JPS6337779A - Ghost improvement method - Google Patents

Abstract

PURPOSE:To remove a ghost effectively by an extremely simply method by subtracting the output of an adjusting means which adjusts the amplitude and sign of an orthogonal synchronous detection component from the output of a delay means which delays an in-phase synchronous detection component. CONSTITUTION:A distributor 3 distributes an input signal from a band-pass filter 2 into three and one of them is led to a video image carrier regenerating circuit 4 to generate a carrier wave which is in phase with and orthogonal to a video carrier wave. The in-phase carrier wave is led to and detected by an in-phase synchronous detecting circuit 5, and the passed through a low-pass filter (LPF)16 whose band is limited almost to 4 MHz, thereby obtaining a video signal which contains a ghost. An orthogonal synchronous detecting circuit 10 performs orthogonal synchronous detection and then the signal is passed through an LPF211 whose band is limited almost to 1 MHz, thereby obtaining only the low-frequency component of the ghost. The amplitude and sign of the low-frequency component of the ghost are adjusted by an amplitude and sign adjuster 12 to the same amplitude and sign of the component signal of he ghost outputted by a delay line 7 and the adjusted signal is subtracted by a subtracter 8 to remove the low-frequency component of the ghost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ghost improvement method for improving the picture quality of a television suffering from ghost problems.

[Prior Art] Conventionally, methods of controlling antenna directivity and equalizing waveforms using a transversal filter using a CCD have been put into practical use in order to improve ghosts on television.

[Problems to be Solved by the Invention] The first improvement method using antennas uses a plurality of antennas, so it is not suitable for use in a moving object such as a car.

The ghost removal method using the second transversal filter requires about 100 taps in the transversal filter, so it takes more than 10 seconds to determine the tap coefficients, which causes flutter and ghosts on a TV set in a car. It is difficult to apply to things that change rapidly, such as C
One drawback is that CDs are expensive.

Therefore, the purpose of the present invention is to use a special antenna,
To provide a ghost improvement method that can effectively remove ghosts in an extremely simple method without requiring a long time for adjustment unlike a transversal filter.

[Means for Solving the Problems] In order to achieve such an object, the present invention includes a first detection means for in-phase synchronous detection of a video carrier signal extracted by receiving a television broadcast wave; , a second detection means for orthogonally synchronously detecting the video carrier signal; a delay means for time-delaying the in-phase synchronously detected component from the first detection means; It is characterized by comprising an adjusting means for adjusting the sign, and a subtracting means for subtracting the output of the adjusting means from the output from the delay means.

For example, a component signal obtained by in-phase synchronous detection of a television broadcast wave and a component signal obtained by quadrature synchronous detection are extracted, and the amplitude and sign are adjusted so that ghost component signals of each other are canceled out.

[Operation] According to the present invention, it is possible to constantly track and eliminate the low-frequency components of ghost interference waves contained in a television broadcast wave signal.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIGS. 2(A) to 2(D) are characteristic diagrams of the operation of each part in the configuration of FIG. 1.

In the figure, 1 is an input terminal, 2 is a bandpass filter (BP
F), 3 is a distributor.

4 is a video carrier reproduction circuit, 5 is an in-phase synchronous detection circuit, 6 is a low pass filter (LPF), and 7 is a delay circuit, which corrects delay time. 8 is a subtracter, and 9 is an output terminal.

10 is a quadrature synchronous detection circuit, 11 is a low-pass filter (LP
F2), 12 is an amplitude/sign adjuster, which adjusts the amplitude and polarity sign (plus or minus) of the manually input signal.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 2.

In FIG. 1, a radio frequency (RF) or intermediate frequency (IF) television signal containing a ghost is input from an input terminal 1. The band pass filter (BPF) 2 has the characteristics shown in Figure 2 (A) and is used to flatten the frequency characteristics of the video signal after being detected. It may be replaced with a wave device having the characteristics shown in B).

Distributor 3 divides the input signal from BPF 2 into three parts, one of which is
One is led to the video carrier wave reproducing circuit 4. A video carrier wave reproducing circuit 4 generates carrier waves whose phases are in-phase and orthogonal to the video carrier wave.

The in-phase carrier wave is guided to the in-phase synchronous detection circuit 5 for synchronous detection, and when it is passed through the LPF 6, which has the characteristics shown in Fig. 2 (C) and whose band is limited to around 4 MHz, a video signal containing ghosts is obtained. It will be done.

On the other hand, the orthogonal synchronous detection circuit lO performs orthogonal synchronous detection and IM
Figure 2 (L with DJ characteristics) with band limit around Hz.
When passed through PF211, only the low frequency components of the ghost are obtained.

The amplitude and sign (function and polarity) of this ghost low-frequency component signal are adjusted by the amplitude sign adjuster 12 to make it the same amplitude and sign as the ghost component signal output from the delay line 7, and then subtracted by the subtracter 8. This allows you to remove the low-frequency components of the ghost.

That is, when paying attention to the double-side band transmission region of a television broadcast wave signal that includes a ghost, a video signal and a ghost signal exist in the in-phase component, but only a ghost signal exists in the orthogonal component. Therefore, ghosting can be improved by extracting orthogonal components in the double-sided band transmission region and subtracting them from the in-phase component.

In order to further understand the above-mentioned operation, it will be explained using commonly used mathematical expressions.

As is well known, the television broadcast wave signal f(t) containing the ghost of the kitchen can be expressed as in equation (1). The first and second terms are video signals, the third and fourth terms are ghost signals, g(·) is an in-phase component, and h(·) is a quadrature component.

f(t)=g(t)cosωct −h(t)sinω
ct+γ・g (−τ)cos (ωc(−τ)◆
φ)−γ・h (tr) sin (ωe(t−r)+
φ) Here, ωC: image carrier angular frequency, γ: amplitude ratio with respect to the ghost image, τ: delay time with respect to the ghost image, φ: high frequency phase difference between the ghost carrier wave and the image carrier wave, provided that the phase difference with respect to the ghost image is ψ
:ωCτ−φ.

When the TV broadcast signal in equation (1) is subjected to in-phase synchronous detection and passed through a low-pass filter 6 with a cutoff frequency around 4 MHz with the characteristics shown in Figure 2 (C), equation (2) is obtained. . The first term is the image, and the second and third terms are the ghost.

g(1)◆γ・g(−τ) cos (ωCτ−φ)+
γ・h(tr) sin ((LICT −φ)
(2) Here, considering the low frequency component near Iz (IM) and below, the orthogonal component h(·) of the third term of equation (2) is;.

In addition, by performing orthogonal synchronous detection of the television broadcast wave signal of equation (1),
When the signal is passed through a low-pass filter 11 having a cutoff frequency near IMHz with the characteristics shown in FIG. 2(D), equation (3) is obtained. Note that g' (.) represents the low frequency component of g(.).

γ・g' (t-τ) sin (ωCτ-φ) (3) (
Equation 3) is the low-frequency component of the ghost, and it differs only in amplitude from the low-frequency component of the second term in Equation (2), so (
By adjusting the amplitude and sign of equation (3) and subtracting from equation (2), the low frequency component of the ghost can be removed.

Since the power spectrum of the video signal is concentrated in the low frequency range, the improvement effect of removing the low frequency component of the ghost is significant.

Note that this embodiment may be performed digitally by performing ^/D conversion on the human input signal from the input terminal l.

FIG. 3 is a block diagram showing the structure of another embodiment of the present invention in which a signal for cancellation can be automatically adjusted.

Components similar to those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

13 is a low pass filter (LPF2), 14 and 18
1 is a differentiation circuit, 15 is an absolute value circuit, and 16 is a maximum value holding detection circuit.

17 and 19 are voltage holding circuits, 20 is a division circuit, 21
is a vertical synchronization timing generation circuit.

FIG. 4 is a waveform diagram of the operation of each part in the embodiment of FIG. 3.

The operation will be explained below with reference to FIGS. 3 and 4.

I from the in-phase synchronous detection output signal by the low-pass filter 13
M) Extract the signal below lz. FIG. 4(A) shows this waveform. This filter 13 is the same as the low-pass filter 11. The falling portion of vertical synchronization is extracted by the differentiating circuit 14. This waveform is shown in FIG. 4(B). The absolute value circuit 15 and the maximum value holding detection circuit 16 detect the one having the maximum absolute value of the amplitude among the plurality of ghosts, and the voltage holding circuit 17 extracts the signed amplitude. The waveforms of these parts are shown in Figure 4 (C), (D) and (E).
Shown below.

Here, in FIG. 4(D), what is indicated by a dotted line is that in this embodiment, since it is necessary to remove the vertical synchronization falling waveform in FIG. 4(C), it is controlled and erased by the vertical synchronization timing. It is shown that.

On the other hand, an orthogonal synchronous detection output is extracted from the output of the low-pass filter 11, and a falling edge of the vertical synchronous signal is extracted by a differentiating circuit 18 similar to the differentiating circuit 14. The voltage holding circuit 19 holds the output of the differentiating circuit 18 based on the maximum value detection signal of the maximum value holding detection circuit 16. FIG. 4(F) shows the waveform. The vertical synchronization timing generation circuit 21 controls three voltage holding circuits 16, 17 and 19 in synchronization with the vertical synchronization timing. The outputs of the voltage holding circuits 17 and 19 are led to the divider circuit 20, and the output is used as the amplitude sign adjustment circuit 1.
By controlling 2, amplitude adjustment can be automated. Fourth
Figure (G) shows the output waveform of the divider circuit 20.

Here, if an impulse, a ghost reference signal, or the like can be used in place of the falling portion of vertical synchronization, the differentiating circuits 14 and 18 can be omitted.

The above operation reduces the outputs of the low-pass filters 11 and 13 to A
/D conversion may also be performed digitally.

In order to make it easier to understand the operation of automatically adjusting the amplitude and sign as described above, it will be explained below using the above-mentioned formulas.

That is, in order to detect the falling edge of the vertical synchronization signal as a ghost component g (t), this is band-limited to near IMI (Z) and differentiated.Here, h (・); The third term of is zero.

Furthermore, on the time axis, the video component of the first term in equation (2) and the ghost component of the second term can be separated. Since there are actually multiple ghost components, the ghost component with the maximum absolute value of amplitude is extracted. Similarly, the ghost component of orthogonal synchronous detection according to equation (3) is extracted and divided to create the coefficients shown by equation (4) below.

γ・g'' (with −)・cos (oneφ with ωC)/(γ
・g' (−)・sin (ωCτ−φ))=c
ot(ωCτ−φ) (4) For the video period, by multiplying equation (3) by the coefficient found in equation (4) and subtracting it from equation (2), we can obtain an image with the low-frequency components of ghosts removed. It will be done.

[Effects of the Invention] According to the present invention, it is possible to follow and improve fast-changing ghost interference, and it is also possible to improve ghost interference in a car-mounted television receiver and flutter caused by radio interference caused by an aircraft. It is valid. Furthermore, it is possible to cope with and improve ghost interference, which has a very long delay time and which is difficult to improve using a method using a CCD transversal filter.

According to the present invention, since a variable delay line such as a transversal filter is not used, the configuration is simple and the cost can be reduced. It is also effective in improving proximity ghost interference in teletext broadcasts.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIGS. 2(A) to (D) are characteristic diagrams showing the operation of each part of an embodiment of the present invention, and FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention. FIGS. 4(A) to 4(G) are waveform diagrams showing the operation of each part of another embodiment according to the present invention. l...Input terminal, 2...Band pass filter (BPF), 3...Distributor, 4...Video carrier wave regeneration circuit, 5...In-phase synchronous detection circuit, 6, 11. 13...Low pass filter (LPF), 7.
... Delay circuit, 8... Subtractor, 9... Output terminal, lO... Orthogonal synchronous detection circuit, 12... Amplitude/sign adjuster, 14, 18... Differentiator circuit, 15... - Absolute value circuit, 16... Maximum value voltage holding circuit, 17, 19... Voltage holding circuit, 20... Division circuit, 21... Vertical synchronization timing generation circuit.

Claims (1)

[Scope of Claims] A first detection means for in-phase synchronous detection of a video carrier signal extracted by receiving a television broadcast wave; a second detection means for orthogonal synchronous detection of the video carrier signal; Delay means for time-delaying the in-phase synchronous detection component from the first detection means; Adjustment means for adjusting the amplitude and sign of the orthogonal synchronous detection component from the second detection means; Output from the delay means. , and subtraction means for subtracting the output of the adjustment means.