JPS60199275A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To suppress effectively growth of unnecessary taps caused by tap gain correction control from being increased while suppressing the increase in the visually residual ghost to a minimum value by setting larger the leakage at the tap gain correction that the leakage with respect to the tap contributing to the elimination of remote ghost as to the tap contributing the erasure of nearby ghost. CONSTITUTION:A leakage amount arithmetic circuit 70 inputs a tap gain {c1} read from a tap gain memory 48 and decides the leakage 11 by formula I , where beta(i) is a coefficient being a function of a tap number (i), and the beta(i) is predetermined to a value as shown in Fig., larger when the (i) is near zero and smaller as the ¦i¦ increases, where i=0 is the case with the main tap. In expressing an upper limit of a ghost level not causing so much mental feeling of disorder regardless of the presence of ghost on a pattern as DU ratio (desired signal versus undesirable signal ratio in dB) as a permissible ghost value, the characteristic is shown roughly in Fig. That is, the residual ghost larger to some degree is permitted to a nearby ghost having a delay time of <=2muS than a ghost having a delay time of >=5muS.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a ghost erasing device in a television receiver, etc.

[Technical background of the invention and its problems] Figure 1 shows a known example of a ghost canceling device using a transversal filter with variable tap gain. This method uses the front vertical part (the part that moves from the third line to the fourth line) of the vertical synchronization pulse (the part that moves from the third line to the fourth line). 37.November 1978) 0
In FIG. 1, reference numeral 20 denotes a transversal filter with a variable tap gain, and a delay element 2 with 0 taps consisting of a delay element 21 with taps, a loading circuit 22, and an adder circuit 23.
The delay time T between taps of 1 is a value smaller than the reciprocal of twice the highest frequency of the input video (e.g. 0.1 μs).
choose. The total number of taps is determined depending on the range of delay (advance) time of the ghost to be erased. For example, if the total number of taps is 100, a time range of 10 μs can be covered. A delay element 5 having a delay time MT (M is 0 or a positive integer) is connected in parallel with the transversal filter 20.
0 is provided, and its output and transversal filter 2
The outputs of 0 are combined by an adder circuit 51. Among the taps of the transversal filter 20, the tap of the MT that opens when delayed is called a reference tap, the tap with a short delay time is called a forward tap, and the tap with a long delay time is called a backward tap. Now, if M = 20, if there are 100 taps, 2
This means that leading ghosts up to .mu.s and lag ghosts up to 8 .mu.s can be eliminated. The weight circuit 22 attached to each tap is a multiplication circuit, and its coefficient is the tap gain.

The tap gain of the reference tap is expressed as Co, the tap gain of the front tap is C-M-C-1, the tap gain of the rear tap is C
It will be expressed as 1-CN.

The value of tap gain CB (i = -M - N) is usually
The absolute value is less than 1. Note that the functions of the delay element 50 and the reference tap are collectively referred to as a king tap for convenience.

In other words, a king tap is a tap with a delay time MT when the waveform equalization circuit 60 consisting of the delay element 50, the transversal filter 20, and the adder circuit 51 is regarded as one new transversal filter as a whole. be. At this time, the tap gain of the king tap becomes l + CO.

In such a waveform equalization circuit 60, the tap gain (c
i) If (the sequence of C-M-CN is expressed as (C1)) is set to an appropriate value, the ghost components (including waveform distortion caused by filters, etc.) present at the input terminal 10 will be
At the output terminal 30, it is substantially cancelled. This tap gain may be automatically controlled to minimize the ghost component of the output as shown in the sixth order.

First, from the input video No. 18 applied to the input terminal 10, only a predetermined length of the leading edge of the vertical synchronization pulse of interest is extracted under the control of the timing circuit 44, and this is extracted by the differentiator 40. The input waveform is stored in the input waveform memory 41 via. On the other hand, only a predetermined length of the output video signal from the output terminal 30 at the same time is extracted and stored in the error waveform memory 46 via the differentiation circuit 42 and the reference waveform subtraction circuit 43. Here, the reference waveform supplied to the reference waveform subtraction circuit 43 is generated by the reference waveform generation circuit 45 under the control of the timing circuit 44. The waveform stored in the input waveform memory 41 in this way is transferred to the Lanceversal filter 20 at a sampling interval of 01 μS ().
[xk
). Similarly, the output waveform of the differentiation port j842 is (ykl), the reference waveform generated by the reference waveform generation circuit 45 is (rk), and the error waveform that is the output of the subtraction circuit 43 is (ek).
It is written as Kek=yk-rk). However, the differentiating circuits 40 and 42 are unnecessary if an impulse waveform is inserted in advance as a reference waveform into the input video signal. In this way, the error waveform (ek) is stored in the error waveform memory 46. Note that when looking at the actual signal waveform, there is a time lag of MT between (xk) and 0'kl, but in order to simplify the notation in the formula below, the place that should originally be written as yk+-14 will be written as yk. (+ in ')
The same applies to 'lH).

Next, (Xk) and (ehl) are read out from each of these waveform memos 1J41, 46 using a clock of an appropriate frequency, and a correlation calculation expressed as follows is performed. Here, the correlation range [P.

Q] is usually set to a value of about P=-2M and Q=2N. d
The physical meaning of l is the delay time i T (T is the tap interval)
This is the approximate size of the ghost.

On the other hand, the tap gain memory 48 stores the tap gain (C1) of each tap, and its initial value is C−M −
CH: It's Q. Each time the calculation of the first equation is completed for one of i = -M to N, the tap gain ci is read out from the tap gain memory 48, and ci, new ” CL, ol(1-adi ” '
(After making the correction represented by J (a is a positive minute value), the tap gain memory 48
Return to The calculations expressed by equations (1) and (2) are performed for all i (i=-M-N) during one field, and this is executed by the tap gain correction calculation circuit 4.
It is 7.

The above calculation is repeated every time a new reference waveform is received (ie, once per field). By continuing this, the error waveform (ek) gradually approaches 0 (that is, the output waveform (yk) approaches the reference waveform (rkl)).

Finally (C1) is a certain value (C1). It converges to pt, but the output waveform (yk) at this time is.

The residual error defined by t is minimized (see the above-mentioned document).

In principle, tap gain correction can be done using Equation (2), but when Equation (2) is applied to a practical device, the spectrum of the input video signal, the influence of noise, the frequency of the transversal filter 20, etc. characteristics and even tap gain memory 48
Due to the influence of the finite number of bits in (C1
) does not necessarily converge to the optimal value (Cz)opt, and the tap gain ('i )n011111, which is originally insignificant, is changed to ['
It is added to 1lopz.

(C1). . There is no particular problem if lae is small, but depending on the combination of the various conditions mentioned above (C1
). . If iae is ignored, it will be as large as @'s, or in some cases (C1). . 16° may not converge to a constant value and may diverge over time.

(C1). The growth of olse is particularly remarkable when, in order to simplify the device (= instead of equation (1), d1=C1...(4) is used as its approximation) (such a control method is It is called forcing algorithm).

As mentioned here (C1). . In order to suppress the growth of 18°, C1, new ” 'i, 01 (1-adi-βC1
1old - (5) Case or 'i, nrw=C1, oil adl rsgn (cl
, 016) - = (6) A method using the control equation expressed as .Showa 58
(February). The third term on the right side of each of the above equations means "leak", and its magnitude is 0 with respect to tap gain (C1).
It has the effect of giving the mind strength to move towards the future. Chapter (6)
The control based on equation (6) is called "proportional leak control" and the control based on equation (6) is called "constant leak control."

The above-mentioned "leak control" is (C1). . 16. Via is extremely effective in suppressing the growth of the world, but on the other hand, it has the following drawbacks. In other words, if the leakage is large, β in equation (6) is large, or f is set large in equation (6), etc.
(C1)ゎ. 16. The suppression effect is great, but at the cost of this, even the taps that should originally contribute to ghost erasure are suppressed (
C1). , t, but only grows to a value that is somewhat slower in absolute value than (cll.pt). As a result, the magnitude of the residual ghost at the ghost canceler output is reduced to β or 1 increases in proportion to y.In this way, suppressing the growth of unnecessary taps (c(1no1se) and reducing the residual ghost canceller are contradictory to each other, and when designing a ghost canceller, 5
An appropriate compromise between the two must be found to determine β,' or 1. However, there is an unnecessary tap (C1).

. Since the degree of growth of iae generally increases with the total number of tags in the transversal filter, in a ghost canceler with a wide ghost cancellation time range (i.e., a large number of taps), both the growth of unnecessary tags and the residual ghost level will increase. It was difficult to keep both values below satisfactory values.

[Object of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide a ghost erasing device that can achieve a desired ghost erasing performance while suppressing the growth of unnecessary taps to a sufficiently small level. shall be.

[Summary of the Invention] The present invention provides a waveform equalization circuit including a variable tap gain transversal filter, a tap gain memory that stores a tap gain value to be given to the transversal filter, and a tap gain read out from the tap gain memory. and a tap gain modifying means for re-inputting the value of The tap value includes a means for applying a leak in a direction toward zero, and a means for setting the magnitude of the leak applied by this means to be large in the vicinity of the king tap and smaller as it moves away from the king tap. It is a feature.

[Effects of the Invention] According to the present invention, attention is paid to the fact that the ghost detection ability of human vision is more insensitive to so-called close ghosts with a short delay time than to ghosts with a long delay time. By setting the leakage value during tap gain correction control for taps that contribute to the elimination of close ghosts to be larger than the leakage value for taps that contribute to the elimination of distant ghosts, it is possible to increase the residual ghost visually. It is possible to realize a high-performance, highly stable ghost canceling device that can effectively suppress the growth of unnecessary taps caused by tap gain correction control while minimizing the .

[Embodiment of the Invention] FIG. 2 shows the overall configuration of an embodiment of the present invention, and many of its basic components are the same as in FIG. 1. Therefore, in FIG. 2, parts common to those in FIG. 1 are indicated by the same numbers, and detailed explanation thereof will be omitted. Newly added parts in FIG. 2 are a leak amount calculation circuit 70 and a subtraction circuit 71.

The leakage calculation circuit 70 manually calculates the tap gain (C1) read from the tap gain memory 48 by calculating 11=β(i
)c, (β(i)>O) ...(γ) or 11=r(i)fignci (r(i)>O) −(
The leakage amount 11 is determined by 8+. Here, the coefficient β (
+> or r(i) is a function of tap number i, and if i = O is the king tap (delay [0), then β(
+) (or r(i)) is predetermined to a value that is large when l is around 0 and becomes smaller as the value of l becomes larger, as shown in FIG.

The tap gain correction performance circuit 47 in FIG.
1) or (4)) is performed. Its output is + of the subtraction circuit 71
On the other hand, the output of the leak i calculation circuit 70 (the equation (γ) or the equation (8)) is supplied to one side (the subtraction input) of the subtraction circuit 71. Ru. Therefore, the output of the subtraction circuit 71 is changed to CI. When expressed as 6W, it is CI. ,=CI-adL-β(i)ct=
(1−β(river c1− adl −(9) or cl, n@W = Ct −adl −r (i)sg
ncl +++ 101, which is re-inputted into the tap gain memory 48 as an updated tap gain.

Part 9 (9).

flo) formula, C1,. ld is abbreviated as i:c1.

Furthermore, as is clear from the expression of equation (9), from C1 to β
(i) Subtracting ci means (1-!(+
)) is completely equivalent, so the software that actually realizes the control of equation (9) does not necessarily have to be based on the combination of the leakage calculation circuit 70 and the subtraction circuit 710, but can be As shown in FIG. 4, this is also possible with a configuration using a multiplication circuit 72.

The coefficient β(i) ('E fc is γ
The effect produced by changing (i)) according to the tap number 1 as shown in Figure 3 on the back will be described below.

It is known that the ability of human vision to detect ghosts on a TV screen varies depending on the ghost delay time, and that the detection ability is relatively reduced for ghosts with short delay times. The DU ratio (desired signal to unnecessary signal ratio) is the upper limit of the ghost level that does not cause psychological discomfort even if there is a ghost.

If expressed in dB), the characteristics will be as shown in Figure 5. That is, for a nearby ghost with a delay time of about 2 μs or less, a somewhat larger residual ghost can be tolerated than for a ghost with a delay time of 5 μs or more.

As shown in Fig. 3, if a larger leak is applied to the nearby ghost, the residual ghost of the nearby ghost will certainly increase as a physical quantity Vi, but
The result is that this does not pose much of a problem in terms of visual psychology.

On the other hand, when looking at the growth of unnecessary taps, the effect of suppressing the growth of unnecessary taps increases as the amount of leakage increases for adjacent taps.

The effects of suppressing the growth of unnecessary taps are: (1) Prevention of runaway (divergence) of tap gain correction control (2)
) Avoidance of increase in output noise (8) Avoidance of non-linearity generation due to excessive input when realized with an analog circuit such as a CCD (charge-coupled device) such as a transversal filter circuit (4) Avoidance of non-linearity generation due to excessive input For example, it is possible to prevent oscillation of a cyclic filter circuit when a cyclic configuration is adopted, and the present invention makes it possible to realize an extremely stable ghost canceling device without sacrificing much of the ghost canceling performance.

Next, we will discuss some other configuration methods that are different from the above embodiments but also meet the spirit of the present invention. First, the formula for determining the leakage amount is not necessarily the formula (7) or the formula (7). It is not limited to Equation (8) and is generally 1,
=β(i)f(cl-*, C1-+1.-+c>, C
s+i, -c++k) +++As shown in (2), even if the leakage for the first tap is a function of the tap gains of the taps before and after including the tap gain of the first tap, the coefficient β(1) is included in the present invention if it varies by 1.

Tap gain correction performance 3 again! (For example, Equation (9)) does not necessarily have to be realized by hardware, but can also be realized by a combination of a microprocessor and software.

Furthermore, among the variable tap gain taps of the transversal filter 20 shown in FIG. A configuration in which the difference circuit 43 is omitted is often used in a ghost canceling device, but the present invention can be similarly applied to such a circuit configuration.

Furthermore, regarding the waveform equalization circuit 60, in addition to the transversal filter 20' for the front tap, the rear tap has a configuration of a cyclic filter 20' including a transversal filter in the feedback loop as shown in FIG. It is also possible.

The present invention can be similarly applied to this case as well.

Also, the way to give dl in the third term on the right side of equation (9) is as shown in equation (1).
It is not limited to Equation or Equation (4), and any of various conventionally known modifications can be applied.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional ghost erasing device, and FIG. 2 is a block diagram of an embodiment of the ghost erasing device of the present invention.
Fig. 3 is a diagram showing that the magnitude of the leak coefficient differs depending on the tap number, Fig. 4 is a block diagram showing another configuration method of the leak providing circuit, and Fig. 5 shows that the ghost tolerance limit differs depending on the coast delay time. FIG. 6 is a diagram showing the configuration of a waveform equalization circuit in another embodiment of the present invention. 47.Tap gain correction calculation circuit 48...Tap gain memory 60...Waveform equalization circuit including transversal filter Representative Patent attorney Nori Chika Keisuke (and 1 other person) Fig. 2 Fig. 3 Fig. 4 Fig. 5 Figure ρ 2 6 4? Ghost delay Kakuya (μS)

Claims (1)

[Claims] (1) A waveform equalization circuit including a variable tap gain transversal filter, a tap gain memory that stores the value of the tap gain to be given to the transversal filter, and a tap gain value read from the tap gain memory that applies the tap gain value to the waveform. In the ghost canceling device, the tap gain correcting means corrects the output signal of the equalization circuit in a direction to decrease the value and re-inputs the corrected signal into the tap gain memory, wherein the tap gain corrector 11ii has a value for each tap, respectively. Ghost erasure comprising means for applying a leak in a direction toward zero, and means for setting the magnitude of the leak applied by this means to be large near the king tap and smaller as it moves away from the king tap. Device.