JPS6334379Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a rotating head type magnetic recording and reproducing device (VTR) that records and reproduces color video signals. A studio equipped with a recording device and a time base corrector with a relatively simple circuit configuration.
This is what we are trying to provide on VTR.

The mainstream of magnetic recording and reproducing devices for color video signals is the helical scan type VTR, which uses a rotating head to form a video track diagonally on a tape. especially for home use
VTRs are compact and have sacrificed image quality to some extent compared to those for broadcasting, but at the expense of significantly reducing tape consumption, compact high-density recording models have been developed. For example, in a VHS system VTR, the diameter is 62 mm.
Color video signals are recorded diagonally onto a 1/2 inch wide tape using two video heads placed 180 degrees apart from each other on a 1/2 inch rotating cylinder.

Regarding broadcasting VTRs, 2-inch VTRs and 1-inch VTRs have traditionally been used as portable VTRs for news gathering (ENG), but because the devices are large and heavy, there is a strong need for smaller and lighter versions, and they have been developed for industrial use. The 3/4-inch U-standard STR, which was small and lightweight, came to be widely used for news reporting. However, this 3/4 inch U standard
Since a VTR has a cylinder diameter of 110 mm and a tape width of 3/4 inch, there are limits to miniaturization. Furthermore, as a video signal recording method, the luminance signal (approximately 3 MHz) and color signal (3.58 ± 0.5 MHz) are separated from the composite color video signal, and the separated luminance signal is frequency modulated on the high frequency side. The luminance signal and chrominance signal bands are limited because a method is used in which the frequency side is removed, the color signal is converted to a low frequency, and these are frequency multiplexed and recorded as a spectrum as shown in Figure 1. The normally reproduced luminance signal is -6 dB at 3 MHz, and the color signal band is from the subcarrier frequency (3.58 MHz).
It is about -6dB at a point 500KHz away. moreover,
In this recording method, since the color signal is a quadrature two-phase modulation signal, it is necessary to transmit both amplitude and phase information, and it is affected by VTR time axis fluctuations.
Hue unevenness and saturation unevenness occur on a color monitor, and since the band of the luminance signal is limited, the resolution is insufficient, and the image quality is unsatisfactory for broadcasting.

Furthermore, in the ENG system, dubbing is performed several times as shown in FIG. In Figure 2, 2-1 is a color camera and a portable VTR.
are shown integrated. This portable VTR
A news interview is conducted at 2-1, and the tape 2-4 on which the interview was conducted is played back on the first studio VTR 2-2, and the playback signal is recorded on the second studio VTR 2-3 for only the necessary period. Dubbing is performed by so-called electronic editing. Although not shown in FIG. 2, such dubbing is further performed one or two times as necessary. In this way, the dubbed signal is guided to the time base corrector (TBC) 2-5 in FIG. 2, and time base fluctuations are removed.
A color video signal for broadcasting can be obtained at the output terminal 2-6. As mentioned above, when there are many dubbing processes like this, the quality of 3/4-inch images deteriorates significantly, resulting in insufficient resolution, color bleeding, uneven hue, and uneven saturation.

In view of the above-mentioned drawbacks, the present invention provides a method for obtaining high-quality reproduced images suitable for broadcast news reporting, etc., and eliminates time axis fluctuations with a relatively simple configuration when correcting the time axis. The aim is to obtain stable, high-quality broadcast video signals.

Embodiments of the present invention will be described below based on the drawings. FIG. 3 is a plan view showing the head arrangement on the head cylinder in one embodiment, FIG. 4 is a front view of the same, FIG. 5 is a diagram showing the recording pattern on the tape, and FIG. 6 is a block diagram. .

In Figs. 3 and 4, A, A' and B,
B' represents two sets of heads arranged at the same height on the circumference of the cylinder at 180° intervals. The image tracks T A and T _B shown in FIG.
T _B is image track T _A ',
4 and 5, T _A and _{T B respectively} represent the track widths of the A and A' heads and the B and B' heads.
_TP represents the track pitch and _TS represents the space.
Now, the diameter of the cylinder, the number of rotations, the values of X and Y,
By appropriately determining the values of T _A , T _B , and T _S , the tape speed, and the angle between the tape and the recording path, the recording pattern shown in Figure 5 will be obtained. As an example, if T _A is set to be greater than T _B and the cylinder diameter is approximately the same as that of a VHS type VTR,
It can be set to record approximately 20 minutes using a 2-hour VHS cassette.

Now, one embodiment of the recording and reproducing method for obtaining high quality images according to the present invention is shown in FIG. 6, and will be described in detail. In FIG. 6, 1 is a luminance signal input terminal. Reference numeral 2 denotes a color difference signal input terminal, into which, for example, an RY signal or an I signal is input. The following will be explained as an I signal. 3 is another color difference signal input terminal,
For example, a BY signal or a Q signal is input.
The following will be explained as a Q signal. Each signal input terminal 1,
Inputs 2 and 3 correspond to the outputs of the color camera in the portable VTR for news reporting shown in Fig. 2, and are wideband luminance signals, I signals, and Q signals.

Now, the luminance signal from the luminance signal input terminal 1 is band-limited by a low-band filter 4 that limits the band to, for example, 4 MHz, and then a circuit (not shown) that clamps the luminance signal emphasizes the high-frequency components. The signal is passed through an emphasis circuit, a circuit that clips the signal to a level corresponding to the highest recordable frequency, and is led to an FM modulator 7. This FM modulator 7
Accordingly, the luminance signal is FM modulated to have a frequency deviation of, for example, 4.4MHz to 6.0MHz, and after being amplified by the recording amplifier 10, it is sent to the video head 15 since the switch _S1 is set to the R side during recording. is added to the recording medium and recorded on the recording medium with a spectrum as shown in FIG. 7A.

On the other hand, the I signal from the color difference signal input terminal 2 is, for example,
After being band-limited by a low-pass filter 5 with a 1 MHz band, and passing through a clamp circuit, an emphasis circuit, a clip circuit, etc. similar to the luminance signal described above, the frequency deviation is, for example, 5 to 6 M by the FM modulator 8.
Hz, the band is limited to approximately 3MHz to 8MHz by a bandpass filter 11, and the signal is guided to an adder 13.

Furthermore, the Q signal from another color difference signal input terminal 3 is band-limited by a low frequency filter 6 having a band of, for example, 0.5 MHz, and passed through a clamp circuit, an emphasis circuit, a clip circuit, etc. similar to the luminance signal described above. After that, the signal is FM modulated by the FM modulator 9 so that the frequency shift is, for example, 0.75MHz to 1.25MHz, and the band is limited to 0 to 2MHz by the low frequency converter 12.
It is guided to an adder 13. After adding the FM-modulated I and Q signals in this way and amplifying them in the recording amplifier 14, since the recording switch _S1 is connected to the R side, they are added to the video head 16 and sent to the seventh
The spectrum is recorded on the recording medium as shown in Figure B.

The luminance signal video heads 15 are heads A and A' in FIG. 3, and the color signal video heads 16 are heads B and B' in FIG.
By recording in this manner, the track width of the luminance signal can be increased, and since the chrominance signal is not frequency-multiplexed and superimposed on the luminance signal, a reproduced image with a high S/N and high resolution can be obtained. Also, although the track width of the chrominance signal is narrow, the I signal has a bandwidth that is approximately 1/1 that of the luminance signal.
4. The Q signal is about 1/8, which reduces triangular noise caused by FM modulation, and provides sufficient S/
N can be secured. usually portable
Since the VTR simply goes to the news gathering site and records it, it is sufficient that it has the functions described above. Therefore, the circuit size is not too large, and if it is configured based on a VHS type VTR, for example, the cylinder diameter is smaller than one based on a 3/4 inch U standard VTR, so it will be much more compact.
It is lightweight, and, as mentioned above, since the luminance signal and color signal are recorded in separate heads, there is no need for band limitation, and high-quality images can be recorded.

Since it is necessary to perform dubbing in a studio VTR, both the recording circuit described above and the reproduction circuit described below are required. Next, the reproduction circuit will be explained.

The FM modulated luminance signal reproduced by the video head 15 passes through the P terminal of the switch _S1 , and is amplified by the preamplifier 17. Although not shown, amplitude fluctuations due to uneven hitting of the tape head are removed by a limiter circuit. , a reproduced luminance signal is obtained by the FM modulator 18, the approximately 4 MHz band low frequency filter 19, and the de-emphasis circuit. On the other hand, video head 1
The FM color signal reproduced by 6 is the P of switch _S2 .
After passing through the side, the signal is amplified by a preamplifier 21, guided to a band wave generator 22 and a low band wave generator 23, and separated into an FM modulated I signal and an FM modulated Q signal. This 2
The signals each pass through limiter circuits similar to those for the luminance signal, and FM demodulated reproduced I and Q signals are obtained by FM demodulators 24 and 25, low-frequency amplifiers 26 and 27, and their respective de-emphasis circuits. . The timings of the obtained reproduced I signal, reproduced Q signal, and reproduced luminance signal are adjusted using the timing adjustment delay devices 28 and 20 so that their time timings match. In this way, when dubbing signals whose timings have been matched, the luminance signal, I signal, and Q signal are taken out from the terminal group 29. For example, in FIG. 2, the first studio VTR 2-2 is set to playback mode, and the VTR
The signal from terminal 29 of the second studio VTR2
If the studio VTRs 2-3 are connected to the input terminals 1, 2, and 3 of the VTR 2-3 and set to recording mode, baseband dubbing will be performed. It is necessary to play back the tape that has been edited in this way and convert it into a color signal for broadcasting. Therefore, these luminance signals, I signals, and Q signals are guided to encoder sections shown in FIG. 6 30 to 39 and TBC sections (time base correction sections) shown at 40 to 46.

For convenience of explanation, the operation will be explained starting from the TBC section.
The TBC section removes time axis fluctuations in the signal that occur in the VTR. The configuration method involves converting the video signal into a digital quantity using an AD converter, storing the video information in the digital memory using a clock according to the jitter, and reading it out using a regular clock that does not include jitter to correct the time axis. Things to do, CCD
Using analog memory such as (CHARGE COUPLED DEVICE), compare the phase of the sync signal containing jitter and the regular sync signal, and depending on the difference,
There are some that correct the time axis by changing the clock that drives the CCD and using the CCD as a variable delay line. Here, an example using the CCD described later will be described. A sync separator 41 converts the sync signal from the jitter-containing video signal coming from the encoder section.
A phase comparator 43 compares the phase of this with a signal from an internal periodic signal input terminal 42 that does not have jitter, and a VCO (voltage controlled oscillator) 44 is driven by the phase difference voltage. With this configuration, if the time axis of the video signal entering the CCD 40 is shorter than the local synchronization signal,
If the oscillation frequency of the VCO 44 is set to be low, the signal transmission time within the CCD 40 becomes longer, the time axis is automatically corrected, and a signal with time axis fluctuations corrected is obtained at the output terminal 46. At this time, the oscillation frequency of the VCO 44 is usually selected to be around four times the color subcarrier frequency fsc (3.579545 MHz in the case of the NTSC system). Also usually TBC
A color subcarrier corresponding to the jitter of the synchronization signal is output from the subcarrier. This is a 3/4 inch VTR
The jitter of the color signal of the low frequency conversion method used in ) is necessary for operation. This color subcarrier is 4/1
It is created in the countdown circuit 45.

Next, the operation of the encoder section will be explained. If the switch 37 is now turned to the a side, the counter 35 is triggered by the pulse of the 4fsc signal obtained through the quadrupling circuit 36. Also, the synchronous separation circuit 30
The counter 35 is reset R using the synchronization signal separated in synchronization. Although not shown, the pulses from the counter 35 form clamp pulses, blanking pulses, burst flag pulses, and the like. Also, it can be obtained from the midpoint side of the switch 37.
A balanced modulator 33 performs quadrature two-phase modulation of the I and Q baseband signals using pulses of the fsc signal, and the adder 34 adds them to the luminance signal to obtain a composite color signal. This signal is led to the TBC section, and a time-base corrected composite color signal is obtained at the output terminal 46.

However, even if there is no TBC section, there are many cases where it is desired to view images in color on a monitor. A crystal oscillator 38 is provided for this purpose. If the switch 37 is now turned to the b side, the color subcarrier is constant and does not include jitter, so the color signal modulated by quadrature two-phase with this color subcarrier is connected to the output terminal 39 of the color monitor. It can be observed by However, since the luminance signal does not pass through the TBC section, it contains some jitter. The composite color signal that can be observed at the output terminal 39 is a heterodyne mode signal in which the luminance signal and color signal are not interleaved, unlike the above-mentioned direct mode video.

In this way, the encoder section has a circuit that switches between the color subcarrier of the circuit that generates the fsc signal and the color subcarrier that has the same jitter as that included in the synchronization signal (including the luminance signal). This allows it to work in either mode.

Also, instead of providing the switch 37, two systems each of a counter, a quadrupling circuit, and a balanced modulation circuit are provided, one of which is always connected to a color monitor in heterodyne mode and used for monitoring color images, and the other is used for monitoring color images.
It can be connected to the TBC section and used exclusively for direct mode. This configuration is shown in FIG. Here, 33', 34', and 35' are 33, respectively.
These are a balanced modulator, an adder, and a counter having the same configuration as 34 and 35, 38' is a fixed oscillator having an oscillation frequency four times fsc, and 45' is a 1/4 countdown circuit.

FIG. 9 shows the encoder section and TBC section in more detail than in FIG. 6. Luminance signal Y is input terminal 5
It is input from 7. 30 is a synchronization separation circuit which separates and outputs a horizontal synchronization signal H and a vertical synchronization signal V, resets each counter 35, and outputs the horizontal synchronization signal H and vertical synchronization signal V.
and the input signal. A 4fsc pulse is obtained from the output of the quadrupling circuit 36, and the counter 35 is triggered. Pulses from each stage of this counter 35 are guided to a decoder 56 to obtain various timing pulses. 53 is a clamp pulse for clamping at a clamp position within the horizontal retrace period, 54 is a blanking pulse for removing noise in the horizontal and vertical retrace periods, and 55 is for forming a burst signal. burst flag pulses are obtained. 60 is an inverter that adds burst flag pulses of opposite polarity to the I signal and Q signal, respectively. 33a is a balanced modulator for I signal, and 33b is a balanced modulator for Q signal. The fsc is obtained from the midpoint side of the switch 37, and the I signal is modulated by this fsc. Q
The signal is modulated by fsc which is phase shifted by 90 degrees by a phase shifter 33c. By adding the modulated outputs of 33a and 33b, a quadrature two-phase modulated wave is obtained at 61. The adder 62 adds the quadrature two-phase modulated wave from 61, the luminance signal with the horizontal blanking period blanked, and the synchronization signal whose waveform has been shaped by separating the synchronization signal included in the luminance signal. A composite color signal is obtained at the output of the switch 64. Switches 37 and 64 are interlocked; if connected to the a side, a color signal with time axis correction can be obtained using the TBC section; if connected to the b side, time axis correction cannot be performed, but the color signal can be You can view color images.
Note that even if you connect the output of the a side of the switch 64 to the color monitor as it is, the color synchronization will not work properly because the color subcarrier changes on the time axis.
Unable to see normal color images. Further, the output of the switch 64 on the a side is guided to the TBC section.

The configuration of this TBC section is shown using a digital memory as an example. The composite color signal is exchanged into digital information by AD converter 65 and written to memory 66. The timing of writing to the memory 66 is controlled by the 4fscVCO 67. Write counter 68, 4fscVCO67,
The phase comparator 69 constitutes a phase lock loop, and the horizontal scanning frequency _H = obtained by counting down from the horizontal synchronization signal synchronously separated from the composite color signal from the a side of the switch 64 and the 4fscVCO 67.
2/455×4fsc) to obtain 4fsc that responds to the jitter included in the synchronizing signal, which is written into the memory 66 at a speed corresponding to the jitter. As mentioned above, the TBC section is usually provided with a color subcarrier output terminal that responds to jitter in the horizontal synchronization signal. This is obtained by the 1/4 down counter shown at 70. This is guided to the a side of the switch 37, and then the balanced modulators 33a and 33b
The I and Q baseband signals are quadrature two-phase modulated. By doing so, the luminance signal and the color signal contain the same jitter. Write this to the memory 66 with the 4fscVCO67 output including jitter,
Reading is performed using a clock from a fixed 4fsc crystal oscillator 72, and when converted into an analog signal by a DA converter 73, a time-axis corrected composite color signal is obtained at an output terminal 74.

However, if you want to monitor a color image without the TBC section, you can connect it to the b side of switches 37 and 64. At this time, the crystal oscillator 38 is oscillating fsc that does not include jitter, so the switch 64
In the composite color signal obtained on the side, the luminance signal has jitter, but the color signal has no jitter, so a color monitor can display a normal color image without losing color synchronization.
However, the normal interleaving relationship between the luminance signal and chrominance signal is broken, so the so-called standard
It's not an NTSC signal.

As mentioned above, according to the present invention, the luminance signal
The two chrominance signals are also FM modulated and frequency multiplexed, the luminance signal and the chrominance signal are recorded on tape using separate heads, the reproduced signals are FM modulated, and the baseband luminance signal and I signal,
By switching the subcarrier for quadrature two-phase modulation of the I and Q signals between a subcarrier that responds to the jitter contained in the luminance signal and a subcarrier obtained from a crystal oscillator. , color images can be monitored even without a TBC section.

Furthermore, as shown in FIG. 8, if two systems of balanced modulators are provided, outputs dedicated to TBC and dedicated to monitor can be taken out.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the recorded signal spectrum of a conventional VTR, Fig. 2 is a system diagram explaining ENG, and Fig. 3 is a plan view showing the head arrangement of a video signal recording and reproducing apparatus according to an embodiment of the present invention. 4 is a front view of the same, FIG. 5 is a recording pattern diagram of an embodiment of the present invention, FIG. 6 is a basic block diagram of a recording/reproducing system of an embodiment of the present invention, and FIG. FIG. 8 is a block diagram showing the main part of another embodiment of the present invention, and FIG. 9 is a detailed view of the main part of FIG. 6. 1, 2, 3... Input end, 7, 8, 9... FM modulator, 13, 34... Adder, 15, 16... Video head, 18, 24, 25... FM demodulator,
30, 41...Synchronization separation circuit, 33...Balanced modulator, 35...Counter, 36...4 multiplier circuit, 3
7...Switch, 38...Crystal oscillator, 40...
CCD (memory element), 43... Phase comparator, 44...
...Voltage controlled oscillator (VCO), 45...1/4 countdown circuit.

Claims (1)

[Scope of utility model registration request] At least two sets of heads A and B are provided, the luminance signal to be recorded is frequency modulated and recorded by head A, and the two baseband color difference signals to be recorded are
After converting it into a channel frequency modulation signal, it is recorded on the B head, and during playback, the signals from the A and B heads are each frequency demodulated to obtain a reproduced luminance signal and a reproduced color difference signal, which are then converted into a horizontal synchronization signal separated from the reproduced luminance signal. A first state in which synchronized color subcarriers are formed and the two baseband color difference signals reproduced by the color subcarriers are quadrature two-phase modulated; and a fixed color subcarrier is oscillated by a crystal oscillator, and the fixed color subcarrier is A circuit is provided to switch the two baseband color difference signals reproduced in the second state to or simultaneously exist in a second state of quadrature two-phase modulation, and add these to the reproduced luminance signal so that the two baseband color difference signals reproduced in the first state are quadrature modulated to the reproduced luminance signal. A composite color signal is created by interleaving the two-phase modulated reproduced color difference signal, and the composite color signal is guided to a time axis corrector to obtain a time axis corrected composite color signal. A video signal recording and reproducing device characterized in that it is used for observing a normal color image by guiding it to a color monitor or the like.