JPH028378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pickup control device for a disc playback device such as a video disc or a digital audio disc, which separates a tracking or focus error signal into a high frequency component and a low frequency component, and separates a tracking or focus error signal into a high frequency component and a low frequency component. By limiting the levels of the signals and then combining them again to form a tracking or focus control signal, it is possible to prevent mechanical damage to the pickup device due to high-level low-frequency signals in the tracking or focus error signals, and to control the tracking or focus control signal. This is done so that the responsiveness to high frequency signals in the focus error signal is not reduced.

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 to follow the optical pick up head 4 as it crosses the track, producing a "peep" sound.
This will generate a sound. 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 a 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. As the disk continues to play and the tracking displacement becomes large enough that the tracking control coil 6 cannot handle it, the tracking displacement detection circuit 24 outputs a feed request signal, which is sent from the system control circuit 37 via the feed motor drive circuit 40. to drive the feed motor 8.

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 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 phase 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
The disk rotation motor 3 is controlled via the disk rotation servo circuit 22 so that these phases coincide with each other.

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 temporarily stored in the memory circuit 28 at the timing of the reproduction 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 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, as a tracking error detection method in a tracking servo, for example, there is a method using a tracking detection beam separate from an information signal reading beam. In addition, focus error detection methods in focus servo include, for example, an astigmatism method in which the reflected light from a disk is passed through a cylindrical lens to produce astigmatism, and the light is received by a 4-split photodetector to obtain a focus error signal. There is. Figure 2 shows the principle, and Figure 2a
The laser beam is divided into three beams (+1st order light, 0th order light, -1st order light) by a diffraction grating, and these are lined up at a slight angle to the track 51, as shown in the figure.
Spots A, B, and C are connected on the surface of pit 50. As shown in FIG. 2b, three photodiodes 52A, 52B, and 52C receive the reflected light from the spots A, B, and C, respectively. Photodiode 52 configured as a 4-split photodetector
Spot B, which is received at point B, is determined by detecting the sum of the incident lights of the photodetectors at the diagonal positions of this four-split photodetector by the reproducing RF signal detection circuit 55, and detecting the sum of the incident light of the photodetectors at the diagonal positions of the four-split photodetector. By taking the difference at 56, it is used as an error signal for focus servo, and by taking the sum of the incident lights of the four-split photodetector, it is used for information signal reproduction.
A tracking error detection circuit 52 obtains a difference signal from spots A and C received by photodiodes 52A and 52C, and detects a tracking error.

When tracking or focus control is performed using the tracking or focus error detection signal obtained by the circuit shown in FIG. 2, conventionally, as shown in FIG.
4 and 57 to the tracking control coil 6 or the focus control coil 5, respectively. However, with this type of device, if the tracking or focus error detection signal contains a low frequency signal with a high level, the offset position in response to the control signal is too large, causing the actuator of the optical pickup head 4 to There was a risk of mechanical destruction. Furthermore, the open-loop characteristic of the tracking or focus control device in Figure 3 is -12 dB/Oct as shown in Figure 4, and the gain of the high-frequency signal in the tracking or focus error signal decreases as the frequency increases. If the gain of the tracking or focus control circuit is lowered simply to prevent mechanical damage to the optical pickup head 4, it will no longer respond adequately to high frequency signals.

The present invention has been made in view of the above-mentioned points, and prevents mechanical damage to a pickup device due to a high-level low frequency signal in a tracking or focus error detection signal. It is an object of the present invention to provide a pickup control device that prevents a decrease in responsiveness to band frequency signals.

According to this invention, a tracking or focus error detection signal is separated into a high frequency component and a low frequency component, the level of the low frequency component is limited, and then these are combined again to create a tracking or focus control signal. ing.

Hereinafter, an embodiment in which the present invention is applied to a tracking servo will be described with reference to the accompanying drawings. In the following embodiments, parts common to those in the circuit of FIG. 3 are given the same reference numerals.

In FIG. 5, photodiodes 52A, 5
2B and 52C each receive light from three spots irradiated onto the recording surface of the disk. The light reception signal from the photodiode 52B is used for focus servo and information signal reproduction. The difference between the light reception signals from the photodiodes 52A and 52C is taken by an error detection circuit 53, and a tracking error detection signal is obtained.

The tracking error detection signal is separated into a high frequency component and a low frequency component by a high frequency loop filter 62 and a low frequency loop filter 63. After the level of the low frequency component is limited by a limiter 64, it is added to the high frequency component in an adder circuit 65. Therefore, the adder circuit 65 outputs a tracking error detection signal in which the low frequency components are limited to a certain level and the high frequency components remain intact. The output signal of the adder circuit 54 is applied to the tracking control coil 6 to drive the optical pickup head 4 (FIG. 1). This prevents mechanical damage to the optical pickup device due to high-level low-frequency signals, and also realizes tracking control with good responsiveness to high-frequency signals.

FIGS. 6a to 6e show examples of waveforms at each part of FIGS. 5a to 5e. FIG. 6a shows the original tracking error detection signal, and the portion showing a constant value of ±B indicates a state where a large tracking error has occurred and the power supply voltage ±B of the error detection circuit 53 is output. 6b and 6c show high frequency components and low frequency components obtained by separating the signal in FIG. 6a by a high frequency loop filter 62 and a low frequency loop filter 63, respectively. The maximum level of the low frequency component shown in FIG. There is. Therefore, by using the limiter circuit 64, ±
I try to clamp it at the B′ level. By adding the high frequency component in FIG. 6b to the signal in FIG. 6d, the level of the low frequency component is limited as shown in FIG. 6e, and the high frequency component is included as is. A tracking error detection signal is obtained.
Therefore, by driving the tracking control coil 6 with this signal, there is no risk of mechanically destroying the actuator of the optical pickup head 4, and the same high frequency response as before can be ensured.

FIG. 7 shows a specific example of the circuit shown in FIG. The high-frequency loop filter 62 and the low-frequency loop filter 63 are constituted by active filters using operational amplifiers 66 and 67, respectively. In this case, the values of the resistors and capacitors of both filters 62 and 63 may be set so that the sum of the transfer functions constitutes an optimal loop filter for the servo loop.
Limiter 64 is Zener diode ZD1, ZD2
The clamp voltages +B' and -B' are set by , and the adder circuit 65 is composed of an operational amplifier 68.

In the above embodiment, the present invention is applied to a tracking control device for an optical disc playback device, but it can also be applied to a focus control device for the same disc playback device.

As explained above, according to the present invention, a tracking or focus error detection signal is separated into high frequency components and low frequency components, the low frequency components are clamped at a certain level, and then these are combined again. Since it is used for tracking or focus control, it is possible to prevent mechanical damage to the actuator of the pickup device due to low frequency components, and to ensure sufficient responsiveness to high frequency components.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the entire control system in a digital audio disk playback device, Figure 2
The figure shows the principle of tracking or focus error detection using the 3-beam system, Figure 3 is a block diagram showing a conventional pickup control device using the error detection method shown in Figure 2, and Figure 4 is the diagram shown in Figure 3. FIG. 5 is a block diagram showing an embodiment of the invention, FIGS. 6 a to e are waveform diagrams of each part of a to e in FIG. This figure is a circuit diagram showing a specific example of the circuit of FIG. 6. 1...disc, 2...turntable, 3...
...Disk rotation motor, 5...Focus control coil, 6...Tracking control coil, 7......
Objective lens, 20... Master clock generation circuit,
22...Disk rotation servo circuit, 42...Display section, 52A, 52B, 52C...Photodiode, 53...Tracking error detection circuit, 56...
...Focus error detection circuit, 62...High band loop filter, 63...Low band loop filter, 64...
...Limitsuta.

Claims (1)

[Claims] 1. A high-pass filter and a low-pass filter that separate a tracking or focusing error signal into high-frequency components and low-frequency components, a limiter that limits the level of the output signal of the low-pass filter, and a limiter that limits the level of the output signal of the low-pass filter. A pickup control device for a disc playback device, comprising an adder circuit for adding an output signal and an output signal of the high-pass filter, and the output signal of the adder circuit is used for tracking or focus control.