KR0122765Y1 - Video signal recording apparatus - Google Patents

Abstract

The present invention relates to an apparatus for processing a video signal to be recorded, the component of which is preemphasis for preemphasizing a signal component in a predetermined first frequency band in the video signal to generate a pre-emphasized video signal. Means for frequency modulating a carrier with a pre-emphasized video signal to be recorded, and a signal component having a second frequency within the first predetermined frequency and having a level higher than a threshold level from the video signal. Means for solving, and a multiplier for multiplying the outputs of the modulating means and the drawing means to make the amplitude of the frequency modulated signal from the modulating means higher than the amplitude in the remainder at the portion when the withdrawn signal is obtained. Means and recording amplification means for amplifying the output of said modulation means.

Description

Video signal processing device

The present invention relates to an apparatus for processing a video signal suitable for recording for a video tape recorder. In particular, the present invention relates to an apparatus for processing a video signal to be recorded, in which a so-called level inversion phenomenon is avoided.

In a conventional video tape recorder (VTR), a signal component having a high frequency band in the video signal is pre-emphasized to improve the S / N (signal-to-noise) ratio, and the pre-emphasized video signal is frequency modulated to the recording side. The pre-emphasis video signal is recorded and de-emphasized, and restored to the original video signal on the reproduction side. If the signal level of the high frequency component of the pre-emphasized video signal is increased too high, a non-watching effect such as overmodulation or the like may have an effect on the video signal during FM modulation. Thus, in order to ensure that the level of the signal component of the video signal on the recording side of the TVR does not exceed the threshold level, the video signal is clipped and then frequency modulated.

For example, when the video signal 1 shown in FIG. 1a passes through a pre-emphasis circuit (not shown), the high frequency component of the video signal 1 is differentiated to show the black level as shown in FIG. 1b. Sharp undershoot (5) and sharp overshoot in the trailing edge portion (3) and in the leading edge portion (2) for the back level. Generate part (4). In Fig. 1B, reference numerals 19 and 21 denote predetermined black and white clipping levels.

If the pre-emphasis video signal is provided to the next FM modulation circuit as it is, and the FM-modulated video signal is recorded on the magnetic tape to be reproduced, the FM-modulated video signal is so-called overmodulation state, so called extreme. Level reversal will occur.

The reason why the level reversal phenomenon, for example, the white peak level inversion phenomenon occurs, will be described with reference to FIGS. 2A through 2C.

As shown in FIG. 2A, the FM modulated video signal 1a suddenly rises from the black level of the original video signal to the black level of the rising section 2. Therefore, as shown in FIG. 2B, the magnetization pattern 7 in the portion 2 in which the frequency is changed from low frequency to high frequency becomes a pattern in which the magnetized pattern b is canceled by the magnetized pattern a. That is, in the reproduction waveform 8 of the video signal, as shown in FIG. 2C, the amplitude 9 of the reproduction waveform in which the magnetization pattern a is changed to the magnetization pattern b is reduced, and the reproduction waveform 8 crosses the zero level. It does not form. As a result, on the reproduction side of the VTR, the FM demodulation circuit determines that the frequency of the video signal is considerably low, so that the luminance signal is brought to the black level.

The above reversal phenomenon also occurs at black level peaks for the following reasons.

That is, if the video signal is pre-emphasized and then the pre-emphasized video signal is FM modulated, for example, the frequency of 3.6 MHz to 4.8 MHz is extended to about 2 MHz to 6.5 MHz, resulting in a third harmonic. An abnormal zero crossing occurs due to the phase difference between the primary and the tertiary high frequencies so that the FM demodulation circuit determines the black level as the white level.

Without such level inversion, the S / N ratio of the video signal is lowered at the top of the overshoot portion 4 or the undershoot portion 5.

In order to eliminate this drawback, the prior art slides a clipper or relevance between the preem and sheath circuit and the FM modulation circuit to clip the overshoot portion 4 or undershoot portion 5 at a level above any threshold level. It has been proposed to provide a circuit.

The proposed method will be described with reference to FIG. 3 shows an example of a known video signal recording apparatus.

In FIG. 3, the video signal 1 is provided to the video input terminal 10, passed through the next pre-emphasis circuit 12, and pre-emphasized in the pre-emphasis circuit 12. In the pre-emphasis circuit, the pre-emphasis video signal is provided to the FM modulation circuit 13, and frequency-modulated in the modulation circuit. The FM video signal is supplied to the magnetic head 14, and the FM video signal is recorded on the magnetic tape 15 by the magnetic head. The clipper or level slice circuit 18 is provided between the preemphasis circuit 12 and the FM modulation circuit 13. The level slice circuit 18 uses the NPN transistor 16, for example. In the level slice circuit 18, the signal line 20 of the video signal from the pre-emphasis circuit 12 is connected to the emitter e of the NPN transistor 16, and the collector C is directly connected to the reference voltage source + B of 12V. Connected. The base b of the NPN transistor 16 is also connected to the adjustment sliding contact 17 of the potentiometer 22 to perform a so-called back clipping operation in which the back level side of the video signal is clipped. The capacitor 11 is connected between the sliding contact 17 of the potentiometer 22 and the ground, and each clipping level is adjusted by the potentiometer 22 connected to the reference voltage source + B.

The known TVR in which the level slice circuit 18 using the NPN transistor 16 is provided in the recording system circuit as described above cannot overcome the following defects. In other words, the signal component clipped by the level slice circuit 18 is dropped from the video signal restored to the original state by the dephasis circuit on the reproduction side, and the reproducibility of the door waveform is reduced by the above-described clipping. In other words, the video signal 1 as shown in FIG. 4A is pre-emphasized on the recording side of the VTR, and the overshoot portion 4 of the video signal 1 is predetermined as shown in FIG. 4B. When sliced to the upper slice level 21, after the waveform distortion portion 22s corresponding to the sliced signal component is de-emphasized, it is generated from the video signal reproduced on the reproduction side as shown in FIG. 4C. Since the conventional level slice circuit 18 slices the video signal itself, when the slice level is increased, not only the waveform is distorted but also the sliced information is completely lost. It is known that improvements in waveform characteristics and inversion are opposed to each other. Therefore, it was very difficult to improve the waveform characteristics while preventing inversion.

On the other hand, in order to flatten the frequency characteristic of the video signal in a known recording / reproducing system of TVR, the recording current (current of the frequency modulated video signal) provided to the magnetic head (rotational magnetic head) when the frequency signal of the video signal increases. Reducing has been proposed.

For the above reason, when the frequency characteristic is not applied to the write current instead of providing the level slice circuit, the attenuation of the high frequency component of the FM modulated video signal is reduced, so that the occurrence of the inversion phenomenon can be prevented. On the other hand, the frequency characteristics of the video signal cannot be smoothed in the VTR's playback system.

By the way, since the high frequency component around the frequency of about 1 MHz or more tends to attenuate in the electromagnetic conversion characteristics, if the write current supplied to the magnetic head (rotary magnetic head) decreases with increasing frequency, each frequency Attenuation of the components is emphasized.

It is therefore an object of the present invention to provide an improved apparatus for processing video signals to be recorded.

Another object of the present invention is to provide an apparatus for processing a video signal to be recorded, which can suppress as much as possible the deterioration in the frequency characteristics and waveform characteristics of the video signal.

Another object of the present invention is to provide an apparatus for processing video signals to be recorded, which can prevent the so-called inversion of the back level and the black level.

Another object of the present invention is to provide a device suitable for use in a recording and reproducing apparatus such as a TVR in processing a video signal to be recorded.

According to one aspect of the present invention, an apparatus for processing a video signal to be recorded

a) preemphasis means for preemphasizing a signal component in said video signal at a first predetermined frequency band to generate a preemphasized video signal;

b) modulation means for frequency modulating the carrier with the pre-emphasized video signal to be recorded;

c) means for withdrawing a signal component having a second frequency within said first predetermined frequency and having a level above a threshold level from said video signal;

d) multiplier means for multiplying the output of said modulating means and said drawing means to make the amplitude of the frequency modulated signal from said modulating means higher in part when said outgoing signal is obtained than in the remainder;

e) recording amplification means for amplifying the output of said modulation means.

1A and 1B are waveform diagrams useful for describing preemphasized video signals.

2A to 2C are waveform diagrams useful for explaining why so-called inversion occurs.

3 is a block diagram showing an embodiment of a known video signal recording apparatus.

4A to 4C are waveform diagrams used to explain defects occurring in the known apparatus of FIG.

5 is a block diagram of an embodiment of an apparatus for processing video signals recorded according to the present invention.

6A-6E are waveform diagrams useful for explaining the operation of the apparatus shown in FIG.

7 is a block diagram of another embodiment of a video signal processing apparatus to be recorded according to the present invention.

8 is a characteristic graph of write current versus regenerated RF level.

9 is a block diagram of another embodiment of a video signal processing apparatus to be recorded according to the present invention.

10 is a block diagram of another embodiment of a video signal processing apparatus to be recorded according to the present invention.

* Explanation of symbols for the main parts of the drawings

12 pre-emphasis circuit 13 FM modulation circuit

23: drawing circuit 24: level changing circuit

132: level limit circuit

Other advantages and objects of the present invention are apparent from the description of the preferred embodiments described with reference to the accompanying drawings, wherein like reference numerals designate like numbers and parts.

5 shows a first embodiment of a video signal processing apparatus recorded according to the present invention.

In Fig. 5, the signal input terminal 10 is connected to the input side of the pre-emphasis circuit 12 whose output side is connected to the input side of the frequency modulation circuit 13. The output side of the pre-emphasis circuit 12 is connected to the input side of the drawing circuit (level slice circuit) 23. The output side of the frequency modulation (FM) circuit 13 and the drawing circuit 23 are both connected to the input side of the level changing circuit (parallel modulator) 24. The output side of the level change circuit 24 is connected to the input side of the write amplifier circuit 25. The output side of the write amplifier circuit 25 is connected to a magnetic head (rotating magnetic head) 14. The output side of the write amplifier circuit 25 is connected to a magnetic head (rotating magnetic head) 14. The magnetic head (damping resistor is connected in parallel to the winding) 14 is in contact with the magnetic tape 15.

The operation of the apparatus of the present invention configured as described above will be described with reference to FIGS. 6A to 6E constituting the waveform diagram.

In the embodiment of FIG. 5, the luminance signal (video signal) 1 separated from the composite color video signal as shown in FIG. 6A is applied to the signal input terminal 10. As shown in FIG. In this case, the video signal 1 comprises a large amplitude component 26 causing a so-called inversion phenomenon.

The video signal 1 applied to the input terminal 10 is supplied to the pre-emphasis circuit 12, and the rising and falling sections of the video signal in the pre-emphasis circuit are differentiated, as shown in FIG. 6B. It is preemphasized to generate overshoot and undershoot portions 4 and 5. The overshoot portion 4 and the undershoot portion 5 are generated in the large amplitude component 26 of the video signal 1.

The video signal 27 emphasized by the emphasis circuit 12 is provided to the frequency modulation circuit 13 such that the high frequency component of the signal is emphasized as shown in FIG. 6B, and in the frequency modulation circuit 13 The frequency modulated video signal 28 shown in FIG. 6C is typically frequency modulated to derive from the frequency modulating circuit 13.

The pre-emphasized video signal 27 from the pre-emphasis circuit 12 is provided to the drawing circuit (level slice circuit) 23, by which the drawing circuit predetermined level LS as shown in Fig. 6b. The signal component having the higher level is extracted from the video signal from which the extracted signal 29 is pre-emphasized as shown in FIG. 6D. The next frequency modulated video signal 28 and the extracted signal 29 are both provided to a level changing circuit (in this embodiment, a parallel modulator 24, in which both signals are frequency modulated video signals 28). Is changed in response to the extracted signal 29 as shown in 6e or the frequency modulated video signal 28 is modulated in such a manner that its amplitude is modulated by the extracted signal 29.

As a result, the level changing circuit 24 generates a frequency modulated video signal 30 having an amplitude 31 corresponding to the level of the extracted signal 29. The frequency modulated signal 30 having the amplitude 31 is provided to the write amplifier circuit (voltage-current converter) 25. In this case, as the write amplifier circuit 25 provides a write current (frequency modulated signal current) to the magnetic head 14 in which a winding is connected in parallel with a damping resistor, the current decreases as the frequency increases, and the characteristic of the video signal is increased. Becomes flat. The video signal is thus recorded on the magnetic tape 15. The above-described drawing circuit 23 and the level changing circuit 25 are not limited to the parallel modulation circuit, but for example, a variable gain amplifier capable of increasing or decreasing the amplification of the signal in response to the level of the level slice circuit 23. It may be made of a circuit.

In the embodiment shown in FIG. 5, a drawing circuit (or level slice circuit) 23 is connected to the output side of the preemphasis circuit 12. As shown in FIG. Meanwhile, the drawing circuit 23 may be connected to the input side of the preemphasis circuit 12. The modified embodiment of the present invention will be described with reference to FIG. In FIG. 7, parts similar to those in FIG. 5 will be denoted by the same reference numerals and will not be described in detail any further.

In the embodiment shown in FIG. 7, the video signal 1 applied to the input terminal 10 is provided to the preemphasis circuit 12 and the drawing circuit 23. The drawing circuit 23 of FIG. 7 is similar to the circuit shown in FIG. In the case of Fig. 5, the drawing circuit 23 is connected to the output side of the pre-emphasis circuit 12, and the drawing circuit 23 is made high by supplying the video signal 1 in which the high frequency component is already pre-emphasized. It is necessary to extract the signal component of the level. On the other hand, in the case of Fig. 7, since the video signal 1 at the input side of the pre-emphasis circuit 12 is provided to the drawing circuit 23, the bandpass filter BPF must be provided at the front of the level drawing. An internal circuit configuration of the drawing circuit 23 will be described in detail later with reference to FIG. 7.

In the drawing circuit configuration, the video signal 1 applied to the input terminal 10 is provided to the base of the emitter follower transistor 30T in which the emitter is grounded through the resistor 31R. The emitter of the transistor 30T is connected to the base of the transistor 35 through a bandpass filter BPF of the series circuit of the capacitor 32, the coil 33, and the resistor 4. The bandpass filter BPF is configured to have a range of passbands related to the frequency characteristics of the preemphasis circuit. For example, the center frequency of the bandpass filter BPF is 4.5MHz and the passband is quite wide. The transistors 35 and 36 constitute a level slice circuit in the form of a non-additive mixer. The base of the transistor 36 is connected to the sliding contact 41a of the variable resistor (or potentiometer) in which the slice level of the video signal 1 is determined. Emitters of transistors 35 and 36 are connected to each other and grounded through resistor 37. The output terminal as the drawing circuit 23 comes from the contact between the emitters of the transistors 35 and 36. The output signal generated at the output terminal is provided to the level change (control) circuit 24. Transistor 34, resistors 43, 44, 45, 38 and capacitor 39 constitute a bias circuit BI for performing temperature compensation of the above-described level slice circuit SL. The resistor 44 is a variable resistor in which the sliding contact 44a is connected to the base of the transistor 42.

After that, the operation of the drawing circuit 23 will be described again. Among the signal components of the video signal 1, frequency components, for example, around 4.5 MHz, which can cause the above-mentioned inversion, are drawn out by the bandpass filter BPF and provided to the level slice circuit SL. In the signal component column, a signal component having a level higher than the slice level provided to the base of the transistor 36 is generated across the load resistor 37 as an output signal. The level change circuit 24 is controlled by the output signal. When the level of the output signal from the bandpass filter BPF is lower than the slice level, the transistor 35 is cut off so that the signal generated at the output of the drawing circuit 23 becomes a constant voltage according to the slice level. The other operation is the same as that of the circuit configuration shown in FIG.

According to the circuit configuration shown in FIG. 5, since a signal component having a level higher than a predetermined level is drawn from the output signal from the preemphasis circuit 12 by the drawing circuit 23, an inversion phenomenon occurs. The difficult signal components are also drawn out by the drawing circuit 23 even if they have a level higher than the predetermined level. At this time, the level of the frequency modulated signal is increased by the extracted signal. In the circuit configuration shown in Fig. 7, the signal in the vicinity of the signal having a frequency component that is likely to cause a so-called inversion phenomenon is drawn out, and a signal component having a level higher than the predetermined level of the extracted component is again drawn out to have an efficiency. It is increased.

According to the circuit arrangement shown in FIGS. 5 and 7, the large amplitude portion 26 (FIG. 6B) of the video signal 1 or the high frequency portion of the frequency-modulated video signal 28 (FIG. 6C) The inversion phenomenon can be prevented by increasing the amplitude of the video signal and recording the video signal in a form such that, during reproduction, the level of the frequency modulated video signal having the enlarged amplitude portion is sufficiently high to be able to be demodulated. In this case, if the amplitude of the video signal is too large, the amplitude of the reproduced frequency modulated video signal is reduced. This reason will be described later with reference to FIG. 8 which is a characteristic graph.

In general, when a signal is provided to the magnetic head 14 and recorded on the magnetic tape 15, an RF is shown in which the abscissa indicates the recording current value and the ordinate is reproduced as shown in the graph of FIG. In the case of indicating the level of the signal, the relationship curve 134 therebetween exhibits a characteristic having a point 135 which becomes the maximum reproduction RF level when the recording current increases and even if the recording current value increases above the point 135. And the reproduced RF level is lowered. This property is called a magnetic demagnetization action in magnetic recording (hereinafter the action area is called a magnetic device action as shown by the oblique area in FIG. 8). The point 135 at which the maximum reproduction RF level appears is adjusted and selected in accordance with the recording of the signal, but if the amplitude 31 of the frequency modulated video signal 30 (FIG. 6E) is too large, the adjusted point 135 Is arranged in the direction in which the reproduced RF level is reduced or in the direction of the magnetic element region 136, thereby increasing the possibility of amplitude reduction of the frequency modulated video signal.

Therefore, another embodiment of the present invention that can overcome the above-described deficiency will be described with reference to FIG. 9 composed of a block diagram. In FIG. 9, similar parts corresponding to those of FIG. 5 will be denoted by the same reference numerals and will not be described in detail. The circuit configuration of FIG. 9 is almost similar to that of the apparatus of FIG. 5, wherein the output terminal of the drawing circuit 23 is connected to the input terminal of the level limiting circuit 132, and the output terminal of the level limiting circuit 132 is a level changing circuit. It is connected to one input terminal of (24).

The operation of the circuit configuration of FIG. 9 is as follows.

The extracted signal 29 (Fig. 6D) is generated from the drawing circuit 23. The level of the extracted signal 29 is the write current value point 135 where the write current value does not correspond to the magnetic element region 136 and the reproduced RF level is correct as shown by the curve 134 in FIG. In the case of being limited to the second threshold level LS2, the signal component of the high level drawn signal 29 can be sliced, and a drawn signal with a limited signal level can be obtained. Next, the level of the frequency modulated video signal 28 (FIG. 6C) is changed in response to the output from the level limit extracting signal as shown in FIG. 6E. In other words, the frequency modulated video signal 28 is amplitude modulated in relation to the level limited outgoing signal component.

As a result, the level changing circuit 24 supplies the frequency modulated video signal 30 (FIG. 6E) having an amplitude 31 whose level corresponds to the level of the limited outgoing signal 29 as shown in FIG. 6D. Occurs. The frequency modulated video signal 30 having the amplitude 31 is provided to the write amplifier circuit 25 (voltage-current converter), and the write current (frequency modulated video signal) is provided to the magnetic head 14.

On the other hand, in the embodiment shown in FIG. 9, the connection relationship between the level limiting circuit 132 and the drawing circuit 23 is drawn out from the drawing circuit 23 after the level limiting circuit 132 generates the level limit signal. Exchangeable to obtain a signal. In addition, the drawing circuit 23 and the level limiting circuit 132 may be combined with each other.

In the circuit configuration of the embodiment shown in FIG. 9, it is possible to prevent the reproduced RF signal from decreasing even if the write current value increases in the magnetic recording. As a result, so-called magnetic elements can be prevented, the inversion phenomenon can be reduced, and the quality of the video signal can be prevented from being degraded.

10 is a block diagram of another embodiment of the present invention. In the above embodiment, the level limiting circuit 132 is connected to the rear end of the level changing circuit 24 as shown in FIG.

In this case, the frequency modulated video signal 30 shown in 6e is limited to the second threshold level LS2 (Fig. 8).

According to the video signal processing apparatus of the present invention, as described above, the frequency characteristic and the waveform characteristic of the video signal can be prevented by increasing the amplitude of the frequency modulated video signal in a portion where inversion is likely to occur, and thus, a large amplitude The high frequency component attenuated by reproducing the frequency-modulated video signal of the input video signal having is concealed by the pre-emphasized low frequency component, and the phase of the frequency signal is difficult to be detected, thereby preventing inversion.

In addition, according to the video signal processing apparatus of the present invention, it is possible to obtain a reverse phenomenon prevention circuit that can suppress the occurrence of the reverse phenomenon while minimizing the reduction of the frequency characteristics and the waveform characteristics of the video signal.

Although the above description has been described based on the embodiments of the present invention, modifications can be made by those skilled in the art without departing from the spirit and scope of the present application.

Claims (1)

An apparatus for processing a video signal to be recorded, comprising: a) preemphasis means for preemphasizing a signal component having a first predetermined frequency band in the video signal to generate a preemphasized video signal; b) modulation means for frequency modulating the carrier with the pre-emphasized video signal to be recorded, and c) a signal component having a second frequency band within the first predetermined frequency band and having a level greater than a threshold level from the video signal. Extracting means for extracting a signal; d) multiplying the outputs of the modulating means and the extracting means so that the amplitude of the frequency-modulated signal from the modulating means is greater than the amplitude in the remaining portion when the extracting signal is obtained; And a recording amplification means for amplifying the output of said multiplication means.