JPH0524718B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a recording circuit for a video tape recorder that records luminance signals, color signals, audio signals, pilot signals, etc. on a video track, and particularly relates to a recording circuit for a video tape recorder that records luminance signals, color signals, audio signals, pilot signals, etc. on a video track. The present invention relates to a recording circuit suitable for recording the above signals on a tape and a vapor-deposited tape.

[Prior art] Conventional video tape recorders are designed to use only iron oxide tape, so different types of tape such as high-performance coated metal tape or vapor-deposited tape are used. I couldn't do it. The signals recorded on the video track on the videotape may include frequency-modulated luminance signals, audio signals, low-frequency converted chroma signals, tracking control pilot signals, and PCM-converted audio signals. Since these signals each have the optimum recording level and equalization characteristics for the tape used, the recording circuit of the video tape recorder must be switched so that each signal has the optimum characteristics for each tape.

[Object of the Invention] An object of the present invention is to provide a recording circuit for a video tape recorder that eliminates the drawbacks of the prior art and makes it possible to write each signal under optimal conditions on a metal-coated tape or a vapor-deposited tape. It's about doing.

[Summary of the Invention] The present invention uses a recording/reproducing metal head with excellent saturation characteristics to saturately record frequency-modulated luminance signals and audio signals converted to PCM, and also records the above signals as a high-frequency bias. After mixing multiple signals (e.g., a low-converted chroma signal, a frequency-modulated audio signal, and a pilot signal), the recording level is set to be different for each tape, metal-coated tape and vapor-deposited tape. Provide a current level switching circuit to

Conventionally, the optimum recording current for signals recorded in saturation with metal-coated tapes is 2 to 3 dB higher than that of vapor-deposited tapes, and conversely, the optimum recording current for signals recorded in bias is 1 to 2 dB higher for vapor-deposited tapes; The side wave enhancement effect was smaller with vapor-deposited tape, and it was thought that compensation for these effects was necessary.

This means that the magnetic layer thickness of the metal coated tape is 3~
It was estimated from the fact that the thickness of the vapor-deposited tape is about 0.1 μm, compared to 6 μm, and that the Hc is about 1300 and about 900. When we actually conducted experiments using ferrite heads and sendust bulk heads, we obtained results that were consistent with the above common knowledge.

However, when we found the optimal recording conditions for metal-coated tape and vapor-deposited tape using a video head made by sputtering Sendust thin films with a thickness of 5 to 10 μm, we found that the metal-coated When the optimum recording current determined for the tape was used for the vapor-deposited tape, the C/N
It was found that there was almost no deterioration of the tape, and the lower side wave enhancement effect was extremely similar to that of the coated tape. The optimum recording current for an actual vapor-deposited tape may be 1 to 2 dB lower than that for a coated tape, but even with an overcurrent of 1 to 2 dB, C/N deterioration hardly occurs, and conversely, the frequency-modulated luminance In the case of a signal, the energy of the lower sideband is nicely emphasized, resembling the characteristics of painted tape. Furthermore, the recording current for bias-recorded signals can be set to a large value, so that the reproduction level when a vapor-deposited tape is reproduced can be increased, and the difference from the reproduction level of a coated tape can be reduced.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the frequency characteristics when recording and reproducing the metal-coated tape and the vapor-deposited tape used in the present invention using a Sendust sputter head. In FIG. 1, 1 is the characteristic of the metal-coated tape, and 2 is the characteristic of the vapor-deposited tape.The reproduction level of the coated tape is higher below 2MHz, and the reproduction level of the vapor-deposited tape is higher above 2MHz.

FIG. 2 is a diagram showing an example of the output signal spectrum of the recording circuit of the present invention. For the signal recorded on the video track shown in FIG. 7, the solid line indicates the recording current for the coated tape. The dotted line indicates the recording current level for the vapor-deposited tape. In Fig. 2, 3 is a pilot signal whose frequencies are f ₁ ≒6.5f _H , f ₂ ≒7.5f _H ,
f ₃ ≒10.5f _H , f ₄ ≒9.5f _H (however, f _H is the horizontal synchronization frequency), and the recording level is the coating level, assuming that the carrier level of the frequency-modulated luminance signal (hereinafter referred to as Y _FM ) is OdB. It is approximately -29dB for shaped tape and -25dB for vapor-deposited tape. 4 is a low frequency converted chroma signal (hereinafter referred to as _CL ), and the frequency is
(47 + 1/4) f _H in NTSC system, (47 -
1/8) f _H , and the recording level was set to -14 dB for coated tape and -10 dB for vapor-deposited tape. 5 is a frequency modulated audio signal (hereinafter referred to as A _FM
), the frequency was chosen to be 1.5±0.1 MHz, and the recording level was chosen to be -25 dB for coated tape and -21 dB for vapor-deposited tape. 6 is the lower sideband wave of Y _FM , 7 is the carrier of Y _FM , and 8 is the upper sideband wave of Y _FM , and the carrier frequency is 4.2MHz due to synchronization degradation.
The white peak was selected as 5.4MHz, and the recording level was OdB.
The same recording level has been selected for both coated tape and vapor-deposited tape.

FIG. 3 is a diagram showing an example of the output spectrum of the recording circuit of the present invention, and shows a signal recorded on the overlap track shown in FIG. 7. In Figure 3, 3 is the pilot signal and the recording level is -
25dB was selected, and the recording level was chosen to be the same for coated tape and vapor-deposited tape. 9 is
Audio signal converted to PCM (hereinafter referred to as A _PCM )
10 is the carrier of A _PCM , 11 is the lower sideband wave of
A This is the upper sideband wave of _PCM , and the recording level is set to OdB, which is the same for both coated and vapor-deposited tapes.

FIG. 4 is a diagram showing the relationship between the recording current and the reproduction level at 5 MHz, and 12 shows the characteristics of the coated tape.
13 shows the characteristics of the vapor-deposited tape. The optimum recording current for vapor-deposited tape is about 2 dB lower than that for coated tape. However, even when recording is performed on a vapor-deposited tape using the optimum current for the coated tape (that is, recording at a recording current that is 2 dB higher than the optimum recording current for the vapor-deposited tape), the deterioration in the playback level is 0.5 dB or less, which is sufficiently permissible.

Figures 5 and 6 show the cross-modulation characteristics of the tape head system, and Figure 5 is a recording spectrum diagram.
FIG. 6 shows a spectrum diagram of the reproduced signal, where the solid line shows the level of the coated tape and the dotted line shows the level of the vapor-deposited tape. In the diagram, 14 is _CL carrier, 15 is Y _FM
16 is a spurious signal having a frequency of (Y _FM -2C _L ), and 17 is a spurious signal having a frequency of (Y _FM - C _L ).

If the recording level of the Y _FM carrier 15 is selected to be approximately 2 dB higher than the optimum recording current, the reproduction level of the Y _FM carrier will be approximately +3 dB, assuming that the coated tape is OdB, and the reproduction level of the vapor-deposited tape is approximately +3 dB.

The recording level of C _L carrier 14 is spurious 1
6 and 17 are preferably as high as possible within the range below the allowable value. In Figure 5, the _CL recording level of the coated tape is -14 dB, and that of the vapor-deposited tape is -14 dB.
It is set at 10dB. At this time, the _CL playback level is approximately the same regardless of the tape, as shown in FIG. The spurious level is approximately +3 dB higher than that of the painted tape.

Since the allowable value of spurious is determined by the value relative to the carrier level of Y _FM , the spurious characteristics are almost the same in this state.

If the Y _FM recording level of the vapor-deposited tape is selected as the optimum recording current of the vapor-deposited tape, the spurious 1
6, 17 to be equivalent to Figure 6,
It is necessary to set the recording level of _CL to -12dB. The reproduction level of C _L at this time is -2 dB lower than that of the coated tape. In this way, the vapor deposition tape
Selecting the Y _FM recording current to be larger than the optimum recording current has the advantage of improving the reproduction level of the bias-recorded C _L , A _FM , and pilot signals.

As shown in FIG. 1, there is also a difference in frequency characteristics between the coated tape and the vapor-deposited tape. This difference is caused by recording the Y _FM signal at the optimum recording current for each tape.
There is no problem with the reproduced image quality of coated tape, but the reproduced image quality of vapor-deposited tape lacks resolution and becomes blurry. Conversely, if a coated tape is recorded at the optimum recording current, and a vapor-deposited tape is recorded at a current larger than the optimum recording current, the reproduced image quality of the vapor-deposited tape will be similar to that of the coated tape, and the problem will disappear. . This is because increasing the recording current by 2 dB means emphasizing the lower sideband, and from this point of view as well, it is preferable not to switch the recording current for Y _FM rather than tape.

FIG. 7 is a diagram showing an embodiment of a tape pattern formed on a video tape by the recording circuit of the present invention. In FIG. 7, diagonal tracks 19, 20
is formed by winding a video tape around a rotating cylinder at an angle of 200 degrees or more, 19 is a video track corresponding to a winding angle of about 180 degrees, 20 is an overlap track corresponding to an overlap winding part, 21, Reference numeral 22 indicates optional tracks provided on both sides of the tape, 23 indicates the tracing direction of the video head, and 24 indicates the running direction of the video tape.

FIG. 8 is a diagram showing an example of the frequency characteristics of the recording equalizer used in the present invention. FIG. 9 is a block diagram showing one embodiment of the recording circuit of the present invention.

In FIG. 9, 70 is an audio signal input terminal;
42 is a circuit that converts the analog signal into PCM and compresses the time axis to approximately 1/7, 38 is a circuit that sets the recording current of A _PCM , 71 is a video signal input terminal, 51
is an AGC that controls the brightness signal level to a constant value
(Automatic Gain Control) circuit, 49 is an LPF for extracting the luminance signal, 48 is a C _pnb filter for removing the color subcarrier of the NTSC system,
47 is a clamp circuit that fixes the voltage at the peak of the synchronization signal to a constant value, 46 is a dynamic emphasis circuit, 45 is a main emphasis circuit, 44 is a frequency modulator, 43 is an HPF, and 39 is a recording of Y _FM. Current setting circuit, 62 is BPF for extracting chroma signal,
60 controls to keep the birth level at a constant value
ACC (Automatic Color Control) circuit, 59 is a circuit that boosts only the burst level by 6dB, 58
is a dynamic enhancement circuit, 57 is a frequency converter, and 56 is a carrier generator {(47+1/4f _H +
f _SC } or {(47-1/8) f _H + f _SC }. However, f _SC is the color subcarrier frequency. 55 is an LPF, 72 is an audio signal input terminal, 66 is a non-linear circuit, 65 is an emphasis circuit, 64 is a frequency modulator, 69 is a pilot signal generator, 54 is a mixer, and 53 is a recording equalizer, an example of which is shown in FIG. , 52 and 68 are recording level switching circuits, 67 is a device for detecting the type of tape, 4
0, 41 is a recording current level setting circuit, 34, 3
5, 36, and 37 are signal switching circuits, which are connected to the black circle (upper side) when the video head is recording an overlap track, and to the white circle (lower side) when recording a video track. .
Reference numerals 30, 31, 32, and 33 are buffer amplifiers with flat amplitude characteristics, 28 and 29 are write amplifiers with flat amplitude characteristics, 27 is a rotary transformer, and 26 is a video head. 50 is a detector that detects the amplitude of the luminance signal.

A feature of the embodiment shown in FIG. 9 is that the recording level switching circuit 52 is installed on the output side of the mixer 54. By doing so, the recording level switching circuit can have an extremely simple configuration.

FIG. 10 shows an example of a recording level switching circuit.
In Fig. 10, 73 is an input terminal, 74 is an output terminal, and 75 is a control terminal. _Q1 is conductive when recording on coated tape, and _Q1 is cut off when recording on vapor-deposited tape. . If 201og (R ₂ /R ₁ +R ₂ ) is set to -4dB, the characteristics shown in Figure 2 can be obtained.

Another feature of the embodiment shown in FIG. 9 is the location where the recording equalizer 53 is installed. The recording equalizer 53 is necessary for the output signal _CL of the LPF 55, but it may also equalize the _AFM and pilot signals. In this case, since the equalization circuit acts to suppress harmonic spurious, there is no need to separately provide a spurious suppression filter.

Recording current level setting circuit 41 in FIG.
The recording level switching circuit 68 is necessary to accurately set the pilot signal level recorded in the overlap track section, but even if the recording level of the pilot signal is increased, the error rate of A _PCM will only slightly deteriorate. In some cases, the recording current level setting circuit 41 and the recording level switching circuit 68 may be omitted, as long as the level is set higher than the level recorded on the video track. FIG. 11 is a block diagram showing an embodiment of the recording circuit of the present invention when there is no need to record A _PCM . Figure 11 is the 9th
The switches 34, 35, 36, and 37 in the figure have been removed, and their explanation will be omitted.

[Effects of the Invention] According to the present invention, the recording characteristics of the metal-coated tape and the vapor-deposited tape can be made equal by simply using a simple recording level switching circuit, and the reproduced image quality of the luminance signal can be made the same. By using the frequency modulated luminance signal as a bias, it is also possible to equalize the reproduction levels of recorded signals.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing an example of the characteristics of the tape used in the present invention, FIGS. 2 and 3 are characteristic diagrams showing an example of the recording current spectrum generated from the recording circuit of the present invention, and FIG. 4 is a characteristic diagram showing an example of the characteristics of the tape used in the present invention. 5 is a characteristic diagram showing an example of the recording current spectrum, and FIG. 6 is a characteristic diagram showing the characteristics of the tape used in the present invention.
A characteristic diagram showing an example of head system spurious characteristics,
FIG. 7 is a diagram showing an example of a tape pattern formed by the recording circuit of the present invention, FIG. 8 is a characteristic diagram showing an example of the characteristics of the recording equalizer used in the present invention, and FIG.
10 is a block diagram showing an embodiment of the recording circuit of the present invention, FIG. 10 is a circuit diagram showing an embodiment of the recording level switching circuit used in the present invention, and FIG. 11 is a block diagram showing another embodiment of the recording circuit of the present invention. FIG. 2 is a block diagram showing an example. 49... LPF for luminance signal sampling, 44... Frequency modulator, 57... Frequency converter for chroma signal low-frequency conversion, 69... Pilot signal generator, 54
... Mixing circuit, 52 ... Recording level switching circuit, 6
7... Tape discrimination device.

Claims (1)

[Claims] 1. A luminance signal that is frequency-modulated on a metal-coated tape and a vapor-deposited tape, a chroma signal that is frequency-multiplexed to the lower band of the lower wave signal of the luminance signal, and a chroma signal that is frequency-multiplexed to the lower band of the lower wave signal of the luminance signal. A device that simultaneously records a frequency-multiplexed pilot signal on a tape using a magnetic head, which uses a magnetic head in which a thin metal film constitutes the main magnetic circuit, and also sets the recording current level of the frequency-modulated luminance signal. a recording level switching circuit that switches the recording current level of the chroma signal; and a recording level switching circuit that amplifies the output signal of the recording level switching circuit and the output signal of the recording level setting circuit to supply a recording current to the magnetic head. and a device for determining the type of tape, and the recording level setting circuit allows the frequency-modulated luminance signal to The recording current value is set to the optimum recording current value when recording on a substantially metal-coated tape, and the level switching circuit is controlled by the discrimination device. 1. A recording circuit for a video tape recorder, characterized in that the recording current level of the chroma signal is made larger than that when the signal is recorded in the chroma signal.