JPH0156454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called one-beam type tracking servo device in an optical disc playback device, and by providing two systems of tracking error detection circuits and combining their output signals, each tracking error can be detected. Changes (drifts) in characteristics due to temperature of the multiplier circuits included in the detection circuit are mutually canceled out.

The digital audio disk playback device is
The entire control system is configured as shown in FIG.

In FIG. 1, a disk 1 is placed on a turntable 2 and driven by a disk rotation motor 3. As shown in FIG. The optical pick-up head 4 houses a semiconductor laser, an optical system, a light receiving element, a focus control coil 5, a tracking control coil 6, etc., and irradiates the recording surface of the disk 1 with laser light from an objective lens 7, and also reflects the laser light. Light is received through an objective lens 7. The optical pickup head 4 is fed in the radial direction of the disk 1 by a feed motor 8.

A signal detected by the optical pickup head 7 is sent to a demodulation circuit 12 via a preamplifier 9, an AGC (Auto Gain Control) circuit 10, and a waveform shaping circuit 11.

The focus servo circuit 13 detects the shift in focus of the laser beam based on the light reception signal, and
The focus control coil 5 is driven so as to focus on the recording surface. This focus servo circuit 1
3, when operating with normal loop gain during feed operation due to random access, etc., the focus actuator vibrates as the optical pick-up head 4 crosses the track, producing a beeping sound. Put it away. However, if the focus servo is not activated at all, a regenerated clock for constant linear velocity (CLV) control cannot be obtained. Therefore, here, the loop gain is muted by a command from the system control circuit 37 during the feed operation. In the tracking servo circuit 14, a tracking error detection circuit 15 detects the deviation of the laser beam with respect to the pit row based on the light reception signal, and drives the tracking control coil 6 to correct the deviation. When the reproduction of the disk progresses and the tracking displacement becomes large enough that the tracking control coil 6 can no longer handle it, the tracking displacement detection circuit 24 outputs a feed request signal.
The feed motor 8 is driven from the system control circuit 37 via the feed motor drive circuit 40.

The output signal of the waveform shaping circuit 11 is sent to the demodulation circuit 12.
It is also used to create detection signals for constant linear velocity (CLV) disk rotation servos. That is, the output signal of the waveform shaping circuit 11 is applied to the clock regeneration circuit 16, where the clock signal is regenerated. The synchronization signal detection circuit 17 detects the synchronization signal included in the output signal of the waveform shaping circuit 11 and outputs this synchronization signal. The synchronizing signal output from the synchronizing signal detection circuit 17 is frequency-divided by a frequency dividing circuit 18 and applied to a phase comparator circuit 19. The phase comparison circuit 19 compares the phases of this signal with a signal obtained by dividing the master clock generated from the master clock generation circuit 20 by the frequency division circuit 21, and then outputs the signal via the disk rotation servo circuit 22 so that the phases match. Controls the disk rotation motor 3.

The demodulation circuit 12 uses EFM (Eight to Fourteen).
Modulation) Demodulates the modulated and recorded signal on disk 1 to the original 8-bit signal, and removes unnecessary items such as combined bits and synchronization signals. Data control circuit 26, error correction circuit 2
7. In the memory circuit 28, the signal output from the demodulation circuit 12 (signal of disk 1 recorded in an interleaved manner) is de-interleaved and restored to the original signal, and the presence or absence of an error is checked, and the signal containing an error is detected. Errors are corrected by the error correction circuit 27, and those that cannot be corrected are corrected. Further, the corrected and corrected signal is once recorded in the memory circuit 28 at the timing of the reproduced clock signal, and is read out at the timing of the master clock, thereby aligning the data and absorbing uneven rotation of the turntable 2. ing.

The signal read out from the memory circuit 28 (a signal in which the right channel signal and the left channel signal are arranged alternately in a time division manner) is applied to the D/A converters 29 and 30, respectively, and is separated into left and right channels at the timing of the master clock. and then converted to the original analog signal (audio signal).

The subcode detection circuit 36 detects a subcode (address, track number, time code, etc.) from the signal demodulated by the demodulation circuit 12 and sends it to the system control circuit 37. The system control circuit 37 inputs the address, track number, etc. specified by the operation key 38 via the decoder 39, compares it with the detected subcode, and sends the address, track number, etc. specified by the operation key 38 via the feed motor drive circuit 40 so that they match. Drive the feed motor 8. Further, the system control circuit 37 displays the detected subcode on the display section 42 via the drive circuit 41.

The entire digital audio disc playback device is constructed as described above.

By the way, the tracking error detection circuit 15
Conventional tracking error detection methods include the following.

(1) 3-beam system As shown in Figure 2a, three beams (+1st order light A, 0th order light B, -1st order light C) separated by a diffraction grating are sent to the track 51 with a slight beam. Spots are connected on the surface of the pit 50 in an angled line. Then, as shown in FIG. 2b, the reflected beams A, B, and C are received by three photodiodes 52A, 52B, and 52C. Beam B received by photodiode 52B is used for focus servo and signal reproduction. The beams A and C received by the photodiodes 52A and 52C are sent to an error detection circuit 53, where a tracking error is detected, and the tracking control coil 6 is driven via the tracking servo circuit 54 so that the error is eliminated. do.

This three-beam system requires a diffraction grating, such as a grating lens, to diffract the laser beam into three beams, and a photodetector element that detects the ±1st-order diffracted light (52A, 52
Since C) is required, there is a drawback that the structure becomes complicated.

(2) Wobbling method As shown in FIG. 3, this method reflects a laser beam 56 by a beam splitter 57, a swinging mirror 58, and a tracking mirror 59, and converges it by an objective lens 60. In this device, a signal from an oscillator 63 is applied to a piezoelectric element (not shown) and a swinging mirror 58 is oscillated to cause the laser beam 56 to vibrate minutely on the recording surface of the disk 61. Since the servo band needs to be up to 1KHz, for example, select the oscillation frequency 58 to be around 5KHz.
Shake with an amplitude of about 0.1 μm. When the reading beam is shifted to the left and right, the respective detected waveforms have opposite phases, which are detected by a synchronous detector 65 via a bandpass filter 64 in synchronization with the original oscillation frequency, and are tracked. The direction and magnitude of the error are detected. By applying this tracking error signal to the drive circuit 67 via the phase compensation circuit 66, the tracking mirror 59 is deflected to cause the beam spot to follow the track.

This wobbling method requires the swinging mirror 58 and its driving device, so it has the disadvantage of a complicated structure.

(3) One-beam method This method uses a four-split photodetector to perform information signal (video information, audio information, etc.) detection, focus control, and tracking control with a single beam. The principle of tracking error detection in this method will be explained using FIGS. 4 and 5.

As shown in FIG. 4, the photodetector 69 is composed of four divided photodetectors 69A, 69B, 69C, and 69D, and the X direction is arranged in the direction of the information track and the Y direction is arranged in the direction orthogonal to the information track. , pit78
A beam spot 77 is irradiated onto the target, and a photodetector 69 receives the reflected light. At this time, Fig. 4a,
The positional relationship between the pit 78 and the beam spot 77 shown in b and c, respectively (Fig. 4 a shows a state in which the spot 78 is shifted to the right, Fig. 4 b shows a state in which there is no deviation, and Fig. 4 c shows a state in which the spot 78 is shifted to the left). The light and dark pattern on the photodetector 69 is displayed at times t ₁ , t ₂ ,
As t ₃ changes, Fig. 4 a, b,
c, they change as shown on the right.
At this time, each element 69A, 69 of the photodetector 69
Regarding the output signals a, b, c, and d of B, 69C, and 69D, if HTD=(a+c)-(b+d) RF=a+b+c+d, then HTD and RF change as shown in FIG. Figure 5a shows spot 77 relative to pit 78.
When the pit 78 and spot 77 are shifted to the right, Fig. 5b shows the difference between the pit 78 and the spot 77, and Fig. 5c shows the pit 7.
This is a case where spot 77 is shifted from point 8. In the case of Figure 5b, HTD is always 0, but
In the case of FIGS. 5a and 5c, the pit 78 changes as it moves due to the rotation of the disk, and its phase leads or lags RF by 90 degrees depending on the direction of the tracking error. Therefore, tracking error detection can be performed by detecting this change in phase.

FIG. 6 shows an example of a circuit for detecting tracking errors using the above principle.

In the circuit of FIG. 6, each photodetector 69A to
Diagonal addition circuit 7 for the output of 69D
0 and 71 respectively, the sum of these two added values is detected by an adding circuit 73 to obtain an information signal, and the difference between the output signals of the adding circuits 70 and 71 is detected by a subtracting circuit 72.
This difference signal is multiplied by a signal obtained by shifting the above-mentioned information signal by 90 degrees by a phase shift circuit 74 for detection by a multiplier circuit 75, and smoothed by a low-pass filter 76 to obtain a tracking error signal.

This one-beam system has the disadvantage that the temperature characteristics of the multiplier circuit 75 are poor, and therefore errors occur in the tracking error signal due to drift and the like.

This invention is an improvement on the above-mentioned one-beam method, and by providing two systems of tracking error signal detection circuits and combining their output signals, the characteristics of the multiplier circuit included in each tracking error detection circuit are changed by temperature. It is an object of the present invention to provide a tracking servo device for an optical disc playback device, which cancels out each other.

According to this invention, instead of multiplying after taking the difference signal as shown in FIG. 6, by multiplying each signal at a stage before finally taking the difference signal, two multipliers These drifts are canceled out at the stage of taking the difference signal.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 7, the photodetector 80 includes four divided light receiving areas 80A, 80B, 80C, and 80D. The adding circuit 81 adds the output signals of the light receiving elements 80A and 80C on one of the diagonal lines. The addition circuit 82 connects the light receiving element 8 on the other diagonal.
Add the output signals of 0B and 80D. Addition circuit 8
3 adds the output signals of adder circuits 81 and 82 to obtain a disk information signal. The phase shift circuits 84 and 85 are composed of, for example, differentiating circuits, and the addition circuits 81 and 82
Shift the phase of the output signal by 90°. Multiplier circuits 86 and 87 multiply the output signals of phase shift circuits 84 and 85 by the output signal of adder circuit 83. Multiplication circuit 8
The output signals of 6 and 87 are smoothed by low-pass filters 88 and 89, respectively, and a subtraction circuit 90 detects their difference signal, that is, a tracking error signal.

The signal waveforms of the portions a to j in Fig. 7 are
They are shown in Figures a to j, respectively. The waveforms shown in FIGS. 8a and 8b, that is, the output waveforms of the adder circuits 81 and 82, would be exactly the same if there were no tracking error, but if a tracking error occurs, a phase shift occurs in a direction corresponding to the direction of the error. In Figure 8, time T1
This shows a state in which the direction of the tracking error is reversed after .

The adder circuit 83 adds the signals shown in FIG. 8a and b to obtain the signal shown in FIG. 8c. In addition, the phase shift circuit 8
4 and 85, the signals in FIG. 8 a and b are differentiated. As a result, the signals in FIG. 8a and b become as shown in FIG. 8d and e.
As shown in Figures 8a and 8, the phase is shifted by 90° and the peak value is fixed at a constant value (because the linear velocity is constant in the CLV method,
(This is because the rising and falling slopes of the signal b are constant). Multiplying circuits 86 and 87 multiply the signal in FIG. 8c and the signals in FIG. 8d and e, respectively, to obtain the signals in FIG. 8f and g, respectively. For the signals f and g in Figure 8, when there is no tracking error, the positive and negative waveforms are equal, but when a tracking error occurs, the waveforms are either positive or negative depending on the direction of the error. becomes larger. Therefore,
These signals are passed through low-pass filters 88 and 88, respectively.
89, waveforms as shown in FIG. 8h and i are obtained. If the multiplier circuits 86 and 87 are of the same type, the signals of h and i in FIG.
The changes in temperature characteristics of Nos. 6 and 87 are included in the same direction. Therefore, if the difference between these signals is taken in the subtraction circuit 90, the subtraction circuit 90 will produce the following signal as shown in FIG.
As shown in FIG. 2, a signal containing only tracking error information is obtained by canceling out the influence of the temperature characteristics of the multiplier circuits 86 and 87.

FIG. 9 shows another embodiment of the invention. Here, parts common to the embodiment of FIG. 7 are given the same reference numerals. In the embodiment shown in FIG. 9, phase shift circuits 84 and 85 are inserted in the output lines of adder circuits 81 and 82, respectively, whereas in the embodiment shown in FIG. A phase shift circuit 93 is inserted in the transmission line. In this circuit as well, a tracking error detection signal exactly the same as in the case of FIG. 7 is obtained from the subtraction circuit 90. If the configuration is as shown in FIG. 9, only one phase shift circuit is required, so the overall configuration is simplified.

FIG. 10 shows yet another embodiment of the invention. Here, photodetectors 80A, 80B,
Of 80C and 80D, adjacent ones are combined instead of diagonal ones, the subtraction circuit 100 subtracts the output signals of the photodetectors 80A and 80D, and the subtraction circuit 101 subtracts the output signals of the photodetectors 80B and 80C. The signal is being subtracted. The outputs of subtraction paths 100 and 101 are applied to multiplication circuits 102 and 103, respectively. On the other hand, in the addition circuit 104, the photodetector 80A,
The adder circuit 105 adds the output signals of the photodetectors 80B and 80C, and the adder circuit 106 adds the output signals of the photodetectors 104 and 105.
The output signal of the disk is multiplied to obtain the information signal of the disk. The output signal of the adder circuit 106 is sent to the phase shift circuit 107.
The phase is shifted by 90°. multiplication circuit 102,
At step 103, the signals from the subtraction circuits 100 and 101 are multiplied by the signal from the phase shift circuit 107 to perform detection. The output signals of the multiplication circuits 102 and 103 are smoothed by low-pass filters 108 and 109, respectively, and subtracted by a subtraction circuit 110 to be output as a tracking error signal.

As explained above, according to the present invention, in a one-beam tracking servo circuit using a four-split photodetector, two tracking error signal detection circuits are configured, and each system is provided with a detection multiplication circuit. Since the tracking error signal is obtained by combining the output signals of these two multiplier circuits, the temperature-induced drift of the multiplier circuit can be canceled out, and accurate tracking control can be performed.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the entire control system in a digital audio disk playback device, Figure 2
Figure a is a diagram for explaining the principle of conventional three-beam tracking control, Figure 2 b is a block diagram of a tracking error detection system in three-beam tracking control, and Figure 3 is a diagram of conventional wobbling type tracking control. A block diagram showing the control system, FIG. 4 shows the relationship between the deviation of the beam spot 77 with respect to the pit 78 and the bright and dark pattern projected on the photodetector 69 in conventional one-beam tracking control using a four-split photodetector 69. Figure 5 is a diagram showing the difference in signals obtained due to the difference in bright and dark patterns in Figure 4. Figure 6 is a diagram showing the principles of Figures 4 and 5. FIG. 7 is a block diagram showing an example of a conventional one-beam tracking control circuit using the present invention. FIGS. Signal waveform diagram, No. 9
1 and 10 are block diagrams showing other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Disc, 2... Turntable, 3... Disk rotation motor, 5... Focus control coil, 6
...Tracking control coil, 7...Objective lens, 2
0... Master clock generation circuit, 22... Disk rotation servo circuit, 42... Display unit, 50, 60... Time constant circuit, 51... Superimposition circuit, 52... Bypass path, 6
9...4-split photodetector, 77...beam spot, 7
8...Pitsuto.

Claims (1)

[Claims] 1. A 1-beam tracking servo device using a 4-split photodetector, comprising: means for creating a sum signal of detection signals from the photodetector; and means for dividing the detection signals into groups of two. comprising means for synthesizing, two multiplier circuits for respectively multiplying the added signal and the two sets of synthesized signals, and means for synthesizing the outputs of these two multiplier circuits to create a tracking error signal. A tracking servo device in an optical disc playback device.