JPH01291590A - Tracking servo method for vtr of helical scanning system - Google Patents

Abstract

PURPOSE:To effectively utilize tape width and to realize the low cost, miniaturization, and light weight of a device by detecting mean level difference between two carrier frequency signals in a chrominance signal component included in a reproducing luminance signal component, and controlling the feed speed of a magnetic tape corresponding to the level difference. CONSTITUTION:In performing the readout output of a Y head 4, the carrier chrominance signals of frequencies C1 and C2 recorded on C tracks at both sides are mixed as adjacent signals other than the luminance signal component. A low-pass component including the carrier chrominance signals of the two frequencies C1 and C2 is separated and extracted in performing the readout output of the Y head 4, and furthermore, the carrier chrominance signals of the two frequencies C1 and C2 are extracted at BPFs 31 and 32, respectively, and after they are rectified at rectifier circuits 33 and 34, the level difference of the two signals is detected at a differential amplifier 35. A sample and hold circuit 36 holds a differential signal level replying to a burst gate pulse, and supplies it as a tracking error signal to a driving capstan motor.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a tracking servo method in a helical scan type VTR.

BACKGROUND TECHNOLOGY 1 A head helical force scan VTR has the advantage of being able to record at high frequencies even if the rotating drum has a small diameter (half the diameter of a two-head system). As shown in Figure 2, it is necessary to provide a guard width between tracks on the recording tape pattern, which has been an obstacle to high-density recording on tape.

Furthermore, in conventional VTRs, a special control track was provided as shown in Figure 7 to control the magnetic tape feed speed so that the center of the head always coincided with the center of the track. However, this was a disadvantage in making effective use of the tape.

Summary of the Invention The present invention has been made in view of the above points, and provides a helical scan type VTR that can contribute to the effective use of magnetic tape.
The purpose of this invention is to provide a tracking servo method.

The tracking servo method according to the present invention separates a color signal component from a color video signal, converts the frequency, and transfers the frequency-converted color signal component and the original luminance signal component to adjacent tracks on a magnetic tape using a cross-azimuth head. At the same time as recording, different frequency conversion is performed alternately for each field on the color signal component, and when reproducing the magnetic tape, the average level of two carrier frequency signals in the color signal component included in the reproduced luminance signal component is It is characterized by detecting the level difference and controlling the magnetic tape feeding speed according to this level difference.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing the circuit configuration of a recording system of a helical scan type VTR to which a tracking servo method according to the present invention is applied. In the figure, an NTSC color video signal is separated into a luminance (Y) signal component and a color (C) signal component in a YC separation circuit 1. The separated luminance signal component is converted into a low carrier FM modulated wave in the FM modulation circuit 2 (for example, 5.6 MHz for the sync tip and 7 MHz for the white peak). The FM-modulated luminance signal is supplied to a Y head 4 as a first rotary head via a rotary transformer 3 and recorded on a magnetic tape (not shown).

On the other hand, the frequency of the separated color signal component is converted to the lower frequency side with respect to the luminance signal component in the low frequency conversion circuit 5. The low-pass conversion color signal frequency at this time is set to a frequency of IM Hz or higher, for example, around 1.5 MHz, and two frequencies CI and C2, which differ for each field, are set as described in detail later.

This two-frequency CI.

The switching of C2 is performed in synchronization with a switching pulse generated in the switching pulse generation circuit 9 in synchronization with a vertical synchronization signal separated and extracted from the color video signal. This low-frequency conversion color signal is superimposed with a digital audio signal, which will be described later, as a bias in a mixing circuit 6, and then supplied to a C head 8 as a second rotary head via a rotary transformer 7, where it is recorded on a magnetic tape. Ru.

At this time, the vertical synchronizing signal is recorded on the track so that it is located near the end of one track. This is 1/2 of the conventional
This process is different from that used in inch VTRs, in which a luminance signal and a low frequency conversion color signal are recorded in a superimposed manner. The analog audio signal is digitized by the A/D converter 10, then converted into a predetermined format signal by the signal processing circuit 11, and supplied to the mixing circuit 6.

A Y head 4 and a C head 8 are mounted adjacent to each other on a rotating drum (not shown), and as shown in FIG. (Y) Rack). Further, each gap between the Y head 4 and the C head 8 has an appropriate azimuth angle difference from each other. The diameter of the rotating drum is 24 [mi], and the rotation speed is 59. 9
4 [rps] and record 1 field/track. In addition, the angle of tape winding around the rotating drum is 36
Even if it is not 0@, if it is about 330 degrees, it is possible to record the video signal period excluding the V blanking period in one field.

DAT (Digital Audio) as a magnetic tape
Tape recorder) type cassette tape (tape width 3,
81101. Using a tape length of 58,680 mm), the relative speed between the tape and the head was approximately 4°5 m/5e.
FIG. 3 shows an example of a tape pattern according to this recording method designed to have a cs recording time of about 20 minutes.

If the DAT standard is applied to the digital audio signal superimposed on the low-frequency conversion color signal, the tape winding will be approximately 20 mm square.
It is possible to record continuous two-channel 16-bit audio signals with a track length equivalent to 0°. Since this digital audio signal requires a band of 3.5 MHz, it is recorded at a recording frequency of 4 MHz to 7.5 MHz.

Furthermore, the portion outside the recording section of the digital audio signal is
Let us record a signal corresponding to digital 0.

In addition, as mentioned earlier, two frequencies CI and C2, for example C1-1, 341, which differ for each field, are used as color signal frequencies.
3MHz (85,25f+), C2-1,443
When using 6MHz (91,75fH), as is clear from FIG.
C) The color signals carried by rack) are recorded as different frequencies on both sides of the Y track. This two-frequency CI r C2 carrier color signal is used as a pilot signal for tracking servo, which will be described later. Here, Y
By appropriately selecting the azimuth angle of the track,
Interference with video signals can be eliminated. Note that fH is the horizontal scanning frequency (15734, 26 Hz).

In this way, by recording only the luminance signal component separated from the NTSC composite signal and FM modulated on the Y track, it is possible to record low-frequency conversion color signals, audio FM signals, etc. compared to conventional 1/2-inch VTRs. Because there is no such thing, the lower sideband can be secured sufficiently wide, so in this example, a horizontal resolution of about 500 lines can be expected.

In addition, as the low-pass conversion color signal frequency, 1/2 inch VT
In R, a frequency of about 650K to 750KHz was used, but in this example, by changing this frequency to around 1.5MHz, the band of the color signal component can be made sufficiently wider than before, and a good result can be achieved. You can get results.

In this example, regarding the audio signal, DAT
Although it is assumed that recording is performed as a digital audio signal based on the system, it is also possible to employ an audio FM signal depending on the case.

FIG. 4 is a block diagram showing the circuit configuration of the reproduction system. In the figure, the read output of the Y head 4 is supplied to an HPF (bypass filter) 21 and a synchronous separation circuit 21 via a rotary transformer 3, and is also supplied to a tracking servo system (not shown). The luminance signal component that has passed through HPF20 is FM
After FM demodulation in the demodulation circuit 22, the YC mixing circuit 2
3. In the synchronization separation circuit 22, the horizontal synchronization signal and vertical synchronization signal contained in the read output of the Y head 4 are separated and extracted. The separated and extracted horizontal synchronization signal is supplied to the tracking servo system, and the vertical synchronization signal is supplied to the switching pulse generation circuit 24. The switching pulse generating circuit 24 generates switching pulses at one field period in synchronization with the vertical synchronizing signal.

On the other hand, the read output of the C head 8 passes through the rotary transformer 7
It is supplied to a PF (low pass filter) 25 and a high HPF 26. In the LPF 25, color signal components are extracted,
In the HPF 26, audio signal components are extracted. The color signal component that has passed through the LPF 25 is sent to the frequency conversion circuit 2.
7 and converted back into a 3.58 MHz carrier color signal. Here, the carrier color signal frequency input to the frequency conversion circuit 27 is two frequencies C1 and C2 that differ for each field (for example, C+-1, 3413MH2, C2-1, 4436M
Hz), the frequency conversion circuit 27 converts the carrier color signals of the two frequencies cl and c2 to 3.58 MHz by alternately switching between the two conversion systems in synchronization with the switching pulses generated from the switching pulse generation circuit 24. Convert to a carrier color signal. This 3.58 MHz carrier color signal is mixed with a luminance signal in the YC mixing circuit 23 and output as a reproduced video signal. The audio signal component extracted by the HPF 26 is supplied to an audio processing system (not shown) and subjected to signal processing.

FIG. 5 is a block diagram showing an example of a circuit configuration of a tracking servo system included in the reproduction system.

In the figure, during the read output of the Y head 4, in addition to the luminance signal component, two frequencies C, which are recorded in the C tracks on both sides,
, C, are mixed in as adjacent signals. A low frequency component including the carrier color signal of the two-frequency CI*C2 is separated and extracted from the read output of the Y head 4 in the LPF 30. Furthermore, from the passing output of LPF30, B
PF (band pass filters) 31 and 32 extract carrier color signals of two frequencies cl and c2, respectively. After each extracted carrier color signal is rectified by rectifier circuits 33 and 34, a differential amplifier 35 detects the level difference between the two signals. This difference signal is fed to a sample/hold circuit 36. The sample/hold circuit 36 generates a difference signal level in response to a burst gate pulse generated during a burst signal period from a burst gate pulse generation circuit 37 in synchronization with the horizontal synchronization signal separated and extracted by the synchronization separation circuit 21 in the reproduction system. The capstan motor (which drives the tape) uses this as a tracking error signal.
(not shown).

In this way, two frequencies CI and C2, which differ for each field, are used as color signal frequencies, and the level difference between the two frequencies cl and c2 mixed as adjacent signals in the read output of the Y head 4 during reproduction is detected. This makes it possible to servo control the tape feed speed so that the center of the Y head 4 always coincides with the center of the Y track, eliminating the need to provide a special control track, and making effective use of the tape width. Become. Furthermore, by using the value sampled and held in the burst signal portion as a comparison result of the two signals, a stable signal level can be ensured regardless of changes in the color signal level due to the subject.

Incidentally, in the above embodiment, the case where the application is basically applied to a 1-head helical scan type VTR was explained.
Although not limited to this, the tracking servo method according to the present invention basically uses 2 heads (or 4 heads).
It is also applicable to a helical scan type VTR. 2
An example of a tape pattern for a head is shown in FIG.

As described in detail, according to the tracking servo method of the present invention, the frequency-converted color signal component obtained by separating the color signal component from the color video signal and converting the frequency and the original luminance signal component are mutually separated. While recording on a magnetic tape with a cross azimuth head on adjacent tracks, the color signal components are alternately subjected to different frequency conversion for each field, and when playing back the magnetic tape, the color signal components included in the reproduced luminance signal component are By detecting the average level difference between the two carrier frequency signals and controlling the feeding speed of the magnetic tape according to this level difference, there is no need to provide a special control track, making effective use of the tape width. At the same time, by eliminating the need for controllers and trawl heads, the equipment can be made lower in cost, smaller in size, and lighter in weight.

Furthermore, by detecting the average level difference between the two carrier frequency signals in the burst signal part, the signal level is stable in this part, so it is possible to ensure a stable signal level that is related to changes in the color signal level due to the subject. become.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of a recording system of a helical scan VTR to which the tracking servo method according to the present invention is applied, and FIG. 2 shows the positional relationship between the Y head and C head and the loci of the Y track and C track. diagram showing,
Figure 3 is a diagram showing an example of a tape pattern according to this recording method when a DAT type cassette tape is used.
The figure is a block diagram showing the circuit configuration of the playback system, Figure 5 is a block diagram showing an example of the circuit configuration of the tracking servo system in the playback system, and Figure 6 is a diagram showing an example of the tape pattern when applied to two heads. , FIG. 7 is a diagram showing a tape pattern of a conventional 1/2 inch VTR. Explanation of symbols for main parts 1... YC separation circuit 2. Old... FM modulation circuit 4... Y head 5... Low frequency conversion circuit 8...・C head 21...
・Synchronization separation circuit 22...FM demodulation circuit 23.
... Yc mixing circuit 27 ... Frequency conversion circuit 35 ... Differential amplifier 36 ... Sample/hold circuit Applicant
Pioneer Corporation

Claims (2)

[Claims] (1) Separate the color signal component from the color video signal and record the frequency-converted color signal component obtained by frequency conversion and the original luminance signal component on a magnetic tape in adjacent tracks using a cross-azimuth head, and performing different frequency conversions on the signal component alternately for each field, and detecting an average level difference between two carrier frequency signals in the color signal component included in the reproduced luminance signal component when reproducing the magnetic tape; A tracking servo method for a helical scan type VTR, characterized in that the feeding speed of the magnetic tape is controlled according to this level difference. (2) A tracking servo method for a helical scan type VTR according to claim 1, wherein the average level difference is detected in a burst signal portion.