JPS5940377A - Pickup servo circuit - Google Patents

Abstract

PURPOSE:To reduce the noise level which is due to the leakage of PCM signals as in the case of a 3-spot optical pickup, by increasing the loop gain in an access mode to reset a prescribed gain in a normal reproduction mode and to realize a quick and accurate access and at the same time setting the loop gain at the minimume necessary level in the normal reproduction mode. CONSTITUTION:A switch control circuit 21 delivers a high control signal when it gives an access to a pickup 4 at a point A and connects a switch circuit 20 to the (b) side from the (a) side to increase the loop gain of a servo loop by an amount equal to the gain of an amplifier 22. The circuit 21 is set at a low level at a point B when an access is over and connects the circuit 20 to the (a) side. Then a reproduction is carried out when the loop gain is reduced.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a pickup servo circuit for a disc playback device;
In particular, the present invention relates to a pickup servo circuit suitable for optical discs.

[Prior art]

In an optical audio disc or video disc playback device, the optical pickup must track the signal track, and a pink-up servo is essential.0 Figure 1 shows the track in an optical disc playback player. FIG. 2 is a diagram showing an outline of a servo.

The pickup 4 detects a servo control error signal from the optical disc 1, and returns it to the actuator 8 for driving the pickup 4 via an amplifier 59, a phase compensation circuit 6, and a drive amplifier 7, forming a servo loop. , the pickup 4 is made to track the signal truck. In FIG. 1, the pickup 4 detects the servo error signal as well as the recording signal on the signal track and inputs it to the digital signal processing circuit 9. The output of the digital signal processing circuit 9 is converted into an audio signal by a DA converter 1o, and the recorded signal is reproduced as sound via an audio amplifier 11 and a speaker 12. Disk 1 is connected to motor 2. The motor shaft 3 rotates the motor 2, but since this is not essential to the present invention, a description of the rotation speed control of the motor 2 will be omitted.

FIG. 2 is a diagram showing an outline of the servo error signal detector and recorded information detector of the pickup 4, and the optical parts are shown in a simplified manner. 13. ~162 is a signal track, 1
3o and 13. The area between 131 and 132 is shown in the card band' between the signal tracks. In the signal track 131, a hole called a bit is carved in the shape shown by a broken line, but for convenience, it is shown as two solid lines. Second
The pickup shown in the figure is called a 3-spot type, and has an optical spot 41 for detecting recorded information and an optical spot 41 for detecting a servo error signal.
Move as a body. These light spots are placed on disk 1.
The intensity of the reflected light is detected by each photodetector as a change in current, but in this figure, these photodetectors are explained as being displayed by their respective light spots. The output of the light spot (photodetector) 41 is converted into a voltage by a current-voltage converter 45 and guided to the digital signal processing circuit 9 via an output line 15. The outputs of the light spots (photodetectors) 42 and 43 are differential and are connected to a current-voltage converter 44.
A servo error signal is input to the output line 14 and outputted to the output line 14. The detection principle of the servo error signal will be explained with reference to FIG. The same amount will be applied to the signal track 131, and the remaining part (this part is also equal to 42+43) will be applied to the guard band, and the difference between the two detectors will be 0. Light spot 4] is (1)
When the state is to the right of the track 131 shown by the broken line, all of the light spots 42 enter the guard band, and the light spot 4
3 is the signal track 13. Since it is at the center of , the difference between the two results in the maximum positive value shown in (b) of (3) in the same figure. Similarly, when the optical spot 4] shifts to the left of the signal track 131 as shown by the dotted line in (1), it exhibits a negative maximum value as shown in e-) in (3). As can be seen from the above explanation, an error signal as shown in 5) can be obtained with respect to the displacement of the optical spot.

By the way, when the signal recorded on the signal track 161 is a PCM signal, the spectrum of the signal extends to near direct current as shown in FIG. voltage converter 4
In addition to the servo control signal, a leakage portion of this PCM signal is outputted to the output No. 4. Since this leakage signal is different from the servo control signal, there is a problem in that the actuator 8 is driven unnecessarily, and the actuator 8 generates noise in the audio band.

Therefore, in order to reduce the above noise, a variable gain amplifier (variable gain amplifier) 50 is arranged in the servo loop from the pickup 4 to the actuator 8 as shown in FIG. The playback state of the disc is determined by detecting the number of errors in the signal, and the gain of the variable gain amplifier is controlled by the determined output.
We previously proposed a method to achieve a constant loop gain regardless of the disk in a patent application.

In FIG. 5, the amplifier 5 in FIG. 1 is replaced with a variable gain amplifier 50, and the number of errors per fixed time obtained from the digital signal processing circuit 9 is detected by the reproduction state discriminator 16, so that the number of errors is reduced. The same reference numerals as in FIG. 1 indicate the same components, except that the gain of the variable gain amplifier 50 is controlled via the control line 17. Signal i recorded on the disk
In the case of digital information, the recorded information is a combination of data and parity signals (Di-1,
Pi-1), (Di, Pi L...
....

(Di +5. Pi +5), . . . , each pair is divided into frames Fi-1, Fi, . . . , Fi+5 .
...It is usually recorded as a closed page. Therefore, the digital signal processing circuit 9 can determine whether or not the data is an error by checking each data with the parity signal in each frame. By counting the errors for each frame for a certain period of time, it is possible to know the number of errors per certain period of time.

Therefore, the number of errors per certain period of time is measured, and if there is no increase in errors, the gain of the variable gain amplifier 50 is lowered by a certain amount.
Also, if you repeat this operation to measure the number of errors and set the servo loop gain a certain amount higher than the gain where the error increased, you can set the minimum gain necessary and the noise problem will be resolved. do.

However, although this does not cause any problems under normal operating conditions, it has the disadvantage that it takes a long time to close the track loop when accessing a certain song, etc., because if the loop gain is low, the pull-in ability is reduced.○ [Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a pickup servo circuit that is stable and fast even during access, pulls into a track, and operates with the minimum necessary loop gain during normal operation.

[Summary of the Invention] Therefore, the present invention aims to solve the problem by increasing the loop gain during access and operating at a predetermined gain detected by the method shown in FIG. 5 during normal playback. Embodiment] FIG. 7 is a diagram showing an embodiment of the present invention, 0 switching circuit 20.
．． Except for the switching control circuit 21 and the amplifier 22, the same symbols as in FIG. 1 indicate the same components. The system of FIG. 7 operates as shown in FIG. As shown in FIG. 8(B), the switching control circuit 21 selects [(ig
hJ control signal is output, and the switching circuit 20 is switched from (A) to (
b) side to increase the loop cane of the servo loop by the gain of the amplifier 22. Access has ended■
At this point, the switching control circuit 21 becomes [LowJ], and the switching circuit 20 is connected to the (a) side and the loop gain is lowered to perform reproduction. FIG. 9 shows another embodiment of the present invention.
This is an example in which the present invention is applied to the system shown in the figure. Since the variable gain bandpass filter 50 in FIG. 9 is realized by a circuit as shown in FIG. 10, the gain increase at the time of access does not require the switching circuit 20 as in the example shown in FIG. Although the illustration shows that the switching control circuit 21 issues an instruction as to whether or not the playback status discriminator 16 is being accessed, it has the function of determining whether or not the playback status discriminator 16 is being accessed, and plays the same role as the switching control circuit 21. In that case, the switching control circuit 21 is not necessarily a necessary circuit.

In the example shown in FIG. 9, the gain can be changed stepwise, so that fine gain control can be performed not only during access but also after access.

FIG. 11 is a diagram showing a time chart of this example. ■
Since the point is being accessed, the loop gain is increased and the target location is accessed.

At point (■) where access is completed, the gain is returned to the gain for normal playback in stages. According to this method, a sudden change in the loop gain can be avoided, so it is possible to avoid the phenomenon of loop deviation due to a sudden decrease in gain after the end of access, and it is possible to smoothly move from access to normal playback.0 [Advantages of the Invention] As explained above, according to the present invention, by increasing the loop gain at the time of access in the disk playback device, access can be performed quickly and accurately, and at the same time, the loop gain can be set to the minimum necessary level during normal playback. Accordingly, 6
As seen in spot optical pickups <P CM
Noise caused by signal interference can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an optical disc reproducing device, Figs. 2 and 3 are diagrams for explaining the principle of obtaining an error signal for track servo, and Fig. 4 is a diagram showing the spectrum of a PCM signal recorded on a disc. Figures 5 and 6 are diagrams explaining a system for reproducing a disc by setting the loop gain to the minimum necessary level, and Figures 7 and 8 are diagrams showing an embodiment of the present invention and its explanation. 9 and 10 are diagrams showing other embodiments of the present invention, and FIG. 11 is a diagram for explaining the same. 1...Disk 4...Pickup 20...Switching circuit 21...Switching control circuit substitute Concave Figure 7 Figure B ■ ■ Figure 19 Figure 11 Figure Y2O Figure 5θ Continuation of page 1 0 Inventor: Masafumi Nakamura, Home Appliance Research Laboratory, Hitachi, Ltd., 292 Yoshida-cho, Totsuka-ku, Yokohama 0 Inventor: Takashi Takeuchi Hitachi, Ltd. Home Appliance Research Laboratory, 292 Yoshida-cho, Totsuka-ku, Yokohama

Claims (1)

[Claims] 1. In a playback device for a disc in which position information such as a division number, track number, or time between songs is also recorded in addition to a main signal such as a music or video signal, a pickup; A servo circuit for causing the pickup to follow a signal track, an access control circuit for quickly accessing the target track for the pickup, and a switching circuit for switching a loop gain of the servo circuit, and the switching circuit is driven by the access control circuit. A pickup servo circuit characterized in that the loop gain is made different during access and during steady playback. 2. The loop gain switching circuit of the servo circuit is a variable gain amplifier, and the access control circuit changes the gain of the variable gain amplifier to make the loop gain different between access and steady playback. pickup servo circuit. 6. The device according to claim 1 or 2, further comprising a timer, which causes the servo loop gain during access to be changed stepwise to the servo loop gain during steady state after the access of the pickup is completed. pickup servo circuit.