JPS62265870A - Reference signal generating circuit for removing ghost - Google Patents

Abstract

PURPOSE:To improve performance removing a ghost by overlapping a digital signal string whose transmission speed is larger than that of the doubled video band of a television signal and using said overlapped string as a ghost removal reference signal. CONSTITUTION:A timing generating circuit 2 generates a transmission clock larger than the doubled video signal band with the aid of a television signal string generating circuit 1. A digital signal string generating circuit 4 generates the digital signal string at the timing of the transmission clock in synchronization with a color subcarrier frequency, and a signal overlap circuit 3 overlaps the digital signal string with a television signal. Since power that the digital signal string has is greater than that of a single pulse, the influence due to noise can be reduced if the digital signal string is used as a reference signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is designed to reduce the vertical retrace period of a television signal in order to remove group delay distortion, single frequency amplitude characteristic distortion, ghost, etc. that occur during the transmission of a television signal. The present invention relates to a reference signal generation circuit for ghost removal superimposed on the reference signal.

Conventional technology Traditionally, vertical inter! The difference signal of the leading edge of the 1Ill signal was used. (Reference: Onishi et al., “
"Automatic Ghost Removal from Television Images" (NHK Giken Monthly Report, 1973) The conventionally used reference signal will be explained with reference to FIGS. 4 and 5. In FIG. 4, lOO is the leading edge of the vertical synchronizing signal, 101 is a ghost, and 102 is a vertical equalization pulse. The ghost 101 is a delayed version of the leading edge 100 of the vertical sync signal. FIG. 5 shows a signal waveform obtained by subtracting the leading edge portion 100 of the vertical synchronization signal and the ghost 101. FIG. In the figure, 103 is a difference signal of the leading edge portion 100 of the vertical synchronization signal, and 104 is a difference signal of the ghost 101. Difference signal 103 of leading edge of vertical synchronization signal
A difference signal 104 between the signal and the ghost indicates an impulse response of the transmission system, and is used to remove the ghost.

Furthermore, the Japan Broadcasting Corporation has proposed a ghost removal reference signal (OCR) as shown in FIG. (Reference: Obara et al., A Study of Reference Waveforms for Ghost Removal, TV Science and Technology Report, RE81-6. 1982.) In the same figure, 1
10 is a bar signal, 111 is a pulse signal, 112 is a color burst, and 113 is a horizontal synchronization signal. Pulse signal 1
11 is used to estimate the impulse response of the transmission system. Further, the bar signal 110 is used to detect the occurrence of sag due to the transversal filter.

Problems to be Solved by the Invention The problem with conventionally using a vertical synchronization signal as a reference signal for ghost removal is that the signal quality of the synchronization signal of a television signal is not as good as that of a video signal such as DG or DP. This is because the parameters indicating signal quality are not guaranteed. Furthermore, the synchronization signal portion of a television signal modulated with an RF signal has the highest signal power and is susceptible to nonlinear distortion. Therefore, the correlation between waveform distortion between the video signal and the synchronization signal due to ghosts and the like is not perfect, and when the leading edge of the vertical synchronization signal is used as a reference signal for ghost removal, it is difficult to sufficiently remove ghosts.

Furthermore, in the reference signal for ghost removal proposed by the Japan Broadcasting Corporation, the pulse signal 111 is equivalent to a 1.5T pulse (half-width 187
．． 5 ns) pulses are required. (Reference: Ohara et al., System Study of Adapter Type Ghost Canceller, TV Science and Technology Report, IT52-1. 1984) However, in the case of such a pulse signal, proximity is a problem in teletext broadcasting. It is difficult to obtain information for correcting ghosts, group delay distortion, single frequency spreading characteristic distortion, etc. This is because the impulse response to the transmission distortion is expressed as a collection of many pulses in the vicinity of the original pulse. This is because it is difficult to separate the latter pulse from the original pulse.

Also, since it is a single pulse, its signal power is small;
It was easily affected by noise.

Furthermore, even in the time range in which ghosts can be removed, the method using the vertical synchronization signal leading edge 100 as a reference signal,
For ghosts delayed by 1/2 horizontal period or more, it is delayed (it is not possible to determine whether No. 3 is due to the reference signal or another signal is delayed. This is shown in Fig. 7). , will be explained using Fig. 8. Fig. 7 is a signal diagram showing a delayed ghost of 1/2 horizontal period or more. In the figure, 100 is the leading edge of the vertical synchronization signal, 102 is the equivalent pulse,
Reference numeral 105 is a ghost created by the delay of the equivalent pulse 102. FIG. 8 is a signal diagram showing a signal obtained by subtracting the leading edge portion 100 of the vertical synchronization signal and the ghost 105. In the figure, 103 is a difference signal of the vertical synchronizing signal leading edge 100;
06 is the difference signal of the ghost 105. Figures 7 and 8
From the figure, it is not possible to distinguish whether the ghost 105 is a ghost caused by the equivalent pulse 102 or whether it is caused by two ghosts in which the vertical synchronizing signal leading edge 100 is delayed.

Therefore, the ghost removal range of the ghost removal device using the vertical synchronization signal leading edge 100 as a reference signal is at most 1/2.
There is only a horizontal period. In addition, the standard signal for ghost removal proposed by the Japan Broadcasting Corporation has the following signal format:
Ghosts with a delay time of 16.8 microseconds or more cannot be removed for the same reason as above.

In view of the above-mentioned problems, the present invention uses, as a reference signal for ghost removal, a digital signal train in which the transmission speed of the digital signal train is higher than twice the video band of the television signal. Provides a reference signal for ghost removal that is a signal with higher power than a pulse signal, can also remove ghosts with a delay of 1/2 or more time period, and is transmitted under exactly the same conditions as other video signals. It is.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a circuit that superimposes a reference signal for ghost removal on the vertical retrace period of a television signal, so that the transmission speed of the digital signal train is higher than that of the television. This generates a digital signal train that is larger than twice the image band of the image signal.

Effect of the Invention The present invention uses the means described above to superimpose a digital signal train on a television signal, the transmission speed of which is more than twice the video band of the television signal, and use it as a reference signal for ghost removal. To provide a reference signal for ghost removal that is a signal with higher power than a single pulse signal, can also remove ghosts delayed by 1/2 horizontal period or more, and is transmitted under exactly the same conditions as other video signals. It is something.

Embodiment FIG. 1 is a circuit configuration diagram showing an embodiment of a reference signal generation circuit for ghost removal according to the present invention. In the figure, l is a television signal generation circuit, 2 is a timing generation circuit,
3 is a signal superimposition circuit, and 4 is a digital signal string generation circuit. This operation will be explained below. From the output of the television signal train generation circuit 1, a timing generation circuit 2 generates a transmission lock larger than twice the video signal band. The digital signal train generating circuit 4 generates a digital signal train at the timing of this transmission lock, the phase of which is synchronized with, for example, the color subcarrier frequency. This digital signal string is superimposed on a television signal by a signal superimposition circuit 3.

FIG. 2 is a waveform diagram showing an example of a reference signal for ghost removal superimposed during the vertical retrace period. In the same figure, 2
1 is a digital signal train, 22 is a signal train superimposition period, 23 is a color burst, and 24 is a horizontal synchronizing signal. In this example, the vertical synchronization signal during the vertical retrace period and the signal string superimposition period 2 shown in FIG.
2, the signal sequence is superimposed as a binary N RZ (sign),
A digital signal train 21 is obtained.

Next, a description will be given of how the superimposed digital signal sequence is used as a reference signal for ghost removal.

FIG. 3 is a circuit configuration diagram showing a ghost removal device using a transversal filter as an example of a ghost removal device. In the figure, 11 is a transversal filter, 12 is a tap gain control circuit, and 13 is an error signal train generation circuit. A television signal containing a ghost is processed by a transmission system that generates group delay distortion, frequency amplitude characteristic distortion, ghost, etc., and finally a transversal filter 11 having an inverse characteristic. Ghosts etc. are removed. From this output signal, an error signal train generating circuit 13 generates an error signal train corresponding to waveform distortion due to removal errors such as group delay distortion, single frequency amplitude characteristic distortion, and ghost. The tap gain control circuit 12 is controlled by the error signal train and the input signal of the transversal filter 11.
The transversal filter 11 is controlled using an algorithm such as the least square error method so that the error signal sequence is minimized, that is, the group delay distortion 1 frequency amplitude characteristic distortion, ghost, etc. are removed. .

The error signal sequence is obtained by selecting the digital signal sequence, which is a reference signal, from the television signal that has been transmitted and from which the group delay distortion, frequency amplitude characteristic distortion, ghost, etc. have been removed by the transversal filter 11;
It is obtained as a difference between the expected signal string corresponding to the selected digital signal string that is included in the error signal string generation circuit 13 or calculated by the error signal string generation circuit 13.

The power of the digital signal train is greater than the power of a single pulse. Therefore, if the digital signal train is used as a reference signal, the influence of noise is less than when using a conventional single pulse.

Further, the least square error method or the like is used as a control method for the transversal filter 11, and the error signal sequence is correlated with a human input signal sequence or the like to obtain a correction amount only for the tap amount. Even if the signal contains errors due to signals other than the reference signal, the influence can be removed. Therefore, it is also possible to remove ghosts with a delay longer than 1/2 horizontal period.

As described above, according to this embodiment, by using a digital signal train whose transmission speed is higher than twice the video band of a television signal as a reference signal for ghost removal, the transmission speed of the digital signal train is faster than that of a single pulse signal. It is possible to obtain a reference signal for ghost removal that is a high-power signal and can remove ghosts with a delay of more than 1/2 million period, and that is transmitted under exactly the same conditions as other video signals. It is possible to enhance the ghost removal effect.

Effects of the Invention As described above, based on the present invention, a digital signal train whose transmission speed is higher than twice the video band of the television signal is superimposed on a television signal to obtain a standard for ghost removal. By using it as a signal,
- Power is larger than the pulse signal (no. 8, and using correlation calculations such as the least square error method, it is possible to remove ghosts delayed by more than 1/2 horizontal period, and the conditions are exactly the same as other video signals) The signal becomes a reference signal for ghost removal transmitted by the ghost removal device, thereby improving the ghost removal performance of the ghost removal device.

[Brief explanation of drawings]

FIG. 1 is a block diagram in one embodiment of the present invention, and FIG.
The figure is a waveform diagram showing a reference signal for ghost removal of the present invention,
FIG. 3 is a circuit configuration diagram showing a ghost removal device, and FIGS. 4, 5, 6, and 7. FIG. 8 is a waveform diagram showing a conventional ghost removal reference signal. 1...Television signal generation circuit, 2...
...High definition device, 3...Signal superimposition circuit, 4
... Control circuit, 5 ... Digital signal train generation circuit, 11 ... Transversal filter, 12 ... Tuff gain control circuit, 13 ...
...Error signal string generation circuit, 21...Digital signal string, 22...Signal string superimposition period, 23.
...Color burst, 24...Horizontal synchronization signal. Name of agent Patent attorney Toshio Nakao (1 person) Figure 1 Figure 2 Figure 3 4rXJ /〃 Figure 5

Claims (3)

[Claims] (1) In a reference signal generation circuit for ghost removal that superimposes a reference signal for ghost removal on the vertical retrace period of a television signal, a digital signal train whose transmission speed is more than twice the video band of the television signal A reference signal generation circuit for ghost removal characterized by generating a signal train. (2) The reference signal generation circuit for ghost removal according to claim (1), characterized in that the transmission speed of the digital signal train is twice the video band of the television signal. (3) The reference signal generation circuit for ghost removal according to claim (2), characterized in that the transmission speed of the digital signal train is twice the color subcarrier frequency of the television signal.