JPH0797834B2 - Reference signal generator for ghost removal - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost removing reference signal generating device for removing group delay distortion, frequency amplitude characteristic distortion, ghost, etc., generated during transmission of a television signal. Is.

2. Description of the Related Art Conventionally, as a most effective means for removing a ghost generated during transmission of a television signal, there is a ghost removing device using a transversal filter as shown in FIG. This is a thing which considers the transmission system which produces | generates a ghost as one filter, produces | generates the filter characteristic used as the reverse characteristic by the said transversal filter, and removes a ghost.

The most important point in the ghost elimination device using this transversal filter is the reference signal for estimating the filter characteristic of the transmission system. As the reference signal, the differential signal at the leading edge of the vertical synchronizing signal is used.
(Reference: Onishi et al., Automatic ghost removal of TV images,
(Showa 53.5 NHK STRL Monthly Report) Regarding the previously used reference signal,
This will be described with reference to FIGS. In FIG. 8, 100 is a leading edge portion of the vertical synchronizing signal, 101 is a ghost, and 102 is a vertical equalizing pulse. The ghost 101 is the leading edge portion 100 of the vertical sync signal.
Is late. FIG. 9 shows a signal waveform when the leading edge portion 100 of the vertical synchronizing signal and the ghost 101 are differentiated.
In the figure, 103 is a differential signal of the front edge portion 100 of the vertical synchronizing signal, and 104 is a differential signal of the ghost 101. The difference signal 103 at the leading edge of the vertical synchronizing signal and the ghost difference signal 104 indicate the impulse response of the transmission system, and this is used to remove the ghost.

The problem with using a vertical sync signal as a reference signal for ghost elimination is that the signal quality of the sync signal of the television signal is guaranteed by a parameter that indicates the signal quality of the video signal such as DG and DP. That is not done.
Further, the sync signal portion of the television signal modulated into the RF signal has the highest signal power and is easily subject to nonlinear distortion. Therefore, the correlativity of the waveform distortion between the video signal and the sync signal due to ghost is not perfect, and it is difficult to sufficiently remove the ghost when the leading edge of the vertical sync signal is used as the reference signal for ghost removal.

Therefore, the Japan Broadcasting Corporation has proposed a ghost elimination reference signal (GCR) as shown in FIG. (Reference: Ohara et al., Examination of reference waveform for ghost removal TV Technical Report, RE81-6, Showa 56.2) In the figure, 110 is a bar signal, 111 is a pulse signal, 112 is a color burst, 113 is a horizontal sync signal. Is. The pulse signal 111 is used to estimate the impulse response of the transmission system. Also bar signal 11
0 is used to detect the occurrence of sag by the transversal filter.

As another proposal, a ghost eliminating reference signal (GCR) as shown in FIG. 3 has been proposed. (Reference: Japanese Patent Application No. 60-156458) Problems to be Solved by the Invention As mentioned above, the vertical synchronizing signal, the signal of FIG. 3, the signal of FIG. 10, etc. are used as reference signals for ghost elimination. There is. Among them, the use of the vertical synchronizing signal is not suitable because the ghost removing capability is insufficient as described above, and it is necessary to insert the ghost removing reference signal within the vertical blanking period. The signal in Fig. 10 and the signal in Fig. 3 are considered to have advantages and disadvantages, respectively.

For example, in FIG. 10, the pulse signal 111 is equivalent to 1.5T pulse (half-value width 187.5n
Second) pulse is required. (Reference: Ohara et al.,
System study of adapter type ghost canceller TV
However, in the case of such a pulse signal, the signal power is small and it is easily affected by noise and the like. Furthermore, the tenth
When using the bar signal and pulse signal in the figure, whether the delayed signal is due to the reference signal or the other signal is delayed with respect to the delayed ghost of 1/2 horizontal period or more I can't tell.

On the other hand, when a digital signal train is used, it has a larger power than a single pulse signal, and it is possible to remove delayed ghosts of 1/2 horizontal period or more by using a correlation calculation such as the least square error method. There is. On the other hand, there is a limit to the signal band that can remove ghosts.

Means for Solving the Problems In order to solve the above problems, the present invention is directed to generating a digital signal train which is either a predetermined one or a plurality of kinds of signal trains or a pseudo-random signal train. 1 ghost elimination reference signal generator and sin squared waveform or si
A second ghost removing reference signal generating circuit for generating a pulse signal having any of nX / X waveforms, a signal superimposing circuit having a television signal input terminal, and a switching control circuit, the signal superimposing circuit Is connected to the first ghost removing reference signal generating circuit, the second ghost removing reference signal generating circuit, and the switching control circuit, and the digital signal train is provided in a period other than the synchronizing signal within the vertical blanking period. The two kinds of ghost removing reference signals of the pulse signal and the pulse signal are switched for each field to be superimposed in the vertical blanking period, or to be superimposed in two different horizontal scanning periods of the same field.

Action The present invention, by the means described above, by superimposing a digital signal sequence on a television signal and using it as a ghost elimination reference signal, it is a signal with a power larger than that of a single pulse signal, and a half horizontal period or more. The invention also provides a signal capable of removing delayed ghosts, and further uses a pulse signal as a reference signal for ghost removal to provide a signal capable of removing ghosts up to a high frequency component of a video signal.

Embodiment An embodiment of the ghost eliminating reference signal generator of the present invention will be described below with reference to the drawings.

FIG. 1 shows a ghost eliminating reference signal generating circuit of the present invention. In FIG. 1, 1 is a first ghost eliminating reference signal generating circuit for generating a digital signal sequence, 2 is a second ghost eliminating reference signal generating circuit, 3 is a television signal input terminal, and 4 is a signal superimposing circuit. Reference numeral 5 is a switching control circuit, and 6 is an output terminal. In FIG. 1, the first ghost removing reference signal generating circuit 1 generates a digital signal train. The second ghost removing reference signal generating circuit 2 generates a pulse signal. In the signal superimposing circuit 4, the respective output signals of the first ghost removing reference signal generating circuit 1 and the second ghost removing reference signal generating circuit 2 are output in accordance with the output of the switching control circuit 5 to the vertical return of the television signal. Superimpose on the line period. This output is obtained at the output terminal 6, which is modulated by an RF modulator (not shown) and transmitted.

On the receiving side, the group delay distortion, frequency amplitude characteristic distortion, ghost, etc. generated in the transmission system are removed by using the ghost removing reference signal.

FIG. 2 is a block diagram showing an example of the configuration of the first ghost removing reference signal generating circuit 1 in FIG. Second
In the figure, 11 is a signal train generation circuit, 12 is a modulation circuit, and the above constitutes the first ghost removing reference signal generation circuit 1. In FIG. 2, the signal train generated by the signal train generating circuit 11 is modulated by the modulating circuit 12. A typical example of this modulation method is the NRZ modulation method.

FIG. 3 is a waveform diagram showing an example of the ghost eliminating reference signal superimposed during the vertical blanking period. In the figure, 30
Is a digital signal sequence, 31 is a signal sequence superposition period, 32 is a color burst, and 33 is a horizontal synchronization signal. In this example, the signal train is superposed as a binary NRZ signal in the signal train superimposing period 31 shown in FIG. 3 other than the vertical synchronizing signal in the vertical blanking period and the vertical equalizing pulse period, and the digital signal is superposed. The signal train 30 is obtained.

The output of the signal sequence generation circuit 11 is a predetermined one or a plurality of types of signal sequences or a pseudo-random signal sequence.

Here, the pseudo-random signal sequence is obtained by selecting a signal sequence that is sequentially superimposed on a television signal from a signal sequence obtained based on a random signal generation algorithm such as an M sequence, or is a read-on-memory. It is obtained by sequentially selecting a signal sequence corresponding to the amount to be superimposed on the television signal from the signal sequence recorded in, for example, and shows a signal sequence that can be considered to be almost random. In addition, the predetermined one or a plurality of types of signal sequences, one or a plurality of types of signal sequences arbitrarily selected from the pseudo-random signal sequence, or a specific suitable for ghost removal One or more signal sequences are shown.

Next, how to use the superimposed digital signal sequence as a reference signal for ghost removal will be described.

FIG. 4 is a circuit configuration diagram showing a ghost removing device using a transversal filter as an example of the ghost removing device. In the figure, 20 is a transversal filter, 21 is a control circuit, and 22 is an error signal sequence generation circuit.
A television signal including a ghost is transmitted through a transmission system that generates group delay distortion, frequency amplitude characteristic distortion, ghost, etc., and finally a transversal filter 20 having an inverse characteristic. Ghosts etc. are removed. From the output signal of this transversal filter 20,
The error signal string generation circuit 22 generates an error signal string corresponding to waveform distortion such as the group delay distortion and the frequency / amplitude characteristic distortion. The error signal train and the transversal filter 20
With the input signal of, the control circuit 21 controls the transversal filter 20 using an algorithm such as a least squares error method so that the error signal sequence is minimized, that is,
Control is performed so as to remove the group delay distortion, frequency amplitude characteristic distortion, ghost, and the like.

As a method of obtaining the error signal sequence, in the error signal sequence generation circuit 22, first, a signal obtained by binarizing the output of the transversal filter 20 according to the determination standard inside the receiver is obtained, and the signal of the transversal filter 20 is used as a reference. The error between the output and the binarized signal is obtained, and this is output as an error signal string.

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

Further, by using the least square error method or the like as the control method of the transversal filter 20, by calculating the correction amount of the tap weight by correlating the error signal sequence with the input signal sequence, etc. Even if an error due to a signal other than the reference signal is included in, the effect can be removed. Therefore, it is possible to remove the delayed ghost of 1/2 horizontal period or more.

On the other hand, the advantage of the ghost removing reference signal using the pulse signal is that the frequency characteristic extends to a high frequency band as described above. Therefore, it is possible to remove the ghost even in the high range of the video signal. Even in the case of a pulse signal, it is possible to remove the ghost by using the ghost removing device shown in FIG.
The error signal sequence generation circuit 22 of FIG. 4 has a reference pulse waveform due to a memory or the like, finds an error between it and the output of the transversal filter 20, and outputs this as an error signal sequence. The control circuit 21 repeatedly corrects the tap weight of the transversal filter 20 by calculating the error signal sequence and the input signal sequence to remove the ghost.

FIG. 5 shows an example of a waveform diagram of a ghost removing reference signal using a pulse signal. The example of the signal in FIG. 5 uses sinX / X signal. This signal is characterized by having a substantially flat frequency characteristic within the band.

Next, a method of signal superposition will be described. FIG. 6 is an example of a waveform diagram when the first ghost removing reference signal and the second ghost removing reference signal are superimposed in the vertical blanking period for each field. In this case, for example, 18H
It is more efficient to use the same horizontal period such as 281H in the vertical blanking period.

FIG. 7 is an example of a waveform diagram when the first ghost eliminating reference signal and the second ghost eliminating reference signal are superimposed in different horizontal periods within one field. As an example of the overlapping period, for example, two horizontal periods of 18H and 19H can be used.

As shown in FIG. 6 and FIG. 7, the ghost removal is performed by using the digital signal sequence as the ghost removal reference signal and the ghost removal by using the pulse signal in combination. The ghost removing performance of the removing device can be improved.

EFFECTS OF THE INVENTION As described above, according to the present invention, by superimposing a digital signal sequence as a first ghost removing reference signal on a television signal, a signal having a power larger than that of a single pulse signal, In addition, it is possible to remove the lag ghost of 1/2 horizontal period or more by using the correlation calculation by the least square error method, etc. Furthermore, by superimposing the pulse signal as the second ghost removal reference signal, the video signal component It becomes possible to remove ghosts up to a high range, and these can improve the ghost removal performance of the ghost removal device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention, FIG. 2 is a block diagram showing an example of a configuration of a first ghost removing reference signal generating circuit of the present invention, and FIG. 3 is a first ghost of the present invention. FIG. 4 is a waveform diagram showing a removing reference signal, FIG. 4 is a block diagram of a ghost removing device, FIG. 6 is a waveform diagram showing an example of a waveform of the ghost removing reference signal of the present invention, and FIG. 7 is a ghost removing device of the present invention. FIG. 5 is a waveform diagram showing another example of the waveform of the reference signal for use in the present invention, FIG. 5 is a waveform diagram showing an example of the second reference signal for removing ghost of the present invention, FIG. 8, FIG. 9 and FIG. It is a wave form diagram which shows an example of the reference signal for ghost removal. 1 ... First ghost elimination reference signal generation circuit, 2 ...
Second ghost elimination reference signal generation circuit, 4 ... Signal superposition circuit, 5 ... Switching control circuit, 11 ... Signal sequence generation circuit,
12 …… Modulation circuit, 20 …… Transversal filter, 21
...... Control circuit, 22 …… Error signal string generation circuit, 30 …… Digital signal string, 31 …… Signal string superposition period.

Continuation of the front page (56) References JP-A-58-191576 (JP, A) JP-A-60-39944 (JP, A) JP-A-59-40781 (JP, A) Television Society Technical Report Volume 4 No. 40 (Sho 56-2-26) P. 33-38 (Masaharu Ohara et al. "A study of reference waveform for ghost removal")

Claims (3)

[Claims] 1. A first ghost eliminating reference signal generating circuit for generating a digital signal sequence which is either a predetermined one or a plurality of types of signal sequences or a pseudo-random signal sequence, and a sin-squared waveform. Or a sinX / X waveform, a second ghost elimination reference signal generating circuit for generating a pulse signal, a signal superimposing circuit having a television signal input terminal, and a switching control circuit. A circuit is connected to the first ghost removing reference signal generating circuit, the second ghost removing reference signal generating circuit, and the switching control circuit, and the digital signal is provided in a period other than a synchronizing signal within a vertical blanking period. A ghost eliminating reference signal generating device, wherein two kinds of ghost eliminating reference signals of a column and the pulse signal are superimposed. 2. A signal superimposing circuit switches between an output of a first ghost removing reference signal generating circuit and an output of a second ghost removing reference signal generating circuit for each field according to the output of the switching control circuit. The reference signal generator for ghost removal according to claim (1), characterized in that they are superposed within a vertical blanking period. 3. A television set in which a signal superimposing circuit switches between an output of a first ghost eliminating reference signal generating circuit and an output of a second ghost eliminating reference signal generating circuit by the output of the switching control circuit. Different 2 within the vertical blanking period of the signal
The ghost eliminating reference signal generating device according to claim 1, wherein the reference signal generating device overlaps in one horizontal scanning period.