JPS59156095A - Video signal record reproducing device - Google Patents

Abstract

PURPOSE:To enable stable discrimination of color difference signals and realization of faithful reproduction of waveform by performing switching of color difference signal in back porch period during horizontal blanking period. CONSTITUTION:Line switch pulse is generated in a line switch pulse generating circuit 5 from a synchronizing signal (a) obtained in a synchronizing separator circuit 4, and the color difference signal is switched alternately every 1H to obtain line sequential color difference signal. When FM modulating the color difference signal, oscillating frequency is made different every 1H taking line discrimination in reproduction into consideration. For stable clamping, switching point of the line switch must be set at a position delayed from the position of synchronizing signal. However, if the delay is excessive, the switching point appears on the picture. Former waveform is reproduced correctly from the beginning of blanking to the switching point when the switching point is set during back porch period.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a video signal recording and reproducing device.
In particular, the present invention relates to an apparatus that performs FM modulation and records line-sequential color difference signals.

[Prior art]

A video tape recorder (hereinafter referred to as a VTR) is a common device for recording video signals, and can be roughly divided into two types: those for broadcasting and those for general home use.

For home use, small and lightweight devices are required, so improvements have been made to signal recording methods, but it cannot be said that sufficient image quality is necessarily achieved.

In order to improve the shortcomings of home VTRs, VTRs that record video signals using components have recently appeared. One of these methods is to achieve high image quality of chroma signals by converting color difference signals (for example, R-Y signals and B-Y signals) into line-sequential signals, performing FM modulation, and then recording and reproducing the signals. The drawback of this method is that it is necessary to return the reproduced signal to the original two continuous color difference signals without error. Therefore, in order to distinguish the color difference signals during playback, the horizontal blanking frequency is made different between the R-Y signal and the B-Y signal during recording, and this difference in frequency is detected during playback. A commonly used method is to determine whether the Y signal or the BY signal is being reproduced. However, in addition to varying the frequencies, the position at which the signals are switched is also important for determining color difference signals and faithfully reproducing waveforms.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality video signal recording and reproducing device that can realize stable discrimination of color difference signals and faithful reproduction of waveforms.

[Summary of the invention]

In the present invention, by switching the color difference signal during the bank porch period in the horizontal sylanking period, when clamping the reproduced color difference signal, the transient caused by switching does not become a problem, and the reproduction line discrimination is sufficient. It is possible to secure a wide gate pulse width that provides excellent performance.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a video signal recording and reproducing apparatus. 1 is the luminance signal input terminal 1. 2 is the first color difference signal (R
-Y) input terminal, 6 is the input terminal of the second color difference signal (B-Y), 4 is the sync separation circuit, 5 is the line switch pulse generation circuit, 6 is the pre-emphasis circuit, 7 is the FM modulation circuit s, a is a bypass filter (EPF), 9 is an adder circuit,
10 is a recording amplifier, 11 is a recording head, 12 is a recording medium, 13 is a line switch circuit, 14 is a pre-emphasis circuit, 15 is an FM modulation circuit, and 16 is a low-pass filter (
LPF), and the recording thread is configured as described above.

First, the recording system will be explained. The brightness signal input to the input terminal 1 is intensified in high-frequency components by a pre-emphasis circuit 6, subjected to tMM modulation in an FM modulation circuit 7, and low-frequency components are removed by an EPF 9, and then supplied to an adder circuit 9. Ru. The first color difference signal (R-?) input to the input terminal 2 and the second color difference signal (B-Y) input to the input terminal +6 are sent to the line switch circuit 15 at 1E (H is the horizontal scanning period). (representing 0)) are switched alternately and line-sequentialized. The control signal for line sequentialization is generated by extracting a synchronization signal from the luminance signal in a synchronization separation circuit 4 and in a line switch pulse generation circuit 5. The line-sequential color difference signal is sent to a pre-emphasis circuit 14.
The high frequency band is emphasized, the signal is subjected to lj'M modulation in the FM modulation circuit 15, and only necessary components are extracted in the LPF 16 and supplied to the addition circuit 9. An adder circuit 9 mixes a signal obtained by FM modulating the luminance signal and a signal obtained by FM modulating the color difference signal.

This FM signal is amplified by a recording amplifier 10 and then recorded on a recording medium 12 via a recording head 11.

Next, the reproduction system will be explained. 17 is a playback head, 18
is a regenerative amplifier, 19 is an HPF, 2o is an FM demodulation circuit, 2
1 is L P /', 22 is a de-emphasis circuit, 25
is an LPF, 24 is a 1B delay circuit, 25 is a line discrimination circuit, 26 is a line switch circuit, 27 and 60 are FM demodulation circuits, 28 and 51 are LPFs, 29 and 62 are de-emphasis circuits, 34, 55, and 56! Clamp circuit, 63
67 is an encoder circuit, and 6B is an output terminal.

The operation of each part will be briefly explained along the signal flow. The signal recorded on the recording medium 12 is reproduced by the reproduction head 17,
The reproduced minute signal is amplified to a sufficiently large level by the regenerative amplifier 18 and supplied to the HPF+9 and the LPF 251. The FM luminance signal is extracted at HI'F1q (lPM luminance signal is
The demodulation circuit 20 demodulates the signal into a video signal, which passes through the LPF 20 and the emphasis circuit 22 and returns to the original luminance signal.

On the other hand, for the chroma signal, after the P'M line sequential color difference signal is extracted by the LPF 2s, it is sequentially processed by the 1H delay circuit 24, the line discrimination circuit 25, and the 2 inch circuit 26 (R-
Two FM signals, F) and (B-Y), are obtained. This 2
FM demodulation circuits 27, 50,
LPF2B, 51, de-emphasis circuit 29, 52
The signal is then returned to (RY) and (B-Y) color difference signals.

The luminance signal and the two color difference signals are transferred to the next clamp circuit 34,
After being clamped at 35 and 56 and subjected to DC reproduction, it is converted by an encoder circuit 57 into a television signal in which a luminance signal and a general color signal are mixed, and is output from an output terminal 68.

FIG. 2 shows waveforms at various parts of the recording system.

- is a luminance signal, (1') and (tsu) are two color difference signals (R
-Y), (B-)'), g) is a line-sequential color difference signal, (3) is a line switch pulse, and (power)
is a synchronization signal separated from the luminance signal CY).

A line switch pulse (3) is generated from a synchronization signal W) obtained by a synchronization separation circuit 4 in a line switch pulse generation circuit 5, and color difference signals are alternately switched every 1B to obtain a line-sequential color difference signal. When performing P'M modulation on this color difference signal, the oscillation frequency is varied for each 1R in consideration of line discrimination during reproduction. As a result, for example, the blanking of (R-y) is 1.2 MHz, and the blanking of (B-Y) is 1.2 MHz.
The frequency is 5 MHz, and this frequency difference is used for discrimination.

Next, the position of the line switch will be explained.

The playback line switch must be in the same position as it was during recording. This is because a frequency offset is added during recording, so if there is a difference between recording and reproduction, there will be a difference in the blanking of the reproduced signal. However, even if recording and playback are the same, whiskers occur in the blanking of the playback signal.

FIG. 3 shows the configuration of the reproducing line switch circuit, and FIG. 4 shows the waveforms of the FM signal and demodulated signal.

Line switch times #! 126 is made up of two switches 40 and 41, and the signals before and after the 1B delay circuit 240 are switched every 1B by a control signal, resulting in continuous (N-Y)
and (B-Y) FM signals are obtained.

Figure 4- shows the input signal of the 1B delay circuit 24, (A)
is the output signal of the 1B delay circuit 24, (1) is the (RY) signal output from the line switch circuit 26, and (2) is the (B-y) signal. As shown in (1) and (2), the output of the line switch circuit 26 is a continuous signal, but since the signal around 1B is switched, the phase becomes discontinuous at the switching point. When this signal is F-ki demodulated, a large transient occurs at the switching point, and as it passes through the LPF and de-emphasis circuit, it becomes a long-tailed noise. The band of the color difference signal is relatively narrow (15MEz, although it varies depending on the recording method etc.)
(approximately 1 MHz in the device of this embodiment), so the LP
F and de-emphasis cause a long tail, and the phase discontinuity occurs every time, so the noise waveform also becomes 1.
It differs from H to H, and significantly damages the blanking waveform. As a result, there is a possibility that a clamping error will occur in the next-stage clamping circuit M35, M56. When creating a line switch pulse, it is easiest to use a synchronization signal of the luminance signal and switch at the rising edge of the synchronization signal. FIG. 4(3) shows the reproduced waveform of the diene'phasis circuit output when the switching point is set at this position. Except for the front porch period, the blanking waveform is completely different from the original signal. It is easiest to use a synchronization signal separated from the luminance signal as the clamp pulse, but clamping such a signal will result in a clamp error, which will significantly degrade the image quality. Although this problem can be solved by using a front porch or a lamp, the problem arises that the circuit becomes complicated because it is necessary to delay the separate synchronization signal. Furthermore, since the front porch period is about 2 μsec, the clamp period needs to be even shorter, about 1 μsec. In addition, the clamp pulse synchronization signal must be generated with a time delay of about 1H, and there is a risk of clamping outside the blank period or clamping transient noise due to delay time drift or equipment jitter, so it is not possible to clamp stably. The problem also arises that it is difficult to do so.

From the above, for a stable ramp, the switching point of the line switch must be set at a position that lags behind the position of the synchronization signal. But if you slow it down too much, a switching point will appear on the screen. Considering the amount of overscan, it is necessary to set the switching point at least within the blanking period.

4th hardness) is a reproduced waveform when the switching point is set in the back porch period as shown in FIG.

As is clear from the figure, since the original waveform is correctly reproduced from the start of blanking to the switching point, ramping can be performed reliably. Furthermore, the synchronization signal separated from the luminance signal can be used as it is as a clamp pulse, which simplifies the circuit.

The switching points of the line switches have been explained above from the viewpoint of clamp performance, but there are also limitations due to the performance of line discrimination during S' reproduction. FIG. 5 shows a part of a typical configuration of the line discrimination circuit 250, and its operation will be briefly explained below together with FIG. 6 showing waveforms of each part. The input terminal 50 has an F
The M color difference signal (FIG. 6 (7)) is input, and the signal is extracted by the gate' circuit 51 only during the period of the gate pulse (FIG. 6 (A)) supplied from the gate pulse input terminal 59.
The output has a frequency fR every 1H as shown in Figure 6 (2).
, fs is obtained. This signal is a filter circuit with a very high Q.

52, and the difference in frequency is converted into a difference in imaging width through an envelope detection circuit 53 at the next stage. (See Figure 6)
, (3)) Furthermore, the 172B gate circuit 54 extracts and separates the ftt component and the fn component every 1H, and the ripples are suppressed in the next integrating circuits 55 and 56, and the signal is converted into a DC signal with a different voltage. Become. These two signals are compared in voltage by a comparison circuit 58, and the magnitude relationship between the voltages is outputted to the output terminal 58 as a digital signal. 172H gate circuit 5
If the frequency relationship of the signal extracted at 4 is reversed, the output terminal 5
Since the signal No. 8 is inverted, line discrimination can be performed.

By the way, even if the Q of the filter circuit 52 were made infinite, a signal would appear in the output of the gate circuit 51 at a location where it should not originally appear. This is because the signal is gated in bursts, which broadens the spectrum. In addition to the fact that the Q of the filter circuit 52 is actually finite, signal leakage due to the spread of the spectrum makes line discrimination difficult. FIG. 7 shows the calculation results of the frequency response when the frequency (fR) corresponding to the blanking of the color difference signal (RY) is 1.2 MJlz and the width of the gate pulse is T. If T is chosen to be 10μεtc, exactly 13 ME,! The response becomes zero, and (B-
I') corresponding to the blanking of the color difference signal, e, (
By setting fB> to 16 MHz, leakage from fR to frt can be eliminated.

On the other hand, as T becomes narrower from 10 μsec, the amount of leakage increases. Male 8 figure, fs 1.2MHz, fB
When 1.5 ME z, the gate width T and j from j
This shows the relationship of leakage to B. T to 10
If it is μsec, the amount of leakage can be reduced to zero, which has the effect of maximizing line discrimination performance. In this case, the switching point of the line switch may be set very close to the end of blanking. If the gate width is narrowed, the amount of leakage increases, or if it is -5 dB or less, line discrimination is possible, and the required gate width is about 45 μsec or more. A synchronization signal is a pulse that satisfies this condition. Since the synchronization signal separated from the luminance signal can be used as it is as a gate pulse, the circuit is simplified, and the switching point of the line switch can be selected anywhere during the back porch period.

Although FIG. 1 shows a configuration in which line sequentialization is performed and then P'M modulation, it is clear that a similar effect can be obtained by FM modulating each signal and then performing line sequentialization.

〔Effect of the invention〕

According to the present invention, line discrimination can be performed stably, blanking of color difference signals can be faithfully reproduced, and complicated signal processing is not required, so that a high-quality and inexpensive video signal recording and reproducing device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a video signal recording and reproducing apparatus according to the present invention, FIG. 2 is a waveform diagram of each part of FIG. 1, and FIG.
The figure shows the configuration of the reproduction line switch circuit in Figure 1. Figure 4 is a waveform diagram explaining the operation of Figures 1 and 3. Figure 5 shows the line discrimination circuit in Figure 1. FIG. 6 is a waveform diagram explaining the operation of FIG. 5, and FIGS. 7 and 8 are characteristic diagrams showing the spread of the spectrum due to the gate. 4.55... Synchronous separation port P, 5... Line switch pulse generation circuit, 8, 15... P' M modulation circuit, 1
1... Recording head, 12... Recording medium, 13.26
... line switch circuit, 17 ... playback head, 2
5... line discrimination circuit, 54. ;5,56...clamp circuit. Proxy defense 1 + - Akira Takahashi Ha 1st prisoner, 2 2nd group 3rd ward 4th ward d

Claims (1)

[Claims] A device for recording on a recording medium a P'M signal modulated by a luminance signal and a P'M signal modulated by two pre-emphasized color difference signals, which are alternately switched every horizontal scanning period and line-sequentialized. A video signal recording and reproducing apparatus characterized in that the switching of the line sequentialization is performed during a back porch period of horizontal blanking of the luminance signal.