JP2969628B2 - Video signal transmission device - Google Patents

Description

The present invention relates to a video signal transmission apparatus for recording / reproducing or transmitting / receiving a video signal, and more particularly to a video signal transmission apparatus which performs non-linear emphasis on a video signal. The present invention relates to a video signal transmission apparatus of a system of performing FM modulation and transmission after the modulation.

(Prior Art) Generally, in a VTR or a video disc, a video signal is FM-modulated and recorded. When FM signals are recorded and reproduced, the noise distribution after FM demodulation tends to increase as the frequency increases. Such noise is called triangular noise. As a method to suppress triangle noise and improve S / N,
An emphasis / de-emphasis circuit that emphasizes (emphasizes) a high frequency component of a video signal and deemphasizes (suppresses) the high frequency component during demodulation has been used.

A non-linear emphasis / de-emphasis circuit that changes the emphasis characteristic according to the amplitude of an input signal has also been proposed. This means that when the amplitude of the input signal is large, the emphasis amount is small, and when the amplitude is small, the emphasis amount is large.

In a nonlinear emphasis / de-emphasis circuit, high-order harmonics are generated in principle. In this case, if the characteristic from the output terminal of the nonlinear emphasis circuit to the input terminal of the nonlinear deemphasis circuit is flat, the higher-order harmonics generated by the nonlinear emphasis circuit are transmitted to the nonlinear deemphasis circuit as they are, so that the nonlinear It is canceled by the emphasis circuit and does not appear in the final output. However, in the VTR, a delay type or pulse count type FM demodulation circuit having a band limiting function is used on the reproduction side, so that the signal input to the nonlinear de-emphasis circuit is limited by the band limitation by the FM demodulation circuit. The higher-order harmonics generated in are removed.
Therefore, there is a problem that a higher-order harmonic newly generated in the nonlinear de-emphasis circuit remains without being canceled and the waveform of the reproduced video signal is deteriorated.

(Problems to be Solved by the Invention) When the non-linear emphasis / de-emphasis circuit is used as described above, a high-order harmonic generated by the non-linear de-emphasis circuit is mixed into the final output, and the waveform is deteriorated. Was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a video signal transmission apparatus that prevents high-order harmonics generated in the process of nonlinear emphasis / de-emphasis from being mixed into a final output irrespective of band limitation of an FM demodulation circuit.

[Configuration of the invention] (Means for solving the problem) A video signal transmission device according to the present invention converts a video signal composed of a luminance signal and a chrominance signal into a digital signal by a first A / D converter. By the first digital processor
After converting the TCI signal into an analog signal by a first D / A converter, smoothing the signal by a first low-pass filter, and further transmitting the analog signal to a transmission system through a nonlinear emphasis circuit and an FM modulation circuit. 1 and an FM signal supplied via the transmission system is demodulated by an FM demodulation circuit and converted to a digital signal by a second A / D converter via a non-linear de-emphasis circuit and a second low-pass filter. After that, the luminance signal and the chrominance signal are separated by a second digital processor into a luminance signal and a chrominance signal.
A second device for converting the analog signal by the D / A converter and then smoothing the image signal by a third low-pass filter to restore the video signal, wherein the second low-pass filter sets the band of the TCI signal to fo. When the sampling frequency of the second A / D converter is fs, the output signal of the non-linear de-emphasis circuit has a characteristic of attenuating high-order harmonic components at a frequency of fs-fo. .

Other video signal transmission devices according to the present invention are the same as those described above for the second device, except that the first device converts a video signal composed of a luminance signal and a chrominance signal into a digital signal by a first A / D converter. After being converted into a signal, the signal is converted into a TCI signal by a first digital processor, the TCI signal is converted into an analog signal by a first D / A converter, and then passed through a non-linear emphasis circuit, and the output of the non-linear emphasis circuit is output. The signal is smoothed by a first low-pass filter, and high-order harmonic components are attenuated before being transmitted to a transmission form through an FM modulation circuit.

The present invention can be applied to any of a video signal recording / reproducing device and a transmitting / receiving device. The first device is a recording device or a transmitting device, and the second device is a reproducing device or a receiving device. Therefore, the transmission system in the present invention includes both a recording medium and a transmission path. Further, the present invention can be applied to only the reproducing device or only the receiving device.

(Operation) In the present invention, the high-order harmonics generated by the nonlinear emphasis circuit are blocked by the band limiting function of the FM demodulation circuit, while the high-order harmonics generated by the nonlinear de-emphasis circuit are generated by the nonlinear emphasis circuit. High-order harmonics are not canceled and appear at the output of the nonlinear de-emphasis circuit without being canceled, but because the low-pass filter is provided at the output side of the nonlinear de-emphasis circuit,
This higher order harmonic will not be mixed into the final output. Therefore, waveform degradation of the video signal restored on the reproducing side or the receiving side is reduced, and the reproduced image quality is improved.

Further, in the present invention, even when moiré occurs due to higher-order harmonics generated in the nonlinear emphasis circuit, the reproduced image quality is reduced by reducing the amount of moiré by the low-pass filter provided on the output side of the nonlinear emphasis circuit. improves.

(Example) Hereinafter, an example of the present invention is described with reference to drawings.

FIG. 1 shows a configuration of a video recording / reproducing apparatus (VTR) according to a first embodiment of the present invention. FIG. 6 shows a signal waveform and a frequency spectrum of each part in FIG.

In the recording side in FIG. 1 (a first device), to the input terminal 1 is given input video signal of a frequency f ₀ shown in example FIG. 6 (a). Taking the case where the input video signal is a high definition video signal as an example, the center frequency of f ₀ is 12MHz, for example. This input video signal is input to the nonlinear emphasis circuit 2.

The non-linear emphasis circuit 2 is a circuit that emphasizes a high-frequency component of an input video signal in accordance with an emphasis amount corresponding to the signal amplitude, and is configured, for example, as shown in FIG. 2 (a) or (b). FIG. 2 (a) shows an example of a feed-forward type configuration, in which a video signal input to an input terminal 21 is supplied to one input terminal of an adder 24 through a low-pass filter 22 and a compressor 23. An input video signal is directly supplied to the other input terminal of the adder 24. The output signal of the adder 24 is sent to the output terminal 25. FIG. 2B shows an example of a feedback type configuration, in which a video signal input to an input terminal 21 is supplied to one input terminal of an adder 24, and an output of the adder 24 is sent to an output terminal 25. At the same time, the signal is supplied to the other input terminal of the adder 24 via the low-pass filter 22 and the compressor 23.

The compressor 23 has, for example, the input / output characteristics shown in FIG. 3, and its output is shown in FIG. 6 (b). Such a compressor 23
For example, an amplitude limiter or a logarithmic amplifier can be used. As shown in FIG.
The output of 23 includes a high-order harmonic (particularly, an odd-order harmonic) component, which is output from the nonlinear emphasis circuit 2 as shown in FIG. 6 (c), for example, the addition in FIG. 2 (a). It also appears at the output of unit 24. The energy of the higher harmonic component increases as the amount of emphasis of the nonlinear emphasis circuit 2 increases.

The output signal of the nonlinear emphasis circuit 2 is a linear emphasis circuit 3 whose emphasis amount is constant regardless of the signal amplitude.
The FM signal is input to the FM modulation circuit 4 through the interface and converted into an FM signal suitable for recording, and then recorded on the magnetic tape 6 by the recording head 5.

The FM signal recorded on the magnetic tape 6 is transmitted to the reproducing side (second
Is reproduced by the reproducing head 7 in the device (1). The recording head 6 and the reproducing head 7 may use a common magnetic head. The FM signal reproduced by the reproducing head 7 is amplified and amplitude-limited by a preamplifier
Demodulated by the demodulation circuit 9.

FIG. 5 shows an example of the FM demodulation circuit 9. In FIG. 5, a video signal supplied to an input terminal 41 is supplied to one input terminal of an EOR (exclusive or) circuit 43 via a delay line 42, and to the other input terminal of the EOR circuit 43. Given directly. The output of the EOR circuit 43 is sent to an output terminal 45 via a low-pass filter (LPF) 44. This circuit is known as a delayed FM demodulation circuit,
Often used in R. As another example, a pulse count type FM demodulation circuit or the like can be used. When such an FM demodulation circuit 9 is used, due to the band limitation as shown in FIG. 6 (d) by the LPF 44, the output of the LPF 44 becomes as shown in FIG. 6 (e) as shown in FIG. 6 (e). Adder
The high-order harmonic component present at the output of 24 (the output of the nonlinear emphasis circuit 2) no longer appears.

Returning to FIG. 1, the video signal demodulated by the FM demodulation circuit 9 is input to the non-linear de-emphasis circuit 11 via the linear de-emphasis circuit 10 whose de-emphasis amount is constant regardless of the signal amplitude. The non-linear de-emphasis circuit 11 is a circuit that suppresses a high-frequency component of an input video signal in accordance with a de-emphasis amount corresponding to the signal amplitude, and is configured, for example, as shown in FIG. 4 (a) or (b). FIG. 4 (a) is an example of a feedback type configuration,
The video signal input to the input terminal 31 is supplied to one input terminal of an adder 34, and the output of the adder 34 is sent to an output terminal 35 and added through a low-pass filter 32 and a compressor 33. The other input of the unit 34 is provided. FIG. 4 (b)
Is an example of a feed-forward type configuration, in which a video signal input to an input terminal 31 is a low-frequency elimination filter 32 and a compressor 33.
To one input terminal of the adder 34. Adder
An input video signal is directly applied to the other input terminal of the input terminal 34.
The output signal of the adder 34 is sent to an output terminal 35.

When the feedforward type configuration shown in FIG. 2 (a) is used for the nonlinear emphasis circuit 2, the feedback type configuration shown in FIG. 4 (a) is used for the nonlinear deemphasis circuit 11, and conversely, the nonlinear emphasis circuit 11 is used. Circuit 2
When the feedback type configuration shown in FIG. 2 (b) is used, the feedforward type configuration shown in FIG. 4 (b) is used for the nonlinear de-emphasis circuit 11 so that the characteristics of the nonlinear emphasis circuit 2 The characteristics of the de-emphasis circuit 11 can be made complementary.

The compressor 33 has, for example, the input / output characteristics shown in FIG. 3, similarly to the compressor 23 in the nonlinear emphasis circuit 2 shown in FIGS. 2 (a) and 2 (b). Therefore, the output of the linear de-emphasis circuit 10 to the nonlinear de-emphasis circuit 11,
When a signal as shown in FIG. 6E after the high-order harmonic component is removed by the FM demodulation circuit 9 is input, the output of the nonlinear de-emphasis circuit 11 is as shown in FIG. As shown, a high-order harmonic (odd-order harmonic) component appears.

However, in the present invention, the output of the non-linear de-emphasis circuit 11 is input to the LPF 12 so that high-order harmonic components generated in the non-linear de-emphasis circuit 11 are removed as shown in FIG. 6 (h). Thereafter, it is guided to the output terminal 13. The pass band of this LPF 12 is desirably the same as the pass band of the LPF 44 in the FM demodulation circuit 9 shown in FIG. This means that among the higher harmonics generated by the nonlinear emphasis circuit 2, the linear emphasis circuit 3 to the FM modulation circuit 4 to the recording head 5 to the magnetic tape 6 to the reproduction head 7 to
This is because the components transmitted through the path from the preamplifier / limiter 8 to the FM demodulation circuit 9 to the linear deemphasis circuit 10 are canceled by the nonlinear deemphasis circuit 11, and the components not transmitted are attenuated by the LPF 12.

FIG. 7 shows a second embodiment of the present invention, which differs from the first embodiment in that an LPF 14 is inserted between the non-linear emphasis circuit 2 and the linear emphasis circuit 3 on the recording side. This LPF
The 14 roles are as follows.

The output signal of the non-linear emphasis circuit 2 contains an odd harmonic component as shown in FIG. 6 (c).
Therefore, when the output signal of the non-linear emphasis circuit 2 is supplied to the FM modulation circuit 4 via the linear emphasis circuit 3 for modulation, a sideband of the FM signal caused by the harmonic component is generated. The influence of this sideband does not matter when the carrier frequency in the FM modulation circuit 4 is high,
When the carrier frequency is low as in R, moiré may occur. The moiré amount is determined by the emphasis amounts of the emphasis circuits 2 and 3 and the carrier frequency, frequency shift amount and circuit type of the FM modulation circuit 4.

In a multi-vibrator type FM modulation circuit generally used in the past, the frequency spectrum of the output of the multi-vibrator type FM modulation circuit is lower than that of the folded component of the lower band and the third harmonic of the carrier as shown in FIG. The sideband component causes moiré. The output signal of the nonlinear emphasis circuit 2 is
This is a composite wave of a fundamental wave component and an odd-order harmonic. Generally 2
When FM modulation is performed with a composite wave of two frequency components,
The fundamental wave and sideband of FM wave when FM modulation is performed with one frequency component signal is FM with another frequency component signal.
It becomes a modulated FM wave. For example, nonlinear emphasis circuit 2
Is composed of a fundamental wave and a third harmonic and has a small modulation index. In such a case, the insertion of the nonlinear emphasis circuit 2 significantly increases the third sideband component, and as shown in FIG. 8 (b), the third lower sideband and the FM wave existing as a folded component. The third sideband of the third harmonic enters the transmission band of the FM wave and increases the amount of moire.

On the other hand, when the LPF 14 is inserted on the output side of the nonlinear emphasis circuit 2 as shown in FIG. 7, high-order harmonic components at high frequencies are reduced, so that the amount of moire can be greatly reduced. It is also possible to obtain the same characteristics shown in FIG. 8 (a) as in the case where FM modulation is performed without passing through. Note that the characteristics of the LPF 14 may be set so that the amount of moire does not matter.

FIG. 9 shows a third embodiment of the present invention. For example, a Y signal (luminance signal) having a band of f ₁ = 20 MHz and f ₂
An input video signal composed of a C signal (color signal) in a band of = 8 MHz is supplied. This input video signal is supplied to the first A / D converter 5
After being sampled by 1 at a sampling frequency of, for example, 27 MHz and converted into a digital signal having an appropriate number of bits, the digital signal is input to a recording processor 52 as a first digital processor. The recording processor 52 performs a predetermined process on the digitized input video signal, for example, a TCI (Time C) of a band of f ₀ = 12 MHz for two channels so that the input video signal can be easily recorded on the magnetic tape 6.
ompressed Integration) Performs conversion to a signal. The output of the recording processor 52 is supplied to a first D / A converter 53.
After being converted into an analog signal by the first LPF 54 and further smoothed by the first LPF 54, the signal is recorded on the magnetic tape 6 by the recording head 5 via the nonlinear emphasis circuit 2, the linear emphasis circuit 3 and the FM modulation circuit 4.

On the other hand, an FM signal reproduced from the magnetic tape 6 by the reproducing head 7 passes through a preamplifier / limiter 8, an FM demodulation circuit 9, a linear de-emphasis circuit 10, a non-linear de-emphasis circuit 11, and a second LPF 55, and then a second LPF 55. A / D converter
The signal is converted into a digital signal by 56, and then a process opposite to that of the recording processor 52, that is, a process of separating the TCI signal into a Y signal and a C signal is performed by a reproduction processor 57 as a second digital processor. Playback processor
The output of 57 is converted to an analog signal by a D / A converter 58, and is further smoothed by a third LPF 59.
Sent to

Here, the second LPF 55 is basically for removing high-order harmonic components generated in the nonlinear de-emphasis circuit 11, similarly to the LPF 12 in the first and second embodiments. The LPF 55 does not need to be a filter having the same characteristics as the LPF 44 (see FIG. 5) in the FM demodulation circuit 9 and may be an LPF that satisfies the following two conditions.

(1) the passband is f _0. (2) In order to suppress aliasing noise in the second A / D converter 56, when the sampling frequency in the A / D converter 56 is f _S (for example, f _S = 27 MHz is selected), nonlinear de-emphasis is performed. The high-order harmonic component of the output signal of the circuit 11 is sufficiently attenuated at the frequency of f _S −f ₀ . In this case, the high-order harmonic components generated by the nonlinear de-emphasis circuit 11 are not completely removed by the LPF 55 alone, but are not completely removed by the LPF 55.
LPF59 can be completely removed. By making the second LPF 55 have the above-described characteristics, the LPF 55
May be a filter having a characteristic whose cutoff characteristic is relatively gentle as compared with the LPF 12 in the first and second embodiments, thereby making it possible to reduce the cost.

FIG. 10 shows a fourth embodiment of the present invention, in which the first LPF 54 in FIG. 9 is removed and a first LPF 54 is provided between the nonlinear emphasis circuit 2 and the linear emphasis circuit 3 instead.
F61 is inserted. Since this LPF 61 has both functions of the first LPF 14 (FIG. 7) in the second embodiment and the first LPF 54 (FIG. 9) in the third embodiment, it is advantageous in reducing the price. Become.

FIG. 11 shows a fifth embodiment of the present invention. The input video signal supplied to the input terminal 1 first passes through the non-linear emphasis circuit 2, is input to the first A / D converter 51 via the first LPF 62, and is converted into a digital signal. After being converted into, for example, a TCI signal by the recording processor 52 in the same manner as in the third and fourth embodiments, the D / A converter 53 and the second LPF 6
3 (corresponding to the LPF 54 in FIG. 9) and the FM modulation circuit 4, and are recorded on the magnetic tape 6 by the recording head 5.

The FM signal reproduced from the magnetic tape 6 by the reproducing head 7 passes through a preamplifier / limiter 8 and an FM
After being converted into a digital signal by the D converter 56, the signal is returned to the Y signal and the C signal by the reproduction processor 57, and the D / A converter 58, the nonlinear de-emphasis circuit 11, and the third LPF 5
The signal is sent to the output terminal 13 via the terminal 9.

The nonlinear emphasis circuit 2 has a characteristic that the emphasis amount is small when the amplitude is large, and the emphasis amount is increased when the amplitude is small. That is, when the input signal amplitude is large, the output signal amplitude is slightly increased as compared with when the input signal amplitude is small. Therefore, the output of the nonlinear emphasis circuit 2 is changed to LP
When input to the A / D converter 51 via F62, the dynamic range of the input signal of the A / D converter 51 is compressed.
The dynamic range of the converter 51 (the level range of the input signal that can be A / D converted) can be used effectively.

As is well known, quantization noise occurs in A / D conversion and D / A conversion operations. As shown in FIGS. 9 and 10, when the non-linear emphasis circuit 2 is inserted after the A / D converter 51 and the D / A converter 53, triangular noise caused by FM modulation can be suppressed. Noise cannot be suppressed.

In contrast, in the embodiment of FIG. 11, the A / D converters 51 and D
The nonlinear emphasis circuit 2 is provided before the A / A converter 53 to emphasize the high frequency components of the minute amplitude signal,
Since the signal is input to the converter 51, an effect that the non-linear emphasis circuit 2 can suppress quantization noise can be expected. Therefore, when the configuration of the present embodiment is applied to a VTR, even after a large number of dubbing edits are repeated, the deterioration of the signal due to the quantization noise is small, and a good reproduced image can be obtained.

Although the embodiments of the present invention have been described above, the present invention can be variously modified and implemented without departing from the gist. For example, in the embodiment, the case of the VTR has been described. However, the present invention can be applied to transmission / reception of a television or the like, or can be applied only to a reproduction-only device such as a video disc player or a television receiver.

[Effects of the Invention] According to the present invention, high-order harmonics generated in the nonlinear de-emphasis circuit can be prevented from being mixed into the final output to significantly reduce waveform distortion, and high-order harmonics generated in the nonlinear emphasis circuit can be reduced. Since the amount of moire caused by harmonics can be reduced, a good reproduced image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing a specific example of a nonlinear emphasis circuit used in the present invention. FIG. 3 is a diagram showing input / output characteristics of a compressor in the nonlinear emphasis circuit. FIG. 4 is a specific diagram of a nonlinear deemphasis circuit used in the present invention. FIG. 5 is a diagram showing an example. FIG. 5 is a diagram showing a specific example of an FM demodulation circuit used in the present invention.
FIG. 7 is a diagram showing a signal waveform and a frequency spectrum of each part for explaining the operation of the embodiment of FIG. 1, FIG. 7 is a block diagram showing a second embodiment of the present invention, and FIG. FIG. 9 shows a frequency spectrum for explaining the operation of FIG.
10 and 11 are block diagrams showing third, fourth and fifth embodiments of the present invention. 2 ... Non-linear emphasis circuit, 4 ... FM modulation circuit, 5
...... Recording head, 6 ... Magnetic tape, 7 ... Reproduction head, 9 ... FM demodulation circuit, 11 ... Non-linear de-emphasis circuit, 12 ... Low-pass filter (second low-pass filter), 14 ... First Low-pass filter, 51 ... 1st A /
D converter 52, a recording processor (first digital processor), 53 first D / A converter 54 54 first low-pass filter 55 second low-pass filter 56
... Second A / D converter, 57... Reproduction processor (second digital processor), 58... Second D / A converter, 59.
... a third low-pass filter, 61, 62 ... a first low-pass filter, 63 ... a second low-pass filter.

Claims (2)

(57) [Claims] An image signal comprising a luminance signal and a chrominance signal is transmitted to a first signal.
After converting to digital signal by A / D converter of
Is converted to a TCI signal by the digital processor of
A first device that converts a signal into an analog signal by a first D / A converter, smoothes the signal with a first low-pass filter, and sends the signal to a transmission system through a non-linear emphasis circuit and an FM modulation circuit; Demodulated by an FM demodulation circuit through a non-linear de-emphasis circuit and a second low-pass filter, and converted into a digital signal by a second A / D converter. , The luminance signal and the chrominance signal are separated into analog signals by a second D / A converter, and then smoothed by a third low-pass filter to restore a video signal. And the second low-pass filter sets the band of the TCI signal to f
o, when the sampling frequency of the second A / D converter is fs, the non-linear de-emphasis circuit has a characteristic of attenuating high-order harmonic components of an output signal at a frequency of fs-fo. Video signal transmission device. 2. A video signal comprising a luminance signal and a chrominance signal,
After converting to digital signal by A / D converter of
Is converted to a TCI signal by the digital processor of
After the signal is converted into an analog signal by a first D / A converter, the signal is passed through a non-linear emphasis circuit, and the output signal of the non-linear emphasis circuit is smoothed by a first low-pass filter and high-order harmonic components are attenuated. A first device that sends out to the transmission system through an FM modulation circuit, and an FM signal supplied through the transmission system is demodulated by an FM demodulation circuit, and is then transmitted through a non-linear de-emphasis circuit and a second low-pass filter. After being converted into a digital signal by a second A / D converter, the signal is separated into a luminance signal and a chrominance signal by a second digital processor, and the luminance signal and the chrominance signal are converted into an analog signal by a second D / A converter. And then restores the video signal by smoothing with a third low-pass filter, and the second low-pass filter sets the band of the TCI signal to f
o, when the sampling frequency of the second A / D converter is fs, the non-linear de-emphasis circuit has a characteristic of attenuating high-order harmonic components of an output signal at a frequency of fs-fo. Video signal transmission device.