JPS63267066A - Ghost removal device - Google Patents

Abstract

PURPOSE:To remove a near-by ghost with high precision by generating a pseudo ghost based on a difference between a prescribed reference signal waveform included in a television signal and the reference signal waveform which has been extracted from the television signal and removing the ghost in terms of cancellation. CONSTITUTION:A tap gain control part 1 is provided with a reference signal waveform storage part 10, an A/D conversion part 11, a reference signal waveform detection part 12, a normalizing part 13, a storage part 14, a reading part 15, a difference calculation part 16, a correlation calculation part 17, an origin decision part 18, a storage part 19 and a reading part 20. The prescribed reference signal waveform included in the television signal is held, the reference signal waveform included in the television signal is extracted and the difference of the outputs is calculated. The pseudo ghost is generated based on the outputs and the ghost in the television signal is removed in terms of cancellation with using the outputs. Thus, all the ghosts including near-by ghosts having a short delay time can be removed in high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ghost removal device installed in a television receiver.

In conventional technology television receivers, delayed signals are superimposed on the signals directly received by the antenna, which are received after passing through various reflection paths caused by nearby terrain, buildings, vehicles, and other moving objects. be done. For this reason, multiple images generally appear within the receiving screen, albeit to varying degrees. The delayed signal that causes this multiple image to appear is called a ghost, and the phenomenon in which this signal becomes so large that it becomes an eyesore and the image quality deteriorates is called a ghost disorder.

Conventionally, in order to remove the above-mentioned ghost, a ghost removal apparatus having a configuration as shown in the block diagram of FIG. 7 has been developed.

That is, in the pseudo-ghost generation circuit 72 composed of a transversal filter, the television signal on the input terminal I is subjected to signal processing using a combination of delay and addition to generate a pseudo-ghost that is in opposite phase to the ghost.
It is supplied to one input terminal of adder 74. The other input terminal of the adder 74 is supplied with the television signal on the input terminal (2) via the delay circuit 73. Therefore, the television signal from which the ghost has been removed by cancellation with the pseudo-ghost of the opposite phase is output from the adder circuit 74, and is supplied to the subsequent stage via the output terminal 0.

As shown in the block diagram of FIG. 8, the pseudo ghost generation circuit 72 of FIG. 7 includes a plurality of delay devices 81a connected in series.
, 81b...81n, multiplier groups 82a and 82b for multiplying the outputs of these delay devices by tap gains, respectively.
... 82n and an adder 83 that mutually adds the outputs of these multipliers, and - an A/D converter 80 and a D/A converter 84 placed before and after the transversal filter. has been done.

In general, ghosts change from time to time depending on various factors, such as changes in the wavelength of received radio waves due to channel switching, and traffic conditions of moving objects such as vehicles, aircraft, and ships passing nearby. Therefore, the transversal filter constituting the pseudo-ghost generation circuit 72 in FIG. 7 is required to simulate the ever-changing ghost by dynamically controlling the delay time and tap gain at high speed.

The gain control circuit 71 in FIG. 7 that controls this delay time and tap gain includes an A/D converter 71a, a base point determination circuit 71
b1 memory 71c and a difference calculation circuit 71d, calculates the delay time and tap gain to be dynamically controlled based on the ghost actually included in the television signal, and sends these to the register 75 and the signal line 76. and is supplied to the pseudo ghost generation circuit 72.

FIG. 9 is a conceptual diagram for simplifying and explaining the operating principle of the ghost removal apparatus shown in FIGS. 7 and 8. FIG.

The tap gain generation circuit 71 detects the ghost of the falling portion of the vertical synchronization signal shown in waveform (A) in FIG. 9, and determines the set values of the tap gain and delay time. In other words, if you enlarge the falling part of the vertical synchronization signal above,
As shown in the waveform (B), an anti-phase ghost is generated that delays by a certain time τ from the fall and rises stepwise by an amount of amplitude g. This waveform (B) is sampled at a predetermined period by the A/D converter 71a of the tap gain control circuit 71, and converted into a time series of discrete signals having amplitudes as shown in waveform (C).

The base point determination unit 71b, memory 71C, and difference calculation unit 71d, all of which are known, subtract the amplitude of the immediately preceding sampling point from the amplitude of each sampling point in the waveform (C), so as to obtain the waveform (D) as an example. A differential signal is generated and supplied as a tap gain to the pseudo ghost generation circuit 72 via the register 75. The pseudo-ghost generation circuit 72 that has received this tap gain generates a pseudo-ghost with an opposite phase as exemplified by waveform (E), and adds this to the addition circuit 7.
Supply to 4. As a result, the adder circuit 74 outputs the waveform (
As exemplified in F), a television signal from which ghosts have been removed is output by canceling them with pseudo ghosts of opposite phase.

Problems to be Solved by the Invention The performance of the conventional ghost removal devices shown in FIGS. 7 and 8 is insufficient. In particular, the performance of removing nearby ghosts having a short delay time of about 0.5 μs or less is insufficient. The problem is that it is not.

Means for Solving the Problems ゛The ghost removal device of the present invention includes a reference signal waveform holding means for holding a predetermined reference signal waveform included in a television signal, and a reference signal waveform holding means for holding a predetermined reference signal waveform included in a television signal; A reference signal waveform extraction means for extracting a signal waveform, a difference calculation means for calculating the difference between the outputs of these two means, a pseudo ghost generation means for generating a pseudo ghost based on the output of the difference calculation means, and the pseudo ghost generation means. and ghost canceling means for canceling ghosts in the television signal using the output of the means, and is configured to eliminate all ghosts with high precision including close ghosts having a short delay time. There is.

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.

In the figure, I is an input terminal, 1 is a tap gain control circuit, 2 is a pseudo ghost generation circuit, 3 is a delay circuit, 4 is an adder circuit, 0
is the output terminal.

In the tap gain control section 1, 10 is a reference signal waveform storage section, 11 is an A/D conversion section, 12 is a reference signal waveform detection section,
13 is a standardization section, 14 is a storage section, and 15 is a reading section. Further, 16 is a difference calculation section, 17 is a correlation calculation section, 18 is a base point determination section, 19 is a storage section, and 20 is a reading section.

In the ghost removal device of this embodiment, the waveform (A
), the waveforms of the rising and falling portions of the vertical synchronization signal are used as reference signals. As this vertical synchronization signal, one that is assumed to have been separated from the composite video signal and A/D converted at the output stage of the television transmitter is selected.1 For example, a staircase waveform with a sufficiently short fall time is A sampling value that has been passed through a low-pass filter circuit with a cut-off frequency of 4.2 MHz and then A/D converted is stored in advance as a reference signal waveform in the storage unit IO when this tap gain control circuit 1 is manufactured. . This stored reference signal waveform exhibits a standardized staircase waveform in which the amplitude drops from 1 to 0, as illustrated by the dotted line connecting white circles in the waveform (B) of FIG. Storage unit as a set of sampled values! is maintained within θ.

On the other hand, the reference signal waveform actually included in the television signal that appears on the input terminal l when this television receiver is used is illustrated by the solid line connecting black circles in the waveform (B) of Fig. 2. As shown, the shape exhibits the influence of a ghost that drops from the amplitude 1 to O and then rises by the amplitude g one hour later. The waveform of the received reference signal is converted into a digital signal by the A/D converter 11, and then sent to the standardization unit 13, the storage unit 14, and the readout unit 15.
It is supplied to the difference calculation section 16 through the.

The difference calculating section 16 subtracts the sampling value of the ideal reference signal read from the storage section 10 from the sampling value of the actual reference signal supplied from the reading section 15, thereby obtaining the waveform (C) in FIG. Calculate the time series of the difference signal of amplitude g as exemplified in . Continuing, the difference calculation unit 16
By calculating the difference in the time axis direction for the time series of the calculated difference signals, the difference signal between the waveforms and on the time axis as illustrated in FIG. 2(D) is calculated.

This difference signal is supplied to the register 5 as a tap gain control signal via the storage section 19 and the readout section 20. The pseudo-ghost generation circuit 2 generates a pseudo-ghost as illustrated in waveform (E) in FIG. 2 based on the tap gain, and supplies this to one input terminal of the addition circuit 4. The television signal on the input terminal 1 is supplied to the other input terminal of the adder circuit 4 while being delayed by the delay circuit 3 by the same time as the tap gain control. Therefore, from the addition circuit 4, as illustrated in waveform (F) in FIG. 2, the first-order component g of the ghost is canceled out and replaced by the second-order component g2 by the output of the pseudo-ghost generation circuit 2. Finally, a television signal including the ghost that has been reduced by a factor of g is output, and is supplied to the subsequent display section via output terminal 0.

The operation in a special case where the ghost delay time τ is sufficiently larger than the fall time of the reference signal has been explained above using the waveform diagram in FIG. On the other hand, the operation in a general case including a so-called proximity ghost where the delay time τ is less than or equal to the fall time of the reference signal will be explained with reference to the waveform diagram of FIG.

In this case as well, the rising portion of the vertical synchronizing signal as shown in waveform (A) in FIG. 3 is used as the reference signal, and the third
An ideal enlarged waveform of the falling portion as illustrated by the dotted line in waveform (B) in the figure is stored in advance in the reference signal waveform storage unit 10. On the other hand, the reference signal waveform extracted from the actually received television broadcast signal shows the frequency characteristics (high The waveform is distorted due to the influence of

In the difference calculation unit 16, the sampling value of the ideal reference signal waveform illustrated by the dotted line is subtracted from the sampling value of the actual received waveform illustrated by the solid line, and the waveform (C
) is calculated as a time series of the difference signal. Furthermore, the difference calculation unit 16 further calculates the difference in the time axis direction for the time series of the difference signals, thereby calculating the time difference between the waveforms and the difference signal on the time axis as illustrated in FIG. 3(D). The series is calculated and supplied to the register 5 as a tap gain control signal via the storage section 19 and the readout section 20.

In addition, in the time series of the difference signal in FIG. 3(D), the time difference (T) between adjacent sampling points is given to the later sampling point, and the output of the transversal filter is shorter than its input with the sampling period T. Because it is delayed by twice as much,
A delay time of (N+1/2)T is given to the television signal by the delay circuit 3.゛When calculating the difference explained using the waveforms in Figures 2 and 3,
It is necessary to adjust the timing between the stored ideal reference signal waveform and the actually received reference signal waveform. This timing adjustment includes rough adjustment of the read timing by the reference signal waveform detection section 12 and the readout section 15, and a rough adjustment of the readout timing by the reference signal waveform detection section 12 and the readout section 15. This is performed in combination with fine adjustment of the read timing by the correlation calculating section 17 and the base point determining section 18.

That is, the reference signal waveform detection section 12 has a built-in differential circuit, a timer, etc., and detects with rough accuracy the changing points of the reference signal waveform that appear in the television signal, and sends the data from the storage section 14 to the readout circuit 15. By commanding the start of readout, the timing between both reference signal waveforms is roughly adjusted.

FIG. 4 shows the reading section 15. 3 is a timing chart for explaining fine adjustment of read timing by the correlation calculation unit 17 and the base point determination unit 18. FIG.

The three dotted lines in the waveform (A) are all ideal reference signal waveforms held in the storage unit 10, and each represents a waveform P when read from the storage unit 10 at a certain timing.
, the waveform P-s when the waveform P-s is read out three sampling points earlier than this, and the waveform P when the waveform P-s is read out three sampling points later than this. Further, a solid line waveform Q illustrates an actual reference signal waveform that is affected by a ghost contained in a received television signal and frequency characteristics of the receiving system.

The waveform (B) in FIG. ). In addition, the waveform (C) is the reference signal waveform Q and P
This is a time series of the difference signal calculated from the left, and the time series of the difference signal on the time axis is as shown in waveform (c). Furthermore, the waveform (D) includes reference signal waveforms Q and P,
This is a time series of the difference signal calculated from the above, and the time series of the difference signal on the time axis is as shown in waveform (d).

The correlation calculation unit 17 calculates the time series of the difference signals on the time axis of the difference signals between the reference signal waveforms as exemplified by waveforms (b), (C), and (d), and calculates the time series of the difference signals on the time axis. Supply to 17. The base point determining unit 18 calculates the sum of the squares of the time series of the supplied difference signals, and finely adjusts the read timing of the reading unit 15 in units of one sampling interval so that this sum becomes minimum. In the example of FIG. 4, the readout timing of the readout unit 15 is finally determined so that the stored reference signal waveform P is selected with respect to the received reference signal waveform Q.

In addition, as a method for determining the positional relationship between waveforms P and Q in FIG. 3(A), the sample point closest to the midpoint of the flat portion before and after waveform Q is taken as the base point of waveform Q, and is brought closer to that of the memorized reference waveform. Alternatively, there is a method in which the point at which the time-series difference of the waveform Q is maximum is set as the base point of the waveform Q.

The above-mentioned difference between the stored ideal reference signal waveform and the actually received reference signal waveform is caused not only by proximity ghosts but also by the frequency characteristics (mainly high-frequency limiting characteristics) of the transmitting system, antenna system, and receiving system. arise due to In either case, since both can be considered to be similar phenomena, the image quality can be improved by the same signal processing.

When the ghost is large, the second-order component gt as exemplified by waveform (F) in FIG. 2 cannot be ignored. For example,
Assume that the time series of the difference signal exemplified by the waveform (D) in FIG. 2 becomes that exemplified by the waveform (A) in FIG. In this case, as can be easily inferred from the waveform (F) in Fig. 2, the secondary ghost shown in the waveform (B) in the same figure is caused by the cancellation of gr in the waveform (A) in Fig. 5. will occur.

Similarly, for the cancellation of go, a secondary ghost shown in waveform (C) occurs, and for the cancellation of g2, the waveform (
A secondary ghost shown in D) will occur.

Generally, if the difference series is gi (i=-N”N),
The intensity of the newly generated ghost is Σ Σgi・g J
(i*J--N-N), and the delay time is i+j)T for the sampling period T.

Therefore, by considering the second-order ghost that occurs to cancel the -th-order ghost, and giving the transversal filter a tap weight that includes a component for canceling these in advance, it is possible to By extending the idea of 0 or more that can also remove the next ghost component,
If necessary, third-order or higher-order ghost components can also be removed.

In order to reduce random noise contained in the received signal, an addition function may be added to the storage section 14 in FIG. 1 to add a desired reference waveform several times.

In the above, a configuration has been exemplified in which the waveform of the falling portion of the vertical synchronization signal is used as it is as the reference signal waveform. However, as illustrated in FIG. 6, a configuration may be adopted in which a predetermined signal waveform is inserted as a reference signal waveform at a predetermined location within the vertical blanking period.

In addition, the set of sampling values of the falling part of the vertical synchronization signal is stored as is as a reference signal waveform, and after calculating the difference with the corresponding sampling value actually received, the difference signal between these waveforms is An example of a configuration for calculating the difference on the axis is illustrated. However, the difference value on the time axis for the sampling value of the falling part is calculated in advance and stored, and the difference value on the time axis for the corresponding sampling value actually received is also calculated and then stored. It may also be configured to calculate the difference between the two.

Further, in order to prevent the ghost removal performance from deteriorating due to the difference in the levels of waveforms P and Q, a configuration is illustrated in which the standardization unit 13 is installed before the storage unit 14. However, if the performance of the amplitude adjustment mechanism (not shown) at the front stage of the input terminal I is good, the installation of the normalization section 13 can be omitted, and the installation location may be between the reading section 15 and the difference calculation section 16. You can also change it to .

Note that the normalization section 13, difference calculation section 16, correlation calculation section 17, base point determination section 18, etc. in FIG. 1 can be realized in hardware, or can be realized in software using a microcomputer or the like. You can also do it.

Effects of the Invention As explained in detail above, the ghost removal device of the present invention includes a reference signal waveform holding means for holding a predetermined reference signal waveform included in a television signal, and a reference signal waveform holding means that holds a predetermined reference signal waveform included in a television signal. a reference signal waveform extraction means for extracting the reference signal waveform; a difference calculation means for calculating the difference between the outputs of these two means; a pseudo ghost generation means for generating a pseudo ghost based on the output of the difference calculation means; Since the configuration includes ghost canceling means for canceling ghosts in the televised signal using the output of the ghost generating means, all ghosts including nearby ghosts having a short delay time of about 0.5μ3 or less can be eliminated. The effect is that removal can be performed with high precision.

[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 FIGS. 2 and 4 show the reference signal waveform being held and the received reference signal regarding the operation of the ghost removal device shown in FIG. 1. FIG. 4 is a waveform diagram for explaining the operation of calculating a difference signal from a signal waveform, generating a pseudo ghost, and canceling the ghost in a television signal.
, a waveform diagram for explaining fine adjustment of the timing when determining the base point by the correlation calculating unit 17 and the base point determining unit 18, fifth waveform diagram.
The figure is a conceptual diagram for explaining the occurrence of second-order or higher-order ghosts and the method for removing them. Figure 6 is a waveform diagram for explaining other examples of reference signal waveforms. Figures 7 and 8 are 9 is a block diagram showing the configuration of a conventional ghost removing device, and FIG. 9 is a waveform diagram for explaining the operation of the conventional ghost removing device. DESCRIPTION OF SYMBOLS 1... Tap gain control circuit, 2... Pseudo-image ghost generation circuit, 5... Register, lO... Reference signal waveform storage section, 11... A/D conversion section, 12... Reference Signal waveform detection section, 15... Reading section, 16... Difference calculation section, 17... Correlation calculation section, 18... Base point determination section. Patent applicant: NEC Home Electronics Co., Ltd. (1 other person)

Claims (1)

[Scope of Claims] Reference signal waveform holding means for holding a predetermined reference signal waveform included in a television signal; and reference signal waveform extraction means for extracting the reference signal waveform contained in the television signal. , a difference calculation means for calculating the difference between the outputs of both the reference signal waveform holding means and the extraction means; a pseudo ghost generation means for generating a pseudo ghost based on the output of the difference calculation means; 1. A ghost removal device comprising: ghost cancellation means for canceling ghosts in a television signal using the output.