JPH1011844A - Auto-tracking device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an unstable analog element and to find the best tracking point by adjusting the tracking phase to minimize the bit error rate of a reproduced digital signal. SOLUTION: At the time of reproducing a video record with an error correction code parity given at the time of video recording of a digital signal, an error at the reproducing time is automatically corrected, and also a bit error rate (g) is calculated by an error code correcting circuit 13 with an error correcting code. Then, at the time of starting auto-tracking, tracking of certain unit amts. is shifted in turn as similar to the conventional manner, and hence after deciding a rough tracking range by the size of a reproduced envelope signal (c) obtained at this time, tracking below a unit amt. in this range is shifted in turn, and in order to minimize the error rate (g) of the digital signal read out by a rotary head at this time, a tracking phase is decided by an output of an error rate size comparing circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic tracking (international patent classification G11B 5 / 588A) of a rotary head type magnetic recording / reproducing apparatus for recording / reproducing a digital signal.

[0002]

2. Description of the Related Art In a rotary two-head type helical scan type VTR, video signals are sequentially recorded on a magnetic tape as inclined recording tracks inclined with respect to the longitudinal direction of the magnetic tape by a rotating head. It is necessary for the rotating head to accurately trace the recording track, and therefore, a control signal synchronized with the rotation phase of the rotating head during recording is sequentially recorded by the control head as a recording track along the longitudinal direction of the magnetic tape, At the time of reproduction, for example, the running speed of the tape is controlled and the tracking servo is applied so that the reproduced control signal is locked at a certain phase with the head switching pulse generated from the PG signal which is the phase information of the rotary head. Can be

However, when the recorded VTR differs from the reproduced VTR, for example, a tracking mono-multivibrator for adjusting the relative phase between the head switching pulse and the reproduction control signal is provided, and the value of the mono-multivibrator is changed. Accordingly, an auto-tracking method is employed in which the relative position between the inclined recording track formed on the magnetic tape and the rotary head is changed so that the envelope of the reproduction signal obtained from the rotary head is maximized.

Specifically, the relative phase between the head switching pulse and the reproduction control signal is slightly displaced so that the envelope signal of the reproduction signal from the rotary head is maximized, and the reproduction envelope signal before and after the displacement is displaced. A method has been employed in which the magnitude is compared to determine the phase at which the envelope signal is maximized.

Hereinafter, a conventionally proposed auto-tracking method will be described with reference to the drawings. FIG.
FIG. 3 is a block diagram of an auto tracking device in normal reproduction. Reference numeral 1 denotes a head motor that drives the head cylinder 2 to rotate, and 9 denotes a capstan motor. Both are rotated at predetermined speeds in a speed control circuit (not shown), and at the same time, the phase reference signal a obtained by dividing the output of the reference oscillator 4 through the frequency divider 5 and the rotation of the head cylinder 2 The PG signal, which is a phase signal, is phase-compared by a phase comparator 3, phase control is applied to the head motor 1 so that the phases of the two signals are locked, and the phase reference signal a is used as a tracking monomultivibrator (M
M) The phase of the signal delayed in 6 and the reproduction control signal b from the control head 7 are compared by the phase comparator 8, and the phase of the capstan motor 9 is controlled in accordance with the phase difference, so that the phase is changed to a certain phase. It locks on Ф.

At this time, by varying the time constant of the tracking MM 6, the phase Ф can be varied, that is, the relative position between the recorded inclined recording track and the rotary head can be changed. Then, the reproduction signal d obtained from the rotary head is guided to the envelope detection circuit 11 via the head amplifier 10 to create an envelope signal c corresponding to the amplitude of the reproduction signal. At the start of auto-tracking, a certain amount of tracking is sequentially shifted, and the magnitude of the envelope signal c obtained at that time is compared by an envelope magnitude comparison circuit 15, and a tracking shift circuit is used so that the envelope signal c becomes maximum. Tracking M via 12
Change the time constant of M6.

[0007]

As described above, the conventional VT
In the auto tracking based on only the magnitude of the envelope of the reproduction signal devised in R, the envelope itself fluctuates under the influence of the luminance change of the recorded image or the change of the image itself, and thus the envelope signal at the time of measurement becomes the maximum. The phase is not always the best track point, and it is very difficult to secure the tracking accuracy required when recording and reproducing a high-density signal with a recording rate exceeding 19 megabits / sec. There was a problem that the playback screen was disturbed due to lack of resolution.

[0008]

In order to solve the above-mentioned problems, an auto-tracking device according to the present invention monitors a bit error rate of a reproduction digital signal read from a rotary head, and detects a phase of a head switching pulse and a phase of a reproduction control signal. Is slightly displaced, and the magnitude of the bit error rate of the reproduced digital signal before and after the displacement is compared to determine the phase at which the error rate is minimized.

According to the present invention, an unstable analog element such as a change in luminance of a recorded image, a change in an image itself, or a change in a recording magnetic field can be eliminated, and an automatic tracking which can find the best tracking point can be obtained. Equipment can be provided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An automatic tracking apparatus according to a first aspect of the present invention changes the relative positions of a tilted recording track formed on a tape-shaped recording medium and a rotary head that scans the tilted recording track. An auto-tracking device for finding the best point of a reproduction signal obtained by scanning an inclined recording track with the rotary head,
Monitoring the error rate of the reproduced digital signal read from the rotating recording track from the rotating head, and changing the relative position of the rotating recording track and the rotating head so that the error rate is minimized,
An unstable analog element such as a change in luminance of a recorded image or a change in the image itself can be eliminated, and the best tracking can be realized.

Next, in the automatic tracking apparatus according to the present invention, the relative position of the inclined recording track formed on the tape-shaped recording medium and the rotary head that scans the inclined recording track is changed, and An auto-tracking device for finding the best point of a reproduced signal obtained by scanning a recording track with the rotary head,
The relative position between the tilted recording track and the rotary head is changed so that the envelope of the reproduced signal read from the tilted recording track from the rotary head is within a predetermined range from the maximum value, and the envelope of the reproduced signal is adjusted to the maximum value. When the value is within a predetermined range from the value, the relative position between the inclined recording track and the rotary head is changed so that the error rate of the reproduction signal becomes smaller. First, rough tracking is determined according to the magnitude of the envelope of the reproduction signal read from the rotating head, and then the best point is automatically fine-tuned according to the magnitude of the error rate of the reproduction digital signal. After the approximate tracking range is determined,
By comparing the bit error rate of the reproduced digital signal and determining the phase at which the error rate is minimized, unstable analog elements such as changes in the luminance of the recorded video and changes in the video itself can be eliminated. The best tracking can be realized at high speed.

(Embodiment) An embodiment of the present invention described in claims 1 and 2 of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of an auto-tracking device of the present invention at the time of reproduction, and the same reference numerals are given to the same constituent blocks as those in the conventional example of FIG.

The difference from this conventional example is that the head amplifier 1
0 is output to the envelope detection circuit 11
And an error code correction circuit 13 for inputting a digital signal sequence f demodulated by the envelope detection circuit 11 and correcting an error of a digital code, and the error code correction circuit 1 which is simultaneously calculated at the time of error code correction processing.
The bit error rate g representing the error occurrence rate of the reproduced signal with respect to the recording signal which is the output of 3 is input to the error rate magnitude comparing circuit 14, and the output is output to the tracking shift circuit 1.
2 is input.

Next, the operation of the error code correction circuit 13 will be described. In the description of the present embodiment, the block description at the time of recording is omitted, but for example, in the D-VHS system, an error correction code parity is added in advance at the time of recording a digital signal, and the digital signal is recorded on a tape. At the time of reproduction, on the contrary, the error at the time of reproduction is calculated and automatically corrected by the error code correction circuit 13 by the error correction code, and at the same time, the bit error rate g is also calculated. The error code correction coding is constituted by a conventionally known Reed-Solomon code. For this reason, the best tracking at the time of reproducing a pre-encoded digital signal has the same result as determining the tracking phase so as to minimize the bit error rate. Further, the bit error rate g indicating the error correction state output from the error code correction circuit 13 and the tracking value have a correlated quadratic relationship as shown in FIG.

In this embodiment, at the start of auto-tracking, a certain amount of tracking is sequentially shifted in the same manner as in the prior art, and the approximate tracking range is determined based on the magnitude of the reproduced envelope signal c obtained at that time. Within the range, the tracking of the unit amount or less is sequentially shifted, and the output of the error rate magnitude comparison circuit 14 is set so that the bit error rate g of the digital signal read out from the rotating head obtained at that time is minimized. It is configured to determine a tracking phase.

[0016]

As described above, according to the present invention, unstable analog elements such as a change in luminance of a recorded image, a change in the image itself, and a change in a recording magnetic field can be eliminated, and the best tracking point can be obtained. Can be found.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic tracking device of the present invention.

FIG. 2 is a diagram showing a relationship between a bit error rate and a tracking value in the embodiment of the auto tracking device of the present invention.

FIG. 3 is a block diagram of a conventional auto tracking device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Head motor 2 Head cylinder 3 Phase comparator 4 Reference oscillator 5 Divider 6 Tracking MM 7 Control head 8 Phase comparator 9 Capstan motor 10 Head amplifier 11 Envelope detection circuit 12 Tracking shift circuit 13 Error code correction circuit 14 Error rate Size comparison circuit

Claims (2)

[Claims] 1. A reproduction signal obtained by changing a relative position between an inclined recording track formed on a tape-shaped recording medium and a rotary head that scans the inclined recording track, and scanning the inclined recording track with the rotary head. An automatic tracking device that finds the best point of, monitors the error rate of the reproduced digital signal read from the tilted recording track from the rotary head, and determines the relative position between the tilted recording track and the rotary head so that the error rate is minimized. An auto tracking device characterized by changing. 2. A reproduction signal obtained by changing a relative position between an inclined recording track formed on a tape-shaped recording medium and a rotary head for scanning the inclined recording track, and scanning the inclined recording track with the rotary head. An auto-tracking device for finding the best point, wherein the relative position between the tilted recording track and the rotary head is changed so that the envelope of the reproduction signal read from the rotary recording track from the rotary head is within a predetermined range from the maximum value. And when the envelope of the reproduction signal is within a predetermined range from the maximum value, changing the relative position between the tilted recording track and the rotary head so that the error rate of the reproduction signal becomes smaller. An automatic tracking device.