JPS5896470A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To complete ghost elimination with a transversal filter, by making the amplitude of ghost fitted to black level equal to that fitted to white level. CONSTITUTION:An amplified intermediate frequency signal is applied to a band pass filter 11 having very narrow band width and varying the intermediate frequency, and a multiplier 13 taking product between the output of the filter via a limiter 12 and an intermediate frequency signal. The output of the multiplier 13 is applied to a transversal filter 17 via a low pass filter 14. Thus, the amplitudes of ghost fitted to white and black levels of the video signal are made equal even at any phase of the carrier of the ghost signal, allowing to eliminate ghost with a transversal filter 17.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ghost removal device for a television receiver.

Ghosting is one of the major causes of deterioration of image quality in television receivers, and various methods have been attempted to prevent ghosting.

One of them is a method using a transversal filter. This method will be explained below.

Let to(t) be a television signal without ghosts. Also,
For simplicity, the ghost is t = nτ (n = 1.2.
3. ...N1 and τ is a constant), the signal 1 (1) containing a ghost is
It is created using the following formula.

N' However, Cn is the size of the ghost signal Finding this Fourier transform, we get The following equation can be obtained using

Therefore, as shown in Section 1, in order to remove ghosts using the ghost removal device 1 having the transfer function G(ω) and obtain a ghost-free signal Fo(ω) at its output, the following +11 The formula %formula% should hold true. From this, the following (2) 2G
(ω)=FO(ωVF(ω)) is obtained. From the above equation (2), the following equation is obtained.

Then, finding this 7-lier inverse transformation, we get g(t) = Sat rG(, ), jmt d*2π-.

etc., the following relationship to That is, is obtained.

This equation gives the impulse response of the ghost removal device 1 having the transfer function G(ω), and hardware can be configured based on this equation. That-
An example is shown in FIG.

This example is a case where N is 3 in the above formula. Second
In the figure, 2 is a delay element with delay time τ, 3 is a tap amplifier with gain -cn (n-1, 2, 3), and 4 is a tap amplifier with gain -cn (n-1, 2, 3).
5 is an adder, 5 is an automatic gain control circuit that automatically controls the gain of each tap amplifier 3, 6 is a video signal input terminal, 7 is a video signal output terminal, 18 is a reference signal generator, and 19 is a reference signal generator. This is a comparator that obtains the ghost component from the difference with the video output signal.

This method is called a feedback type because the output of each delay element 2 is fed back to the large sword via the corresponding tap amplifier 3.

On the other hand, in Equation (2) above, if the size of the ghost is small, that is, it can be expressed as the following (Equation 31). When this inverse Fourier transform is obtained, g(t) = J (t)-ΣCn'(tBτ)n=1.

When the hardware is constructed according to this formula, it becomes as shown in FIG. 3. In FIG. 3, the same reference numerals as in FIG. 2 refer to the same parts, and all parts are the same as those in FIG. 2. Since this type does not constitute a feedback loop, it is called a feedforward type in correspondence with the above-mentioned type.

Now, in the ghost removal device as described above, the synchronization signal section is mainly used to detect ghosts because the waveform does not change depending on the broadcast content (picture).

FIG. 4(A) shows a waveform diagram of the vertical synchronizing signal. The vertical synchronizing signal is a pulse with a pulse width of 27 μs, which has equalization Hals groups 22 before and after it, as is well known. When a ghost exists, the DC value in the flat area changes as shown by the hatched area in Figure 4 (B). The gain control circuit 5 modifies the gain of the tap amplifier 3 to be modified by an appropriate value.

Such a synchronization signal portion exists in a television signal where the degree of modulation is relatively shallow, that is, near the black level. Therefore, when the detection method is envelope detection, a problem arises in that the ghost attached to the white level does not disappear, as described below.

As shown in Figure 5, for a desired signal modulated with a square wave with a modulation depth of 80 (the carrier is not shown), the ghost level is 16 dB (1/2), and the carrier position is Assume that a ghost with a phase difference of 90° exists.

In the same figure, X and Y represent the white level and black level of the desired signal, respectively, and kX and kY represent the white level and black level of the ghost signal. 1 in Figure 5: A, B, C, The relationship between the desired signal and the ghost in each section indicated by D is expressed as shown in FIG. 6 (4) to (c). In these figures, vectors in the vertical direction represent desired signals, and vectors in the horizontal direction represent ghosts. Therefore, the sum of both vectors, that is, the amplitude of the signal including the ghost, is as shown in FIG. 7 for each section.

Here, assuming that envelope detection is used as the detection method, W is demodulated as a video signal with the amplitude in Figure 7 remaining 1. As is clear, the shaded area 24B in the figure,
24W is a ghost component. As can be seen, the size of the go, '() 24B attached to the black level is different from the size of the ghost 24W attached to the white level.

In the above example, the case of envelope detection is described, but the so-called quasi-synchronous detection method detects by extracting only the carrier with a band-pass filter, amplifying and shaping it, and multiplying it with the converted signal. Even if this method is adopted, the Q of the bandpass filter cannot be made high considering the frequency deviation of the intermediate frequency signal, so there is no big difference from the envelope detection method, and exactly the same problem occurs.

As described above, in a ghost removal device using a transpersal filter, (1) ghost detection is performed at the black level.

(2) In the case of envelope detection method and pseudo-synchronous detection method,
The size of the ghost that appears on the black level is different from the size of the ghost that appears on the white level.

As a result, ghosts attached to the black level can be removed, but ghosts attached to the white level cannot be removed, or ghosts may be added instead.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to equalize the size of the ghost appearing on the black level and the size of the ghost appearing on the white level, and to completely remove ghosts by a transpersal filter.

In order to achieve the above-mentioned object, the present invention provides an amplified intermediate frequency signal with a very narrow bandwidth and
A bandpass filter whose center frequency can be varied and a multiplier that multiplies the output of the bandpass filter and the intermediate frequency signal, and the output signal of the multiplier is
By feeding the video signal through a low-pass filter connected to the output of the multiplier to a transversal filter connected to the low-pass filter, no matter what the phase of the carrier of the ghost signal is, The feature is that the size of the ghost appearing on the black level and the ghost appearing on the white level are made equal, and the ghost is removed by a transversal filter in the final stage.

Specific embodiments of the ghost removal device according to the present invention will be described below with reference to the drawings. FIG. 8 is a diagram showing an embodiment of the present invention.

In the figure, 8 is an antenna, 9Fi chainer, 10 is an intermediate frequency amplifier circuit, 11 is a narrow band band pass filter having a variable capacitance diode, 12 is a limiter, 13 is a multiplier, 14 is a low-pass filter, 15 1 is an amplitude integrator, 16 is a voltage sweep circuit, and 17 is a transversal filter.

This embodiment operates as follows.

First, when switching channels, the output voltage of the voltage sweep circuit 16 is once reset to Ov. Therefore, as shown in FIG. 9(A), the center frequency of the bandpass filter 11 having a variable capacitance diode is the frequency of the intermediate frequency signal outputted from the chainer 9, taking into account the variation from channel to channel. It is set sufficiently lower than IF.

As the output of the voltage sweep circuit 16 gradually increases as shown in FIG.
The capacitance of the variable capacitance diode constituting this decreases. Therefore, the center frequency of the bandpass filter 11 is the ninth
It gradually increases as shown by the arrow in Figure (4).

In this way, the center frequency of the bandpass filter 11 approaches the intermediate frequency signal frequency IFJ output from the cheese 9, so the amplitude detector 15 connected to the output of the limiter 12 receives a detection output. You will be able to get it.

By detecting this state, the voltage sweep of the voltage sweep circuit 16 is stopped and the voltage is maintained at a constant voltage.

As a result, the intermediate frequency signal output from the chip 9 is within the band of the band pass filter 11. This relationship is shown in FIG. 9(4)(b).

The carrier component of the intermediate frequency signal thus obtained is sent to the multiplier 13 via the limiter 12, where it is multiplied by the intermediate frequency signal output from the intermediate frequency amplification circuit 10.

When this output is input to the low-pass filter 14, a video signal is obtained as its output. When this video signal is supplied to the transversal filter 17, ghosts contained in the video signal can be removed by a known method.

Now, in the ghost removal device that operates as described above, if the band of the bandpass filter 11 is sufficiently narrow,
The reason why the ghosts appearing at the black level of the video signal and the ghosts appearing at the white level of the video signal are equal in size will be explained next.

As can be easily understood from the vector diagram in FIG. 6, when a ghost is mixed into the desired signal, the phase of the composite signal, that is, the phase of the intermediate frequency signal output from the chainer 9, changes constantly.

Now, consider a case where the phase of the sine wave changes from 0° to 1800°, for example, as shown in FIG. 10(,). This signal (,) has the same amplitude and phase θ° as shown in Fig. 10(b), and a signal with twice the amplitude as shown in Fig. 10(c).
And the sum 7elII and the signal with a phase of 180° can be obtained.

When the waveforms (b) and (c) above pass through narrowband bandpass filters, the sideband components forming the envelope are removed, so the waveforms as shown in (d) and (e) in the same figure are obtained. , a waveform with a slow rise is obtained.

Therefore, when a signal with waveform (,) is input to a bandpass filter, the output waveform is represented by the sum of waveforms (d) and (.). That is, in this case, a certain delay time td is required for the phase change of the output.

This is shown in FIG. 10(f).

As can be seen from the above, if the band of the bandpass filter is narrow, the sideband components such as narrow #1 will be greatly attenuated, so the rise of the waveforms (d) and (・) will be significantly slowed down. . Therefore, even if there is a phase change in the input signal of the band-pass filter, the output of the band-pass filter will not follow the phase change of the input.

That is, the phase of the output of the bandpass filter 11 in FIG. 8 does not follow the change in the phase of the output of the tuner 9, but is kept substantially constant.

In this situation, the video signal is obtained as follows. That is, as shown in the vector diagram of FIG. 11, if the desired signal vector is OA and the ghost signal vector is OR, the composite signal vector is OC, and these vectors change every moment. However, the detection axis vector oc' supplied from the bandpass filter 11 via the limiter 12 does not change.

The video signal obtained at the output of the low-pass filter 14 is
Since each vector has a detection axis component, the video signal (i.e., detection output) when there is a ghost is oc
'is. As is clear from FIG. 11, this is equal to the sum of the component OA' due to the desired signal and the component OB' due to the ghost.

That is, QC'=OA'+OB'=OA eoaθ+OReosφ. On the other hand, the detection output when there is no ghost is 0A.
cosθ, the change in detection output due to the addition of ghost is D == OB cowψ=beosφ However, 0B=
It becomes b. From this, the change dD in the detection output due to the change in the size of the ghost can be written as dD == db cosφ.

As shown in Fig. 5, let the white level and black level of the desired signal be X and Y, respectively, and the size of the ghost be k.
The white level and black level of the ghost signal are k
X, kY becomes 0. Therefore, since the black level is -2<ghost, db=k(Y-X), the change in detection output due to a change in ghost is
It is expressed by the following formula (4). Furthermore, since the ghost that appears on the white level is also db=k(Y-X), the change in the detection output due to the change in the size of the ghost in this case is expressed by the following formula (5) % Formula % (5) As is clear from a comparison of equations (4) and (5), the magnitudes of both are equal. Therefore, the subsequent transversal filter 17 can completely eliminate not only the ghost attached to the black level but also the ghost attached to the white level.

As described above, according to the present invention, since the center frequency of the bandpass filter is made variable, even if the output intermediate frequency of the chainer deviates, it is possible to reliably obtain an intermediate frequency signal. Since the width is set sufficiently narrow, carriers with a constant phase can be extracted.

Therefore, it is possible to equalize the size of the ghost appearing at the black level and the ghost appearing at the white level of the video signal. Therefore, even if a ghost is detected at a black level such as in a sync signal part, the ghost can be completely removed by the transversal filter.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram showing the ghost removal device, Figures 2 and 3 are block diagrams of transversal filters, Figure 4 is a waveform diagram showing the synchronization signal, and Figure 5 is the relationship between the synchronization signal and its ghost. 186 is a vector diagram showing the relationship between the synchronization signal and its ghost, and FIG.
FIG. 8 is a block diagram showing an embodiment of the cloudy ghost removal device of the present invention, and FIGS. 9 and 10 are waveform diagrams for explaining the operation of FIG. 8. , Figure 11 is also a vector diagram. l... Ghost removal device, 2... Delay element, 3...
- Tap amplifier, 4... Adder, 5... Automatic gain control circuit, 11... Band pass filter, 12... Limiter, 13... Multiplier, 14... Low pass filter,
15... Amplitude detector, 16... Voltage sweep circuit, 17...
・Transversal Filter Representative Patent Attorney Hiraki Michi 1 Figure 22 Figure 4 Off Figure 25 Figure +s! "'(C)"'
([)) ”・5 years old 8 figures Makimaga 10 Kindergarten years old 11 figures

Claims (2)

[Claims] (1) A variable frequency bandpass filter that receives an intermediate frequency signal from a TV screen, a detector that detects that an intermediate frequency signal is obtained at the output of the bandpass filter, and the detector. a voltage sweep circuit that stops the voltage sweep by the output of the circuit and controls the tuning frequency of the band pass filter with the output voltage; a multiplier that multiplies the intermediate frequency signal by the output of the band pass filter; and the multiplier 1. A ghost removal device comprising: a low-pass filter supplied with the output of the low-pass filter; and a transversal filter supplied with the output of the low-pass filter. (2) Transversal filters are connected in cascade with each other, and the low-pass filter includes a plurality of delay elements supplied with the output of the transversal filter, and a plurality of tap amplifiers that amplify the output of each delay element. an adder that adds the outputs of the respective tap amplifiers; a second adder that adds the output of the low-pass filter to the output of the adder; a reference signal generator; Claim 1 comprising: a comparator that calculates the difference between the output of the adder and an automatic gain control circuit that controls the gain of each tap amplifier based on the output of the comparator. The described ghost removal device.