JP2532977B2 - Auto tracking circuit - Google Patents

Description

The present invention relates to an automatic tracking circuit used in a helical scan type magnetic recording / reproducing apparatus.

(B) Conventional technology The applicant has previously disclosed JP-A-1-288184 (H04N5 / 783).
At the time of special playback, the tape running phase is changed to reduce the playback output level of the video head (noise portion).
We proposed an auto-tracking circuit that displaces the head output switching timing within the reference period.

(C) Problem to be Solved by the Invention However, when performing auto-tracking using a video tape recorder adopting the above-described configuration, it may be difficult to displace the reproduction level lowering portion within the reference period. .

The cause is an abnormality in the contact state of the rotary head with the tape at the scanning start portion, an abnormality in the linearity of the recording track, and the like.

Therefore, if auto-tracking is executed in such a reproduction state, the tape traveling phase change state continues, the tracking state constantly changes, and an unstable reproduction screen is formed.

(D) Means for Solving the Problem Therefore, according to the present invention, in the automatic tracking circuit that sequentially changes the tape running phase state so that the reproduction output lowering portion is within the noise pull-in range, the tape running phase changing state is cycled. It is characterized in that the noise pull-in range is expanded after being pressed.

(E) Action Therefore, according to the present invention, after the noise pull-in control,
The noise pull-in control is executed again for the expanded noise pull-in range.

(F) Example Hereinafter, the present invention will be described with reference to an illustrated example.

In the present embodiment, the present invention is applied to an auto-tracking circuit of a VHS type video tape recorder which draws a reproduction output level lowering portion into a noise drawing range at the time of double speed reproduction, and FIG. 1 is a schematic block diagram of its main part. The figure is shown.

As is clear from FIG. 1, this embodiment has a main head MA,
The reproduction output obtained by alternately scanning the main head MH and the reproduction-only sub head SA, which is arranged in opposition to the azimuth by 180 degrees, is input to the head switching circuit 1 to output the bet output switching pulse RF. According to the above, the reproduction output is alternately selected and converted into a continuous reproduction signal. The reproduction signal is amplified by the AGC amplifier 2 and then input to the video signal processing circuit 3 and the dropout detection circuit 4.

The dropout detection circuit 4 generates a dropout detection pulse which becomes a low level during the noise generation period, that is, an attenuation portion of the reproduction signal level during double speed reproduction.

The noise position sampling means 5 counts the period from the rise of the head output switching pulse RF to the rise of the dropout detection pulse with a 2 kHz clock.

This count value is used as the comparison input of the noise position comparison means 6 of the microcomputer. This noise position comparison means 6
Compares the reference value generated by the reference value generating means 8 with the count value, generates a signal for fixing the tracking center value on the assumption that the noise pull-in is completed if the reference value or less, and if the tracking value is 15 or less. A signal that changes the center value by -3 is generated, and if it is 15 or more, a signal that changes the tracking center value by +3 is generated.

The tracking control means 7 continues to sequentially change the tracking center value to be output in three steps in accordance with the output of the noise position comparison means 6 until the noise pull-in state is reached.

The tracking mono-multi 9 delays the control signal generated by the control head CH according to the tracking center value, and this delayed signal is supplied to the capstan servo 10 as a reference input.

Therefore, the capstan motor 11 which inputs the capstan servo output continues to sequentially change the tape running phase by a predetermined amount until the noise drawing state is reached.

Waveform diagrams A1, A2, and A3 in FIG. 2 show changes in the reproduction signal output level in a normal noise pull-in state. A1 is a state before noise pull-in, A2 is a pull-in halfway state, and A3 is a noise pull-in completed state. Shown respectively. As is clear from the figure, when the noise pull-in is completed in the normal state, all the noise components are eliminated.

On the other hand, the waveform diagrams B1, B2, and B3 in FIG. 2 show the change in the reproduction signal output level for performing the noise acquisition control in the video tape recorder in which the reproduction output level tends to decrease at the scanning start portion, and B1 represents the noise extraction. The previous state, B2 is a state in the middle of pulling in, and B3 is a desirable noise pull-in state. As is apparent from the figure, it is understood that the noise component extends outside the noise pull-in range even in the desirable noise pull-in state in the abnormal state. Therefore, in such a state, the tape running phase state continues to change without stopping.

In this embodiment, even in such a state, the noise pull-in range is expanded to detect the noise pull-in state. The expansion of the noise pull-in range is to change the initial reference value "3" to "4" after the tape running phase changing state has made one round, that is, when the tracking control means changes the tracking center value 10 times. is there. Therefore, the tracking control means 7 changes the tracking center value to
After changing 10 times, the reference value changing pulse is set to the reference value setting means 8
The reference value setting means 8 changes the initial reference value “3” to “4”. Therefore, the subsequent reference value becomes “4”, and when the noise pull-in cannot be performed in the expanded noise pull-in range, the reference value is increased by 1 and the noise pull-in range is increased until the noise pull-in is completed. Continue to be expanded.

As a result, as indicated by CI, C2, and C3, the dropout detection output, that is, the noise generation portion is included in the noise pull-in range when the noise pull-in range is expanded.

FIG. 3 is a flow chart showing the operation procedure of the microcomputer. As is clear from this figure,
In step S1, it is first judged whether or not the reproduction mode is the double speed mode, and then in the second step S2, the reference value m is set to "3".
Set to. Further, the number of times of changing the tracking center is set to "0" in the third step S3, and the tracking center value is set to the initial value in the fourth step S4. After that, in the fifth step, the noise position, that is, the count value n is read, and in the sixth step, it is determined whether or not the count value is 15 or less. If it is above, the tracking center value is increased by 3 steps in the 10th step S10. If it is less than the eleventh step, if it is less than n, it is further judged in the seventh step S7 whether or not the count value n is m or less.
If it is> m, the tracking center value is reduced by 3 steps in the 9th step S9 and the process proceeds to the 11th step. If n ≦ m, it is regarded as the tracking pull-in state and the tracking center value is fixed in the 8th step. finish.

In the eleventh step S11, the tracking value change count x is updated, and in the twelfth step, it is judged whether or not the update value x has reached "10". If it is less than "10", the process returns to the fifth step and the tape running phase Judging the noise pull-in state due to the update of
If it is "10", the reference value is updated in the 13th step S13, the process returns to the 3rd step S3, and the noise pull-in control is started from the initial state.

As described above, according to this embodiment, the tape running phase is 3
The sheet is step by step, and the noise pull-in range is expanded by one step each time the shift makes one round, and the noise pull-in state is always detected.

(G) According to the present invention, by expanding the noise pull-in range, the desired tracking state is detected regardless of the recording state or the reproducing state, and the reproducing screen becomes stable. Is large.

[Brief description of drawings]

FIG. 1 is a circuit block diagram according to the first embodiment of the present invention, FIG. 2 is an explanatory diagram of a reproduced signal waveform thereof, and FIG. 3 is an operational procedure explanatory diagram of a microcomputer. 5: Noise position sampling circuit 8: Reference value setting circuit 4: Dropout detection circuit

Claims (2)

(57) [Claims] 1. A helical scan type magnetic recording / reproducing apparatus for sequentially changing a running phase of a tape so as to control a reproduction output reduction portion of a rotary head to fall within a noise drawing range. An auto-tracking circuit, characterized in that the noise pull-in range is expanded after being pressed. 2. A dropout detection circuit for generating a dropout detection output during a reproduction output decay period of a rotary head,
Counting means for counting the period from the head output switching timing to the dropout detection output deactivating timing with a clock having a constant frequency, and the tape is compared with the reference value by comparing the count value with the reference value. In the helical scan type magnetic recording / reproducing apparatus in which the changing means for sequentially changing the traveling transfer state of is arranged, the reference value setting means for changing the reference value to a large value after the change of the tracking state has been completed, An auto-tracking circuit characterized by being placed.