JPH03150752A - Tracking error detecting device - Google Patents

Abstract

PURPOSE:To detect even the linearity of a video track and to improve the detecting accuracy of a tracking error by performing the comparison between the phased of two reproduced clocks which move in proportion to the fluctuation of a time base and detecting the tracking error of the video track. CONSTITUTION:The PLL circuits 4 and 5 produce the reproduced clocks from the digital signals of two channels which are recorded and reproduced by the multi-magnetic heads 1 and 2. The dividing circuits 12 and 12' divide those reproduced clocks. The synchronism detecting circuits 11 and 11' decide the phases of both circuits 12 and 12', and a phase comparator 13 compares these phase with each other. The two digital codes reproduced from both heads 1 and 2 having the azimuths adverse to each other have their time bases fluctuating in the directions adverse to each other as these codes get out of a video track. Thus it is possible to detect the tracking error including the linearity of the video track with high accuracy by having the comparison between the phase of two reproduced clocks moving in proportion to the fluctuation of the time base.

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 digital magnetic recording device that converts a video signal into a digital code and records and reproduces the same.

BACKGROUND OF THE INVENTION Conventionally, tracking error detection devices used in home VTRs create a control track in the longitudinal direction of a magnetic tape using a pulse indicating the rotational phase of a head drum as a control signal, in addition to a video track on which video signals are recorded. It is detected by comparing the phase of the reproduced control signal and the phase of the rotation pulse of the head drum (for example, supervised by Ryo Takahashi, "rVTR Technology" edited by 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 one by one 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 control tracks, it is not possible to detect video track linearity, and it is extremely difficult to improve tracking error detection accuracy.

Furthermore, although the tracking error detection device conventionally used for 8mm video can detect the linearity of the video track, the digital code used in the digital magnetic recording device has signal components up to the low frequency band. Frequency multiplexing the pilot is
There were some drawbacks, such as interference waves for digital codes.

The present invention has been made in view of the above problems, 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 digital codes.

Means for Solving the Problems In order to achieve the above object, the present invention provides two multi-magnetic heads having mutually opposite azimuths,
two PLL circuits that generate reproduced clocks from two-channel digital signals recorded and played back from the two multi-magnetic heads;
two frequency divider circuits that divide the frequency of the two recovered clocks;
a synchronous detection circuit that determines the phase of the two frequency dividing circuits;
a phase comparison circuit that compares the phases of the output signals output from the two frequency dividing circuits, and an amplitude detection circuit that detects the amplitude value of the reproduced digital signal in order to determine the offset value of the phase comparison circuit. and an offset setting circuit that sets an offset value according to the output of the amplitude detection circuit.

Operation According to the above-described structure of the present invention, the time axes of two digital codes reproduced from a multi-magnetic head having mutually opposite azimuths change in opposite directions as they deviate from the video track. Therefore, the tracking error of the video track is detected by comparing the phases of two reproduced clocks that move in proportion to the time axis fluctuation. Therefore, the detection including the video track linearity can be performed, and the accuracy of tracking error detection can be improved. Furthermore, since pilots and the like are not frequency multiplexed on low frequencies, there is no interference with digital codes.

Embodiment 1 A tracking error detection device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a main part of a tracking error detection device according to an embodiment of the present invention, and FIG. 2 is a recording pattern diagram showing a recording pattern on a magnetic tape.

1 and 2 shown in FIG. 2 indicate multi-magnetic heads arranged on the same base, and when the size of the azimuth angle is θ,
Since the multi-magnetic heads 1 and 2 have opposite azimuths, the azimuth of the multi-magnetic head 1 is θ, and the azimuth of the multi-magnetic head 2 is 10. If the tracking shifts in the direction of the arrow in FIG. 2, the power center position of the track T1 reproduced by the multi-magnetic head 1 shifts to the lower side of FIG. Therefore, the time axis will fluctuate and there will be a delay. On the other hand, in the multi-magnetic head 2, the power center position of the track T2 is shifted upward in FIG. Therefore, the time axis changes and progresses.

Also, during playback, time axis fluctuations occur due to the expansion and contraction of the magnetic tape or uneven rotation of the rotating cylinder, but with the multi-magnetic heads 1.2 placed on the same base, the time axis fluctuations are the same and do not pose a problem. .

Next, returning to FIG. 1, the digital code recorded on the magnetic tape 3 is reproduced by the multi-magnetic discs 1 and 2, and sent to PLL circuits 4 and 5 having the same configuration. The reproduced digital signals are input to equalizer circuits 6 and 6'. The equalizer circuit 6.degree.6' corrects the frequency characteristics of the reproduced digital signal so that it becomes a differential characteristic, and outputs the corrected signal to the integrating circuits 7 and 7'. Next, the integration circuits 7 and 7' perform integration to convert the signal into a cosine roll-off waveform that the original digital code had. Next, the phase comparator circuit 8
and 8', a low pass filter (hereinafter referred to as LPF).

) 9 and 9' and voltage controlled oscillator circuits (VCO) 10 and 10' constitute a normal phase-locked loop and generate a reproduced clock phase-synchronized with the reproduced digital signal. P.L.
The reproduced clock output from the L circuits 4 and 5 is sent to the frequency divider circuit 1.
2 and 12'. The frequency dividing circuit 12.12' divides the frequency of the recovered clock in order to widen the dynamic range of the tracking error detection signal. However, if frequency division is performed, the possible phases increase by the frequency division ratio, and the phase cannot be uniquely determined. Therefore, using the data string of the integrating circuit 7, the synchronization detection circuit 11 detects the synchronization pattern added to the reproduced digital signal, and sends it to the frequency division circuit 12 as a time axis reference to uniquely determine the phase. Similarly, the frequency dividing circuit 12' also uniquely determines the phase according to the time base reference of the synchronization detection circuit 11'.

Next, the signals output from the frequency dividing circuits 12 and 12' are input to the phase comparator circuit 13. In the phase comparison circuit 13, the third
As shown in the figure, the signal (a) output from the frequency dividing circuit 12
The phase of the signal (b) outputted from the frequency dividing circuit 12' is compared, and an output as shown in (C) is obtained. Here, as explained in Fig. 2, if the tracking deviates in the direction of the arrow in Fig. 2, the signal (a),
(b) shifts to the dotted line waveform. Therefore, phase comparator circuit 1
The output of step 3 has the waveform shown by the dotted line in (C). Therefore, if the output waveform in Fig. 3(C) is converted into a voltage value using an LPF,
Tracking errors can be detected. Therefore, returning to the first base, the signal output from the LPF 14 becomes the tracking error detection signal.

However, the output of LPFL4 includes an offset value. In other words, there is an error in the installation of the magnetic head during compatible playback.
Alternatively, due to the sensitivity difference between the PLL circuits 4 and 5, etc., the LP
The DC center value of the tracking error signal output from F L 4 changes, causing an offset. Therefore, by detecting the amplitude value of the digital signal reproduced from the magnetic head 2, wobbling the tracking position, and holding the voltage value of the LPF 14 at the tracking position showing the maximum amplitude value, the offset value is detected. do. That is, as shown in FIG.
, and an integrating circuit 18 performs waveform shaping into a waveform with a cosine roll-off rate of 1, and outputs the waveform to a square law detection circuit 19. Here, the reason why the waveform is shaped into a waveform with a cosine roll-off rate of 1 is because, as can be seen from the impulse response waveform shown in FIG. This is because the amplitude value cannot be detected.

Next, returning to FIG. 1, the square law detection circuit 19 squares the signal output from the equalizer circuit 16 and detects the amplitude value. Next, in the offset setting circuit 20, if an offset value is not set, the wobbling signal is output from the terminal 23 to the servo circuit of the digital magnetic recording/playback device to perform wobbling, and the square-law detection circuit 19 According to the output, the output voltage value of the LPF 18 at the position showing the maximum amplitude value is stored as an offset value. Further, the offset setting circuit 20 is configured so that the digital magnetic recording/reproducing main device
The offset value is reset each time the playback mode is set. Next, the adder circuit 21 calculates the difference between the output of the LPF 14 and the offset value of the offset setting circuit 20.
Accurate tracking error is output from terminal 22.

Although not mentioned in the above embodiment, it is best to perform wobbling to determine the offset value at the center of the track, where the SN ratio is the best among the tracks, so that the offset amount can be detected accurately and effectively. It is.

Effects of the Invention As described above, according to the present invention, since tracking errors including video track linearity can be detected, the tracking error detection accuracy can be improved compared to the conventional technique.

In addition, since it does not have a configuration that multiplexes low-frequency pilots like that used in 8 mm VTRs, tracking errors can be eliminated without interfering with the digital code that is the recording signal in the digital magnetic recording device. Detectable and extremely useful. In addition, since the amplitude value of the reproduced digital signal is detected by shaping the waveform into a waveform with a cosine control off rate of 1, the offset value can be determined regardless of the recorded digital signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of a tracking error detection device in an embodiment of the present invention, FIG. 2 is a recording pattern diagram on a magnetic tape of the present invention, and FIG. 3 is a waveform diagram showing phase comparison of the present invention. FIG. 4 is an impulse response waveform diagram in a cosine roll-off waveform. 1.2...Multi magnetic head, 3...Magnetic tape, 4.5...PLL circuit, 8.6', 16...
・Equalizer circuit, 7.7', 18... Integrating circuit, 8.8', 13... Phase comparison circuit, 9.9
', 14...L P Flo, 10'...VCO
l 11, 11'...Synchronization detection circuit, 12.1
2'... Frequency dividing circuit, 15... Amplitude detection circuit,
17... Cosine equalizer circuit, 19... Square law detection circuit, 20... Offset setting circuit, 2
1...Addition circuit. ? '4 Min 0) Line! is a bud f (o -tof

Claims (3)

[Claims] (1) A digital magnetic recording device that converts a video signal into a digital code and records and plays back, comprising two multi-magnetic heads having mutually opposite azimuths, and recording and playing from the two multi-magnetic heads. Two PLL circuits that generate reproduced clocks from two-channel digital signals, two frequency divider circuits that divide the two reproduced clocks output from the two PLL circuits, and the phases of the two frequency divider circuits. and a phase comparator circuit that compares the phases of the output signals output from the two frequency divider circuits, and in order to determine the offset value of the phase comparator circuit, A tracking error detection device comprising: an amplitude detection circuit that detects an amplitude value of a signal; and an offset setting circuit that sets an offset value that determines an offset value in accordance with the output of the amplitude detection circuit. (2) The amplitude detection circuit includes an equalizer circuit that equalizes the reproduced signal into a waveform with a cosine roll-off of 1, and a square-law detection circuit that performs square-law detection of the output of the equalizer circuit. The tracking error detection device according to claim 1. (3) The offset setting circuit is configured to output a wobbling signal that instructs the servo circuit of the digital magnetic recording device to wave the tracking position when the offset value has not been set. The tracking error detection device according to item 1 or 2.