JPH01166692A - Television signal transmission system - Google Patents

Abstract

PURPOSE:To eliminate transmission line distortion by transmitting a luminance signal while split into a low frequency luminance signal (YL) including a band with the transmission line distortion in existence therein and a high definition luminance signal (YH), excluding the band of the signal YL subjected to distortion at the reception side, synthesizing the result with the signal YH and reproducing the synthesized signal. CONSTITUTION:A video signal obtained from a TV camera is subjected to pre-processing, converted into a luminance signal Y and inputted to the reception side. A signal with higher frequency than a frequency f0 lower than the upper limit transmission frequency of the standard system passes through an HPF and the high definition luminance signal YH is extracted. The signal YH is mixed 13 with a subcarrier fSH for high definition luminance signal from an oscillator 14 into carrier high definition luminance information YH', which is shifted into the transmission band of the standard system. The information signal YH' is added 12 with the signal Y and only the frequency in the TV transmission band is sent by an LPF 15. The signal YH is separated 21 from the signal sent at the reception side to obtain the information YH' and the signal YL is formed by subtraction, the result is given to an LPF 25 to obtain a frequency signal YL' lower than the frequency f0 is obtained. Moreover, the information YH' is subjected to frequency conversion by the signal fSH from an oscillator 24, given to an HPF to obtain the signal YH, which is added to the frequency YH'. Thus, the TV signal transmission system without any distortion is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a television signal transmission system, and particularly to a high-definition television signal transmission system that is compatible with a television receiver.

[Conventional technology]

Due to advances in semiconductor technology and demands for higher image quality, the current N
The TSC color television system is being reviewed, and a high-definition television system is being proposed. Among them, one of the major features of the system called HDTV is that it is compatible with receivers and transmission lines. In other words, even a conventional NTSC system receiver can receive images, and conversely, even an EDTV system receiver can receive images using a conventional NTSC system.
It is possible to receive SC system broadcasts. This EDTV
Regarding the method, see 1, for example, JP-A-59-171387.
In addition to the method described in this issue, many other methods have been published.

[Problem that the invention seeks to solve]

One of the characteristics of the above-mentioned conventional technology is transmission path compatibility. However, if we attempt to transmit the EDTV system as proposed in the past over the current transmission line, distortion of the frequency characteristics of the transmission line (amplitude distortion) will occur.

There was a problem in that the received image was affected by group delay distortion (group delay distortion). The EDTV system has a wide luminance signal band of approximately 6 MHz, and in order to transmit this through a conventional 4.2 MHz transmission path, the frequency of high-frequency components is shifted to below 4.2 MHz. However, in the conventional NTSC transmission line, the band is limited by a filter with a steep cutoff characteristic to avoid interference from adjacent channels, and the amplitude characteristic and first group delay characteristic are particularly low at frequencies close to the upper limit transmission frequency of 4.2 MHz. It's getting worse. If the luminance signal is reproduced on the receiving side after passing through such a transmission path, it will be reproduced as a distorted signal at a frequency around 4.2 MHz.

An object of the present invention is to provide a high-definition television signal transmission system that avoids the influence of such transmission path distortion and does not cause deterioration in image quality.

[Means for solving problems]

The purpose of the above is that when dividing a luminance signal into a low-band luminance signal (Yc, Y
This is achieved by combining L with YH except for the band subject to distortion and reproducing the luminance signal.

The transmission upper limit frequency for the band with large transmission path distortion is 4.2 MHz.
If it is located nearby and this is fo ~4.2 MHz,
As Yll, a signal with a higher frequency than fo is extracted by a high-pass filter HPF, and this is converted to f.

IIYL, whose frequency is shifted to a lower band, maintains compatibility with the conventional method by transmitting components up to 4.2 MHz, the same as the conventional method.

On the receiving side, out of YL, fo ~ 4.2 which received transmission line distortion
By removing the MHz band component using a low-pass filter LPF and combining it with YH, a luminance signal that is not subject to distortion is reproduced.

[Effect]

It is desirable that the cut-off frequencies of the above-mentioned HPF on the transmitting side and LPF on the receiving side be precisely matched and have opposite characteristics to each other. As a result, the luminance signal is connected by fo without too much or too little band, and a flat frequency characteristic can be obtained. This is not a problem because it can be easily and accurately realized by digital signal processing.

In order to avoid frequency-shifted YH acid components and transmission path distortion, the band from fo to 4.2 MHz must be shifted to avoid this. This can be solved by selecting the frequency.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram in which the present invention is implemented on the transmitting side, where 11 is a high-pass filter (HPF), 12 is an adder, 13 is a frequency converter, 14 is an oscillator, and 15 is a low-pass filter (
LP F).

A video signal obtained from a television camera is converted into a luminance signal Y through a preprocessing circuit and is input to the circuit shown in FIG. H
PFII is a filter that passes signals with a higher frequency than the frequency fo, and the 0 frequency io for extracting the high-definition luminance signal Yo from the luminance signal is the lower limit frequency at which transmission path distortion, which will be described later, exists. The high-definition brightness signal YH is frequency-mixed by the frequency converter 13 with the high-definition brightness signal subcarrier fsu from the oscillator 14 to become carrier high-definition information YH'.

aY frequency shifted within the NTSC TV transmission band
H' is added with the luminance signal Y by the adder 12, and L
Only frequency components within the TV transmission band are extracted and transmitted by the PF 15.

Next, in Fig. 2, an embodiment of the receiving side will be explained.In Fig. 0, 21 is a circuit 22 for extracting high-definition information from the received EDTV signal.
is an adder/subtractor, 23 is a frequency converter, 24 is an oscillator, 25
26 is a low pass filter (LPF), 26 is a high pass filter (HPF), and 27 is an adder.

The received FDTV signal is demodulated in a preprocessing circuit and ED
The signal becomes a TV signal, and the high-definition information YH' is separated by the high-definition information separation circuit 21. The synthesis and separation of YH' is described in detail in the above-mentioned Japanese Patent Application Laid-Open No. 171387/1983, so the explanation will be omitted here.

In the adder/subtractor 22, YH/ is subtracted from the EDTV signal to obtain the low-band luminance signal YL. mYn' is frequency-mixed with the high-definition luminance signal subcarrier fsu from the oscillator 24 in the frequency conversion 1lI23, and is outputted by the HPF 26. The aS wave is extracted and a high definition signal YH is reproduced. On the other hand, a signal YL having a frequency lower than the aforementioned fo is extracted by the LPF 25 and added to Yn by an adder 27 to reproduce a wideband luminance signal Y.

In the above, 4.2 MHz from fo of the luminance signal
Frequency components up to are included in both Yt and YH/. However, the components included in YL are distorted by the frequency characteristics of the transmission path. Therefore, by removing the distorted components of YL on the receiving side, a distortion-free luminance signal Y can be reproduced.

The operation of the above embodiment will be explained using a frequency spectrum diagram. FIG. 3 is a diagram showing the signal spectrum and filter frequency characteristics of each part in FIGS. 1 and 2. FIG. Figure a shows the mechanism for separating YH from the luminance signal Y and fso. HPFll has a cutoff frequency at fo and separates YH from Y.

YH is frequency-mixed with fsH, and the zero-combined signal that is frequency-shifted to a low frequency band and combined with Y is band-limited by an LPF 15 having a cutoff frequency of 4.2 MHz.

(B in the same figure) C in the same figure shows the transmission line frequency characteristics, from fo to 4.2MH
The characteristics deteriorate in the z region. Therefore, the received signal is distorted as shown in d of the same figure. However, f of the luminance signal included in YH.

The ~4.2MHz component is not distorted at all, so it is LP.
At F25, remove the distorted component of YL and make it YL.
By frequency-shifting H' by fsg and adding it as YH (see e in the figure), a distortion-free luminance signal Y can be reproduced.

As shown in Figure 3e, in order for the frequency characteristics to be flat in the connection between Y and YH, it is necessary to precisely match the cut-off frequency characteristics of HPFII and LPF25 to fa, but by using digital signal processing technology, This can be easily achieved. Also.

The high frequency side signal component of YH' may be applied to a distorted band and cause distortion, but this problem can be avoided by appropriately selecting fso.

In the following embodiment, a method of selecting fsH below Yo is explained, but it is also possible to select above fsHttYu. FIG. 4 shows a spectrum diagram in this case. In this case, the spectrum of YH' is inverted in frequency with that of YH. Therefore, the fo acid component of YII is located on the high frequency side of the transmission band, contrary to the case shown in FIG. Therefore, in order to prevent this component from being subjected to transmission path distortion, fsn must be selected at a frequency lower than twice fo.In the case of Figure 4, the high frequency component of YH is There will be no transmission distortion.

〔Effect of the invention〕

According to the present invention, it is possible to avoid the effects of amplitude distortion and delay distortion that occur near the upper limit frequency in the frequency characteristics of the TV transmission path, so that the amplitude distortion and delay that occur in the component of the luminance signal near 4.2 MHz can be avoided. A distortion-free television signal transmission system can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a transmitting side configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing a receiving side configuration of an embodiment of the present invention, and FIG. 3 is a block diagram showing the configuration of a receiving side of an embodiment of the present invention. Figure 4 shows the signal spectrum and filter frequency characteristics to explain the operation of
The figure is a diagram showing a signal spectrum and filter frequency characteristics for explaining another operating method of FIGS. 1 and 2. 11.26...High-pass filter, 12,22°27
... Adder/subtractor, 13.23... Frequency converter. 14.24... Oscillator, 15.25... Low pass filter, 21... High definition information separation circuit.

Claims (1)

[Claims] 1. The high-definition component of the luminance signal is frequency-converted and transmitted within the same band as the standard method, and can be received by a standard method receiver,
And in a high-definition television signal transmission system that allows a receiver using this system to receive standard system signals,
A high-definition component of the luminance signal is extracted by a high-pass filter whose low cutoff frequency is f_0, which is lower than the upper limit transmission frequency of the standard method, and the high-definition luminance is extracted by a subcarrier for the high-definition component, which is even lower than the frequency f_0. A signal is frequency-converted and transmitted within the same band as the standard method, and the receiving side separates the frequency-converted high-definition luminance signal and reproduces the high-definition luminance signal using the high-definition component subcarrier, and A low frequency component of the received luminance signal is extracted by a low pass filter having a frequency f_0 as a high cutoff frequency, and the low frequency luminance signal component and the high definition luminance signal are added and synthesized to obtain a wideband luminance signal. Accordingly, the frequency f_
1. A television signal transmission system characterized by avoiding amplitude distortion and group delay distortion of transmission line frequency characteristics in a frequency band from 0 to the upper limit transmission frequency. 2. In the television signal transmission system according to claim 1, the high-definition component subcarrier frequency is selected to be less than twice the frequency f_0, and the high-definition luminance signal is the same as the standard method. A television signal transmission system that is characterized by converting frequency components by inverting them within the band.