21 via the tracking actuator coil 21, and tracking servo is performed.

Therefore, according to the configuration of the above embodiment, the region of the tracking error signal that is not used for the tracking servo is eliminated, and the tracking error signal is made to substantially approach the ideal state described above, so that it can be stably and reliably produced. This makes it possible to perform accurate tracking servo operations.

FIG. 3 shows another embodiment of the invention. That is, the output terminal of the subtraction circuit 18 is connected to the phase compensation circuit 1 via the sample hold circuit 27 and the amplifier circuit 28.
9, and the sample and hold circuit 27 as well as the amplifier circuit 28 are controlled by the control signal output from the comparison circuit 24. In this case, the amplifier circuit 28 does not carry out amplification while the control signal is at the H level and directs the input signal as it is to the phase compensation circuit 19, and doubles the input signal level during the period when the control signal is at the L level. It is controlled as follows.

The operation of such a configuration will be explained with reference to FIG. However, FIGS. 4(a) to 4(d) show the signals at points (a) to (d) in FIG. 3, respectively. That is, during the period in which the control signal shown in FIG.
The tracking error signal shown in Figure (b) is as shown in Figure 4 (d).
The signal is supplied as is to the phase compensation circuit 19 as shown in FIG.

On the other hand, during the L level period of the control signal, the sample and hold circuit 27 is in the hold state and the amplifier circuit 28 is in the operating state, so the tracking error signal shown in FIG. 4(b) is as shown in FIG. 4(d). As shown in the figure, the held portion is amplified twice.

Even with such a configuration, although the tracking error signal shown in FIG. 2(h) has a waveform that is different from the ideal waveform described above, it is possible to generate a tracking error signal that can substantially perform a sufficient tracking servo operation. It is something that can be obtained.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as described in detail above, according to the present invention, an extremely good disk is provided which reduces the area not used for tracking servo and generates a tracking error signal that enables stable and reliable tracking servo operation. A tracking error signal generation circuit for a playback device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of a tracking error signal generation circuit of a disc playback device according to the present invention, FIG. 2 is a waveform diagram for explaining the operation of the same embodiment, and FIG. 3 is a diagram of the present invention. FIG. 4 is a waveform diagram for explaining the operation of the same embodiment, FIG. 5 is a block diagram showing a conventional tracking servo means, and FIG. 6 is a conventional tracking servo means. FIG. DESCRIPTION OF SYMBOLS 11... Laser diode, 12... First optical system, 13... Beam splitter, 14... Objective lens, 15... Disc, 16... Second optical system, 17
...Photodetector, 18...Subtraction circuit, 19.
...Phase compensation circuit, 20...Drive amplifier circuit, 21...
- Tracking actuator coil, 22... Addition circuit, 23... Envelope detection circuit, 24... Comparison circuit, 25... Constant voltage source, 26... Subtraction circuit, 2
7...Sample hold circuit, 28...Amplification circuit.

Claims (1)

[Claims] An information signal is read by a pickup element following an information string recorded on a disk, and an error signal corresponding to the deviation of the pickup element from the information string is generated based on the read reproduction signal. A disc playback device comprising tracking servo means for controlling the pickup element to follow the information string based on an error signal, comprising: envelope detection means for extracting an envelope component of the playback signal; and the envelope detection means. A first value corresponding to an area of the error signal to be used for the tracking servo and a first value corresponding to an area of the error signal not to be used for the tracking servo are determined by comparing the signal output from the error signal with a predetermined reference level. a comparing means for generating a binary signal having a value of 2, and a sample state for the error signal when the output of the comparing means becomes a first value, and the output of the comparing means becomes a second value; sample-and-hold means for holding the level of the error signal in the state in which the error signal is held; and amplification means for amplifying at least a signal component corresponding to the held state among the output signals from the sample-and-hold means. A tracking error signal generation circuit for a disc playback device.