JPS6096015A - Automatic equalizer - Google Patents

Abstract

PURPOSE:To suppress unnecessary gain from being progressed while suppressing the absolute level of a residual distortion component in an output signal independently of the level of distortion component included in an input signal by providing leakage obtained through nonlinear conversion of a tap gain series. CONSTITUTION:A leak amount operating circuit 70 and a subtraction circuit 71 are provided additionally. The leak operation circuit 70 inputs a tap gain ci of each tap read from a tap gain memory 48 and operates the leak amount li according to prescribed equation. A tap gain correction operating circuit 47 performs tap gain correcting operation similarly as a conventional case and its output is fed to a non-inverting input of the subtraction circuit 71. An output of said leak amount operating circuit 70 is fed to an inverting input of the subtraction circuit 71. Thus, an output ci,new of the subtraction 71 is inputted again to a tap gain memory 48 as a revised tap gain. The tap gain correction as above aims at minimum residual distortion and unnecessary tap gain.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an equalizer that equalizes a received signal waveform using a transversal filter with variable tap gain. The present invention relates to an automatic equalizer that uses a predetermined waveform to automatically remove linear distortion in a transmission system on the receiving side.

[Technical Background of the Invention and Problems Therewith] A ghost canceling device for a television receiver is known as one application example of an automatic equalizer. Fig. 1 shows a known example of a ghost canceling device using an I-rance versal filter with variable tap gain. (Reference document: Baka Murakami, "Digitalized automatic ghost erasing device," Institute of Electronics and Communication Engineers technical research report EMCJ78-37, November 1978).

In FIG. 1, 20 is a transversal filter with variable tap gain, which is composed of a tapped delay element 21, a loading circuit 22, and an adder circuit 23.

The delay time T between the taps of the tapped delay element 21 is selected to be a value smaller than the reciprocal of twice the highest frequency of the input video signal, for example, 0.1 μs. 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 50 having a delay time MT (M is O or a positive integer) is provided in parallel with the transversal filter 20, and its output and the output of the transversal filter 20 are combined in an adder circuit 51. Among the taps of the transversal filter 20, the tap with a delay time MT is called a reference tap, the tap with a shorter delay time than this is called a forward tap, and the tap with a longer delay time is called a backward tap.

This means that the strike can be deleted. The load 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 c.

, and the tap gain of the front tap is expressed as C-A(~cf1
, the tap gain of the rear tap will be expressed as 01~bee. The value of tap gain C+ (i=-fVI-N) usually has an absolute value smaller than 1. Note that the functions of the delay element 50 and the reference tap are collectively referred to as a main tap for convenience. That is, the main tap is the waveform equalization circuit 6 consisting of the delay element 50, the transversal filter 2o, and the addition circuit 51.
This is a tap with a delay time of M when 0 is regarded as one new transversal filter as a whole.

At this time, the tap gain of the main tap becomes 1 + Co.

In such a waveform equalization circuit 60, the tap gain (C
I) (The sequence of C-t, + to CN7 is expressed as (Ct)) is set to an appropriate value, the ghost component (including waveform distortion caused by the filter, etc.) that existed at the input terminal 10 will be removed from the output. At terminal 30, it is substantially erased. The tap gain can be automatically controlled to minimize the ghost component of the output as follows.

First, from the input video signal applied to the input terminal 10,
Under the control of the timing circuit 44, only a predetermined length of the leading edge of the vertical synchronization pulse of interest is extracted and stored in the input waveform memory 41 via the differentiating circuit 40. 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 M single 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 manner is expressed as (xk) as a sample value series at every sampling interval of 0.1 μS (same as the tap interval of the transversal filter 20). Similarly, the output waveform of the differentiating circuit 42 is (yk
), the reference waveform generated by the reference waveform generation circuit 45 is (r,
), and the error waveform output from the subtraction circuit 43 is expressed as (ek) (ek=yk-rk). however,
The differentiating circuits 40 and 42 are not necessary when an impulse waveform is inserted in advance as a reference waveform into the input video signal. In this way, the error waveform memory 46 stores the error waveform (
ek) will be stored.

In addition, looking at the actual signal waveform, (Xk) and (y
k), there is a time lag called MT, but in order to simplify the notation in the equations below, the place that should originally be written as V k4-h' will be written as yk (the same applies to rl, ・Q>) .

Next, (Xk) and (e+.) are read out from each of these waveform memories 41.46 using a clock of an appropriate frequency, and the correlation expressed as di-Z xk-i ``k'''(1)k; 11 is calculated. Perform calculations. Here, the correlation range [P.

Q] is generally set to a value of about P=-2M and Q=2N. d
The physical meaning of , is the approximate size of a ghost with a delay time of 1T (T is the tap interval).

On the other hand, the tap gain memory 48 stores the tap gain (C1) of each tap, and its initial value is C−M −
CN=Q. Every time the calculation of the first equation is completed for one i of r--N4 to N, the tap gain CI is read out from the tap gain memory 48, and CI, new CI, old -ad, "' ( 2
' (a is a positive minute value) After making the correction represented by ', the tap gain memory 48
Return to The operations expressed by equations (1) and (2) are performed for all i (i −−M−N) during one field, and this is executed by the tap profit 1q correction operator circuit. It is 47.

The above calculation is repeated each time a new reference waveform is received (that is, once per field). By continuing this process, the error waveform (ek) gradually approaches O (that is, the output waveform ()'k) approaches the reference waveform (rk)). Eventually, (C- converges to a certain value (C1)・3.t, but the output waveform (yk) at this time is the one that minimizes the residual error defined by k-12I(2l'). It has become (
(See the above document).

In principle, tap gain correction can be done using Equation (2), but when Equation (2) is applied to an actual device, it is difficult to modify the input video signal due to the magnitude of the input video signal, the effects of noise, and the transversal filter 20. frequency characteristics, and even tap gain memory 4
Due to the influence of the fact that the number of bits of 8 is finite (C
I) does not necessarily converge to the optimal value (Ci), t,
Originally unnecessary tap gain (e・)... (-)
・It will be tightened to +pt.

If (CI) l+ull: is small, there may be no particular problem, or by combining the various conditions mentioned above, (U(C,).*i so becomes too large to be ignored, or in some cases, (cl) ...i5° may not converge to a constant value and may diverge over time.

(Ct). Mountain. The growth of d1 is particularly remarkable because, in order to simplify the device, instead of formula (1), d1
=e, (4) (Such a control method is called a zero forcing algorithm).

In order to suppress the growth of (C1)olse described here, a method has been proposed that uses the control equation expressed as (2J) instead of (2J) (
JP-A-57-145446). This method is the fifth
) If we choose (hj) in the formula to be a low-pass type, we get (CI). ela
Since the positive/negative/positive/negative pattern included in a is effectively suppressed, the growth of (CI)no+5° is suppressed without sacrificing much of the ghost cancellation performance in the low frequency range.

In this method, the unnecessary tap profit IJ (CI) nofa
Although it is quite effective in suppressing the growth of That is, the larger the ghost component contained in the input video signal, the larger the residual ghost will be in proportion. This is an inevitable result of equation (5) being a linear control equation. The problem is not so much the performance of the ghost canceling device, but rather how small the absolute value of the residual ghost is, so it is practically undesirable for the residual ghost to become larger in proportion to the input ghost.

[Object of the Invention] It is an object of the invention to provide an automatic equalizer that can effectively suppress unnecessary tap gain growth while suppressing the tap gain.

[Summary of the Invention] The present invention provides a waveform equalization circuit including a tap gain IQ variable transversal filter, a tap gain memory that stores a tap gain value to be given to the transversal filter, and a tap gain memory that stores a tap gain value to be given to the transversal filter. an automatic equalizer comprising tap gain modifying means for modifying a gain value in a direction that reduces distortion of the output signal of the waveform equalization circuit and re-inputting the gain value to the tap gain memory, A subtraction means is provided in a path until the read tap gain is re-inputted into the tap gain memory via the tap gain correction means, and a plurality of successive series of tap gains read from the tap gain memory are provided. is used as an input, a leakage amount calculation means is provided, and an output of the leakage barrier calculation means is used as a subtraction input of the subtraction means.

Here, the leakage amount calculation means inputs the tap gain series (C1) (i -- M-N) to express it numerically, and corresponds to the first tap to calculate a predetermined number of 11: where fk): Series A and B containing non-zero elements: positive integers (one of A and B can be O); number of stages of forward taps and rear taps of M, N Nidor universal filter; γ: positive constant c; (i<-M, i>N>=0 or a signal equivalent thereto is output.

That is, the gist of the present invention is not to linearly transform a tap gain series, but to provide a nonlinearly transformed tap gain series by taking the polarity of the linearly transformed signal as a leak when correcting the tap gain.

[Effects of the Invention] According to the present invention, residual distortion components in the output signal are reduced regardless of the magnitude of distortion components such as ghosts included in the input signal by adding leakage obtained by nonlinear transformation of the tap gain sequence. It is possible to realize a high-performance, highly stable automatic isolator in which growth of unnecessary tap gain is suppressed while the absolute level of is kept extremely small.

[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 leak amount calculation circuit 70 is a circuit that receives the tap gain (C1) read from the tap gain memory 48 as input and performs the following calculation. Here, 5 (ln For example, f -1=-0,25°fa=0.5.dit=-0,25. Also, γ is a positive infinitesimal constant (. il 'J ril (, in addition to C, -H1~CH, Q -) - with one candle
2A to C--1 and CN-.1 to CN+2B are also required, but since these are outside the range of the tap gain memory 48, C-111-2A to C-1-1-1""'JI"N4 −
Calculate as 1~Chi+211=O−゛(Li).

The tap gain correction calculation circuit 47 in FIG.
1) or (4)) is performed. Its output is + of the subtraction circuit 71
(addition input).

On the other hand, one side (subtraction input) of the subtraction circuit 71 is supplied with the output (Equation (6)) of the leak amount calculation circuit 70 described above.

Therefore, the output of the subtraction circuit 71 can be expressed as CI+new, and this is re-inputted into the tap gain memory 48 as an updated tap gain. However, in Type 9 “+O
1d is simply abbreviated as C1.

The effect of performing tap gain correction using the 0th equation will be explained using a mathematical equation.

First, convert the error waveform (ek) in Fig. 2 to the input waveform (
Expressed using X+l, reference waveform (rk), and tap gain (C8), ek = xk + Σ C1 In the automatic equalizer based on the equation (), the tap profit 'fJ(C1) was successively modified so as to minimize E given by the equation (3). Instead of E, we use 1=-M k=-A, which is obtained by adding a dependent term to this, instead of E. When the tap gain sequence (CI) is regarded as one time-series signal, k corresponds to the output signal sequence when this is passed through a filter with an in/<)less response (f-k). Conventionally, unnecessary tap gain (CI). Since it is empirically known that olnc has a pattern of positive, negative, positive, negative, etc.', the in/<J less response (f-1,) is expressed in a high-pass form (sampling system (or frequency 1 /T neighborhood is called the high range), Σfkel+k is the tap gain (C2)
This selectively emphasizes the middle high-frequency components, that is, the positive, negative, positive, and negative patterns. Therefore, J expressed by the 0°C equation
Minimizing E corresponds to selectively suppressing the unnecessary tap gain in (C1) at the expense of minimizing E. In this case, .mu. means weighting of how much weight is given to the tri pressure of the unnecessary tap gain.

In order to minimize J expressed by the α-th equation, the differential coefficient aJ7'ao of J with respect to CI may be subjected to a second tap gain correction. From equation αj), aJ
It can be obtained by subtracting /δC. However, it is a μ 2 ° “tax.

That is, the tap gain correction according to equations 0 and (6) is aimed at minimizing residual distortion as well as unnecessary tap gain.

As described above, an effect similar to this can be obtained by modifying the tap gain using equation (5). Incidentally, it will be shown below that the control in equation (5) is a control that minimizes the substitution for J in equation (11).

That is, if we assume that the α-th whip equation is partially differentiated with respect to 01, and then substitute the α-th equations to the 08j-th equations into the α-th equation, the equation (5) can be obtained.

That is, the conventional method (Equation (5)) and the method of the present invention (
The difference from Equation (e)) is that in addition to the residual distortion, the sum of squares of the high-frequency components of the tap gain 1q (conventional method) is taken as the evaluation function for minimizing the unnecessary tap gain, or the sum of the absolute values is taken as the evaluation function for minimizing the unnecessary tap gain. (The method of the present invention) is adopted. As a result of this difference, in the conventional method, the absolute amount of tap gain suppression is larger for high-frequency components of the tap gain (C1) that have a large absolute value than for those that have a small absolute value. Therefore, in the method of the present invention, the high frequency component of the tap gain (CI) is suppressed by a substantially uniform absolute amount for all i. Looking at this from the perspective of residual distortion, in conventional systems, the larger the distortion component in the input signal, the more the tap gain of the tap that contributes to equalizing it is suppressed in proportion to its magnitude. , the residual distortion also increases proportionally, whereas in the method of the present invention, the high-frequency components of the tap gain are uniform for all taps, regardless of the magnitude of the distortion component in the input signal. As a result, the magnitude of the residual distortion is almost independent of the magnitude of the distortion component in the input signal.

The difference between the above two equations can be shown in a graph as shown in Figure 3. As shown in the figure, if we take the magnitude of the distortion component included in the input signal on the horizontal axis and the residual distortion on the vertical axis, in the conventional method, the residual distortion is approximately proportional to the input distortion as shown in (a). In contrast, in the method of the present invention, the line is approximately parallel to the horizontal axis, as shown in (b).

For example, if the present invention is applied to a ghost canceling device, and the visual detection limit of ghosts is represented by the dotted line in the figure, the range of input ghost sizes that can reduce residual ghosts below the detection limit is greatly expanded by the present invention. It turns out that Shirokoto.

Next, some modified examples of calculations to be performed in the leak amount calculation circuit 70 will be described.

The calculation performed by the leakage calculation circuit 70 should originally be based on equation (6), but in order to simplify the hardware or to simplify the software when the calculation is performed by software of a microprocessor, it is actually It is also possible to employ an approximation of equation (6), which has a similar effect to equation (6). An example of such an approximation is:

tI in the (1-υ equation) is Δ by taking only the polarity of tl in the equation (6).

It is ternarized into Ol-Δ, and is the 1. In equation (6), out of (fj) expressed by the suffix j, γfa = Δ after emphasizing only the contribution of 0 and ignoring the contribution of f other than j-0. By using these approximations in place of equation (6), the performance of the system is affected to some extent, but the qualitative differences from the conventional system as shown in FIG. 3 are maintained.

The calculations in equations (6), (14;, and (1υ)) can be realized by hardware or microprocessor software, but if the calculation process is shown in a block diagram, 6 to 6. FIG. 4 corresponds to equation (6), FIG. 5 corresponds to equation (α), and FIG. 6 corresponds to equation (c).

In FIGS. 4 to 6, 72 is the formula (6), respectively.
αΦth expression, product-sum calculation block within 0 of (lcJ expression, 7
3 is a polarity discrimination block inside (), 74 is a product-sum calculation block outside () of equation (6) and equation (2), and 75 is a series fk
, 76 is a multiplication block that multiplies by a constant α, 77 is a polarity determination block in () of the α-→ equation, and 78 is a multiplication block that multiplies by a constant.

Note that in the above explanation, γ in equation (6) and α-th
, , and the 10th equation are predetermined constants, but this is for convenience of explanation, and it is possible to select several values of γ and Δ depending on the operating state of the system at that time. Even if a means for selecting and setting one of the values is added, it does not depart from the spirit of the present invention.

Further, regarding the transversal filter shown in FIG. 2, a configuration in which the tap gain is fixed to O and the reference waveform wave circuit 45 and the difference circuit 43 are omitted is often used in ghost canceling devices. The present invention is similarly applicable to any circuit configuration.

Furthermore, with respect to the waveform equalization circuit 60, it is possible to apply the transversal filter 20' and brightness for the front tap in the same way.

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

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional automatic equalizer, FIG. 2 is a block diagram of an embodiment of the automatic equalizer of the present invention, and FIG. 3 is a block diagram of an embodiment of the automatic equalizer of the present invention. A diagram showing changes in output residual distortion with respect to the magnitude of distortion, FIGS. M4 to 6 are diagrams showing specific configuration examples of a leakage calculation circuit that is a component of the present invention, and FIG. FIG. 2 is a diagram showing the configuration of a waveform equalization circuit in an example. 60... Waveform equalization circuit including transversal filter, 48... Tap gain memory, 47... Tap gain correction calculation circuit, 70... Leak amount calculation circuit, 71.
...Subtraction circuit.

Claims (4)

[Claims] (1) A waveform equalization circuit including a variable tap gain transversal filter, a tap gain memory for storing a tap gain value to be given to the transversal filter, and a tap gain value read from the tap gain memory, In the automatic equalizer, the automatic equalizer is equipped with tap gain modifying means for modifying the output signal of the waveform equalization circuit in a direction that reduces distortion and re-inputting the same to the tap gain memory. A subtracting means is provided in a path from which the tap gain is re-inputted into the tap gain memory via the tap gain correction means, and a plurality of successive series of tap gains read from the tap gain memory are input. , a leak group calculation means is provided which outputs a function value of a predetermined function in which the polar sign of the linear sum of these plurality of tap gain series is used as an independent variable, and the output of this leak amount calculation means is used as the subtraction input of the subtraction means. An automatic equalizer characterized by: (2) The leakage amount calculation means is configured to include a tap gain series (c+
) (i=M~N) as input, and J corresponds to the i-th tap.
li: where fk): sequence containing a plurality of predetermined non-zero elements A, B: positive integer (one of A and B may be O) M, N: l-front of lanceversal filter The automatic equalizer according to claim 1, characterized in that the number of stages γ of taps and backward taps is a positive constant e+(!<−M, i>N>=Q). (3) The leakage amount calculation means t-Oyoben (F Kiri1≠- inputs the tap gain series (c+) (i = -M-N), and corresponds to the i-th tap tl: where fk ): Sequence containing a plurality of predetermined non-zero elements A', B: Positive integer (one of A and B can be O) Number of stages of front and rear taps of M, N Nidor universal filter The automatic equalizer according to claim 1, wherein Δ: a positive constant J (i<-M, i>N)=0 is output. (4) The leak amount calculation means calculates a tap gain series (e
l) (+ = -M-N) is input, and corresponding to the first tap, tl: where fk): series A, B containing a plurality of predetermined non-zero elements: positive integers (A, (One of B can be O) M, N: l - number of stages of front taps and rear taps of Lance Barzal filter Δ: positive constant el (i <-M, t > N) = output of Q An automatic equalizer according to claim 1, characterized in that: