JPH0263265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to an information signal reproducing device, and more particularly to an information signal reproducing device equipped with an automatic tracking control device.

The present invention will be explained below using a magnetic recording/reproducing apparatus (hereinafter referred to as VTR) that records video signals on a magnetic tape as an example.

<Description of Prior Art> In recent years, advances in high-density recording have made it possible to record and play over long periods of time with narrow track pitches.
VTR is being developed. When playing back a tape recorded with such a narrow track pitch, the important thing is how to make the playback head track the recorded tape tracks well, and several methods have been proposed so far. It has been implemented. A conventional and common method is to record a control signal synchronized with a vertical synchronization signal (hereinafter referred to as a CTL signal) in advance on a dedicated control track separate from the video track, and when playing back,
Tracking was performed using CTL signals. Recently, unlike this method, four different frequency signals (hereinafter referred to as 4F pilot signals) are superimposed on each field signal of the video signal and recorded on four adjacent video tracks, and when playing back, the A method that obtains a tracking signal from the difference in the reproduction level of 4F pilot signals from both adjacent tracks of a video track to be tracked, and obtains tracking by making both reproduction levels equal has been attracting attention. This method does not require a fixed head, does not require a dedicated track for the tracking signal, and does not require a tracking control signal (hereinafter referred to as
The ATF signal has many advantages, including good frequency characteristics and the ability to control tracking of relatively high frequency components. However, the above-mentioned 4
ATF signals produced using the frequency recording method are subject to variations in the reproduction efficiency between reproduction heads, variations or deviations in head width between reproduction heads, variations in the reproduction level of the 4F pilot signal due to the frequency characteristics of the reproduction head, and variations in the recording level of the 4F pilot signal. Variation,
Due to variations in the playback level of the 4F pilot signal depending on the tape used, stepwise level fluctuations tended to occur in the ATF signal field by field.
Normally, tracking control during playback uses a method that controls the rotational phase of the capstan shaft with respect to the rotational phase reference of the rotating playback head, but the capstan motor that is the object of the control has a frequency response characteristic. Since it is generally several Hz or less, the ATF
It does not follow the level fluctuations that occur in each signal field, but the phase is controlled by the average value. Therefore,
In a helical scan VTR in which the playback head is fixed to a rotating drum, tracking cannot be adjusted for each playback head, so it is affected by the noise component of the ATF signal generated from the heads fixed on opposite sides, resulting in mistracking. It was the cause. Furthermore, the level fluctuation of the reproduced 4f pilot signal also means the level fluctuation of the amount of crosstalk from both adjacent tracks included in it, and since the difference between these two crosstalks is used as the ATF signal, the level fluctuation remains unchanged. This indicates that the tracking error detection sensitivity of the ATF signal is affected, which in turn causes the loop gain of the capstan phase control loop to fluctuate, which is a cause of poor tracking control stability.

<Object of the Invention> In view of the above-mentioned drawbacks, the present invention provides an information signal reproducing device that can perform good tracking control even if there is a level difference between a plurality of types of pilot signals due to their frequency differences. The purpose is to

<Description of Embodiment> An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a basic block diagram of the reproducing apparatus of this embodiment. In the figure, reference numerals 11a and 11b are playback heads attached to opposite positions of a rotating drum (not shown) for playing back the video signal recorded on the tape track and the 4F pilot signal recorded superimposed on the track. , 12a and 12b are rotary transformers for extracting the signals reproduced by the reproduction heads 11a and 11b from the rotating drum, 13a and 13b are the amplifiers, and 14 is a rotary transformer for each of the reproduction heads 11a and 11b to scan the tape. 15 is a video signal processing circuit that demodulates and outputs the video signal from the playback signal from the changeover switch 14; 16 is a video signal processing circuit that separates the 4f pilot signal from the playback signal; 17 is a frequency equalizer for correcting the basic characteristics of the reproduction heads 11a and 11b, especially the frequency characteristics in the band of the 4F pilot signal, and 18 is an auto gain that keeps the reproduction output level of the 4F pilot signal constant. Control amplifier (hereinafter referred to as AGC amplifier), 1
9 shows the regenerated 4f pilot signal and the same frequency rotation as the pilot signal (f ₁ , f ₂ , f ₄ ,
This is a multiplier with a four-frequency signal that oscillates at f ₃ , f ₁ , ...). When the frequencies f ₁ , f ₂ , f ₃ , and f ₄ of the 4f pilot signal are respectively f ₁ < f ₂ < f ₃ < f ₄ , then f ₁ − f ₂ = f ₄ − f ₃ =
F ₁ , f ₄ − f ₂ = f ₃ − f ₁ = F ₂ is set, and 20 is a band pass filter that extracts only the frequency component near frequency F ₁ , and 22 is a band pass filter that extracts only the frequency component near frequency F ₂ . Bandpass filter to be extracted, 21,
23 is a detection circuit of frequencies F ₁ and F ₂ respectively, 24 is a differential amplifier, 25 is an inverting amplifier, and 26 is whether to use the output of the differential amplifier 24 or the output of the inverting amplifier 25 in accordance with the head switching pulse. 27 is an amplifier that amplifies the output of the switch 26; 28 is an input terminal for a head switching pulse indicating that the reproduction heads 11a and 11b have been switched;
9 is an input terminal for a four-frequency signal, 30 is an output terminal for a reproduced video signal, and 31 is a tracking control circuit that drives and controls a tape running system such as a reproduction head or a capstan motor by outputting an ATF signal.

The operation shown in FIG. 1 will be explained below.

A track is formed on a video tape (not shown) for each field of the video signal, and pilot signals of frequencies f ₁ , f ₂ , f ₄ , and f ₃ are sequentially superimposed on the video signal on each track. recorded. The signals reproduced from the reproduction heads 11a and 11b are outputted to a video signal processing circuit 15 and a bandpass filter 16 via rotary transformers 12a and 12b, reproduction amplifiers 13a and 13b, and a changeover switch 14. The video signal component of the reproduced signal is demodulated into a reproduced video signal by the video signal processing circuit 15, and is output to, for example, a TV receiver.

Also, the 4f pilot signal of the reproduced signal is separated only in its band by a bandpass filter 16.
Equalizer 17 and AGC, which will be explained in detail later
The signal is inputted to one input terminal of a multiplier 19 via an amplifier 18. The other input terminal of the multiplier 19 receives an oscillation frequency signal having the same frequency rotation as that of the reproduced 4f pilot signal. Therefore, from the multiplier 19, signals having difference frequencies F ₁ and F ₂ between the oscillation frequency signal and the frequency of the reproduced pilot signal crosstalk component are obtained. Then, the signal near the frequency F ₁ is extracted by the band pass filter 20, and the signal near the frequency F ₂ is extracted by the band pass filter 22.
1 and 23 are detected. Then, the detection output is differentially amplified by a differential amplifier 24, and the output of the differential amplifier 24 and the output obtained by inverting the output by an inverting amplifier 25 are alternately input to an amplifier 27 to obtain an ATF signal. ATF signal output is tracking control circuit 31
The head tracking is controlled by controlling the drive of a capstan motor (not shown).

Figure 2 is a frequency spectrum showing the reproduction level of the 4F pilot signal when the reproduction head is on track well, where A is the output of the bandpass filter 16, B is the output of the equalizer 17, and C is the
This is the output of the AGC amplifier 18.

The reproduced 4f pilot signal obtained from the bandpass filter 16 has the frequency characteristics of the recording and reproducing heads, and the reproducing heads 11a and 11b, as shown in FIG.
The level varies from field to field due to slight differences in width, deviations in mounting position, differences in playback efficiency, frequency characteristics of the videotape used, etc. Of this level difference, the frequency characteristics of recording and playback heads and video tapes,
In particular, regarding the level difference due to the frequency characteristics of the reproduction head, the equalizer 1 which has the opposite frequency characteristics to the frequency characteristics (shown by the broken line in Fig. 2A)
7, the correction is made as shown in FIG. 2B.

Therefore, when the tracking deviates, the reproduction levels of the 4F pilot signals from the tracks adjacent to the reproduced track are also corrected by the equalizer 17 so as to compensate for the frequency characteristics, so that a proper tracking signal can be obtained.

Furthermore, the difference in the width of the reproduction heads 11a and 11b,
Alternatively, level differences due to positional deviations, differences in reproducing head efficiency, etc. are corrected by the AGC amplifier 18 as shown in FIG. 2C, and the reproduction level becomes equal to the AGC level.

By configuring like this, each track
The DC level or gain of the ATF signal does not change, and good tracking is always possible.

In addition, in this example, the equalizer output is
Although it is connected to an amplifier, it is also possible to conversely connect the output of the AGC amplifier to an equalizer. In addition to the equalizer, the compensating means for compensating the frequency characteristics in the band of the pilot signal may be configured to separately extract each frequency of the pilot signal and amplify each frequency with an amplifier having a different gain.

<Description of Effects> As described above, according to the information signal reproducing device of the present invention, the DC level and gain of the ATF signal do not change from track to track, and a good ATF signal can be obtained, resulting in good tracking. Control becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of the reproducing apparatus of this embodiment, and FIG. 2 is a diagram showing a frequency spectrum showing the reproducing level of the 4f pilot signal when the reproducing head is well on-track. In the figure, 11a and 11b are playback heads;
5 is a video signal processing circuit, 16 is a bandpass filter (separation means), 17 is an equalizer, and 18 is a
An AGC amplifier, 19 a multiplier, and 31 a tracking control circuit, respectively.

Claims (1)

[Scope of Claims] 1. An information signal reproducing device for reproducing an information signal from a recording medium in which a plurality of types of pilot signals having mutually different frequencies are recorded together with the information signal in order to obtain a tracking control signal during reproduction, comprising: Reproducing means for reproducing the information signal and the pilot signal; Separating means for separating the plurality of types of pilot signal components from the signal reproduced by the reproducing means; and Separating means for separating the plurality of types of pilot signal components from the signal reproduced by the reproducing means. automatic tracking control means for forming a tracking control signal using the above information, and the automatic tracking control means has means for compensating the frequency characteristics of the plurality of types of pilot signals separated by the separation means. Signal regenerator.