JPS6093889A - Video emphasis circuit of recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent noise due to crosstalk at a horizontal synchronizing signal by outputting a signal not applied with emphasis and a signal subject to emphasis while being switched, selected and syntehsized at a horizontal synchronizing signal period and a video image period. CONSTITUTION:A luminance signal Y after a band pass filter is delayed by tau1 at a delay circuit 22, inputted to a pre-emphasis circuit 5 as a signal YD and becomes an output YP. The YD is led to an input terminal 23b of a switching synthesis circuit 24 through a lead 25. The outputs TP, YD are switched and synthesized during a prescribed period by using a switching signal X1 fed to the circuit 24 and led to an FM modulator 26. A switched and synthesized output YS formed at it is led to an output terminal 27 as an FM luminance signal YFM having a frequency in response to the signal level. Furthermore, a luminance signal Y is inputted to a synchronizing separator circuit 4, a horizontal synchronizing signal HS from the signal Y and the pulse at the synchronism tip, i.e., a horizontal synchronism pulse HP is inputted to a pulse width expanding circuit 28.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a video emphasis circuit in a recording/reproducing apparatus such as a video tape recorder or a video disc player, and particularly relates to a video emphasis circuit for adjusting the position of a horizontal synchronizing signal for each adjacent rack. The present invention relates to a video emphasis circuit that is effective in reducing beat disturbance due to crosstalk in the horizontal synchronizing signal portion when recording is performed with a shift.

[Technical background of the invention]

In general, recording and reproducing devices such as video tape recorders (hereinafter referred to as VTRs) and video disc players (hereinafter referred to as VDRs) (some VDRs can change the recording signal) are unable to eliminate crosstalk from adjacent tracks. This is an important issue. For this reason, some video recording systems have guard bands between video tracks, but recently, recording systems that eliminate guard bands have been adopted with emphasis on increasing recording density. In this method, there is a problem of crosstalk.For example, in a VTR.

By alternately recording with two heads with different azimuth angles, adjacent tracks have different magnetization directions, and during playback, the azimuth loss of the heads is used to pick up signals (crosstalk components) from adjacent tracks. I'm trying to solve the problem without worrying about it.

However, the effect of this azimuth loss becomes weaker as the signal component has a lower frequency, that is, a longer wavelength.

For this reason, for example, in a cassette-type VTR, the color signal recorded after low frequency conversion is recorded with the phase reversed by 180 degrees every IH (H is a horizontal scanning period), and during playback, the color signal is recorded with the phase reversed by 180 degrees. The noise component due to crosstalk is removed by the operation. Here, the recording circuit system of the cassette type VTR is
This will be explained with reference to the diagram.

In FIG. 1, an input terminal 1 is a terminal that receives a television signal sent from a tuner (not shown), and a brightness signal Y is separated from the television signal TV at this input terminal 1 by a low-pass filter 2, and a band-pass filter 3 The color signal Cr is separated by the synchronization separation circuit 4, and the horizontal synchronization signal Hs and the vertical synchronization signal Vs are separated by the synchronization separation circuit 4. The luminance output Y of the low-pass filter 2 is high-frequency emphasized by a pre-emphasis circuit 5 and input to an FM modulator 6. This FMMl171i6 has a frequency of, for example, 3.6MIz to 4MIz depending on the level of the luminance signal.
, 8 M)Tz is generated and output to the recording amplifier 7 as a luminance signal YFM for recording. The output of the recording amplifier 7 is supplied to a mixer 8 which combines it with a color signal.

On the other hand, the color signal after passing through the bandpass filter 3 is A
The signal is input to a ce (automatic color saturation control) circuit 9, and the color signal level is adjusted. This color signal is 3.58 M
Since it is a Hz signal, it is input to the low frequency converter 10 which converts it into a low frequency signal. To this low frequency converter 10, 4.
A 27 MHz modulation signal is input, and the frequency is 3.58
The color signal of Ml(z) and the modulation signal of 4.27 Ml(z
A low frequency converted color signal of Hz is formed as the output of the converter 10. This low frequency converted color signal is input to the mixer 8, combined with the luminance signal YFM input to the mixer 8, and supplied to the primary side of the rotary transformer 110.

The signals induced on the secondary side of the rotary transformer 11 are input to the video heads A and B while being switched every one field period, and are recorded on the tape 12. ).

Further, the horizontal synchronization signal Hs of the synchronization separation circuit 4 is A
input to the FC circuit 13, and the AFC circuit 13 with 688
A local oscillation signal of 1G (z) is formed. This local oscillation signal is input to the frequency converter 14, and
It is mixed with the 3.58 MHz reference signal from the reference oscillator 15 to form the aforementioned 4.27 MHz low frequency conversion modulation signal.

In this manner, the television signal is FM-recorded in which the luminance signal Y is an FM signal with a frequency deviation of 1 or 2 MHz, and the one color signal Cr is a low frequency converted color signal with a low carrier wave. Note that the low frequency conversion color signal is recorded onto one video head with the phase reversed by 180° for each IH by a phase inversion circuit (not shown).

Here, a pre-emphasis circuit 5 provided between the low-pass filter 2 and the FM modulator 6 emphasizes the level of high-frequency components in order to escape from the triangular noise peculiar to FM modulation. The luminance signal Y with the high-frequency emphasis is as shown in FIG. 2.

In FIG. 2, (a) shows the luminance signal Y before being input to the pre-emphasis circuit 5, and (b) is a waveform diagram showing the luminance signal Y with high-frequency emphasis. In these figures, T is I
H period is shown, T1 is a horizontal synchronizing signal period, and T is a video period. Further, this waveform indicates a positive video signal in which the synchronization signal level side is the black level.

In this way, when the luminance signal Y passes through the pre-emphasis circuit 5, the luminance signal Y has a luminance changing portion with many high-frequency components.

A spike SP is generated on the synchronization signal level side and the white level side. Then, the luminance signal Y as described above is
It will be modulated by the FM modulator 6.

[Problems with background technology]

However, the instantaneous frequency of the FM signal in the Suba 6-4782 portion generated on the synchronization signal level side is modulated to an extremely low frequency range, so during playback, video heads A and H
There was a problem that the effect of azimuth loss caused by Therefore, in the reproducing circuit system, the FM demodulated signal is subject to interference due to crosstalk from the adjacent 1-rack. This interference is small in high-energy components near the carrier wave, but becomes large in frequency components far from the carrier wave, such as the spike portion.

On the other hand, the bidet racks 1 to 12 formed on the tape 12 are recorded using various methods as shown in FIG.

(a) shows the horizontal synchronization signal position recorded at the same level between adjacent tracks, and (b) shows the horizontal synchronization signal part where the horizontal synchronization signal position is less affected by the horizontal synchronization signal position and where the azimuth loss effect is small. The crosstalk is mixed into the same horizontal synchronization signal and is not reproduced on the screen. However, in the case of recording method (b).

The problem was that noise due to crosstalk in the horizontal synchronization signal part was reproduced, and striped beads appeared on either the left or right side of the screen.

Therefore, the usual countermeasures are to stop the function of the pre-emphasis circuit 5 during the horizontal synchronizing signal period TI during recording and perform pre-emphasis during the video signal period T, and to perform pre-emphasis during the horizontal synchronizing signal period T during playback. The de-emphasis function is stopped, and the video signal period T is de-emphasized so that @6+±≠, or a circuit is provided to remove the spikes that occur during the horizontal synchronization signal period of the signal after pre-emphasis. That's fine. However, adding a circuit with such a function to a pre-emphasis circuit or the like is not possible.

This has the disadvantage that it affects pre-emphasis characteristics or de-emphasis characteristics, making it impossible to reproduce good signals.

[Purpose of the invention]

The present invention has been made in view of the above points, and is a video emphasis system that can apply emphasis without affecting pre-emphasis characteristics and de-emphasis characteristics and without causing noise due to crosstalk in the horizontal synchronization signal portion. The purpose is to provide circuits.

[Summary of the invention]

In the video emphasis circuit of the present invention, in a recording circuit, a signal without pre-emphasis and a signal with pre-emphasis are input to a switching synthesis circuit, and a switching signal is applied to the switching circuit.

Select a pre-emphasized signal for the video period,
During the horizontal synchronization signal period, a signal is applied to select each signal to which no pre-emphasis is applied, and the signal is combined and output, while in the reproduction circuit system, separate switching is performed between the signal to which de-emphasis is applied and the signal to which no pre-emphasis is applied. A reproduction signal is obtained using a switching signal that is input to a synthesis circuit and formed in the same manner as during recording.

[Embodiments of the invention]

Hereinafter, embodiments illustrated in the drawings will be described.

Here, FIGS. 4 to 7 show drawings according to an embodiment of the present invention, and FIG. 4 is a block diagram of an emphasis circuit according to an embodiment of the present invention in the recording circuit system.
The figure is a block diagram of an emphasis circuit according to the same embodiment of the reproducing circuit system, and FIGS. 6 and 7 are operational waveform diagrams for explaining the present invention in detail. In these figures, the same elements as in FIGS. 1 and 2 are designated by the same reference numerals.

First, in FIG. 4, the luminance signal Y after passing through the bandpass filter 2 (see FIG. 1) is input to the input terminal 21. This luminance signal Y is input to the delay circuit 22, and is output to the pre-emphasis circuit 5 as a signal YD delayed by a delay time 1. The emphasis output Yp of the pre-emphasis circuit 5 is supplied to one input terminal 23a of the switching and combining circuit 24. Also, the delay signal YD
is led out to the other input terminal 23b of the switching and combining circuit 24 through the conductor 25, and the emphasis output Y
p and the direct delay signal Y that does not pass through the emphasis circuit 23.
D is the switching signal X applied to the switching synthesis circuit 24.
The signals 8 and 10 are switched and combined in a predetermined period and are output to the FM modulator 26 at the next stage. This FM modulator 26 is connected to the switching synthesis circuit 24.
The switching composite output Ys formed by the above is outputted to the output terminal 27 as an FM luminance signal YFM of a frequency corresponding to the signal level. Note that this output terminal 27 is connected to the recording amplifier 8 shown in FIG.

Further, the luminance signal Y of the input terminal 21 is transmitted to the synchronization separation circuit 4.
has been entered. However, the luminance signal Y input to this synchronization separation circuit 4 is the same as the television signal TV from the tuner explained in FIG. 1, and FIG. 4 shows a configuration in which the low-pass filter 2 of FIG. 1 is omitted. You can think about it.

This synchronization separation circuit 4 converts the luminance signal Y into a horizontal synchronization signal Hs.
is extracted and output as the pulse at the leading edge of the synchronization, that is, the horizontal synchronization pulse Hp. This horizontal synchronizing pulse Hp is input to a pulse width expansion circuit 28, modulated by the same circuit 28 so that its trailing edge is expanded, and output inverted.

This inverted signal is applied to the switching synthesis circuit 24 as the switching signal XI. That is, the switching synthesis circuit 24 selects the emphasis output Yp of the input terminal 23a by the switching signal X1 at the low (L) level, and selects the emphasis output Yp at the input terminal 23a, and
H) The delayed signal YD at the input terminal 23b is selected by the level switching signal X.

On the other hand, in the reproducing circuit system, the input terminal 29 has
A reproduced luminance signal demodulated by an F''M demodulator (not shown) is input. This reproduced luminance signal is input to a de-emphasis circuit 30 via a delay circuit 22'. is to attenuate high-frequency components of the reproduced luminance signal after demodulation, contrary to the characteristics of the pre-emphasis circuit 5 of the recording circuit system, and at the same time reduce triangular noise in the high-frequency range.Output after this de-emphasis YE is one input terminal 32 of the switching synthesis circuit 31
It is input in a. Further, the reproduced brightness signal is transmitted through the conductor 3.
3 and is input to the other input terminal 32b of the switching and combining circuit 31. This switching synthesis circuit 31 has both input terminals 32
The signals of a and 32b are switched and combined in a predetermined period using a switching signal X and output. The switched and synthesized output is then delivered to an output terminal 34 as a luminance signal Yo for mixing with a reproduced color signal from a mixer (not shown).

The reproduced luminance signal at the input terminal 29 is passed through a low-pass filter 35 to a sync separation circuit 4 used in the recording circuit system.
has been entered. The low-pass filter 35 is provided to remove carrier wave components. Further, the delay time of the delay port M22' is set to 2 in consideration of the time At which the low-pass filter 35 delays the reproduced luminance signal.

That is, the delay time 7□ of the delay circuit 22' is larger than the delay time Δτ of the low-pass filter 35.
If the delay time Δγ is longer than the delay time Δγ, the delay circuit 22' can be used in combination with the delay circuit 22 used in the recording circuit system, and
When the delay circuits 22' and 22 are used in common, there is no need to switch the delay time.

Further, the synchronization separation circuit 4 extracts the horizontal synchronization signal 13- from the reproduced luminance signal as a horizontal synchronization pulse Hp', and converts this horizontal synchronization pulse HP' into a pulse width expansion circuit 28'.
is supplied to. This pulse width expansion circuit 28' is used together with the expansion circuit 28 of the recording circuit system, and like the expansion circuit 28, it expands the trailing edge of the horizontal synchronizing pulse Hp' without changing the leading edge.

is configured to do so. In this way, the horizontal synchronizing pulse Hp whose trailing edge has been expanded is applied to the switching synthesis circuit 31 as the switching signal X.

The operation of the circuit as described above will be explained with reference to FIG.

In FIG. 6, the signal waveforms of each part explained in the above configuration are shown using the same symbols.

First, during recording, the luminance signal Y is delayed by a nominal amount by the delay circuit 22. This distortion is caused by the horizontal synchronization signal Hs of the luminance signal Y.
This is represented by the difference in phase between the leading edge of the tip of Yv and the leading edge of the delayed slide signal Yv. When this delayed signal YD passes through the pre-emphasis circuit 5, its emphasis output Yp becomes a waveform in which a spike waveform SP is superimposed due to high frequency emphasis. This spike waveform SP is formed in both the horizontal synchronizing signal period 14-T and the video period T2. The present invention prevents this spike waveform SP, especially the spike waveform whose level has been lowered to the synchronization signal level side, from becoming a long wavelength signal component by the FM modulator 26 and from being unable to receive the azimuth effect.

Now, the horizontal synchronization pulse Hp extracted by the synchronization separation circuit 4
is not delayed, so its pulse period corresponds in time to the period of the spike waveform portion generated at the leading edge of the horizontal synchronization signal of the emphasis output Yp.

On the other hand, since the trailing edge of this horizontal synchronizing pulse Hp is expanded by the next-stage pulse width modulator 28, the period of the spike waveform portion generated at the leading edge of the horizontal synchronizing signal of the emphasis output Yp is expanded. It corresponds in time to the pulse period of the horizontal synchronizing pulse Hp. therefore,
Inverted output with expanded horizontal synchronization pulse Hp, that is,
The low (L) level period as the switching signal X1 temporally sufficiently includes the spike waveform portion of the horizontal synchronizing signal period of the emphasis output Yp. Similarly, the horizontal synchronization signal of the delayed signal Yn without the spike waveform portion is also included in the low level period of the switching signal X. Therefore, such switching signal X1
According to the receiving switching and combining circuit 24, the delayed signal YD can be selected during the low level period of the signal X1, and the emphasis output Yp can be selected during the high level period of the signal X1. This high-level period change of the switching signal X, sufficiently includes the video period T, and the delayed signal YD during the video period
There is no IFf selection. Here, the switching signal
The low level period of 1 can be made slightly longer than the sum of the delay time 71 of the delay circuit 22 and the horizontal synchronizing pulse period TH. Further, 1□ may be a very small value, and in short, it may be set so that the low level period of the switching signal X1 does not overlap the leading edge of the front porch and the trailing edge of the back porch of the horizontal synchronizing signal 1-1s. The switching composite output Ys formed in this way does not include a spike waveform in the horizontal synchronizing signal interval T,
The horizontal synchronization signal portion can be recorded as a relatively short wavelength signal.

Next, in the reproducing circuit system, the sixth input terminal is connected to the input terminal 29.
It can be considered that the switching composite output Ys shown in the figure is input. If this switching synthesis output Ys is input as is to the de-emphasis circuit 30, the waveform of the horizontal synchronization signal period T1 will deteriorate in high frequencies as shown in the de-emphasis output Yg, and there is a risk that the horizontal synchronization signal cannot be extracted in the later display stage. Because of this, a signal that does not pass through the de-emphasis circuit 30 is selected as the reproduced video signal during the horizontal synchronization signal period, as in the case of recording.

That is, the reproduced video signal equivalent to the switching composite output Ys during recording is delayed by the delay circuit 22'.

With this delay time, is longer than the delay time Δτ of the low-pass filter 35<, Therefore, the delayed reproduced video signal (
The leading edge of the sync tip of Ys) is located well within the horizontal sync pulse HP'. On the other hand, since the trailing edge of the horizontal synchronizing pulse HP' is set to be expanded by the pulse width expansion circuit 28' to a length longer than '1:2', it is possible to sufficiently include the trailing edge of the leading edge of the horizontal synchronizing pulse HP'. This results in
The switching synthesis circuit 31 generates a reproduced luminance signal (not subjected to de-emphasis) during the horizontal synchronization signal period T8 due to switching signal selection.
Ys) is selected, and the output YE that has been de-emphasized during the video period T2 is selected to receive the mixed luminance signal YO that does not include the high-frequency degradation caused by the de-emphasis circuit 30 and the spike waveform. Note that if the expansion width α cannot cover the waveform rounding (high-frequency deterioration) time of the synchronization tip portion caused by the de-emphasis circuit 30, the expansion width α may be further widened.

In this manner, the present invention enables pasting without affecting the characteristics of the de-emphasis circuit (2) and the pre-emphasis circuit 5, without causing noise due to crosstalk in the horizontal synchronization signal portion. Note that if the video emphasis circuit of the present invention can be put to practical use even if the high frequency band at the leading end of the synchronization signal is degraded during reproduction, it is not necessary to apply the present invention to the reproduction circuit system. Furthermore, the present invention may be applied to recordable video disc players other than VTRs.

18- [Effects of the Invention] As explained above, according to the present invention, a signal without emphasis and a signal with emphasis can be switched and selected in the horizontal synchronization signal period and the video period, and then synthesized and output. Therefore, it is possible to prevent noise caused by cross-dog in the horizontal synchronization signal portion, and it is possible to obtain a good reproduced image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the recording circuit system of a conventional VTR.
FIG. 2 is a waveform diagram showing a luminance signal waveform. FIG. 3 is an explanatory diagram for explaining the recording method of a VTR, FIG. 4 is a block diagram showing a video emphasis circuit according to an embodiment of the present invention in the recording circuit system, and FIG. 5 is an implementation of the reproduction circuit system. A block diagram showing a video emphasis circuit according to an example, and FIGS. 6 and 7 are operational waveform diagrams for explaining the present invention in detail. 4... Synchronization separation circuit 5... Pre-emphasis circuit 22, 22'... Delay circuit 24, 31... Switching synthesis circuit 25, 33... Conductor 28, 28'... Pulse width expansion circuit 30... De-emphasis circuit 35... Low-pass filter representative Patent attorney Norichika Kensuke (one person) Figure 1 8 Figure 2 (0) (b) Figure 3

Claims (1)

[Claims] In a recording and reproducing apparatus that performs FM recording and reproduction of a video signal by relative movement between a recording track and a head, at least a recording circuit includes a first circuit that delays the video signal.
means, a second means for applying modulation on frequency characteristics to the delayed video signal, and a binary value corresponds to a horizontal synchronization signal period and a video period of the video signals from the first and second means. and a video signal from the first and second means, respectively, and selects the video signal not subjected to the modulation during the horizontal synchronization signal period according to the switching signal. and a fourth means for selecting, switching, combining, and outputting the modulated video signal during the video period, and the output of the fourth means is recorded on an FM basis. Video emphasis circuit for recording/playback equipment.