JPS61192172A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a malfunction by providing two detection periods, namely, one that has a same detection period as usual and the other that has a detection period to detect a ghost by detecting a signal in a time of over 1/2 of the time of a horizontal period within a vertical blanking period, and terminating the process of the ghost elimination by the output. CONSTITUTION:A long ghost detection part 10 to detect a ghost with a long delay time and a timing pulse generating circuit 11 for a detection are provided. A period that is adequate to the detection of a long ghost is a horizontal period in a vertical blanking period that has no video signal and consists of a horizontal synchronous signal and a burst signal. In a normal state, no outputs of signals differentiated or differenced are exist due to no signals in this period, but when the ghost is mixed, a differentiated output is generated. Judging a level from this output signal, and when the level is higher, it is controlled that the output of a transversal filter 9 is not displayed on the screen so as not to execute a ghost process.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ghost removal device that can be used in television receivers.

FIG. 3 shows the configuration of a general ghost removal circuit in a conventional television receiver. Furthermore, a waveform diagram illustrating a general ghost detection method is shown in FIG.

The principle of removing ghosts will be explained based on FIG.

As is generally well known, in the television broadcast transmission system, if the transfer function in the radio wave propagation system is H(s) and the transfer function in the ghost propagation system is G(8), then the transfer function of the total signal propagation system is , H(!I)・G(s). On the other hand, since the transversal filter surrounded by the dotted line in Figure 3 can have any transfer function, the transfer function of this filter is the transfer function G (s) that is opposite to the transfer function G (s) of the propagation system due to the ghost described above. Function G-'
(s+), ghosts can be removed. The thin part in Fig. 3 shows that this transversal filter 9 acts between reverse transmission &G (
fi), a ghost detection section 5, a tap gain modification circuit 4, and a timing circuit 6 for automatically modifying the gain of each tap so as to have the following characteristics.

Further, the transversal filter 9 includes a tapped delay line 1, a tap gain loading circuit 2, and an adder circuit 3. A video signal containing a ghost is input from an input terminal 7, and one is directly supplied to an adder circuit 3. The other one is supplied to a tapped delay line 1, and each tap output is controlled to an appropriate gain of 1 through a tap gain loading circuit 2, taken out, and supplied to an adder circuit 3. The output of the adder circuit 3 is output to the output terminal 8 while the ghost is removed, and is also supplied as an input to the ghost detection section 6.

The ghost detection section detects residual ghosts and modifies the weighting coefficient of the tap gain modification circuit to reduce the ghosts.
Repeat this operation to remove ghosts.

The timing circuit 6 generates pulses and the like that correctly indicate the position where a ghost is being detected.

The transversal filter shown in FIG. 3 is a so-called output-loaded transversal filter (also has a feedforward type configuration).

The transversal filter 9 may be of an input load type. It can also be configured as a feedback type. In other words, in order to remove ghosts, it is only necessary to correctly control each tap gain of the transversal filter.

Next, detection of ghosts necessary to correctly control the gain of each tap will be explained. As a reference waveform for determining the transfer function of a transmission system, a narrow impulse waveform with sufficiently long flat portions at the front and rear is suitable. The reason for this is that if another signal is near the reference waveform, the ghost of that signal and the reference waveform will overlap, making it impossible to correctly distinguish the ghost. A waveform that perfectly matches this tea juice is not included in current television broadcast waves, but if you take the differential or difference waveform of the leading edge of the vertical synchronization pulse as shown in Figure 4, it will be 27 μS before and after. An impulse waveform with a certain level of flatness can be obtained. Therefore, ghost detection is generally performed in this part.

For example, when two ghosts as shown in Fig. 4 (el) are mixed, the delay time τ1 and amplitude of ghost 1 are 1,
The ghost can be removed by detecting 2 in the delay time τ2 and the amplitude - of the ghost 2, controlling the tap gain loading circuit 2 so that the delay times τ1 and τ2 have a width corresponding to the respective delay times τ1 and τ2, and adding them.

Problems to be Solved by the Invention However, in such a ghost detection method, as can be inferred from FIG. There is a problem that the ghost overlaps with the ghost detection period.

FIG. 6 shows the state. Ghost 3 shown in FIGS. 5(a) and 5(b) has a delay time τ3 of 30 μB or more, and the ghost of the equalization pulse overlaps with the ghost detection period.

As a result, as shown in Figure 6(C), the ghost component of the equalization pulse is judged as a ghost of the reference waveform.
This will result in incorrect detection. A correct ghost has a delay time of τ3 and an amplitude of 3, but there are two detected ghosts, and the delay times are τ4 and 75, and the amplitudes are 4 and -5. For this reason, if the ghost removal process is continued as is, the number of ghost detection units will be reduced by 4 and -6, but a ghost will occur in the video signal, that is, on the screen, which is a problem.

Means for Solving the Problems In the ghost removal device of the present invention, two ghost detection periods are provided, one with the same detection period as the conventional one and one with the same detection period as the conventional one.
As a point, 1/2 of the horizontal period during the vertical retrace period
A detection period is provided to detect the ghost, which causes the long delay time problem mentioned above, by detecting the signal during the above time period, and the output of the detection period is used to stop the ghost removal process.

According to the ghost removal device of the present invention, a new detection period for detecting a ghost with a long delay time can be provided, the state of the detection output can be determined, and processing can be performed to prevent malfunctions. For example, even if it is used in an area where long ghosts of 30 μs or more are mixed, such as the Tokyo subcenter ghost, it will not cause malfunction.

Embodiment Hereinafter, a ghost removal device according to an embodiment of the present invention will be explained with reference to the drawings. FIG. 1 shows a block diagram, and FIG. 2 shows a waveform diagram for explaining the operation. In FIG. 1, blocks that are the same as in the prior art are given the same numbers.

This circuit is characterized in that it is provided with a long ghost detection section 1o that detects ghosts with a long delay time, and a timing pulse generation circuit 11 for detection.

A suitable period for detecting a long ghost is a horizontal period during a vertical retrace period in which there is no video signal and consists only of a horizontal synchronizing signal and a burst signal.

This is shown in FIG. 2(a), Φ). And Figure 2 (C)
The timing pulse generator 11 generates a pulse as shown in FIG. 1, and a ghost during this period is detected.

Normally, there is no signal during this period, so there is no differential or differential signal output, but if a ghost is mixed in as shown in Figure 2 (d), a differential output will occur as shown in Figure 2 (e). . The level is determined from this output signal, and when the level is large, control is performed so that ghost removal processing is not performed and the output of the transversal filter described above is not displayed on the screen. The timing pulse generation circuit 11 can be realized using a mono-multivibrator, a pulse counting method, or the like based on the output of the original timing circuit 6.

In addition, the means for detecting and determining long ghosts requires only a small addition of software in devices that originally use ghost detection means using microcomputers, etc., and can be easily performed using peak detection, etc. It is something.

Effects of the Invention As described above, the ghost removal device of the present invention prevents malfunctions in ghost areas with long delay times, which have conventionally caused malfunctions, because it has means for detecting the presence or absence of long ghosts. This is extremely advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a ghost removal device according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining its operation, and FIG.
This figure is a block diagram of a conventional ghost removal device, FIG. 4 is a waveform diagram for explaining its ghost detection operation, and FIG. 6 is a waveform diagram of the detection section when a long ghost exists. 1...Tapped delay line, 2...Tap gain loading circuit, 3...Addition circuit, 4...
...Tap gain correction circuit, 6...Ghost detection circuit, 6...Timing circuit, 9...
Transversal filter, 10...Long ghost detection circuit, 11...Long timing pulse generation circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (K Figure 3 f--ri-J7'f, Tjt** Figure 4 Figure 5 m-tey→

Claims (1)

[Claims] A ghost removal circuit that inputs a video signal to a transversal filter and automatically removes ghosts by combining the output of the transversal filter with the original video signal, and a horizontal period during the vertical retrace period of the video signal. , means for detecting a signal component included in 1/2 or more of the horizontal period, and means for stopping processing of the ghost removal circuit in accordance with the detected output. Ghost removal device.