JPH04360014A - Auto tracking circuit for magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To perform the reproduction small in crosstalk obstruction from an adjacent track. CONSTITUTION:Envelope detection means (7, 8) detecting the amplitude level of a reproduced RF signal from video heads (1, 2), an A/D conversion means 10 converting the output signal of the detection means into a digital signal, an arithmetic means 11 fetching the output from the A/D conversion means and calculating so that an unnecessary signal reproduced from an adjacent track may be minimum and control means (12, 13) controlling so that the video heads may trace on a recording track optimally by the arithmetic result are provided.

Description

[Detailed description of the invention]

0001 [Purpose of the invention]

0002

[Industrial Application Field] The present invention relates to an auto-tracking circuit for a magnetic recording/reproducing device, and particularly relates to an auto-tracking circuit for a magnetic recording/reproducing device that minimizes crosstalk interference from adjacent tracks picked up by a wide head, especially when recording/reproducing in a long-time mode. The present invention relates to an auto-tracking circuit for a recording/reproducing device.

0003

[Prior Art] In a conventional VTR tracking circuit,
During playback, the point where the amplitude (called the envelope) of the playback RF signal from the video head is maximized is determined, and the microcomputer (called the CPU) determines the amount of tracking shift at this point to control the servo circuit. I have to.

The tracking position at which the envelope is at its maximum can be determined from the relationship between the envelope detection output level and the tracking shift amount as shown in FIG. For example, when the auto-tracking circuit starts operating, the tracking amount is first shifted in an arbitrary direction, and when the detection level drops, the shift direction is reversed, and when the detection level rises, the shift continues and the output level reaches the maximum. Shift further in the same direction with respect to the detection level (Emax) at
Find the shift amount x3 at the point where the detection level decreased by ΔE,
At that point, the direction of shift of the tracking amount is reversed. The re-biopsy wave level rises again, exceeds the output point of Emax, and then calculates the shift amount x1 at the point where ΔE decreases again,
The intermediate value x2 between x3 and x1 is calculated, and an appropriate shift amount is added to x2 (if this shift amount is 0, the midpoint where the re-biopsy wave level is maximum) is set as the optimum tracking position.

By the way, a problem that arises when recording and reproducing in a long-time mode with a VTR is a reduction in image quality. The causes of image quality deterioration in long-duration mode are a decrease in playback S/N due to the video track becoming narrower, and a head wider than the track pitch used to prevent track errors during playback. The purpose is to pick up talk noise.

However, the conventional auto-tracking operation described above controls the head trace so that the playback level from the video head is maximized, and the crosstalk components from adjacent tracks are minimized. It wasn't meant to do any tracking. For this reason, it was not sufficient to eliminate crosstalk interference from adjacent tracks during playback in long-time mode.

[0007]

[Problem to be solved by the invention] As mentioned above, conventionally,
During playback, it was not possible to sufficiently eliminate crosstalk components from adjacent tracks.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an auto-tracking circuit for a magnetic recording/reproducing apparatus that can minimize crosstalk interference from adjacent tracks during reproduction.

[0009] [Structure of the invention]

0010

[Means for Solving the Problems] The present invention includes two or more video heads on a rotating drum, and the pitch of tracks recorded on a magnetic tape is formed narrower than the width of the video heads. , in an auto-tracking circuit of a magnetic recording and reproducing device in which adjacent recording tracks have different inclination azimuth angles, the present invention includes a detection means for detecting an envelope of a reproduction RF signal level from the video head, and an output signal of the detection means. A/D conversion means for converting into a digital signal; a calculation means for taking in the output signal from the A/D conversion means and calculating a tracking shift amount so that the unnecessary signal to be reproduced from an adjacent track has a minimum value; The present invention is characterized by comprising means for controlling the tracing of the video head to the recording track to an optimum value according to the result.

[0011]

[Operation] In the present invention, when recording and reproducing in long-time mode (EP or LP mode), the overlap widths t21 and t22 of the video head to adjacent tracks are calculated so that the crosstalk component is minimized. The optimum tracking shift amount is determined from t21 and t22, and the servo circuit is operated to control the set value. Thereby, the crosstalk signal from the adjacent track becomes the minimum value, and the interference with the necessary reproduction signal is minimized.

0012

[Example] An example will be described with reference to the drawings. FIG. 1 is a block diagram showing an auto-tracking circuit of a magnetic recording/reproducing apparatus according to an embodiment of the present invention.

In FIG. 1, 1 and 2 are video heads, and the video signals reproduced field by field by each head 1 and 2 are amplified by head amplifiers 3 and 4, and then switched field by field by head switching pulses. After a band pass filter (BPF) 7 selects a predetermined frequency band of the reproduced signal, an envelope detection circuit 8 detects the level (envelope) of the selected output. This envelope detection output 9 is converted into a digital signal (that is, converted into a discrete number) by an A/D converter 10, and the output signal is taken in by a microcomputer (CPU) 11 to minimize unnecessary signals reproduced from adjacent tracks. Calculate the tracking shift amount so that the value is the same. Based on the calculation result, the servo circuit 12 sets a shift amount in the tracking shift circuit 13, and drives the capstan drive motor 15 through the motor driver 14.
is controlled to achieve the optimum head trace. The servo circuit 12 is supplied with control pulses obtained from the tape 18 by a control head 16 via a head amplifier 17 in order to perform tracking during reproduction.

Next, the operation will be explained. FIG. 2 shows the track pattern recorded on the magnetic tape 18 and the magnetic head 1 (
Or 2) shows the relationship with the head trace. Now, let us consider the case where a magnetic head having a head width T is tracing a track pattern B1 as shown in FIG. For example, the case where the track width is 19.3 [μm] in VHS NTSCEP mode is shown. W is the track width (W1 is the A track, W2 is the B track), θ is the azimuth angle, T is the head width, t21 is the width of the head that overlaps the A1 track, t22 is the head that overlaps the A2 track. Shows the width of the head.

Further, λ is the wavelength of the recorded signal, e0
is the amplitude of the reproduced signal, ω1, ω2, ω3 are the angular frequencies of the reproduced signal and unnecessary signals, and t is the time.

At this time, the reproduction output E0 from the head is given by equation (1).

[0017]

[Math 1]

In equation (1), the first term is the necessary reproduced signal from track B1, the second term is the unnecessary signal component from track A1, and the third term is the unnecessary signal component from track A2. The ECT shown in equation (6) extracts unnecessary signal components, takes into account the frame correlation of the screen, and sets ω1 = ω2 = ω. Among these, La1 and La2 are the azimuth losses of the head output on track A1 and track A2, respectively. The head width T, the track width W, and the overlap widths t21 and t22 to adjacent tracks are as follows:
There is a relationship shown by equation (3), and if W and T are determined, ECT becomes a function of one variable, and it becomes possible to find the minimum value of ECT. That is, t21 or t22 when ECT becomes minimum can be determined.

First, regarding equation (3), consider the case where the head width T is determined. When the CPU recognizes its own head width T, it controls the amount of tracking shift during playback and detects points x4 and x5 in FIG. 3 where the envelope detection output level begins to decrease. In a range where the envelope detection output level is constant, even if the tracking shift amount is changed, the head width T
is a range that overlaps the required reproduction track B1, and the unknown track width Wx can be easily determined.

For example, looking at the numerical example of the relationship between the tracking shift amount in VHS EP mode and the head trace on the tape, one track is formed at 60 Hz and the track width is 19.3 [μm]. Therefore, 16.7 [m
sec] (= 1/60 [sec]) and approximately 19.3 [μm
], the head moves in the direction across the track on the tape pattern. Therefore, for VHS EP mode, the track width Wx is x4,x in FIG.
5, it can be determined using equation (7).

As a result, as described above, the minimum value of ECT becomes a function of one variable t21 (or t22), and the minimum value and t21 and t22 at that time can be determined. As a result, t
If the CPU 11 determines the track shift amount from 21 and t22 and operates the servo circuit 12 to always control the set value, the desired tracking position will be controlled. Note that the track widths W1 and W2 may differ due to a head step difference in the recording machine, but in that case, crosstalk from adjacent tracks is more severe in narrow tracks, and tracks with originally low playback level, or x5 - x4 [ msec] for both tracks, and for the smaller track,
What is necessary is to determine the tracking shift amount and employ the present invention.

Next, let us consider the recognition of the head width T when the track width W is constant. If the VHS system VT
If R, there are two heads, and their widths are independent. If the head widths are T1 and T2, then T1 and T2 to be determined are exactly W1=W2=19.3[μ
m] (track pitch in EP mode)
By replaying the file and using the same formula (7) used to calculate W above, and examining the points x5 and x4 in Figure 3,
It is clear that the CPU 1 can easily recognize the head widths T1 and T2. This operation may be performed once, such as at the time of shipment from the factory, and the CPU may semi-permanently store it. Regarding the setting of the recorded signal wavelength, it is preferable to select a signal of 2 to 3 MHz (in the case of VHS EP mode). Note that if finding the minimum value of the functions listed here requires a heavy burden on the CPU, it may be possible to use an approximation formula or to have a conversion table set in advance in the ROM.

[0023]

As described above, according to the present invention, by performing auto-tracking, it is possible to realize suitable head tracing and to realize reproduction with less crosstalk interference from adjacent tracks.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an auto-tracking circuit of a magnetic recording/reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the relationship between tape patterns and head trace positions for explaining the operation of FIG. 1;

FIG. 3 is a graph showing the relationship between tracking shift amount and envelope detection output level.

[Explanation of symbols]

1, 2……Video head 7...Band pass filter 8...Envelope detection circuit 10……A/D converter 11……Microcomputer (CPU) 12... Servo circuit 13...Tracking shift circuit 14……Capstan motor 18...Magnetic tape

Claims (1)

[Claims] 1. Two or more video heads are provided on a rotating drum, the pitch of tracks recorded on a magnetic tape is narrower than the width of the video heads, and adjacent recording tracks are In an auto-tracking circuit of a magnetic recording/reproducing device having mutually different inclination azimuth angles, a detection means for detecting an envelope of a reproduced RF signal level from the video head, and an A/D for converting an output signal of the detection means into a digital signal. The conversion means and this A
A calculation means that takes in the output signal from the /D conversion means and calculates a tracking shift amount so that the unnecessary signal reproduced from the adjacent track has a minimum value, and the calculation result,
An auto-tracking circuit for a magnetic recording/reproducing apparatus, comprising means for controlling tracing of the video head to a recording track to an optimum value.