JPS58141432A - Tracking state detecting circuit - Google Patents

Abstract

PURPOSE:To detect the tracking state with simple constitution, by sampling the variance of the reproduced output level at one peak point of the oscillation of a video head and controlling the tracking state by this sampling level. CONSTITUTION:The control voltage applied to a piezoelement P is changed on the basis of the signal where a sawtooth wave having the field cycle which changes the inclination angle in accordance with a tape speed, an AC signal for forced oscillation, and a tracking control signal are superposed. The sawtooth wave is led out from a sawtooth wave generating circuit 2, and the AC signal is led out from a high frequency multiplying circuit 3 through a BPF4. The tracking signal is amplified by a preamplifier 5 and is led out as the tracking control signal through an LPF14. These signals led out in this manner are added in an adding circuit 1 and are amplified to the control voltage through a control amplifier 15 and are inputted to the piezoelement P, and the video head scans the center of a recording track.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking state detection circuit with a simplified circuit configuration.

In a video tape recorder, in order to obtain a clear (no noise band) special reproduction image, the tape winding angle must be slightly altered or the video head must be displaced in a direction perpendicular to the scanning direction. In the latter case, it is common to round the scanning direction of the video head to match the direction of the recording track, and to apply a sawtooth wave to the piezo element that loads and fixes the video head according to the tape speed. There is no guarantee that the video head will scan the center of the recording track. Therefore, the video head is forced to vibrate in the width direction of the track by superimposing an AC signal (frequency sufficiently higher than the field frequency) on the sawtooth wave, and the playback output level etc. at both ends of the vibration are detected and the video head is adjusted. ) A tracking control signal for positioning at the center of the rack is obtained, and the control signal is further superimposed on the sawtooth wave. Various rounding tracking state detection circuits for generating tracking control signals have already been proposed, but all of them require complex circuits.

Therefore, in view of this improvement, the present invention proposes a nine-tracking state detection circuit with a simplified circuit configuration. Hereinafter, the operating principle of the present invention will be explained first.

Figure 1 shows the relationship between the position of the video head with respect to the recording track and its playback output level.
The playback output level (force has a linear attenuation tendency) when it deviates from the center of the recording track ('r).

Therefore, when the video head vibrates sinusoidally, the reproduction output level changes as shown in FIG. In other words, when the video head vibrates around the center of the recording track, the output changes as shown in (a), when it deviates slightly from the center on one side (b), and when it deviates further from the center, it changes significantly (LC). The output changes as shown in (d) when the reproduction output is partially lost due to the deviation, and as shown in (•) when the reproduction output is deviated from the center to the other side. Therefore, if we extract only the changes in the output waveforms shown in these ←) to (・) and perform sampling (S) near one of the peak points of vibration (G), we can obtain the results shown in Figure 3. The section shown below will be clicked/linked. Therefore, it is clear from Fig. 3 that when the video head vibrates around the center of the recording track, the sampling output level becomes a predetermined level υ, and the sampling output level changes depending on the direction of the deviation of the vibration center. The level becomes larger and smaller than the predetermined level. Moreover, the level difference between the predetermined level (■) and the 97 pre/g level (near the center of the recording track) is proportional to the amount of deviation.

Therefore, in this embodiment, tracking control is performed using a circuit configuration as shown in FIG. 4 KWA.

That is, in this embodiment, fluctuations in the playback output level are sampled at one peak point Km of the vibration of the video head, and the tracking state is controlled based on the sampling level.

The operation of this first embodiment will be described below with reference to the enclosure block diagram shown in FIG.

First, in this embodiment, the video head (b) is connected to a piezo element (
The control voltage applied to the piezo element (A) is a sawtooth wave with a field period that changes the tilt angle according to the tape speed, and a ninth AC signal (45011) of forced vibration. The sawtooth wave is generated by a sawtooth wave generation circuit (2).
), whose period corresponds to the scanning of the video head and whose slope is proportional to the tape speed. In addition, the AC signal is a 3QHz head switching pulse that is sent to the frequency multiplier circuit 1.
! 1 into a 450 Hz square wave and is derived via a 450 Hz first pass filter +4).

On the other hand, the tracking signal is derived as follows. First, the head output is amplified by the preamplifier (6), the level is adjusted by the GC circuit (.), and then detected by the first detection circuit (7). 8), only the output change due to forced vibration of the video head is derived. In addition, the above-mentioned MuaC converts the output of the second detection circuit il+ to the MuGC through a 450HH frequency limiting filter so as not to suppress output changes due to forced vibration.
It is used as a control input. The above-mentioned output change is sampled by the sampling pulse (II) obtained by inputting the output of the front frequency multiplier circuit (3) to the phase compensation circuit (11), and the output of this sampling circuit 0 is used for identification. The signal is input to the circuit θ and compared with the above-mentioned nine predetermined levels (to), and the tracking state is derived as a difference output, and is derived as a tracking control signal via a low-pass filter (141).

Note that the difference output is clipped near Ov, υ, and the tracking does not deviate beyond a certain level.@) A tracking control signal is not derived.

Each signal derived as described above is added to the adder circuit +1)
It is added to the control voltage through the control amplifier A, and after death, the piezo element Q? JK people are attacked. Therefore, by applying this control voltage, the video head can scan the center of the recording track, and a reliable reproduced image can be obtained.

Therefore, according to the present invention, from only one side of the vibration, the transformer,
The king state can be detected, and the tracking state can be detected with a simple configuration, which is highly effective.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of changes in playback output with respect to displacement of the video head in a recording track, Fig. 2 is an explanatory diagram of changes in playback output when the video head is forced to vibrate, and Fig. FIG. 2 is an explanatory diagram of each output level when sampling each reproduction output waveform shown in FIG. 2; FIG. 4 shows a circuit block diagram of an embodiment of the present invention. Explanation of main drawing numbers (8)... (2nd) band pass filter, (l or
・Number 7 ring circuit, θ4... identification circuit, (2)...
・Adorable wave generation circuit, (b)...video head, P.
...Piezo element. Figure 1 Figure 2 169- 8s

Claims (1)

[Claims] fil An alternating current signal is applied to a piezoelectric element on which a video head is mounted and fixed, and the video head is vibrated in the width direction of the track, based on changes in the reproduction output level! 1] The tracking control mechanism for positioning the video head at the center of the track includes a band-pass filter that separates a fluctuation component of the playback output level, and a band-pass filter that controls the output of the band-pass filter during one half cycle of the vibration of the video head. A tracking state detection circuit comprising a sampling circuit for sampling and an identification circuit for identifying a tracking state according to a sampling output level.