JPH01286680A - Ghost removing device - Google Patents

Abstract

PURPOSE:To detect a highly accurate zero level detection concerning the reference signal of a differential waveform by providing a zero level detecting means to detect the zero level of a reference waveform at a tap gain preparing circuit. CONSTITUTION:A receiving TV signal supplied to an input terminal IN is supplied to an A/D converting part 11 of a tap gain preparing part 1 and a timing generating part 12. The reference waveform converted to a digital signal by the converting part 11 is supplied to a zero level detecting part 13 and a standardizing part 14. At the detecting part 13, by calculating the average value of the sampling point, only in which the difference value between the adjacent sampling points of the reference waveform synchronized and supplied with to a timing signal supplied from the generating part 12 is smaller than a prescribed value, the zero level of the reference waveform is detected and sent to the standardizing part 14. The standardizing part 14 once holds the sampling point of the reference waveform received from the converting part 11 and respective sampling points are standardized by using the zero level received from the detecting part 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ghost removal device installed in a television receiver.

(Prior Art) In addition to signal components directly received by the antenna, a video signal received by a television receiver includes signal components that pass through various reflection paths from nearby trees, buildings, and moving objects such as vehicles. It also includes signal components that are received with a delay. Therefore, multiple images generally appear within the receiving screen, although there are differences in degree.

A signal component that causes multiple images to appear in the reception screen is called a ghost, and a phenomenon in which the multiple images become so large that they become an eyesore and the image quality deteriorates is called a ghost disturbance.

A device for removing such ghosts uses a transversal filter for generating pseudo-ghosts and a waveform (referred to as a "reference waveform") at a predetermined location of the received television broadcast signal to detect the occurrence of ghosts. It is comprised of a tap gain control circuit that controls the tap gain of the transversal filter, and a signal synthesis circuit.

The tap gain control circuit holds in advance a reference waveform before being affected by ghosts contained in the television signal sent from the broadcasting station, and also controls the waveform from being affected by ghosts from the actually received television signal. The reference waveform is extracted, the influence of ghost is detected from the relationship between the two, and a tap gain is generated to remove this. The transversal filter that receives this tap gain simulates the mechanism of ghost generation based on multiple reflections of signal delay, attenuation, and mutual addition by using a delay circuit group, a coefficient circuit group, and an adder circuit connected in series. Generate ghosts. This pseudo-ghost is usually generated with opposite polarity, is added to the original received television signal in a signal synthesis circuit, and is canceled out by the ghost component contained therein.

As an example of the reference waveform, as shown in FIG. 5(A), the falling edge of the equivalent pulse appearing within the vertical retrace period is used. In this case, a falling edge digital waveform consisting of a group of sampling points indicated by white circles in FIG. 5(B) is previously held in the tap gain control circuit as a reference waveform. The reference waveform extracted from the actually received television signal and converted into a sampling point cloud is delayed by τ time from the falling edge due to the influence of ghost, as illustrated by the black circle in Fig. 5(B). It exhibits a staircase waveform that rises by an amplitude g. The corresponding sampling point of the held reference waveform is subtracted from the sampling point of the received reference waveform, and an inter-waveform difference signal consisting of a group of sampling points shown in FIG. 5(C) is generated.

Subsequently, a difference on the time axis is taken for each sampling point of this inter-waveform difference signal, and a tap gain as shown in FIG. 5(D) is generated. In the transversal filter that has received this tap gain, a pseudo ghost as shown in FIG. 5(E) is generated. By adding the generated pseudo-ghost in FIG. 5(E) and the original received television signal indicated by the black circle in FIG. 5(B), the primary ghost with amplitude g is canceled as shown in FIG. A ghost-removed signal is obtained in which a secondary ghost of amplitude g2 is added instead.

In the tap gain generation described above, first, a waveform difference is performed between the extracted reference waveform and the held reference waveform, and then a difference on the time axis, that is, differentiation is performed. Therefore, if a differential waveform of a staircase waveform is set as a reference waveform from the beginning, a tap gain can be generated simply by performing a difference between waveforms. That is, the reference waveform obtained by differentiating the staircase waveform of FIG. 5, band-limiting it in the frequency band of the television signal, and converting it into a group of sampling points is as shown in FIG. 6(A).

On the other hand, the reference waveform extracted from the actually received television signal and converted into a sampling point group is affected by ghosts and has a distorted waveform, as shown in FIG. 6(B). The tap gain control circuit can generate the tap gain by calculating the difference between the two reference waveforms.

(Problem to be Solved by the Invention) When using a differential waveform as the reference waveform as described above, it is necessary to detect the zero level of the reference waveform when normalizing the amplitude of the reference waveform extracted from the received television signal. Become.

However, as illustrated in FIG. 6(B), the pedestal level of the received television signal is tilted or fluctuated to a considerable extent due to the influence of ghosts, so the zero level of the reference waveform superimposed on it is There is a problem that it becomes difficult to detect with high accuracy.

(Means for Solving the Problems) The ghost removal device of the present invention extracts a reference waveform from a predetermined portion of a received television signal, generates a group of sampling points thereof, and a difference value between adjacent sampling points is set to a predetermined value. The tap gain generation circuit is equipped with zero level detection means for detecting the zero level of the reference waveform by calculating the average value of only the sampling points smaller than , thereby realizing highly accurate zero level detection of the reference signal of the differential waveform. It is composed of

Hereinafter, the operation of the present invention will be explained in detail together with examples.

(Embodiment) FIG. 1 is a block diagram showing the configuration of a ghost removal device according to an embodiment of the present invention.

This ghost removal device generates a tap gain from the difference between a sampling point group of a reference waveform extracted from a predetermined location of a received television signal and a corresponding sampling point group of a reference waveform held in advance. It is equipped with a circuit 1. Furthermore, this ghost removal device includes a transversal filter 2 that receives the generated tap gain from the tap gain generation circuit 1 and generates a pseudo ghost, and a synthesizer that combines the generated pseudo ghost and the ring television signal. The circuit 3 removes ghosts from the original television video signal supplied to the input terminal IN and outputs it to the output terminal OUT.

The tap gain generation circuit l includes an A/D conversion section 11, a timing signal generation section 12, a zero level detection section 13, and a standardization section 1.
4, a reference waveform holding section 16, 17, a difference calculation section 18, and a tap gain holding section 19.

The received television signal supplied to the input terminal IN is supplied to the A/D converter 11 and timing generator 12 of the tap gain generator 1. The timing generation section 12 extracts the synchronization signal from the received television signal and generates a timing signal to be supplied to each section in the tap gain main section 1, such as the A/D conversion section 11, the zero level detection section, and the standardization section 14. do.

The reference waveform converted into a digital signal by the A/D converter 11 is supplied to the zero level detector 13 and the standardizer 14.

As shown in FIG. 2, the zero level detection section 13 includes a 1-sampling delay circuit 21, a subtraction circuit 22, an absolute value circuit 23,
It is composed of a dark value holding circuit 24, a comparison circuit 25, a gate circuit 26, an averaging circuit 27, and a register 28.

An example of the reference waveform that is converted into a digital signal by the A/D converter 11 and supplied to the input terminal ■ of the zero level detector is as follows.
As shown in FIG. 3A, the staircase waveform is sequentially differentiated, band limited by the frequency band of the television signal, and distorted by ghosts. As illustrated in FIG. 3(A), the zero level of this reference waveform fluctuates considerably due to the influence of ghosts and noise with respect to the zero level of the received signal set by a pedestal clamp or the like.

The sampling points of the reference waveform that appear sequentially at the input terminal I are supplied to the addition side input terminal of the subtraction circuit 22 through the delay circuit 21 corresponding to l sampling periods, and are also directly supplied to the subtraction side input terminal of the subtraction circuit 22, as shown in FIG. A difference signal between adjacent sampling points as shown in (B) is created. This difference signal is converted into an absolute value of the difference signal in the absolute value circuit 23, and compared with a predetermined threshold value Lth held in the dark value holding circuit 24. Only when the absolute value of the difference signal between adjacent sampling points is smaller than a predetermined threshold Lth, the comparison circuit 2
The gate circuit 26 is opened by the output of 5, and as shown in FIG.
) are selectively supplied to one input terminal of the averaging circuit 27.

The averaging circuit 27 adds the sampling point supplied from the gate circuit 26 to one input terminal and the previous average value supplied from the output terminal of the register 28 to the other input terminal, and adds the sum to this added value. A new average value is created by multiplying by l/2 and is supplied to the register 28 as the zero level of the reference signal. Register 28 updates the zero level it is holding with a new zero level.

The standardization unit 14 temporarily holds the sampling points of the reference waveform received from the A/D conversion unit 11 and normalizes each sampling point using the zero level received from the zero level detection unit 13.

The difference calculation unit 18 calculates the difference between the sampling point of the normalized reference waveform extracted from the received television signal and held in the reference waveform holding unit 16 and the corresponding sampling point of the reference waveform held in advance in the reference waveform holding unit 17. The difference is calculated and supplied to the tap gain holding section 19 as the tap gain of the transversal filter.

As shown in FIG. 4, the transversal filter 2 includes delay units 42a connected in series in multiple stages.

42b, 42C...42rl, and a multiplier 43 for multiplying the output of each of these delay devices by a tap gain.
a, 4jb, 43c... 43n, an adder 44 that adds the outputs of these multipliers, and an A/D converter 41 and a D/A converter 45 placed before and after these multipliers. A pseudo ghost is generated based on the tap gain supplied from the gain generator l. This transversal
The pseudo ghost generated by the filter 2 is combined with the original received television signal in the combining section 3, and the ghost contained therein is canceled out.

Although the configuration in which the zero level detection section is realized by a combination of a dedicated circuit group has been described above, this may be realized by software processing by a general-purpose processor.

(Effects of the Invention) As explained in detail above, the ghost removal device of the present invention calculates the average value of only the sampling points where the difference value between adjacent sampling points in the extraction reference waveform is smaller than a predetermined value. Since the configuration is configured to detect the zero level of the reference waveform, it is possible to detect the zero level with high accuracy for the reference signal of the differential waveform, and there is an effect that the ghost removal accuracy can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a ghost removal device according to an embodiment of the present invention, and FIG. 2 is a tap gain generation section 1 of FIG.
A block diagram illustrating the configuration of the zero level detection unit 13 of
3 is a waveform diagram for explaining the operation of the zero level detection section 13 in FIG. 2, and FIG. 4 is a waveform diagram for explaining the operation of the zero level detector 13 in FIG.
FIG. 5 is a block diagram illustrating the configuration of the filter, FIG. 5 is a waveform diagram for explaining the principle of ghost removal, and FIG. 6 is a waveform diagram for explaining the problem to be solved by the present invention. DESCRIPTION OF SYMBOLS 1... Tap gain generation part, 2... Transversal filter, 3... Synthesis part, 11... A/D conversion part, 12... Timing generation part, 13... Zero level detection 14... Standardization section, 16.17... Reference waveform holding section, 18... Difference calculation section, 19... Tap gain holding section. Patent applicant: NEC Home Electronics Co., Ltd.

Claims (1)

[Claims:] A tap gain generation circuit that generates a tap gain from the difference between a sampling point group of a reference waveform extracted from a predetermined location of a received television signal and a corresponding sampling point group of a reference waveform held in advance. a transversal filter that receives the generated tap gain and generates a pseudo ghost; and a synthesis circuit that synthesizes the generated pseudo ghost and the original television signal. The gain generation circuit extracts a reference waveform from a predetermined portion of the received television signal, generates a group of sampling points thereof, and calculates the average value of only the sampling points where the difference value between adjacent sampling points is smaller than a predetermined value. What is claimed is: 1. A ghost removal device comprising: zero level detection means for detecting the zero level of a reference waveform.