JPH04130865A - Pre-compensation system for ringing - Google Patents

Abstract

PURPOSE:To facilitate the ringing compensation of a part which is difficult to be compensated in terms of circuit technology by inserting a ringing compensation circuit into the prestage of a filter which is to be ringing-compensated and generating a ringing compensation waveform cancelling a ringing waveform. CONSTITUTION:An input signal is inputted to a compensation waveform generation circuit 2 through an amplitude discrimination circuit 1. It consists of a differentiation circuit and a gate circuit, and it differentiates the edge of the input signal so as to obtain an inclination. When it exceeds a threshold, the differential signal is guided to the compensation waveform generation circuit. A ringing pre-compensation signal is obtained as the output of the compensation waveform generation circuit 2, it is subtracted from the input signal by an adder-subtracter 3 and ringing is pre-compensated. When the signal which is pre-compensated is inputted to the compensated filter 5 through a phase compensation circuit 4, an output signal without ringing can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a filter ringing compensation method, and more particularly to a ringing pull compensation method in which compensation is performed by cascade-connecting a filter in front of a compensated filter.

[Conventional technology]

2. Description of the Related Art There is an active trend toward improving the image quality of TV receivers.

In order to improve the image quality, it is necessary to filter the received TV signal without damaging its high frequency components. However, when the cutoff characteristic of the filter is made steep, ringing occurs near the edge portions of the input signal, which significantly deteriorates the quality of the reproduced image. Therefore, various methods have been devised to eliminate this ringing, such as a method of adaptively switching filter amplitude characteristics and a nonlinear filter called a median filter. In addition to these methods, as a method for removing ringing without degrading the frequency characteristics of the compensated filter, there is a ringing removal method described in Japanese Patent Application No. 1-302118 [Problem to be Solved by the Invention] above. The ringing removal method described in the prior art is as follows:
In all cases, ringing compensation is performed inside the filter that generates ringing. However, it is technically difficult to compensate for ringing in analog circuits that handle large amounts of power, such as the final-stage high-power amplifier of a transmitter or the power amplifier that drives a cathode ray tube. Furthermore, the final output stage of most devices is speakers, TV monitors, mechanical servo systems, etc.
Since these devices include elements other than electric circuits, it is difficult to electrically compensate for the ringing of the entire device. Further, it is necessary to compensate for ringing in an analog filter of a D/A conversion system connected after the digital circuit, and it is complicated to perform ringing compensation in both the digital system and the analog system.

to compensate for ringing in these filters.

There is a concept of compensating the frequency characteristics in advance to prevent ringing from occurring. However, in this case, since the filters are connected in cascade, there is a drawback that the frequency characteristics change.

The purpose of the present invention is to facilitate ringing compensation in parts that are difficult to compensate for in terms of circuit technology, such as large power amplifiers and high frequency circuits.
Another object of the present invention is to provide a method for easily compensating for ringing in devices that include elements other than electric circuits, such as cathode ray tubes and mechanical servo systems, and for which it is difficult to compensate for ringing electrically. Another object of the present invention is to provide a means for using a digital circuit to compensate for ringing that occurs in an analog circuit, such as an analog filter of a D/A conversion system, which is connected after the digital circuit.

[Means to solve the problem]

In order to achieve the above purpose, a ringing compensation circuit is inserted before the filter to be compensated for ringing, thereby generating a ringing compensation waveform that cancels out the ringing waveform, and subtracting it from the input signal of the compensated filter in advance. Make compensation.

The input signal is X, the transfer function of the compensated filter is H(z),
When the output signal is y, y=H(z) umbrella x=y$+r ・・
- (1) In equation (1), y umbrella is the desired ringing-compensated output (y umbrella=H*(z)*x), and r is the ringing waveform. r is r=y-y*=(H(z)-He(z)) umbrella x=
- given by (2).

If the pre-compensation signal C is previously subtracted from the input signal
y*+r−H(z)*c−(3). In order for ringing to be pre-compensated.

It is sufficient that equation (3) is equal to the y umbrella, and the condition is that r=
H(z)ZaiC...(4) It can be expressed as follows.

Therefore, the ringing pre-compensation signal C is (2), (4)
From the formula, c=(H(z)-H-(z))/H(z) It is determined by (5).

A ringing pre-compensation signal is generated when the slope of the edge of the input signal becomes large enough to exceed a certain threshold. Therefore, a gate circuit and a gate control circuit are provided, and when the signal obtained by differentiating the input signal exceeds a certain threshold, the differential signal is guided to the ringing compensation filter. Therefore, the transfer function of the compensation waveform generation filter is expressed by the formula (2). The integral form of Hc(z)=Z(Σ”(h(m)−h*(m))
)/H(z)...(6). In equation (6), Z (umbrella) represents two transformations of Tsu, and Σ
"h(m) represents integrating the coefficient h(m) up to n items. A gate circuit G(z) is provided in the compensation waveform generation filter of equation (6), and the input signal X is differentiated (δX = I
n -X n-1) When inputting from (z)) Umbrella x / H(z)...
(7) It can be expressed as From equations (3) and (7), the a force signal is yc=
H(z) fist(x-c)=(H(z)-G(z)*(H
(z)He(z)))Ningx-(8). In equation (8), if the gate circuit is on, G(z)=1
, when the gate circuit is off, G(z)=O, so yc=H*(z)ax When the gate is on, yc =
H(z)* x At gate off...(9)
It can be seen that if the gate is turned on when the input includes a steep edge signal in which ringing occurs, the ringing pre-compensation can be made into the desired response waveform He(z)ax.

[Effect]

In the above explanation, in order to obtain a pre-compensation waveform, (7
) The root of the denominator polynomial in the equation is a unit circle with two planes (a circle with a radius of 1)
It needs to be within. This means that the compensated filter H(z
) must be a minimum phase shift filter. By the way, a commonly used filter is a linear phase filter that does not cause waveform distortion. Therefore, using a phase correction circuit, the minimum phase shift filter is converted, and then ringing compensation is performed. At this time, since the entire filter becomes a minimum phase shift filter that causes waveform distortion, an antiphase correction circuit is added to the front stage to correct it again to a linear phase filter. Ringing generated by the anti-phase correction circuit can be compensated for by using the compensation waveform generation filter of the pre-compensation circuit.

It is desirable that ringing removal can compensate for only ringing without changing the frequency characteristics of the compensated filter. In the method of the present invention, as shown in equation (9), by using a gate circuit and limiting the compensation waveform synthesis time to only the very vicinity of the edge, the characteristics can be almost the same as those of the original filter. A large amplitude signal that causes ringing is differentiated to extract only the edge portion that causes the ringing (time compressed, so to speak), passes through a gate circuit, and is added to the input signal as a pre-compensation signal. therefore(
Equation 9) behaves as if it has different transfer functions for large-amplitude signals and small-amplitude signals, and ringing (
(leakage from large amplitude signals to small amplitude signals) is removed,
For small amplitude signals, the filter operates almost the same as the original filter characteristics.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

Figure 1 shows the symmetric coefficient FIR filter and the phase-corrected I
FIG. 2 is a configuration block diagram of an embodiment in which the present invention is applied to ringing pre-compensation of a linear phase filter such as an IR filter. In the figure, 1 is an amplitude discrimination circuit, 2 is a compensation waveform generation circuit, 3 is an adder/subtractor, 4 is a phase correction circuit, and 5 is a compensated filter.

Since the compensated filter 5 is a linear phase filter, it is phase-corrected by the 1-phase correction circuit 4 and is set as a minimum phase shift filter.The 0-phase correction circuit is an all-pass filter (A P F : All Pa5s Filter).
Alternatively, a filter can be used which is expanded to FIR and approximated by a finite value. The transfer function of the minimum phase shift filter (compensated filter 5 and phase correction circuit 4) is expressed as H
(z), the transfer function of the compensation waveform generation circuit 2 is expressed as (6) above.
The formula, i.e. Z(Σ”(h (m) −h−(m)))
/H(Z). Here, H umbrella (z) = Σh11
(i) z-'' is a transfer function of a filter with desired characteristics that has an impulse response that does not cause ringing.The compensation waveform generation circuit 2 calculates the ringing It is a filter whose transfer function is obtained by subtracting the desired transfer function without , integrating it, and dividing by the transfer function of the compensated filter. H(z ) is the minimum phase shift filter, and all roots are units of two planes. Since it is within the circle and the stability is compensated, the compensation waveform generation circuit 2 can be realized by hardware.

An input signal is input to the compensation waveform generation circuit 2 through the amplitude discrimination circuit 1. The amplitude discrimination circuit consists of a differentiating circuit and a gate circuit, and differentiates the edges of the input signal to obtain the slope, and when the slope exceeds a certain threshold, guides the differentiated signal to the compensation waveform generation circuit.

A ringing pre-compensation signal is obtained as an output of the compensation waveform generation circuit 2, and this is subtracted from the input signal by an adder/subtractor 3 to perform pre-compensation for ringing. The pre-compensated signal is passed through the phase correction circuit 4 to the compensated filter 5.
An output signal with no ringing is obtained.

The output signal is as shown in equation (8), and operates as He(z) when the gate circuit of the amplitude discrimination circuit 2 is on, and as H(z) when it is off. Therefore, when the input signal contains sharp edges that cause ringing, the ringing can be compensated for by turning on the gate circuit.

The operation of the embodiment shown in FIG. 1 will be explained using the operation waveform diagram shown in FIG. 2.

Assume that a step-like signal as shown by the solid line in 2-a is input. The output signal of the compensated filter 5 when it is not compensated is 2-b. Since the compensated filter 5 is phase-corrected and becomes a minimum phase shift filter, the signal contains ringing only after the edge as shown in 2-b. To compensate for this ringing, a ringing compensation signal like 2-c (waveform 2-b) to a desired output waveform (2-c) is required.
It is sufficient if a waveform obtained by subtracting the dotted line) from the compensated filter is obtained as the output of the compensated filter. To do this, a ringing pre-compensation waveform like 2-d (2-d is obtained by dividing 2-c by the transfer function of the compensated filter 5) is applied to the compensated filter 5.
applied to the input of Ringing compensation is performed only when the input signal contains a steep edge signal. Therefore, a signal obtained by differentiating the input signal as shown in 2-e is obtained from the differentiating circuit of the amplitude discrimination circuit 2, and only when the amplitude exceeds the threshold value, the above-mentioned pre-compensation signal 2-d is input to the adder/subtractor 3. do. In this way, the ringing pre-compensated input signal 2-f
When inputted into the compensated filter 5, a ringing-compensated filter output is obtained as shown in 2-g.

When the input signal is superimposed with a small amplitude sine wave signal as shown by the dotted line in 2-a, a sine wave signal as shown in the dotted line is added to the differential signal 2-e, but this signal does not exceed the threshold. Therefore, it does not appear in the ringing pre-compensation signal 2-d. The sinusoidal signal therefore appears at the output without any modification. That is, although the ringing compensation method of the present invention compensates for ringing, high frequency signal components are not attenuated.

FIG. 3 shows another embodiment according to the present invention. The figure shows an analog minimum phase shift filter (for example, an IIR filter such as LC) used as a post filter of a D/A converter, which is digitally processed to correct the antiphase, and then performs ringing pre-compensation (ringing pre-compensation of the antiphase correction circuit). This is an embodiment in which compensation is also provided. In the figure, 1 is the same amplitude discrimination circuit as in Figure 1;
3 is an adder/subtractor, 31 is an antiphase correction circuit, 32 is a compensation waveform generation circuit, 33 is a D/A converter, and 34 is a compensated filter.

Since the compensated filter is a minimum phase shift filter, an inverse filter can be obtained without phase correction, and the compensation waveform circuit 32 can be configured. However, under actual usage conditions, when the ringing removal operation is not being performed, waveform distortion will occur unless the filter is a linear phase filter. Therefore, an anti-phase correction circuit 31 for correcting the phase of the minimum phase shift filter into a linear phase filter is placed in the ringing compensation circuit. Since the anti-phase correction circuit also naturally generates ringing, it must be compensated for, but this is also used by the pre-compensation waveform generation circuit 32 as compensation for the filter.

That is, the compensation waveform generation circuit 32
The ringing pre-compensation of No. 4 and the ringing compensation of the anti-phase correction circuit 31 are performed simultaneously. The ringing pre-compensated waveform obtained in this way is converted into an analog signal by the D/A converter 33 and inputted to the compensated filter 34 to obtain a ringing-compensated analog output signal.

〔Effect of the invention〕

According to the present invention, ringing can be pre-compensated for various types of filters, regardless of whether they are FIR or IIR. In the method of compensating by adding a pre-compensation waveform to the input signal in advance, an inverse filter must be constructed, so
Although it was limited to a minimum phase shift filter, in the present invention,
Can also be applied to linear phase filters with anti-phase correction.
The scope of application can be expanded. Further, since the analog filter can be pre-compensated via the D/A converter, ringing removal in the analog post filter, which is essential after the D/A converter, can be performed using digital technology. Furthermore, most devices do not directly output electrical signals, but are typically converted into mechanical or optical output signals. These converters are also a type of filter and produce ringing due to transient response. The present invention can also electrically remove these ringings in advance. Furthermore, it can be applied to electrical circuits, such as video power amplifiers in TV monitors and circuits where ringing is difficult to compensate for, such as high-frequency amplification stages, and can be extremely effective.

Furthermore, the present invention enables ringing compensation without deteriorating amplitude characteristics, and uses a method of synthesizing compensation waveforms, so the ringing removal effect is not lost even in signals where edges appear continuously. Therefore, it is effective in improving image quality when used in processing image signals in which edges frequently appear and in TV receivers. Further, the part added to the conventional filter to remove ringing is very small, and all digital processing is performed, so it can be easily integrated into an LSI.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is an operation waveform diagram explaining the operation of FIG. 1, and FIG. 3 is a block diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Amplitude discrimination circuit, 2, 32... Compensation waveform generation circuit, 3... Adder/subtractor, 4... Phase correction circuit, 5.3
4-peak compensated filter, 31... Anti-phase correction circuit, 33...D Compiled diagram of Tomizu

Claims (1)

[Claims] 1. A phase correction circuit is cascaded upstream of a compensated filter whose transfer function is known so that the compensated filter is a minimum phase shift filter, detects edges in the input signal, and calculates the phase By generating a first ringing compensation signal that cancels the ringing generated by the corrected compensated filter, and providing a signal obtained by subtracting the ringing compensation signal from the input signal as an input signal to the filter, the phase-corrected A ringing pre-compensation method is characterized in that it compensates for ringing contained in an output signal of a compensated filter. 2. In the ringing pre-compensation method or the ringing pull compensation method of the minimum phase shift filter according to claim 1, the phase-corrected compensated filter or the compensated minimum phase shift filter is A second ringing compensation signal that compensates for ringing of the anti-phase correction circuit, in which an anti-phase correction circuit that performs phase correction on the filter is connected in cascade before the phase correction circuit or before the compensated minimum phase shift filter; By subtracting the first ringing compensation signal from the output signal of the anti-phase correction circuit and inputting it to the phase correction circuit or the compensated minimum phase shift filter, the ringing generated by the anti-phase correction circuit can be subtracted from the output signal of the anti-phase correction circuit. A ringing pre-compensation method, characterized in that the ringing of the phase-corrected compensated filter or the compensated minimum phase shift filter is compensated at the same time. 3. In the ringing pre-compensation method according to claims 1 and 2, the compensated filter is an analog filter, and an A/D is provided before the compensated filter.
A ringing pre-compensation method, characterized in that a converter is inserted and the ringing pre-compensation is configured by a digital circuit.