JP2661686B2 - Loop gain control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device performing closed loop control. 2. Description of the Related Art In recent years, many recording / reproducing apparatuses, whether for consumer use or for business use, have a control device for stabilizing closed loop control by stabilizing a loop gain. In particular, in a video information reproducing apparatus, closed-loop control is an important factor, and fluctuations in loop characteristics greatly affect reproduction performance. Here, a grooved recording disk playback device (VH
A conventional example of tracking control of a D-system video disk will be described. FIG. 3 shows an example of a conventional loop gain control type tracking control device. A video information recording disk (hereinafter referred to as a disk) has a video information signal recorded on a track 1 and first and second tracking signals FP1 and FP2 of different frequencies recorded on both sides of the track. It is read by the regeneration needle 3 attached to the tip,
The signal is amplified by the high frequency amplifier 4. The amplified video information signal is input to a video processing circuit (not shown), and the amplified first and second tracking signals FP1 and FP2 are input to a tracking high-frequency amplifier 5. High frequency amplifier for tracking 5
Then, the tracking signal from the high-frequency amplifier 4 is further amplified, and the first and second tracking signals FP1 and FP2 are amplified by the first sampling circuit 6 and the second sampling circuit 7, respectively.
To separate. Separated first and second tracking signals FP
1, FP2 enters the switching mute circuit 8. The switching mute 8 switches between the two tracking signals FP1 and FP2 based on the switching pulse 9 to invert the servo polarity, and turns on and off the tracking servo according to the tracking servo ON / OFF signal 10.
The tracking signal output from the switching / mute circuit 8 is constituted by a detector 1
The signals are detected by 1, 12 and input to the differential amplifier 13, respectively.
In the differential amplifier 13, the first and second tracking signals FP1, FP2
A signal corresponding to the difference between the signal levels is output, and the difference signal passes through the variable amplifier
Entered into 16. The difference signal is amplified by the drive amplifier 16 and the pickup 2 is driven in the radial direction of the disk 1 (direction of arrow A) via the drive coil 17. Therefore,
The pickup 2 driven in accordance with the difference signal comprises a first tracking signal FP1 and a second tracking signal F to be reproduced.
It operates so that the signal level of P2 becomes equal, and follows the information track. The gain of the variable amplifier 14 is controlled as follows. That is, only the loop information signal is extracted from the output of the differential amplifier 13 by the bandpass filter 18, and the detection unit 19 performs voltage amplification and detection. The detected loop information signal is
When the magnitude of the loop gain is converted to a voltage, the voltage is compared with a reference voltage 21 by a voltage comparator 20, and an error signal is applied to a gain control terminal of the variable amplifier 14 to change the loop gain. The gain of the variable amplifier 14 is controlled so that the level of the loop information signal becomes equal to the reference voltage 21, and the loop gain becomes constant with respect to the reference voltage 21. Problems to be Solved by the Invention In such a conventional configuration, when the gain of each circuit block in the loop is not constant and the width of the gain is large, the variable gain of the variable amplifier 14 for compensating the width of the gain is large. It is necessary to increase the width, which greatly affects the loop pull-in characteristic. Usually, the condition is that the gain width be within the stable range of the loop. Also, when the tracking servo is turned on by the tracking servo ON / OFF signal 10, the variable
Since the gain of 14 was the maximum, the servo was turned on with a gain more than necessary, and there were problems such as unstable pull-in and disconnection. SUMMARY OF THE INVENTION It is an object of the present invention to provide a loop gain control device capable of improving the pull-in characteristic of a loop and keeping the loop gain constant without considering the width of the gain of each circuit block in the loop. Means for Solving the Problems A loop gain control device according to the present invention includes a control means for controlling a gain of a control loop, a first detection means for detecting a loop characteristic, and a detection signal from the first detection means. And a variable gain means for increasing the gain of the control means with time. Then, a signal of the gain variable means is applied as a control signal of the control means based on the ON signal of the control loop, and the second detection means determines that the detection signal from the first detection means has reached a predetermined value. Is detected, the control signal to the control means is switched from the variable gain means to the detection signal of the first detection means. According to this configuration, the gain of the control loop is increased in a ramp shape by the gain variable means, and the control means controls the gain of the control loop when the detection signal of the first detection means reaches a predetermined level. Is switched from the output of the gain varying means to the detection signal of the first detecting means to form a closed loop, so that the servo can be always turned on within the stable range of the loop, and good pull-in characteristics can be obtained. it can. Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The components having the same functions as those in FIG. 3 showing the conventional example will be described with the same reference numerals. FIG. 1 is a block diagram of a tracking control device of the loop gain control type according to the present invention. The following points are different from the conventional configuration shown in FIG. The first detecting means I for detecting the loop characteristic comprises a band filter 18, a detecting section 19 and a voltage comparator 20, as in the conventional example. In the configuration shown in FIG. A level detector 22 as second detection means II for detecting the level of the output signal; and a variable amplifier 14 as control means III for controlling the loop gain.
Variable means IV for changing the gain of the signal with time
A lamp voltage generator 23 and a switch 24 are added to the configuration of the conventional example shown in FIG. 3, and the switch 24 includes an output signal 27 of the lamp voltage generator 23 and an output signal of the voltage comparator 20. 26
Is selected based on the tracking servo ON / OFF signal 10 and the output signal 28 of the level detector 22, and is applied to the gain control terminal 25 of the variable amplifier 14. The two tracking signals read by the reproducing needle 3 are separated by the first and second sampling circuits 6 and 7, and the output of the differential amplifier 13 is output by the first and second tracking signals FP1 and FP2.
A difference signal corresponding to the level difference is generated. This difference signal is
Drive amplifier via variable amplifier 14 and phase compensation circuit 15
16, the drive amplifier 16 amplifies the current until the pickup 2 can be driven, and the pickup 2 is driven in the radial direction of the disk 1. The reproduction level of the first tracking signal FP1 and the second tracking signal FP2 is reduced. Tracking control is performed so as to be equal. When the tracking servo ON / OFF signal 10 is off, the gain control terminal 25 of the variable amplifier 14 is connected to the lamp voltage generator 23 by the switch 24, and the variable amplifier 14
14 is the state of the attenuation amplifier. As can be seen from FIG. 2, when the tracking servo ON / OFF signal 10 is turned on, the voltage level of the output signal 27 of the ramp voltage generator 23 is synchronized with that signal as shown in FIG. And the gain of the variable amplifier 14 gradually increases. When the gain of the variable amplifier 14 exceeds a certain gain, the tracking control is turned ON (closed loop), and a voltage is generated at the output of the bandpass filter 18 and the detection unit 19 for detecting the loop characteristics as shown in FIG. This voltage appears when the magnitude of the loop gain becomes the magnitude of the voltage, and the voltage increases as the gain of the variable amplifier 14 increases. Next, it is detected by the level detector 22 that this voltage level has exceeded a predetermined level, and the output signal 28 of the level detector 22 is output.
Changes as shown in FIG. 2c. And the level detector 22
The output signal 28 of the voltage comparator 20 is applied to the gain control terminal 25 of the variable amplifier 14 by switching the switch 24, and the loop gain control is turned on, and the loop gain is set to the second value.
It is constant as shown in FIG. The output signal 27 of the ramp voltage generator 23 after the loop gain control is turned on is the same as the case of FIG. 2E in which the voltage is set to zero volts (or an initial value) at the same time when the loop gain control is turned on. , Which holds the voltage value at the time of the ON state.
Although the type can be considered, in the present embodiment, the operation is performed in the case of FIG. 2i in which the voltage value is held. As described above, according to the present embodiment, the gain of the variable amplifier 14 is increased in a ramp shape by the ramp voltage generator 23, and the fact that the output signal level of the detector 19 has reached the predetermined level is detected by the level detector 22. The switch 24 switches from the side of the ramp voltage generator 23 to the side of the voltage comparator 20 (the on-state of loop gain control) at the same time as the detection of the gain of each circuit block in the loop. Even if the width was large, the tracking control could always be turned on within the stable range of the tracking group, and good pull-in characteristics could be obtained. In this embodiment, the loop gain control device is performed by tracking control. However, the loop gain control device can be applied to all devices that perform closed loop control. As described above, according to the present invention, the gain of the control loop is increased with time by the gain variable means, and the detection signal from the first detection means for detecting the loop characteristics of the control loop is increased to a predetermined value. When the second detection means detects that the gain has been reduced, the control loop gain is controlled in accordance with the detection signal of the first detection means. Therefore, the width of the gain of each circuit block constituting the control loop is controlled. Is large, the control can always be started within the stable range of the loop, and good pull-in characteristics can be obtained, and its practical effect is large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of a loop gain control device according to the present invention, FIG. 2 is an explanatory diagram of a loop gain and a signal change of a main part of the device, and FIG. It is a block diagram of a loop gain control device. 14 Variable amplifier, 18 Band filter, 19 Detector, 20 Voltage comparator, 21 Reference voltage, 22 Level detector, 23 Lamp voltage generator, 24 switching Container, I ...
... first detecting means, II ... second detecting means, III ... controlling means, IV ... gain varying means.

Continuation of front page    (56) References JP-A-63-16430 (JP, A)                 JP-A-63-90048 (JP, A)                 JP-A-62-150572 (JP, A)                 JP-A-61-165831 (JP, A)                 JP-A-61-45420 (JP, A)                 JP-A-55-115102 (JP, A)

Claims (1)

(57) [Claims] Control means for controlling the gain of the control loop; first detection means for detecting loop characteristics; second detection means for detecting a detection signal from the first detection means; Gain control means for increasing the gain, applying a signal of the gain control means as a control signal of the control means based on an ON signal of the control loop, and detecting a signal from the first detection means at a predetermined value. A loop gain control device configured to switch a control signal to the control means from the gain variable means to a detection signal of the first detection means when the second detection means detects that the detection has been performed. 2. The gain varying means includes a lamp voltage generator and a switch for selecting a control signal of the control means, and the second means that the detection signal from the first detection means has reached a predetermined value.
The detection means detects and switches the control signal to the control means from the gain variable means to the detection signal of the first detection means, and at the same time when the loop of loop gain control is turned on, the output voltage value of the lamp voltage generator is changed. 2. The loop gain control device according to claim 1, wherein the loop gain control device is configured to hold the value at that time or set the initial value.