JPS5841714B2 - Color Eizou Shingo no Saisei Souchi - Google Patents

Description

[Detailed Description of the Invention] When recording a video signal on a magnetic tape, generally the first
As shown in the figure, two rotating magnetic heads HA and HB are installed at an angular interval of 180°, and a device is used to run the tape 1 along the tape guide drum 2 obliquely over an angular range of approximately 180°. For example, the heads HA and HB are rotated once in one frame, so that the heads HA and HB alternately form one magnetic track per field.

By the way, in the case of color video signals, the luminance signal is usually angularly modulated, such as frequency modulated, so that it occupies the high frequency side of the recordable/reproducible band, and the carrier color signal is frequency-converted to the low frequency side and then recorded. That's what I do.

During playback, as shown in FIG. 2, the playback outputs from the heads HA and HB are supplied to the switching circuit 31 to invert every field formed from pulse signals indicating the rotational angular positions of the heads HA and HB. The switching signal Sp is used to alternately extract each field, and supply this to the high-pass filter 21 through the regenerative amplifier 20 to extract a luminance signal.The luminance signal is supplied to the demodulator 23 through the limiter 22, and the demodulated luminance signal is On the other hand, the output of the amplifier 20 is also supplied to a low-pass filter 25 to take out the carrier color signal whose subcarrier frequency has been converted to fA. is supplied to the frequency converter 28 to convert it to the original frequency, that is, the frequency of the subcarrier is changed to fs
(=3.58MHz), and supplies this to the synthesizer 24 where it is combined with the luminance signal and sent to the output terminal 30.
to obtain a reproduced color video signal.

In this case, the reproduction system is provided with an automatic phase adjustment circuit, so-called APC circuit 32, in order to correct the phase error of the color signal due to jitter.

That is, a reference carrier wave with a frequency of fs from the reference oscillator 33 and an oscillation output with a frequency of fA from the variable frequency oscillator 34 are supplied to the frequency converter 35 to obtain a carrier wave with a frequency of f8+fA, which is then sent to the frequency converter 28. However, the carrier color signal from the frequency converter 28 is supplied to the burst gate circuit 36 to extract the burst signal, which is supplied to the phase detection circuit 37 to compare the phase with the reference carrier wave from the oscillator 33, and calculate the phase. The detection output is supplied to the variable frequency oscillator 34 through the integrating circuit 38 to control its oscillation frequency, and therefore the frequency of the carrier wave for frequency conversion supplied to the frequency converter 28.

By the way, when the recording and reproduction of color video signals are performed alternately by the two rotating magnetic heads HA and HB, the winding direction of the heads HA and HB and the direction between the heads HA and HB and the rotating transformer are changed. Depending on the connections and the connections between the rotating transformer, the recording system, and the reproducing system, the phase of the reproduced transport color signal may be reversed each time the reproduction outputs from the heads HA and HB are switched.

If recording and playback are performed using the same device, there is no problem because the above-mentioned winding direction and connections are adjusted during device manufacturing to prevent this from happening, but if the playback is performed using another device If you do this, something like this will happen.

In this way, when the loop of the APC circuit 32 is stable just before the reproduction outputs from the heads HA and HB are switched, a burst signal is supplied from the circuit 36 to the phase detection circuit 37, and a burst signal is supplied from the oscillator 33 to the phase detection circuit 37. Since the phase difference between the reference carrier waves supplied to circuit 37 is around 900 degrees, even when the reproduction outputs from heads HA and HB are switched and the phase of the reproduced carrier color signal is reversed, the burst signal from circuit 36 and the oscillator Although the phase difference between the reference carrier waves from 33 remains around 90°, since the pull-in range is exceeded, the output of the phase detection circuit 37 does not change immediately, and the oscillation frequency of the oscillator 34 and therefore the frequency converter 28 The frequency of the carrier wave for frequency conversion supplied to the carrier does not change immediately, and it takes a relatively long time for the frequency to change and the phase of the carrier color signal to reach a predetermined phase.

For this reason, at the beginning of the field, that is, at the top of the screen, the hue is not normal.

A similar problem occurs when color video signals are recorded at high density using a special method and then played back.

That is, in this method, as shown in FIG.
The angles of inclination of the gaps gA and gB of the HB and the scanning direction shown by the arrow 3 are made different from each other.

Then, as shown in FIG. 4, 1
Tracks TA and TB alternately formed for each field
The running speed of the tape 1 is selected so that a so-called guard band is not formed between the tapes.

In this case, for recording, as shown in FIG.
is supplied to the frequency modulator 13 to obtain a luminance signal, which is supplied to the frequency modulator 13 to obtain a modulated luminance signal, which is then supplied to the synthesizer 14.

The input color video signal is also supplied to a bandpass filter 15 to extract a carrier color signal C8 whose subcarrier frequency is fS, and is supplied to a frequency converter 16 to convert it to the lower frequency side, that is, the subcarrier frequency is fA. The signal CA is frequency-converted so that it becomes , and this signal CA is supplied to the inverting amplifier 17.

Then, the signal CA from the (a) side output terminal of the inverting amplifier 17
is supplied to one input terminal of the switch circuit 18, and the amplifier 1
7, the signal G from the @ side output terminal is supplied to the other input terminal of the switch circuit 18.

Then, the switch circuit 18 is switched to the state shown in the figure in a section where the head HA forms a track TA, for example, in an odd field, and is switched to the state shown in the figure, in a section where the head HB forms a track TB, for example, an even field. , the state is alternately switched to a state opposite to that shown in the figure every horizontal section.

The output of the switch circuit 18 is then supplied to the combiner 14 where it is combined with the modulated luminance signal, and the combined output is supplied to the heads HA and HB through the amplifier 19.

In this way, the signal CA whose subcarrier frequency is fA and whose phase is constant is recorded as the carrier color signal on the track TA.

On the other hand, the switch circuit 18 alternately extracts a signal cA whose subcarrier frequency is fA and whose phase is constant, and a signal whose phase is inverted with respect to the signal cA for each horizontal interval. , the relative value of “+1” and “-1”
This is equivalent to multiplying and combining the rectangular wave signals that alternately take the value , for each horizontal interval, and this is also equivalent to multiplying the signal CA by balanced modulation with a rectangular wave signal whose frequency is between the horizontal frequency fH. Therefore, a carrier color signal cB having a carrier frequency fB shifted by +fH from fA is recorded on the track TB.

That is, as shown in FIGS. 7A and 7B, carrier color signals CA and CB are recorded in adjacent tracks TA and TB in a frequency interleaving relationship with each other.

During reproduction, as shown in FIG. 6, the reproduction outputs from the heads HA and HB are supplied to a high-pass filter 21 through a reproduction amplifier 20 to extract a modulated luminance signal, which is then transmitted through a limiter 22 to a demodulator. 23, and the demodulated luminance signal is supplied to a synthesizer 24.

During recording, as mentioned above, adjacent tracks TA
Even if a guard band is not provided between TB and TB, the modulated luminance signal is a high frequency signal, so when the head HA scans the track TA, it scans a part of the track TB, and the head HB scans the track TB. Even when it scans part of the track TA, no crosstalk occurs and the synthesizer 24 is supplied with a crosstalk-free luminance signal.

The reproduced output from the heads HA and HB is also supplied to a low pass filter 25 to extract a reproduced carrier color signal.

During recording, as mentioned above, by not providing a guard band between adjacent tracks T and TB, the head H
When A scans track TA, if it scans a part of track TB, the output of filter 25 at this time is
As shown in FIG. 7C, a signal cB interleaved with the signal CA is mixed as a crosstalk component, and when the head HB scans the track TB, this is mixed with the signal cB of the track TA. If a part is scanned, the output of the filter 25 at this time is a mixture of the signal cB and the signal CA interleaved in frequency with the signal cB as a crosstalk component, as shown in Fig. 7.

The output of the filter 25 is supplied to an inverting amplifier 26, and its (
-+) A signal obtained at the measuring output terminal is supplied to one input terminal of the switch circuit 27, a signal obtained at the (→ side output terminal) is supplied to the other input terminal of the switch circuit 27, and the switch circuit 2γ is , similar to the switch circuit 18 during recording by the switching signal Sc, the state is switched to the state shown in the figure in the section where the head HA should scan the track TA, and the state shown in the figure is changed in the section where the head HB is to scan the track TB. The state is alternately switched to a state opposite to that shown in the figure every horizontal section.

Therefore, in the section where the head HA scans the track TA,
The switch circuit 27 is connected through the (G) side output terminal of the amplifier 26.
, the above-mentioned signal CA mixed with the signal CB as crosstalk is obtained.

On the other hand, in the section where the head HB scans the track TB, the filter 25 obtains a mixture of the signal CB and the signal CA as a crosstalk component as described above.
Since the signal cB is nothing but the signal CA and the signal CA which are repeated alternately every horizontal section, in every other horizontal section where the head HB scans the track TB, the switch circuit 27 outputs the following signals: A mixture of the signal CA and the crosstalk component of the signal CA through the (a) side output terminal of the amplifier 26 is obtained, and in every other horizontal section, the switch circuit 27 outputs the ( The signal cA through the @ side output terminal is mixed with the signals as a crosstalk component, and as a result, even in the section where the head HB scans the track TB, the switch circuit 2
7, the signal cA mixed with the signal CB as a crosstalk component is obtained.

Therefore, the output of this switch circuit 27 is transferred to the frequency converter 28.
If the frequency is converted using a wave with a frequency of fs+fA, the frequency converter 28 will convert the subcarrier frequency and the original frequency fs from the predetermined track as shown in FIG. 7E and F, respectively. signals C8A and C8B
1 is obtained by mixing crosstalk components that are frequency interleaved with each other.

Therefore, if the output of the frequency converter 28 is supplied to the C-shaped comb filter 29, the crosstalk component is removed and the original carrier color signal Cs is obtained, as shown in FIG. 7G.

This carrier color signal Cs is supplied to a combiner 24 and combined with the luminance signal.

Therefore, a reproduced color video signal without crosstalk can be obtained at the output end 30.

By the way, in this case, the switching signal Sc is for the heads HA and H.
For example, it is "0" in the section where the head HA scans the tape 1, and it becomes "1" in the section where the head HB scans the tape 1. This can be obtained by supplying the AND gate circuit with a rectangular wave signal and a signal that is obtained by triggering a flip-flop circuit with a horizontal synchronization signal and is inverted every horizontal section.

However, during playback, in the section where the head HB scans the track TB, the switching signal Sc is not necessarily inverted so as to switch the switch circuit 27 as described above, but is reversed so as to switch the switch circuit 27 in the opposite manner. Sometimes I become accustomed to things that I do.

When the switch circuit 27 is switched in this way, signals can be obtained in the section where the head HB scans the track TB compared to the switch circuit 27, without considering crosstalk components.

Therefore, in this case as well, the head HA
Each time the reproduced output from the HB and HB is switched, the phase of the reproduced carrier color signal is reversed, and even if an APC circuit is provided, the same problem as described above occurs.

The present invention solves these problems, and a color video signal reproducing apparatus according to the present invention will be described below with reference to FIG. 8 and subsequent figures.

In the present invention, a phase switching circuit is provided in the loop of the APC circuit to switch the phase difference between the burst signal and the reference carrier wave every time the reproduction output from the head is switched.

The example shown in FIG. 8 is a case in which the present invention is applied to an apparatus for reproducing what has been recorded in a conventional manner, and a phase switching circuit 40 is inserted between frequency converters 35 and 28.

This phase switching circuit 40 includes a phase shifter 41 that shifts the carrier wave of frequency f8+fA obtained from the frequency converter 35 by 900, and the output of the frequency converter 35 and the phase shifter 41.
The switch circuit 42 is the same as the switch circuit 31 that switches the reproduction outputs from the heads HA and HB (switches for each field by the switch signal Sp).

Therefore, according to the device of the present invention, the phase difference between the burst signal from the circuit 36 and the reference carrier wave from the oscillator 33 immediately before the reproduction outputs from the heads HA and HB is switched is 9.
When the reproduction outputs from the heads H and HB are switched from the state of around 00 and the phase of the reproduced carrier color signal obtained from the filter 25 is reversed, the switch circuit 42 is also switched at the same time and the signal is supplied to the frequency converter 28. Since the phase of the carrier wave for frequency conversion changes by 90 degrees, the phase of the carrier color signal obtained from the frequency converter 28 ends up being 90 degrees.
Therefore, the phase of the parsed signal from circuit 36 also changes to 90
0, and the phase difference between this and the reference carrier wave from the oscillator 33 becomes 0 or 180°.

Therefore, the output of the phase detection circuit 37 becomes maximum, and the output of the oscillator 3
Accordingly, the frequency of the carrier wave for frequency conversion supplied to the frequency converter 28 changes immediately, and the phase of the carrier color signal obtained from the frequency converter 28 immediately becomes a predetermined phase, so that the APC loop is quickly stabilized. become

Therefore, there is no possibility that the normal hue will not be obtained at the beginning of the field, that is, at the top of the screen.

As in the example of FIG. 9, the phase switching circuit 40 may be inserted between the frequency converter 28 and the burst gate circuit 36.

Although not shown, there may also be a gap between the burst gate circuit 36 and the phase detection circuit 37, or between the reference oscillator 33 and the phase detection circuit 3.
It may be inserted between 7 and 7.

The example in FIG. 10 is a case where the present invention is applied to a reproducing apparatus that uses the special high-density recording/reproducing method explained in FIGS. 3 to 7, and as in the example in FIG. This is a case where the switching circuit 40 is inserted between the frequency converters 35 and 28.

It is clear that this example also has the same effect as described above.5 As mentioned above, according to the present invention, by simply providing a simple phase switching circuit, the playback outputs from a plurality of heads can be sequentially alternated. It is possible to prevent the phase shift of the reproduced carrier color signal that occurs when the reproduced carrier color signal is taken out, and to reliably obtain the reproduced carrier color signal having a predetermined phase over the entire field.

[Brief explanation of drawings]

Figure 1 is a plan view of an example of a rotating magnetic head device, Figure 2 is a system diagram of an example of a color video signal reproducing device, and Figures 8 to 1 show a special recording and reproducing method for color video signals. These are for explanation purposes. Figure 3 is a diagram showing the state of the magnetic gap of the rotating magnetic head, Figure 4 is a diagram showing the recording state on the tape, Figure 5 is a system diagram of the recording system, and Figure 6 is a diagram showing the state of the magnetic gap of the rotating magnetic head. Systematic diagram of regenerative system,
FIG. 7 is a diagram showing a frequency spectrum for the purpose of explanation.
FIGS. 8 to 10 are system diagrams of an example of the apparatus of the present invention. HA and HB are rotating magnetic heads, 21 is a high-pass filter, 23 is a demodulator, 25 is a low-pass filter, 28 is a frequency converter, 32 is an APC circuit, 33 is its reference oscillator, and 34 is its variable frequency oscillator. , 35 is its frequency converter, 36 is its burst gate circuit, 37 is its phase detection circuit, 38 is its integration circuit, 40 is its phase switching circuit, 4
1 is its phase shifter, and 42 is its switch circuit.

Claims (1)

[Claims] 1. A filter that sequentially and alternately extracts reproduced outputs from a plurality of heads and extracts a reproduced carrier color signal from the alternately extracted reproduced signals, and a frequency converter that converts the frequency of the reproduced carrier color signal obtained from this filter. a carrier wave for frequency conversion that detects the phase difference between the burst signal in the carrier color signal obtained from this frequency converter and the reference carrier wave obtained from the reference oscillator, and supplies the phase detection output to the frequency converter. an automatic phase adjustment circuit for controlling the frequency of the burst signal and the reference carrier; A color video signal reproducing device provided with a phase switching circuit that shifts the phase by a predetermined amount each time the reproduction output from the head is switched so that the phase difference is within the pull-in range of the automatic phase adjustment circuit.