JPH0159790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television ghost removal device using a transversal filter.

Ghost disturbances in television reception have become a major problem in urban areas, and as a countermeasure to this problem, research and development has recently been actively conducted on devices that electrically remove ghost components within television receivers. This is an attempt to remove ghost components by applying the principle of an automatic equalizer in communication systems and using a transversal filter. FIG. 1 shows an example of this type of television ghost removal device.

In FIG. 1, a demodulated television signal entering input terminal 1 is passed through transversal filter 2.
is input. As shown in FIG. 2, the transversal filter 2 includes a tapped delay line 21 made of a charge transfer device such as a CCD, a weighting circuit 22 that multiplies each tap output of the delay line 21 by a tap gain as a weighting coefficient, and a weighting circuit 22. It is composed of an adder 23 that combines the respective outputs of the . In addition, the second
In Figure a, the input is directly added to the delay line 21 and added to the adder 23.
An example of a feed-forward type is shown in which the difference between the input and the output of the adder 23 is taken by the subtracter 24, this difference signal is added to the delay line 21, and the feedback signal is taken out as an output. Shows examples of shapes. Further, although these are all of the output weighted type, the transversal filter 2 may be of an input weighted type in which the input of each tap of the delay line 21 is multiplied by a tap gain.

The tap gain of the transversal filter 2 is stored in the D/A converter 1 from the tap gain memory 11.
2 as a DC voltage to the weighting circuit 22, and this tap gain is modified as follows.

That is, the television signal input to the input terminal 1 is also input to the A/D converter 4, where it is digitized and then applied to the subtractor 5. On the other hand, the output signal of transversal filter 2 is output from output terminal 3.
The signal is guided through a differentiator 6 to a positive/negative determiner 7 consisting of a level comparator. Differentiator 5
The differentiator 6 is for extracting the change in the waveform (reference signal) in section A near the falling edge of the vertical synchronization signal in the television signal shown in FIG. 3a,
The output waveform of the differentiator 6 is shown in FIG. 3b. Then, the output of the differentiator 5 and the signal obtained by converting the output of the differentiator 6 into binary levels of "1" and "0" depending on the sign by the sign determiner 7 are input to the digital correlator 8.

The correlator 8 is composed of a multiplier circuit and an accumulator, and converts the sample value of the output of the differentiator 5 into x _i (i=1, 2, . . .
n, n is the number of samples in interval A), and when the sample value of the output of the sign determiner 7 is y _i , d _k = _o 〓 ⁱ⁼¹ x _i・sgn(y _i+k )...(1) The purpose is to obtain a correlation signal expressed by . however,
k=1, 2, . . . N, where N represents the number of taps of the transversal filter 2. Furthermore, sgn is a symbol representing the sign in parentheses. This correlation signal d _k is input to the sign determiner 9, where code data S _k having a value of ±1 is obtained depending on the sign of d _k . Then, this code data is added to the LSB of the tap gain data in the tap gain memory 11 through the adder 10, thereby correcting the tap gain.

Now, the kth tap gain among N tap gains is
If C _k is assumed, and a positive ghost exists at a position corresponding to the delay time of this kth tap, the code data S _k will be -1, and the value of C _k will increase by 1 for each field. I'm going to go. and,
When C _k reaches the value necessary to eliminate ghosts, a steady state is reached. That is, if C _k at the end of the Mth correction is expressed as C ^M _k , C M+1 k, which is C _k at the end of the M+1st correction, is C M ^{+ 1} _k = C ^M _{k −} It is expressed as α・sgn(d _k )...(2). However, α is a positive constant. Therefore, when the ghost is removed and y _i becomes zero, d _k also becomes zero, so S _k comes to take a value of ±1 with equal probability, and at that point C _k converges.

By the way, in such a device, if the noise component contained in the television signal input to the input terminal 1 is very large, a large noise component also appears in the correlation signal _dk obtained from the correlator 8. In such a case, the convergence of the tap gain may be slow, or
Phenomena such as increased tap gain fluctuations after convergence occur. In particular, fluctuations in tap gain adversely affect the stability of the device and the quality of the received image, posing a major practical problem when applied to television receivers.

In order to solve such problems, the present inventors
Focusing on the periodicity of x _i in equation (1), only the reference signal component can be extracted by using the waveform of the reference signal section of the input television signal as x _i , which is obtained by integrating the waveform every time the reference signal arrives. , we considered improving the S/N of the correlation signal _dk by suppressing noise components that do not have periodicity.

Here, waveform integration is performed by storing the waveform of the reference signal section in a waveform memory and modifying its contents each time the reference signal arrives. In this case, the reference signal section A in Fig. 3 is The stability of the time standard t _p for determining this is a problem. In other words, the time reference t _p is usually created from a synchronization signal and a clock signal extracted by synchronization separation, but the synchronization signal may be affected by jitter due to noise or synchronization deviation due to channel switching or program switching at a broadcasting station. ,
A time lag may occur, and accordingly, t _p will also deviate.

Now, if t _p deviates from the normal state in Figure 4a as shown in Figure 4b, the waveform of the reference signal section A stored in the waveform memory will also change from the solid line state as shown in Figure 4c. It shifts to the state shown by the dotted line. For example, if the number of data bits of one sample value in the waveform memory is 6 bits, the amount of data modified in one field is one LSB bit, that is, 1/2 ⁶ = 1/64. The time it takes for this data to be completely corrected and converged is 64 times the period of one field = 1/60 seconds, or 1.07 seconds. That is, the time constant of waveform integration is 1.07 seconds, and if _tp deviates, it will take this amount of time to correct the contents of the waveform memory. During this time, the tap gain is not corrected correctly, which not only makes it impossible to remove ghosts, but also may cause the system to oscillate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a television ghost removal device that can reduce the influence of noise components and at the same time provide stable operation even with respect to time shifts in synchronization signals.

This invention improves the S/N ratio of the correlation signal by integrating the waveform of the reference signal section of the input television signal and inputting it to one of the correlators. When a shift in the synchronization signal is detected, the operation is stabilized by prohibiting tap gain modification for a predetermined period of time necessary for the contents of the waveform memory for waveform integration to be modified. It is said that

Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 5 shows the configuration of a television ghost removal device according to an embodiment of the present invention. In FIG. 5, the A/D converter 4 in FIG. 1 has been replaced with a waveform integration circuit 30. This waveform integrating circuit 30 is configured as follows.

In the waveform integrating circuit 30, the waveform memory 31 is for storing the waveform of the reference signal section of the input signal, for example, the section A of the vertical synchronizing signal in FIG. 3A, as digital data of n sample values.
The contents are read out serially and become a waveform integral output. This output is input to the differentiator 5, and
The signal is converted into an analog signal by the D/A converter 32 and input to the comparator 33. Comparator 33 compares the levels of the output of D/A converter 32 and the television signal input to input terminal 1, and outputs data of +1 when the former is smaller than the latter, and -1 when larger. The output data of the comparator 33 is then sent to the adder 35 via the sample hold circuit 34 and added to the LSB of the corresponding sample value data read out from the waveform memory 31.
This addition result is written into the waveform memory 31 again.

That is, if the data in the waveform memory 31 is M _i and the sample value of the television signal input to the input terminal 1 is x _i , new data C ^M _i of M _i
is modified by M _i and x _i as follows.

M ^x _i = M _i +1/2 ^m・sgn(x _i −M _i )...(3) However, i is the same as in equation (1), i=1, 2,...
n, n is the number of samples in section A, and m is the number of data bits per sample in the waveform memory 31. If this operation is performed every time a vertical synchronization signal arrives, M _i will eventually become x _i with an accuracy of 1/2 ^m .
converges to a value equal to .

The value of M _i at this time is the value obtained by adding and averaging x _i 2 ^m times, that is, the value obtained by integrating the waveform, and it is assumed that the non-periodic noise component contained in x _i has been removed. Become. The data read out from the waveform memory 31, that is, the waveform integral output, is input to the correlator 8 via the differentiator 5, where a correlation signal _dk with the output of the sign determiner 7 is obtained. This correlation signal d _k is supplied to the tap gain memory 11 via the sign determiner 9 and the adder 10, as in the case of FIG. 1, and the tap gain is corrected.

By the way, the time reference _tp for determining the reference signal section A whose waveform is stored in the waveform memory 31 is created as follows.

The television signal shown in FIG. 6a to the input terminal 1 is also guided to the sync separation circuit 41, where it is separated into a pulse (horizontal pulse) corresponding to the leading edge of the horizontal sync signal shown in FIG. 6b and a vertical sync signal. The signals are separated.

On the other hand, the clock signal from the oscillator 42 is frequency-divided by a frequency divider 43 to the horizontal synchronous frequency, and further divided by the frequency divider 44 to the vertical synchronous frequency. The phase comparator 45 compares the horizontal pulse b from the synchronization separation circuit 41 with the window pulse of the horizontal synchronization frequency shown in FIG. It is checked whether it is within this range or out of this range, and if it is out of this range, a reset signal is sent to the frequency divider 43. In this case, in order to prevent malfunctions due to noise, the number of times the horizontal pulse b deviates from the range of the window pulse c is counted over a certain period of time, and a reset signal is sent to the frequency divider 43 only when a certain count value is reached. You may.

In this way, the oscillator 42 can be set to 3.58M, for example.
If it is synchronized with the Hz color subcarrier, the frequency divided output shown in FIG. 6d, which is synchronized with the horizontal synchronization signal with the precision of the width W of the window pulse c, can be obtained from the frequency divider 43.

This frequency-divided output is further divided by a frequency divider 44 to the vertical synchronization frequency. Phase comparator 46
compares the vertical synchronization signal from the synchronization separation circuit 41 with the frequency-divided output supplied from the frequency divider 44, and supplies a reset signal to the frequency divider 44 when the two are out of synchronization. Synchronize both.

The timing circuit 47 is a circuit that uses a portion of the outputs of the frequency dividers 43 and 44 to generate a timing signal that instructs the above-mentioned time reference _tp , and this timing signal serves as a start signal for writing and reading into the waveform memory 31. given as. In this case, the time reference
Since t _p is created based on the output of the frequency dividers 43 and 44, once the synchronization of the frequency dividers 43 and 44 is established, this time reference t _p and the actual TV input to terminal 1 The relative error between the synchronization signal and the synchronization signal becomes very small, and as a result, jitter in _tp can be prevented.

However, since the time difference between t _p and the actual synchronization signal is allowed by the width W of the window pulse, the time difference in the synchronization signal may occur due to channel switching on the receiver side, program switching on the broadcasting station side, etc. If this occurs, the relative positional relationship between the two may shift. In such a case, as described above, the waveform of the reference signal section A stored in the waveform memory 31 also shifts in time. If this is left as is, the system will become extremely unstable due to the incorrect tap gain during the process of correcting the tap gain.

In order to avoid the above-mentioned inconvenience, the present invention attempts to prohibit modification of the tap gain for a predetermined period of time when a shift in the synchronization signal is detected. In this embodiment, this operation is specifically achieved as follows.

In other words, if there is a time lag in the synchronization signal,
Since the reset signals are output from the phase comparators 45 and 46, the OR gate 48 calculates the sum of these reset signals, and the latch circuit 49 holds the sum for a predetermined time T. While the hold output of the reset signal is obtained from the latch circuit 49, the tap gain correction adder 10 provided on the input side of the tap gain memory 11, for example,
The addition operation is stopped and tap gain modification is prohibited. In this case, the time T for which modification of the tap gain is prohibited is selected to be approximately equal to the time required for the contents of the waveform memory 31 to be corrected after the time reference is shifted due to the time shift of the synchronization signal. Since this time T is usually 100 msec or less, there is no visual problem even if the ghost removal action is not performed during this time. In this way, it is possible to prevent the system from becoming unstable when switching channels or programs.

Furthermore, when the S/N of the television signal is low and the synchronization signal separated by the synchronization separation circuit 41 frequently becomes out of synchronization, the latch circuit 49 is always in the hold state, so that the tap gain is substantially reduced. Corrections will no longer be made on an ongoing basis.
That is, even in a state where the synchronization separation is not performed correctly due to the S/N ratio or the like and the stability of the system cannot be ensured, correction of the tap gain is prohibited.
In such a case, the ghost will not be removed at all, but since there is already a lot of noise on the screen and the ghost is not noticeable, this is much more advantageous than further deterioration of the image due to an incorrect ghost removal operation.

As explained above, according to the present invention, by providing the waveform integration circuit 30, the correlation signal _dk is
Since N is improved, the tap gain converges quickly,
Furthermore, fluctuations in the tap gain can be prevented, malfunctions can be prevented due to time shifts in the synchronization signal, and a stable ghost removal operation can be obtained.

Note that the present invention is not limited to the above-mentioned embodiments, and for example, regarding the tap gain correction algorithm, in addition to the incremental control shown in equation (2), proportional control shown in the following equation may be adopted.

C ^M+1 _k = C ^M _k −α·d _k (4) Moreover, various modifications other than the one shown in equation (1) can be used as the correlation signal d _k . That is, for d _k, basically the input signal {x} of the transversal filter and the output signal {y}
and the reference signal {r}, the error signal {e}=
Generally, it expresses the correlation with {y-r},
d _k in the above embodiments omit {r} and are expressed as {e}
This corresponds to a special case where ={y}. others,
There are the following transformations of d _k , and any of these may be found.

d _k ＝ _o 〓 ⁱ⁼¹ x _i・e _i+k ……(5) d _k ＝ _o 〓 ⁱ⁼¹ sgn(x _i )・e _i+k ……(6) d _k ＝ _o 〓 ^{i= 1} x _i・sgn(e _i+k ) ...(7) d _k = _o 〓 ⁱ⁼¹ sgn(x _i )・sgn(e _i+k ) ...(8) Also, 2 to correlator 8 Regarding the two input signals, in the embodiment described above, the output of the waveform integrator 30 was the signal passed through the differentiator 5, and the output of the transversal filter 2 was made the signal passed through the differentiator 6 and the sign/negative determiner 7. It is not limited to. That is, although operations such as difference or differentiation are one type of linear transformation, such linear transformation may or may not be performed, and sign/negative determination may or may not be performed. In short, the output signal of the waveform integrator circuit 30 and the output signal of the transversal filter may be correlated directly or after performing appropriate operations such as linear conversion or positive/negative determination, by adding them to the correlator 8.

Further, the configuration of the correlator 8 itself is not limited to a digital circuit, but may be an analog circuit, and the waveform integration circuit 30 also converts the input signal into
After D conversion, the waveform may be integrated digitally, the waveform may be integrated analogously, or the waveform may be integrated analogously and then A/D converted.

Furthermore, as a means for prohibiting correction of the tap gain when a time lag in the synchronization signal is detected, not only stopping the addition operation of the adder 10 but also
Stop rewriting the tap gain memory 11,
It is also possible to use means such as stopping the calculation of the correlator 8 or prohibiting input to the correlator 8.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional television ghost removal device, FIGS. 2a and 2b are diagrams showing an example of a transversal filter, FIG. 3 is a waveform diagram for explaining the basic operation of FIG. 1, and FIG. 4a and 4b are waveform diagrams for explaining problems when using a waveform integration circuit, FIG. 5 is a block diagram of a television ghost removal device according to an embodiment of the present invention, and FIG. FIG. 3 is a waveform diagram for explaining the operation. 2... Transversal filter, 8... Correlator, 11... Tap gain memory, 30... Waveform integration circuit.

Claims (1)

[Scope of Claims] 1. A transversal filter with variable tap gain to which a television signal is input, and a reference signal interval defined by a time reference created based on a synchronization signal in the television signal, when the reference signal arrives. The television ghost removal device includes means for integrating a waveform at each time, and means for correcting the tap gain of the transversal filter, further comprising: means for detecting a time lag in a synchronization signal in the television signal; 1. A television ghost removing apparatus comprising means for prohibiting modification of the tap gain while holding data in the tap gain memory for a predetermined period of time.