JPS6112182A - Disc servo device of video tape recorder - Google Patents

Abstract

PURPOSE:To attain the stable number of revolution control by detecting noise in a reproduced video signal and applying an average value of an H synchronizing frequency detection signal to a disc motor turning control system without using an H synchronizing signal during noise period to improve the transient characteristic of a control loop. CONSTITUTION:While an H synchronizing signal 500 is disturbed by the noise in a reproduced video signal at vari-speed reproduction, a gate circuit 17 blocks the input of an H synchronizing frequency detection signal 600 inputted to a disc motor turning control loop and inputs an average value of the signal 600 instead. Then the number of revolution control of the disc motor 14 is executed stably to correct completely the H synchronizing frequency deviation by vari-speed reproduction. Since a filter or the like having a large time constant is not fed in the H synchronizing signal input loop, the response at the transient state of the disc motor turning control loop is kept in an excellent way and the large deviation of the H synchronizing signal is not caused even when the transition from the normal reproduction mode to the vari-speed reproduction molde.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a video tape recorder (hereinafter referred to as VTR).
The present invention relates to a disk servo device during variable speed reproduction.

[Technical background of the invention]

During so-called variable speed playback in which the tape is played back at a different speed than when recording on the VTR 6, the relative speed between the tape and the head changes, so the frequency of the horizontal synchronization signal (hereinafter referred to as H synchronization) of the playback video signal changes.

If this change in the H synchronization frequency becomes large enough to exceed the horizontal synchronization pull-in range of the television receiver, the screen will be distorted. Further, even when the change in the H synchronization frequency is within the above-mentioned pull-in range, the time difference between the color signal and the luminance signal results in an unsightly screen with color shift.

Therefore, in order to solve the above-mentioned inconvenience during variable speed playback, a method has been used that detects the synchronous frequency and controls the rotation of the disc so that the frequency becomes normal. FIG. 2 is a block diagram showing an example of a disk servo thread during variable speed reproduction using this method. Code 1a,
1b denotes two heads mounted on the disk, these heads la.

The M"r on the tape played back by 1b is amplified by playback preamplifiers 2a and 2b, and then input to switch 3. Switch 3 connects the output signals from heads la and lb, and outputs a continuous signal. A reproduced signal 100 is output.The reproduced signal 100 is inputted to the color process circuit 4 and the luminance signal demodulation circuit 5, respectively.The color process circuit 4 outputs the reproduced color signal 200, and the luminance signal demodulation circuit 5 outputs the reproduced luminance signal 300. These signals 200
．． 300 is input to the adder circuit 6 and added, and the result is a video signal 400, which is output.

On the other hand, the reproduced luminance signal 300 is input to the synchronization separation circuit 7, where the H synchronization signal is separated. The separated H synchronization signal 500 is input to the frequency detection circuit 8, where its frequency is detected, and then further input to the addition circuit 12 via the filter 9.

Reference numeral 15 denotes an FG head for detecting the number of rotations of the disk.The output signal of the FG head is waveform-shaped by a waveform shaping circuit 10, and then inputted to a frequency detection circuit 11, where its frequency is detected. This signal is input to the adder circuit 12. In the adder circuit 12, the filter 9
The H synchronous frequency detection signal from the frequency detection circuit 11 and the FG frequency detection signal from the frequency detection circuit 11 are added to create a motor rotation speed control signal. This control signal is the motor drive circuit 1
3 to control the rotation of the disk motor 140 times.

That is, in the conventional disk servo system having the above configuration, the AFC looseness formed by the disk rotation speed signal detected by the FG head 15 causes the disk motor 14 to
The number of rotations, that is, the number of disk rotations, is stably controlled, and the AFC detection output of the H synchronization signal 500 is added to the AFC loose, which further allows fine adjustment of the disk rotation in response to changes in tape speed. It is being done.

[Problems with background technology]

Now, generally speaking, during variable speed playback, the head 18%
lb crosses the track, the reproduced luminance signal 3
Since 00 includes noise, the HfEJ period signal 5
00 is also disturbed by this. This disturbance acts as a disturbance in the disk servo system and disturbs the rotation of the disk, making it impossible to obtain stable reproduced images. Therefore, filter 9
is provided to block this disturbance, and due to the time constant of this filter, the H
Disturbances in the synchronizing signal 500 are prevented from being transmitted to the adding circuit 12. Therefore, although the period of the disturbance depends on the variable speed reproduction speed, the time constant of the filter 90 is selected to be short and long. However, the presence of the filter 9 having such a relatively long time constant has an M influence on the transient characteristics of the disk rotation control loop. In particular, when transitioning from the normal playback mode to the variable speed playback mode, the response of the loop cannot catch up due to the presence of the filter 9, and the H synchronization signal 50
00, there was a problem that a large shift occurred, causing disturbances on the playback screen.

[Purpose of the invention]

In view of the above drawbacks, an object of the present invention is to provide a disk servo device for a video tape recorder that is capable of controlling the rotation speed of a disk motor stably at normal pressure by improving the transient characteristics of the disk rotation control loop. It is in.

[Summary of the invention]

The present invention detects noise in a reproduced video signal, does not use the H synchronization signal obtained from the reproduced video signal during this noise period, and instead uses the average value of the H synchronization frequency detection signal to the disk motor rotation control loop. The above object is achieved by providing a configuration in which the power is supplied to the user.

[Embodiments of the invention]

In the following, an embodiment of the present invention will be described with the same reference numerals as the conventional example.
The description will be given with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a disk servo device for a video tape recorder according to the present invention. The signals on the tape (not shown) reproduced by the heads 1a and 1b are sent to the reproduction preamplifier 2.
After being amplified by a, 2bK, a continuous reproduction signal 100 is generated by a switch 3. This continuous reproduction signal 100 is inputted to a color processing circuit 4 and a luminance signal demodulation circuit 5, which produce a reproduction color signal 200 and a reproduction luminance signal 300, respectively.
and is input to the adder circuit 6. This adder circuit 6 outputs a video signal 400. Reproduction brightness signal 300
is input to the synchronization separation circuit 7, where the H synchronization signal 500
are separated. The separated H synchronization signal 500 is the H synchronization frequency detection signal 600 whose frequency is detected by the frequency detection circuit 8, and this signal 600 is connected to the gate circuit 1.
7 is input.

On the other hand, the reproduced signal 100 is input to the noise detection circuit 16, where the noise generation period signal 700 is detected and input to the gate circuit 17. When the noise generation period signal 700 does not indicate the occurrence of noise, the gate circuit 17 outputs the H synchronous frequency detection signal 600 of the frequency detection circuit 8 as it is as the signal 800 to the addition circuit 12, and when it indicates the occurrence of noise, , and outputs the average value of the H synchronous frequency detection signal to the addition circuit 12 as a signal 800. A rotational speed signal of a disk (not shown) picked up by the FG head 15 is inputted to the addition circuit 12 through the waveform shaping circuit 10 and the frequency detection circuit 11 . The motor control signal that is the output of the adder circuit 12 is input to the motor drive circuit 13, and the motor drive circuit 13 is connected to the disc motor = &14'.
The rotation is controlled based on the motor control signal input to the motor.

Note that the portion indicated by the broken line frame in FIG. 1 constitutes the disk servo device.

Next, the operation of this embodiment will be explained with reference to the operation timing diagram of FIG. 2. General Herad la during variable speed playback
, 1b appear as the level of the reproduced signal 100 shown in the second round decreases.

Therefore, the noise detection circuit 16 performs envelope detection on the reproduced signal 100i and compares this signal level with a predetermined threshold value T shown in FIG. 2 (E) to detect the noise generation period. ing. Therefore, the noise occurrence period signal 700 outputted by the noise detection circuit 16 corresponds to the period in which the H synchronous frequency detection signal 600 shown in FIG. 2 (q) is disturbed by the noise, as shown in FIG. 2 (b). When the signal 700 is at a low level, the time when this low level becomes a noise generation period becomes a noise generation period. The output H synchronous frequency detection signal 600 is passed through and outputted to the adder circuit 12 as a signal 800 shown in FIG. prevents the H synchronous frequency detection signal 600 from passing through, and instead outputs the average value of the H synchronous frequency detection signal to the addition circuit 12 as a signal 800 as shown in Figure 2. Therefore, the addition circuit 12 Signal 8 applied to a disk rotation control loop composed of an FG head 15, a waveform shaping circuit 10, a frequency detection circuit 11, a motor drive circuit 13, and a disk motor 14.
00 is the average value of the H synchronization frequency detection signal 600 during the period when the H synchronization signal 500 is disturbed by noise. Therefore, in the above loop, the above noise generation period is the average value of the H synchronous frequency detection signal 600 and the FG head 1.
The rotation speed of the disk motor 14 is controlled using the disk rotation speed signal from 5.

FIG. 3 is a circuit diagram showing a detailed example of the gate circuit shown in FIG. 1. An H synchronous frequency detection signal 600 is applied to one end of the switches 41 and 42. The other end of the switch 41 is connected to the other end of the switch 42, and a capacitor 43 is provided at this connection. A noise generation period signal 700 is input to the contact switching drive sections of the switches 41 and 42.

The switch 41 is turned on when the noise generation period signal 700 is at a high level, and turned off when the noise generation period signal 700 is at a low level.

The switch 42 is switched to the a side when the noise generation period signal 700 is at a high level, and to the Kb side when the noise generation period signal 700 is at a low level. Therefore, since the switch 42 is switched to the a side while the noise generation period signal 700 is at a high level, the switch 42 outputs a signal 800 through which the H synchronous frequency detection signal 600 passes. Moreover, during the period when the noise generation period signal 700 is at a high level, the switch 4
1 is on, the average value of the H synchronous frequency detection signal 600 is stored in the capacitor 43. Next, during the period when the noise generation period signal 700 is at a low level,
When the switch 42 is switched to the b side, the switch 41
is turned off. Therefore, the average value of the H synchronous frequency detection signal 600 stored in the capacitor 43 is output from the switch 42 as the signal 800. Furthermore, the H synchronous frequency detection signal 600 that is disturbed during this period does not appear on the output side at all because the switch is switched to the b side and the switch 41 is turned off.

According to this embodiment, during variable speed playback, during a period in which the H synchronization signal 500 is disturbed due to noise in the reproduced video signal, the gate circuit 17 prevents the input of the disturbed H synchronization frequency detection signal 600 to the disk motor rotation control loop. Because the configuration inputs the average value of the synchronous frequency detection signal instead, the rotation speed of the disk motor 14 can always be controlled stably, and the H synchronous frequency shift due to variable speed reproduction can be completely corrected. .

Moreover, since no filter with a large time constant is included in the H synchronization signal input loose, the transient response characteristics of the disk motor rotation control loop can be maintained well, and when transitioning from normal playback mode to variable speed playback mode, Also, a good screen can be obtained without causing a large shift in the H synchronization signal.

〔Effect of the invention〕

As described above, according to the disk servo device of the video tape recorder of the present invention, noise in the reproduced video signal is detected, and during this noise period, the H synchronization signal obtained from the reproduced video signal is not used, and instead, the H synchronization signal obtained from the reproduced video signal is not used. By adopting a configuration that supplies the average value of the synchronous frequency detection signal to the FG sustainer loop system of the disk motor, the transient characteristics of the disk motor rotation control loop are improved and stable disk motor rotation speed control is always performed. There are benefits to be gained.

[Brief explanation of drawings]

@Figure 1 is a block diagram showing an embodiment of the disk servo device of the video tape recorder of the present invention, Figure 2 is an operation timing diagram of the device shown in Figure 1, and Figure 3 is the same as that shown in Figure 1. FIG. 4 is a circuit diagram showing a detailed example of a gate circuit. FIG. 4 is a block diagram showing an example of a disk servo system of a conventional video tape recorder. 7... Synchronization separation circuit, 8... Frequency detection circuit, 10
... Waveform shaping circuit, 11 ... Frequency detection circuit, 13
...Motor drive circuit, 14...Disk motor, 16...Noise detection circuit, 17...Gate circuit Fig. 1 Fig. 2 Fig. 3' Fig. 4 n

Claims (1)

[Claims] In a disk servo device that adds the frequency detection signal of the horizontal synchronization signal to the disk rotation control loop during variable speed playback of a video tape recorder to correct the horizontal synchronization frequency deviation caused by variable speed playback, the noise generation period of the playback signal output from the playback head is A noise generation period detection circuit is configured to supply the average value of the horizontal synchronous frequency detection signal to the disk rotation control loop during the noise generation period, and to supply the horizontal synchronous frequency detection signal during periods other than the noise generation period. A disk servo device for a video tape recorder, comprising a gate circuit that supplies the disk rotation control loop as is.