JPH0358592A - Video reproducing device - Google Patents

Abstract

PURPOSE:To reduce moire and to suppress inverting phenomenon by executing the frequency conversion of a reproduced FM video signal and processing the signal by a double limiter circuit composed of a low frequency range emphasis circuit, high frequency range emphasis circuit, first amplitude limit circuit, adder circuit and second amplitude limit circuit. CONSTITUTION:The output signal of a preamplifier 19 is frequency-converted to a lower frequency by a frequency converting circuit 38 composed of an oscillator 20, multiplier 21 and LPF 22. Next, for the output signal of the LPF 22, a low frequency component is emphasized by a low frequency range emphasis circuit 23 and an amplitude is limited by a first amplitude limit circuit 24 afterwards. For the output signal of the LPF 22, a high frequency range component is emphasized by a high frequency range emphasis circuit 25 and afterwards, the signal is added with the output signal of the first amplitude limit circuit 24 by an adder 26. For the output signal of the adder 26, amplitude fluctuation is removed by a second amplitude limit circuit 27. Afterwards, the signal is demodulated by an FM demodulator 28 and a high frequency range is suppressed by a de-emphasis 29. Thus, the mixture of the inverting phenomenon and moire can be prevented.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a video playback device, and particularly to a video playback device such as a video tape recorder or a video disc that plays back video signals recorded as FM signals. Regarding a playback device.

(Prior Art) A recording and reproducing system of a home VTR (video tape recorder) is configured as shown in FIG. 9, for example. In the figure, a video signal inputted from a terminal 1 is high-frequency emphasized by a pre-emphasis circuit 10, then turned into an FM video signal by an FM modulation circuit 3, and recorded on a magnetic tape 17 via a magnetic head 16. Ru.

At this time, in the VTR, an FM modulator that oscillates with a rectangular wave, such as a multi-by-break system, is generally used as the FM modulator 3. As shown in FIG. 10(a), the recorded FM wave spectrum that is the output of the FM modulator 3 consists of a fundamental wave of the carrier frequency fc and odd harmonics, and a third harmonic within the transmission band of fc. Lower sideband waves are mixed in as shown by diagonal lines, and this is one of the causes of moiré.

On the other hand, during reproduction, the FM video signal reproduced from the tape 17 via the head 18 is amplified by a single preamplifier. As shown in Figure 10(b), the frequency characteristics of recording and playback are such that high frequencies are suppressed, so the spectrum of the reproduced FM wave is characterized by emphasizing low frequencies and suppressing high frequencies, as shown in Figure 10(C). The signal is suppressed, resulting in an unbalanced wave on both sides.

When such a signal is directly passed through the amplitude control circuit 55, as is well known, in the part where the video signal suddenly changes from black to white, the level corresponding to the high frequency component of the FM wave changes to the low frequency component. A so-called inversion occurs, where the black level falls to the corresponding level. This inversion phenomenon becomes more pronounced as the degree of modulation of the FM video signal increases.

Note that if we focus on the moiré components, as shown in the shaded area in FIG. 10(e), they exist reduced by the amount of high frequency suppression.

A double limiter method has been devised as a method to avoid the reversal phenomenon. This is a method using a double limiter 4 as shown in FIG. 9, for example, as described in Japanese Patent Publication No. 5G-27927. That is, preamplifier 1
The output signal of No. 9 is input to the double limiter 4, passes through a high-pass filter 50 consisting of a differentiation circuit, has its phase corrected by a phase correction circuit 51, and is then supplied to a first amplitude limiter 52, where it becomes a rectangular wave. . The output signal of the preamplifier 19 that is input to the double limiter 4 is also input to a low-pass filter 53 so that the low-frequency component is emphasized, and is added to the output signal of the first amplitude limiter 52 in an adder 54. be done. The output signal of the first amplitude limiter 52 is input to the second amplitude limiter 55 to remove level fluctuations, and then the FM demodulator 28
The signal is FM demodulated at the FM terminal 2, the high frequency band is suppressed by two de-emphasis circuits, and the signal is output from the output terminal 2.

However, the output spectrum of the second amplitude limiter 55 consists of the fc fundamental wave and odd-numbered harmonics, as shown in FIG. Some waves get in, causing moiré.

(Problems to be Solved by the Invention) As described above, in the conventional technology, there is a problem in that the lower side band of the third harmonic of the FM carrier wave mixes into the transmission band of the FM video signal, causing moiré. The reason for this is primarily F.
The M modulator is oscillating a square wave, and the second thing is that the reproduction F
Even though the high frequency component of the M video signal has been suppressed and the components corresponding to moiré have also been suppressed, by passing it through an amplitude limiter to prevent the inversion phenomenon, the lower third harmonic is again suppressed.
1} This is due to the waves becoming stationary.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video playback device that can reduce moiré, suppress inversion phenomena even when the degree of modulation of an FM video signal is increased, and obtain high-quality playback images.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, a reproduced FM video signal is frequency-converted to a lower frequency or a higher frequency, and then input to a low-frequency emphasis circuit and a high-frequency emphasis circuit.

Then, the output of the first amplitude control circuit that limits the amplitude of the output of the low frequency emphasizing circuit or the high frequency emphasizing circuit and the output of the high frequency emphasizing circuit or the low frequency emphasizing circuit are added and synthesized by an adder. The output of is input to the second amplitude limiter.

(Function) By frequency-converting the reproduced FM video signal in this manner, the lower side band of the third harmonic of the carrier wave is not mixed into the FM transmission band, and moiré can be reduced.

In addition, since processing is performed by a double limiter circuit consisting of a reduction emphasis circuit, a high frequency emphasis circuit, a first amplitude limiting circuit, an adding circuit, and a second amplitude limiting circuit after frequency conversion, even when the cooking level is increased, the reversal phenomenon occurs. will not occur.

Furthermore, the utilization rate of the lower side wave with a good C/N of the reproduced FM video signal is improved, and the S/N is improved.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a video recording and reproducing apparatus according to a first embodiment of the present invention.

In FIG. 1, a video signal inputted from a terminal 1 is inputted to an FM modulator 9 of a fixed-single wave oscillation type after its high-frequency component is emphasized by an emphasis circuit 1o. This sine wave oscillation FM modulator 9 is composed of an FM modulator 11 using a rectangular wave oscillation circuit, a low pass filter (LPF) 12, 15, an oscillator 13, and a multiplier 14.

That is, the output signal of the pre-emphasis circuit 10 is F
The signal is input to the M modulator 11. The FM modulator 11 is shown in FIG.
As shown in a), it oscillates at a carrier frequency f1 that is sufficiently higher than the carrier frequency fc of the FM wave to be recorded. This third harmonic component is removed using the LPF 12 having the characteristics shown in FIG. 2(b).

Next, the signal of the oscillator 13 which oscillates at the frequency FLI and the LP
When the output signal of F12 is multiplied by the multiplier 14, the result shown in FIG.
As shown in e), f Ll− f l and f ,, ten f
, a signal component of , is generated. In addition, although the case where the oscillation frequency (fLl) of the oscillator 13 is set lower than f is shown here, it goes without saying that it may be set to a higher frequency than f1.

Next, by inputting the output signal of the multiplier 14 to the LPF 15 having the characteristics shown in FIG. 2(d), f L,+f
, to obtain an FM wave that oscillates as a real sine wave with an oscillation frequency fL+f+ (corresponding to fc) as shown in FIG. 2(e). This FM wave includes the 10th
The lower sideband component of the third harmonic as shown in Figure (a) is included. The output signal 12 of the LPF 15 is recorded on a magnetic tape 17 via a magnetic head 16.

During reproduction, the FM video signal reproduced from the tape 17 via the magnetic head 18 is amplified by a single preamplifier.

This signal is a signal with reduced emphasis and high frequency suppression as shown in FIG. 2(f).

The output signal of the preamplifier 19 is sent to an oscillator 20 and a multiplier 21.
The frequency is converted to a lower frequency by a frequency conversion circuit 38 consisting of an LPF 22 and an LPF 22.

That is, the output signal of the preamplifier 19 and the signal of the oscillator 20 which oscillates at the frequency fL2 are multiplied by the multiplier 21, and as shown in FIG. 2(g), signal components of fL2fC and fL2+fC are obtained.

This signal is transmitted through an LPF having the characteristics shown in Fig. 2(h).
22, and by removing the signal component of f L2 + f C, f L2 - f shown in Fig. 2 <<1>> is obtained.
A signal component of c is obtained.

In the signal component of fL2fc, the low frequency component is suppressed and the high frequency component is emphasized. If such a signal with unbalanced double-side band waves is directly input to an amplitude limiter, an inversion phenomenon occurs.

In order to avoid this inversion phenomenon, the output signal of the LPF 22 has its low frequency components emphasized through a low frequency emphasis circuit having the characteristics shown in FIG. The output signal of this amplitude limiting circuit 24 is
As shown in Figure 2 (k), it has a third harmonic, but since the amplitude is limited after frequency conversion, the lower side band of the third harmonic leaks into the FM transmission area due to the amplitude limit. There will be no crowding.

Further, the output signal of the LPF 22 is passed through a high frequency emphasizing circuit 25 shown in FIG.
is added to the output signal of the first amplitude limiting circuit 24. The output signal of this adder 26 is input to a second amplitude limiting circuit 27 to remove amplitude fluctuations, then demodulated by an FM demodulator 28, and further suppressed in high frequencies by two de-emphasis units, thereby allowing reproduction. It is output from terminal 2 as a signal.

In the manner described above, it is possible to avoid the inversion phenomenon as well as the mixing of moiré.

FIG. 3 is a block diagram showing a second embodiment of the present invention, and the hole in FIG. 1 is a high-pass filter (HPF) 30.
, a high frequency emphasis circuit 31 and a low frequency emphasis circuit 32. In this case, the oscillator 20, multiplier 21, and HPF 30 constitute a frequency conversion circuit 39 that converts the reproduced FM video signal to a higher frequency.

That is, as in the first embodiment, the output signal of the multiplier 21 becomes as shown in FIG. 4(a). This signal is HPF30
The signal component of fL2-fC is removed. The characteristics of H-PF30 are as shown in Figure 4(b).
This is a characteristic that allows the FM wave of fL2+f() to pass through and removes some of fL2+fc.As for the signal component of fL2+fC, as shown in FIG. If this signal is input directly to the amplitude limiting circuit, an inversion phenomenon will occur.For this reason, HP
The output signal of the F30 is input to the first amplitude limiting circuit 50 after the unbalance of both side bands is corrected by the high frequency emphasizing circuit 31 having the characteristics shown in FIG. 4(d). This prevents the reversal phenomenon.

Here, since the fL2+fc component of the output signal of the amplitude limiting circuit 50 and its third harmonic are separated in frequency as shown in TS4 diagram (d), the lower sideband signal of the third harmonic is ' It does not mix into the FM signal band of L2+f(), thereby reducing moiré.

Further, the output signal of the HPF 30 is low-frequency emphasized by the low-frequency emphasis circuit 32 having the characteristics shown in FIG. 4(e), and then added to the output signal of the first amplitude limiting circuit 50 by the adder 26. . This increases the degree of modulation of the FM wave and increases the C/N
It is possible to increase the addition ratio of low-frequency signal components of fL2+fc, which has a good value, and to improve the S/N ratio.

FIG. 5 is a block diagram showing a third embodiment of the present invention, which differs from FIG. 3 in that the multiplier 35 operates as a square calculation circuit, and the high frequency emphasis circuit 34 and low These are the characteristics of the area emphasizing circuit 35.

That is, the output signal of one preamplifier shown in FIG. 6(a) is squared by the multiplier 33, so that
), the frequency band of the FM wave is converted to the higher frequency side.

The output signal of the multiplier 33 is sent to the first amplitude limiting circuit 52 via the high-frequency emphasizing circuit 34 which increases the characteristic shown in FIG. is input. As in the case of FIG. 3, as shown in FIG. 6(d), 2fc of the output signal of the amplitude limiting circuit 52 and its third harmonic are separated in frequency. Therefore, the lower side of the third harmonic mixed in the FM signal with a carrier wave of 2 f c :;
1} The wave component becomes quantitatively low, and the amount of moiré is reduced.

Further, the output signal of the multiplier 33 is added to the output signal of the first amplitude limiting circuit 52 by the adder 26 via the low frequency emphasis circuit 35 having the characteristics shown in FIG. 6(c). As mentioned above, this increases the degree of modulation of the FM wave, and
It is possible to improve the S/H by increasing the addition ratio of lower sideband waves having frequency components lower than that of 2FO, which has a good C/H.

FIG. 7 is a block diagram showing a fourth embodiment of the present invention. In this embodiment, a high frequency signal detection circuit 36 and a voltage control gain adjustment circuit 37 are provided on the recording side. The high-frequency signal detection circuit 36 includes, for example, a high-frequency emphasis circuit having the characteristics shown in FIG. 8(b) and an amplitude detection circuit, and corresponds to the amplitude of the high-frequency component of the input video signal shown in FIG. 8(a). Outputs a voltage signal. The voltage control gain adjustment circuit 37 receives the output signal of the LPF 15, that is, the FM video signal to be recorded, and controls its amplitude in accordance with the output signal of the harmonic signal detection circuit 37.

Generally, when a signal of a certain frequency is recorded or reproduced, the relationship between the recording current and the reproduction signal amplitude has a saturation characteristic as shown in FIG. 8(C). Therefore, when recording with a recording current that maximizes the reproduction output (optimum recording current), the nonlinear portion of the recording and reproduction characteristics is used. Therefore, in this case, as shown in the shaded area in Figure 8(d), a component corresponding to the lower sideband of the third harmonic of the FM carrier wave fc mixes into the FM signal band, causing moiré. .

On the other hand, if the recording current is lower than the optimum recording current, the linear part of the recording/reproducing characteristics can be used, as shown in Figure 8 (
As shown in e), the FM carrier f. It is possible to lower the level of the component corresponding to the lower sideband of the third harmonic.

The effect of moire is noticeable in terms of image quality when a large amplitude, high frequency signal is input. Focusing on this point, in this embodiment, large amplitude, high frequency video signal components are recorded by lowering the recording current. This makes it possible to suppress the occurrence of moiré without deteriorating the S/N ratio when the video signal is a low frequency signal corresponding to a flat part of an image where noise is easily noticeable.

In the above embodiment, a double limiter using two stages of amplitude limiting circuits was used as the inversion prevention means, but it goes without saying that a plurality of stages of amplitude limiting circuits and adders connected in series may be used.

Further, in the above embodiments, a video recording and reproducing apparatus has been described, but the fourteenth and third embodiments can also be applied to a reproduction-only apparatus, such as a video disc player. On the other hand, regarding the fourth embodiment, any configuration on the playback side may be used.

In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] According to the present invention, it is possible to avoid the lower sideband component of the third harmonic of the FM carrier wave from being mixed into the FM video signal band, and it is possible to prevent the occurrence of moiré.

Furthermore, since it is possible to avoid the inversion phenomenon while preventing the occurrence of moiré, it is possible to increase the degree of modulation (frequency shift) of the FM video signal and improve the S/N ratio.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure shows the frequency spectrum and frequency characteristics of each part to explain the operation of Fig. 1, Fig. 3 is a block diagram showing the second embodiment of the present invention, and Fig. 4 shows the operation of Fig. 3. FIG. 5 is a block diagram showing the third embodiment of the present invention. FIG. 6 is a diagram showing the frequency spectrum of each part to explain the operation of FIG. 5. 7 is a block diagram showing the fourth embodiment of the present invention. FIG. 8 is a diagram showing the frequency spectrum and frequency characteristics of each part to explain the operation of FIG. FIG. 9 is a block diagram showing an example of a conventional video recording and reproducing apparatus, and FIG. 10 is a diagram showing the frequency spectrum and frequency characteristics of each part to explain the operation of FIG. 9. 9... Sine wave oscillation FM modulator, 20... Oscillator, 2
1... power 35, 22... low pass filter, 23.
32.35...Low frequency emphasis circuit, 24.50.52...
- First amplitude limiting circuit, 25.31.34... High frequency emphasis circuit, 26... Adder, 27, 51.53... Second amplitude limiting circuit, 30... Bypass filter, 36
. . . Harmonic signal detection circuit, 37 . . . Voltage control gain adjustment circuit, 38. 39 . . . Frequency conversion circuit.

Claims (4)

[Claims] (1) A means for reproducing an FM video signal, a frequency conversion circuit for converting the frequency of the FM video signal obtained by this means to a lower frequency, and a low frequency band for emphasizing the low frequency range of the output signal of the frequency conversion circuit. an emphasizing circuit; a first amplitude limiting circuit that keeps the amplitude of the output signal of the low frequency emphasizing circuit constant; a high frequency emphasizing circuit that emphasizes the high frequency range of the output signal of the frequency conversion circuit; Video playback characterized by comprising an adder that adds the output signal and the output signal of the first amplitude limiting circuit, and a second amplitude limiting circuit that keeps the amplitude of the output signal of the adder constant. Device. (2) means for reproducing an FM video signal; a frequency conversion circuit for converting the frequency of the FM video signal obtained by this means into a higher frequency; and a high frequency band for emphasizing the high frequency range of the output signal of the frequency conversion circuit. an emphasizing circuit; a first amplitude limiting circuit that keeps the amplitude of the output signal of the high frequency emphasizing circuit constant; a low frequency emphasizing circuit that emphasizes the low frequency range of the output signal of the frequency conversion circuit; and this low frequency emphasizing circuit. and a second amplitude limiting circuit that keeps the amplitude of the output signal of the adding circuit constant. playback device. (3) means for reproducing an FM video signal; a multiplier for squaring the FM video signal obtained by this means; a high-frequency emphasis circuit that emphasizes the high range of the output signal of this multiplier; and this high-frequency emphasis. a first amplitude limiting circuit that keeps the amplitude of the output signal of the circuit constant; a low frequency emphasizing circuit that emphasizes the low frequency range of the output signal of the multiplier; and an output signal of the low frequency emphasizing circuit and the first amplitude. 1. A video reproducing device comprising: an adder that adds the output signal of the limiting circuit; and a second amplitude limiting circuit that makes the amplitude of the output signal of the adder constant. (4) In a video recording device that records a video signal with a magnetic head via an FM modulator that oscillates with a sine wave, the output signal of the FM modulator is input and the amplitude of the output signal supplied to the magnetic head is changed. A video recording device comprising: a gain adjustment circuit; and means for controlling the gain of the gain adjustment circuit according to high frequency components of an input video signal.