JPH04159649A - Tracking error detector - Google Patents

Abstract

PURPOSE:To improve an error detection accuracy by a method wherein the period of a playback clock is measured. CONSTITUTION:Two playback clocks are generated by phase locked loop (PLL) circuits 8 and 9 in accordance with playback digital image signals. If multiple magnetic heads 2 and 3 having azimuth angles opposite to each other perform playback with a discrepancy between tracking positions following the discrepancy of tracking, the periods of the two playback clocks are shifted to the directions opposite to each other following the discrepancy of the tracking. The frequency of the playback clock from the circuit 9 is divided by a frequency divider 11 and its period is measured by a period measuring circuit 10 with the playback clock from the circuit 8. A deducter 13 deducts a period from a reference period circuit 12 from the data from the circuit 10 to calculate the variation of the discrepancy of the tracking. An initial tracking position is detected by a pilot detecting part 4. The initial position is obtained by an output comparing circuit 18 with a timing signal from a timing signal generating circuit 17. The output of an integral circuit 14 is added to the initial tracking position by an adder 19. With this constitution, an error detection accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tracking error detection device for detecting tracking errors in a magnetic recording and reproducing device for recording and reproducing digital video signals.

BACKGROUND OF THE INVENTION Conventionally, tracking error detection devices used in home VTRs control the longitudinal direction of a magnetic tape by using pulses indicating the rotational phase of the head drum as a load control signal, in addition to the video track for recording and reproducing video signals. Tracks are provided for recording, and during playback, tracking errors are detected by comparing the phase of the reproduced control signal and the phase of the rotational pulse of the head drum (for example, supervised by Ryo Hazawa, rVTR technology).

Japan Broadcasting Corporation).

On the other hand, in a tracking error detection device used for 8 mm video, four low frequency pilots with different frequencies are set, and the low frequency pilots are frequency-multiplexed and recorded on the video signal for each video track. During playback, two low frequency pilots recorded on both adjacent video tracks are detected as crosstalk from adjacent video tracks, and a tracking error is detected by comparing the power difference between the two low frequency pilots.

Problems to be Solved by the Invention However, with the above-mentioned conventional method using a control track, video track linearity cannot be detected, and it is extremely difficult to improve tracking error detection accuracy.

In addition, the tracking error detection device used for 8mm video can detect the linearity of the video track, but since the digital signal used for the digital magnetic recording device has signal components up to the low frequency band, the low frequency pilot Constant frequency multiplexing of
There were problems such as interference waves for digital signals.

The present invention has been made in view of the above, and an object of the present invention is to provide a tracking error detection device that detects video track linearity, improves tracking error detection accuracy, and does not interfere with the digital signal. .

Means for Solving the Problems In order to achieve the above object, the tracking error detection device of the present invention adds and records a pilot signal for tracking error detection to a digital video signal at a lower frequency than the preamble signal during the preamble period of the digital video signal. a pilot detection unit that reproduces and detects a tracking initial position from the pilot signal; two multi-magnetic heads having mutually opposite azimuth angles; and a tracking error signal from two digital video signals recorded and reproduced by the two magnetic heads. and an azimuth phase difference detection section that detects.

According to the above-described configuration, the present invention detects a pilot signal during reproduction, detects and corrects the initial tracking position, and when two multi-magnetic heads having opposite azimuth angles come off the video track, two reproduced digital images are The tracking error signal is detected by utilizing the characteristic that the periods of the signals change in opposite directions. Therefore, tracking errors including video track linearity can be detected, and tracking error detection accuracy can be improved. Furthermore, since the pilot signal is inserted into the preamble period of the digital video signal, no interference is caused to the data portion of the digital video signal.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of main parts of a tracking error detection device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 indicates a magnetic tape, and reference numerals 2 and 3 indicate two multi-magnetic heads having opposite azimuth angles.

As shown in FIG. 2(a), a tracking pilot signal having a lower frequency than the preamble signal is frequency-multiplexed and recorded on the magnetic tape 1 during the preamble period of the digital video signal. That is, as shown in FIG. 2(b),
A data generation circuit 22 adds a preamble, a postamble, an error correction code, etc. to the video signal input from the terminal 21, and generates a two-channel digital video signal. Next, the pilot signal generation circuit 23 generates a continuous biloft signal. However, the data generation circuit 22
Count the timing signals indicating the preamble period of
≠f2) to enable accurate detection of the tracking position. Next, the gate circuit 24 gates the pilot signal in accordance with the timing signal indicating the preamble period outputted from the data generation circuit 22 and outputs it to the addition circuit 25 . Next, the adder circuit 25 adds the intermittent tracking pilot signal output from the gate circuit 24 to the one-channel digital video signal output from the data generation circuit 22, and records the signal onto the magnetic tape 1 through the multi-magnetic head 3. do. Next, returning to FIG. 1, the signals recorded on the magnetic tape 1 are reproduced through the multi-magnetic heads 2 and 3. Next, the azimuth phase difference detection section 5 includes an equalizer 6.7, a PLL circuit (PhaseL
(locked Loop) 8, 9, period measurement circuit 10,
It is composed of a frequency dividing circuit 11, a reference period circuit 12, an adding circuit 13, and an integrating circuit 14. Here, equalizer 6.
7 corrects the frequency deterioration of the digital video signal reproduced from the multi-magnetic head 2.3 and converts it into a cosine roll waveform. Next, PLL circuits 8 and 9 generate two reproduced clocks based on the reproduced digital video signal. Here, as shown in FIG. 3, the periods of the two reproduced clocks change as the tracking shifts.

That is, assume that multi-magnetic heads 2 and 3 having opposite azimuth angles are reproduced with their tracking positions shifted in the direction of the arrow as shown in FIG. 3(a). As a result, as shown in FIG. 3(b), the A
Then, the period TA of the recovered clock is T with respect to the reference period T.
A > T, and B reproduced by Multi Magnetic Herad 3
Then, the period TB of the reproduced clock is T with respect to the reference period T.
B<T. Therefore, the periods of the two reproduced clocks reproduced from the multi-magnetic head 2.3 change in opposite directions as the tracking shifts. Next, returning to FIG. 1, the reproduced clock reproduced from the PLL circuit 9 is input to the frequency dividing circuit 11, where the frequency is divided in order to widen the dynamic range of tracking error detection. Next, the period measuring circuit 10 measures the period of the signal output from the frequency dividing circuit 11 using the regenerated clock regenerated from the PLL circuit 8, and outputs period measurement data. Next, the adder circuit 13 subtracts the reference period output from the reference period circuit 12 from the period measurement data output from the period measurement circuit 10 to calculate only the amount of change in tracking deviation and outputs the result. Here, in the period measurement data, the amount of change in tracking deviation is detected according to the theory described above, but the absolute tracking position is unknown. Therefore, an initial tracking position is required. Here, the pilot detection section 4 includes a BPF (band rejection filter) 15, 16, an output comparison circuit 18, and a timing generation circuit 17, and detects the initial tracking position. Here, as mentioned above, the tracking pilot signal is sent to the magnetic tape 1 through the multi-magnetic head 3 at a lower frequency than the preamble signal (for each track, frequencies fl, f) during the preamble period of the digital video signal.
2 are recorded alternately). Therefore, BPF15.
16, both adjacent pilot signals (frequency f1, f2) leaked as adjacent crosstalk signals through the multi-magnetic head 2 are detected and output to the output comparison circuit 18. Further, the timing generation circuit 17 generates a timing signal indicating the preamble period of the digital video signal using a signal (H8W, head switching signal) indicating the recording start position of the magnetic tape 1, and outputs it to the output comparison circuit 18. . Next, the output comparison circuit 18 compares the outputs of the BPF 15.18 in accordance with the timing signal indicating the preamble period outputted from the timing generation circuit 17, and determines where the multi-magnetic head 2.3 is located on the track. , detects the initial position and outputs initial position data.

Next, the integrating circuit 14 performs a reset at the timing signal of the timing generating circuit 17, that is, at the timing when the initial tracking position is detected, and detects the amount of tracking position deviation from the initial tracking position. next,
The adder circuit 19 adds the initial tracking position data that is the output of the output comparison circuit 18 and the output of the integration circuit 14, calculates the tracking error from the track center, and outputs the result.

Furthermore, although this embodiment has described a method of frequency multiplexing a tracking pilot signal in the preamble period of a digital video signal, pilot signals can also be inserted by changing the preamble pattern as shown in FIG. I can do it. That is, in the preamble period, basically, in order to accurately pull in the PLL circuits 8 and 9 of FIG. 1, a single pattern of the highest repetition frequency of the digital video signal is originally recorded. Therefore,
The single pattern with the highest repetition frequency is shown in Figure 4.
A low frequency pilot signal is inserted by changing the DSV (digital integrated value) at a certain period. That is, in the case of FIG. 4(a), DSV 1
=-1:DSV2=4 is repeated to create a pattern that simultaneously satisfies the pattern of the highest repetition frequency and the signal of the pilot signal (period TI). In addition, in the case of FIG. 4(b), DSV3=-4 and DSV4=4 every period T2.
This is repeated to create a pattern that simultaneously satisfies the pattern of the highest repetition frequency and the signal of the pilot signal (period T2). Therefore, FIG. 4(a).

The pattern in (b) is the pilot signal (f
If the data generating circuit 22 shown in FIG. 2 generates the pilot signals instead of frequency multiplexing the pilot signals, the pilot signal can be inserted without frequency multiplexing the pilot signals.
Tracking errors can be detected on the playback side using the same embodiment as in FIG.

Further, the second embodiment includes the main blocks shown in FIG. 5, and can further improve tracking error detection accuracy compared to the first embodiment.

The difference from FIG. 1 is that a maximum value detection circuit 45 is added. In the maximum value detection circuit 45, when the pilot signal is detected by the pilot detection section 34, the reset signal and the initial tracking position data of the integration circuit 44 are determined so that the signal of the pilot detection section 34 has the maximum value as in FIG. The signal passes through the detection circuit 45 as is, resets the integration circuit 44, and is output to the addition circuit 46. Next, in a period other than the pilot signal portion, that is, in a digital video signal portion other than the preamble period, the maximum amplitude value of the output of the equalizer 36 is detected by the maximum value detection circuit 45, and when the maximum amplitude value is detected, the integration circuit 44 is output, and the initial tracking position data is also set to zero and output to the adder circuit 46. By adding the maximum value detection circuit 45 as described above to the configuration, when the pilot signal is detected with an offset in the initial tracking position due to variations in the sensitivity of the multi-magnetic head, the maximum value detection circuit 45 can correct it. It becomes possible.

In addition, in the present invention, an example in which a pilot signal is inserted in a preamble period has been described, but if an edit gap period etc. exists in a period between a video signal and an audio signal in a digital video signal, and in a postamble period, A pilot signal can be inserted similarly to the present invention, and similar effects can be expected.

Effects of the Invention As described above, according to the first embodiment of the present invention, tracking errors including the linearity of the video track can be detected by measuring the period of the reproduced clock. can be improved. In addition, the offset value, which is the problem of azimuth phase difference detection, is solved by inserting a pilot signal, but since the period in which the pilot signal is frequency multiplexed is only the preamble period of the digital video signal, the digital video Tracking errors can be detected without interfering with the signal, which is extremely useful.

It is also possible to insert a pilot signal by changing the pattern of the preamble period, and in that case, the present invention can be implemented without frequency multiplexing the pilot signal.

Furthermore, according to the second embodiment, in addition to the effects of the first embodiment, even if the pilot signal has an offset due to variations in sensitivity of the multi-magnetic head, it is corrected by the maximum amplitude value of the digital video signal. It is extremely effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts showing the configuration of a tracking error detection device in a first embodiment of the present invention, and FIG. 2(a)
2 is a data arrangement diagram showing the insertion period of the tracking pilot signal, FIG. 2(b) is a block diagram of the main part of the recording side when recording the pilot signal of the tracking error detection device in the same embodiment, and FIG. 3(a) 3(b) is a waveform diagram showing the cycle change of the reproduced clock when the multi-magnetic head traces the track according to the trajectory diagram, and FIGS. 4(a) and (b) are
) is a pattern diagram when a pilot signal is inserted by changing the pattern of the preamble period, and FIG. 5 is a main part block diagram showing the configuration of a tracking error detection device in a second embodiment of the present invention. 1.31...magnetic tape, 2. 3. 32. 33
...Multi-magnetic head, 4.34...Pilot detection section, 5.35...Azimuth phase difference detection section,
8, 7. 36. 37... Equalizer, 8.
9. 38.39...PLL circuit, 10.40
...Period measurement circuit, 11.41...Frequency division circuit,
12.42...Reference period circuit, 13.43.
...addition circuit, 14.44...integration circuit, 15,
16... B P F. 17...Timing generation circuit, 18...Output comparison circuit, 19.46...Addition circuit, 22...
- Data generation circuit, 23...Pilot signal generation circuit, 24...Gate circuit, 25...Addition circuit, 45...Maximum value detection circuit. Name of agent: Patent attorney Akira Okaji and two others Fig. 2 (0-n Fig. 3 (α) dη
Ding-・-1βL)il'1FII
ACT TB>T 4th diagram Ri

Claims (4)

[Claims] (1) A magnetic recording and reproducing device that records and reproduces a digital video signal on diagonal tracks on a magnetic tape using a rotating head, wherein a pilot signal for tracking error detection is preambled to the digital video signal during a preamble period of the digital video signal. a pilot detection unit that performs recording and reproduction by frequency multiplexing a frequency lower than that of the signal and detects an initial tracking position from the pilot signal; two multi-magnetic heads having mutually opposite azimuth angles; and recording and reproduction by the two magnetic heads. A tracking error detection device comprising: an azimuth phase difference detection unit that detects a tracking error signal from two digital video signals; (2) A magnetic recording and reproducing device that records and reproduces a digital video signal on diagonal tracks on a magnetic tape using a rotating head, wherein a pilot signal for tracking error detection is applied to the digital video signal in a pattern during a preamble period of the digital video signal. a pilot detection unit that records and plays back the data and detects the initial tracking position from the pilot signal; two multi-magnetic heads having mutually opposite azimuth angles; and two digital video signals recorded and played back by the two multi-magnetic heads. A tracking error detection device comprising: an azimuth phase difference detection unit that detects a tracking error signal from the azimuth phase difference detection section; (3) The pilot signal is recorded and reproduced by periodically changing (digital integrated value) of a constant frequency pattern in the preamble period to generate the pilot signal at a lower frequency than the constant frequency pattern in the preamble period. 2. The tracking error detection device according to 2. (4) A magnetic recording and reproducing device that records and reproduces digital video signals on diagonal tracks on a magnetic tape using a rotating head, the recording and reproducing device including a pilot signal for tracking error detection inserted into a preamble period of the digital video signal. death,
a pilot detection unit that detects the initial tracking position from the pilot signal; and two units having opposite azimuth angles to each other.
an azimuth phase difference detection unit that detects a tracking error signal from two digital video signals recorded and played back by the two magnetic heads; and an optimum tracking position of the azimuth phase difference detection unit;
A tracking error detection device comprising a maximum value detection section that detects and corrects the amplitude value of a digital video signal.