JPS6247369B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform equalizer using a transversal filter.

A transversal filter uses a delay element such as a charge transfer element with multiple taps,
By multiplying the input or output of each tap by an arbitrary weighting coefficient (referred to as tap gain) using a weighting circuit, a filter characteristic having a desired impulse response is realized.

This transversal filter has been conventionally used in television ghost removers and other waveform equalizers. A waveform equalizer using a transversal filter basically inputs the input signal whose waveform should be equalized to the transversal filter, and then uses a differentiator or difference filter to calculate the distortion occurring in the reference signal portion of the output signal. The sample value is detected and sampled by a change detection circuit consisting of a transversal filter, and this sample value is integrated in an analog or digital manner to obtain a weighted control voltage, which controls the tap gain of the transversal filter. .

However, since the above-mentioned change detection circuit is a type of high-pass filter, the distortion detected thereby is mainly high-frequency distortion. Therefore, it is not possible to sufficiently detect low-frequency waveform distortion caused by low-frequency fluctuations in the input signal, deterioration of low-frequency characteristics, DC offset, and the like. In order to suppress this low frequency distortion, a change detection circuit with improved waveform equalization function in the low frequency region is required, but this type of change detection circuit has high gain and high sensitivity. It is necessary to increase the loop gain of the control loop of the waveform equalizer as a whole. For this reason, there was a problem that not only the circuit configuration became complicated, but also that the operation became unstable as the gain became higher.

The present invention has been made in view of the above points, and its purpose is to provide a good waveform equalization function in the low frequency region.
Another object of the present invention is to provide a waveform equalizer that can sufficiently suppress waveform distortion due to DC offset and deterioration of low frequency characteristics, has a simple circuit configuration, and has good stability.

In order to achieve the above object, the present invention detects the amount of amplitude change per fixed section of the reference signal waveform in the output signal after waveform equalization, and corrects the weighted control voltage according to this amount of change. This suppresses low-frequency waveform distortion that occurs in the output signal due to low-frequency fluctuations in the signal, deterioration of the low-frequency characteristics of the control loop, and DC offset.

The present invention will be explained in detail below with reference to Examples.

FIG. 1 shows an embodiment of the present invention, in which the input terminal IN receives an input signal X(t) whose waveform is to be equalized.
(for example, a television signal in the case of a television ghost removal device) is input. This input signal・Given to the input side of filter 1.

In this example, the transversal filter 1 is of an output weighted type, and includes a delay element 11 consisting of a charge transfer element having a plurality of taps, and a weighted filter by multiplying each tap output of this delay element 11 by an arbitrary weighting coefficient. Weighting circuit 12 (W ₁ , W ₂
...W _N ) and this weighting circuit 12 (W ₁ , W ₂ ...W
It is composed of an adder 13 that totals the outputs of the input terminals _N. Note that the unit delay times of the delay elements 11, that is, the delay times τ ₁ , τ ₂ , . . . τ _N between adjacent taps are selected to be equal to τ.

The weighting coefficients or tap gains in the weighting circuits 12 (W ₁ , W ₂ . . . W _N ) are controlled by the control circuit 2 . This control circuit 2 is configured as follows.

In the control circuit 2, first, the reference signal extraction circuit 2
1 is the reference signal included in the output signal Y(t) of the subtracter 3 (for example, the input signal X to the input terminal IN
(t) is a television signal, the vertical synchronization signal is used as the reference signal). , its high frequency distortion components are detected. This change detection circuit 22
The output signal of is sampled by the demultiplexer 23 at time intervals of τ, and each sampled value is distributed to a different output terminal. These sample values are then sent to the weighting circuit 12 (W ₁ , W ₂ . . . ) via the integrator 24 (C 1 , C ₂ . . . _CN ) and the adder 25 (S _{1 ,} S ₂ . . . _SN ), respectively. W _N ) as a weighted control voltage.

The above is a general configuration of a waveform equalizer using a transversal filter, but in order to achieve the above object, the present invention includes the following components in the control circuit 2 to further remove low-frequency waveform distortion. will be established. That is, the reference signal that is the output of the reference signal extraction circuit 21 is also applied to the reference position detection circuit 26 and the waveform detection circuit 28. The reference position detection circuit 26 is a circuit that detects, for example, the starting point (t=t ₀ ) of the reference signal as a reference position, and its output is applied to the timing control circuit 27 . The waveform detection circuit 28 is controlled by the timing control circuit 27 to extract the amplitude of the reference signal at t= _t0 and the amplitude of the reference signal at time t= _tN , and detect the amount of amplitude change (sag amount: low frequency distortion) between them. The output is sent to the adder 25 (S ₁ , S ₂ ) via the integrator 24 (C ₀ ).
...S _N ), and is added to the weighting circuit 12 (W ₁ , W ₂ ...
W _N ) is superimposed in parallel on the weighted control voltage to W N ). Here, t _N -t ₀ is selected to be, for example, t _N -t ₀ =Nτ. N is the number of taps of the delay element 11, and τ is its unit delay time.

FIG. 2 shows a specific example of the waveform detection circuit 28, in which the input terminal 280 is connected to the reference signal extraction circuit 21.
A reference signal from is input. switch 281,
282 are closed for a certain minute time at times t ₀ and t _N , respectively, and thereby the reference signals at times t ₀ and t _N
Each voltage value is held in capacitors 283 and 284, respectively. Then, the difference between these is detected by the subtractor 285 and the difference is detected by the integrator 24.
(C ₀ ).

Next, the operation of this embodiment will be explained with reference to the waveform diagram in FIG. First, for simplicity, the reference signal is assumed to be a rectangular wave with an amplitude E ₀ as shown in FIG. 3a. Here, if the reference signal portion of the _input signal Output signal Y to output terminal OUT after equalization
The reference signal portion of (t) becomes as shown in FIG. 3c, and the waveform distortion is reduced. If the amount of sag included in this FIG.
4 (C ₀ ) and is superimposed in parallel on the weighted control voltage to the weighting circuit 12 (W ₁ , W _{2 .} . . W _N ) by the adder 25 (S ₁ , S _{2 .} . . S _N ). As a result, the output signal waveform for the reference signal portion of the transversal filter 1 is changed to the output of the weighting circuit 12 (W ₁ , W ₂ . . . W _N ) (which is sequentially a
Δ), and the time t _N = N
The output voltage after τ becomes aNΔ. Here, a is the loop gain, which is mainly determined by the DC gain of the integrator 24 (C ₀ ).

In the above case, there is a relationship between Δ ₀ and Δ as Δ ₀ −aNΔ=Δ ……(1) Δ=Δ ₀ /(1+aN) ……(2) Therefore, it appears at the output terminal OUT, etc. The sag amount Δ included in the output signal Y(t) after equalization decreases approximately in inverse proportion to the product of the loop gain a of the waveform equalizer and the number N of taps of the delay element, and the low frequency component is reduced by that amount. waveform distortion will be suppressed. Furthermore, due to deterioration of the low frequency characteristics of the equalizer itself and DC offset within the control loop, a low frequency waveform change occurs in the output signal Y(t) that cannot be sufficiently detected by the change detection circuit 22. Similar effects can be obtained in both cases.

Furthermore, it is no longer necessary to extremely increase the sensitivity, gain, and loop gain of the change detection circuit 22 in order to suppress low-frequency waveform distortion and improve the waveform equalization function in the low-frequency region, as in the past. This has advantages such as not only the circuit design becomes easy and the configuration is simplified, resulting in lower cost, but also improved stability.

In the above embodiment, one transversal filter is used, and the reference position (t=
The detection point (t=t _N ) of the amount of amplitude change from t ₀ ) was selected as one, and t = t _N was selected equal to Nτ, but the point of detection of the amount of amplitude change is arbitrary, and the number can be multiple. It may be hot.

The embodiment shown in FIG. 4 shows an example of this.
As shown in FIG. 5, the waveform detection circuit 28 _{detects the}
t ₂ ...Detect the amount of amplitude change for each t _o . The output voltage corresponding to the amount of amplitude change at each time _{t 1} , t _{2 , . . .} 25 (S
_N1 , _SN2 ...S _No ) and superimposed on the weighted control voltage to the transversal filter 1 ( _TF1 , _TF2 ...TF _o ). In this case, the waveform detection circuit 2
8, the time for detecting the amount of amplitude change is as follows, where the number of taps of the transversal filter 1 (TF ₁ , TF _{2 ,} . . . TF _o ) is N ₁ , N ₂ , . . . _No , and the unit delay time is τ. As shown in Figure 5, t ₁ −t ₀
=N ₁ τ, t ₂ -t ₁ =N ₂ τ, ... t _N -t _N-1 = N _o τ. Note that 29 is a demultiplexer and an integrator for creating a weighted control voltage based on the output of the change detection circuit 22.

Further embodiments of the present invention are shown in FIGS. 6 to 9. In both of these embodiments, the waveform detection circuit 2
By subtracting the output voltage of No. 8 by the detection output of the change detection circuit 22, the weighted gain voltage is indirectly corrected.

In the embodiment of FIG. 6, the change detection circuit 2
2 consists of a differentiator 221 that differentiates the vicinity of the reference signal in the output signal Y(t), and a level comparator 222 that determines whether each part of the differentiated waveform exceeds a certain level. The level determination output is sampled in buffer memory 30 and then digitally stored at each sample point by adder 31 and digital memory 32. As a result, each tap gain is stored in the memory 32 as digital data. The output of this memory 32 is converted into a DC analog signal by a D/A converter 33, and further sampled and held by a sample-and-hold circuit 34, thereby becoming a weighted control voltage for the transversal filter 2.

In this case, the reference signal is a rectangular wave as shown in FIG. 7a, as described above. Now, if a sag of _Δ0 occurs in the output signal Y(t) after waveform equalization as shown in FIG. As shown in c, a direct current component of Δ ₀ /N is generated. Therefore, as shown in Fig. 6, the waveform detection circuit 2
The level comparator 22 adjusts the output voltage of 8 appropriately.
If it is applied to the inverting input terminal of No. 2, the influence of this direct current component is removed, so that the sag as shown in FIG. 7b can be reduced.

That is, if the sag that ultimately remains in the output signal Y(t) is Δ, then the output of the waveform detection circuit 28 (in this case, it is assumed that the integrator 24 (C ₀ ) is included in the waveform detection circuit 28) is aΔ, where a is the DC gain of the integrator. Since a DC voltage of Δ/N is applied from the differentiator 221 to the non-inverting input terminal of the level comparator 222, the level comparator 222
The equivalent DC offset at 2 is Δ′=Δ/
It becomes N-aΔ. This DC offset Δ' is calculated by the weighting circuit 12 in the transversal filter 2.
as a result, the output signal Y
A sag of NΔ' is caused in (t). The sum of this NΔ′ and _Δ0 that exists from the beginning is the final sag amount Δ
becomes. That is, Δ=Δ ₀ +N(Δ/N−aΔ) (3) Therefore, Δ=Δ ₀ /aN (4), and the waveform distortion is suppressed in the same way as described above.

In the embodiment shown in FIG. 8, in the change detection circuit 22 shown in FIG.
(t) and the output signal Y(t) are provided with a correlator 223 that takes a correlation near the reference signal. In this case, the output of the correlator 223 is also added to the waveform detection circuit 28, but of course the output of the reference signal extraction circuit 21 may also be added as in the case of FIG.

Further, in FIGS. 6 and 8, the output voltage of the waveform detection circuit 28 is applied to the inverting input terminal of the level comparator 222, but it may be applied to the differentiator 221 or an amplifier included therein. In addition,
Weighted control voltage generation circuit 5 in FIG. 8 corresponds to the buffer memory 30, adder 31, digital memory 32, D/A converter 33, and sample hold circuit 34 in FIG.

The embodiment of FIG. 9 uses the output signal Y based on the reference signal.
This is an example in which the present invention is applied to a general automatic equalizer that detects a change (distortion) in (t). That is, the change detection circuit 22 in this case includes a reference signal generator 224, a subtracter 225 for obtaining a difference signal between the reference signal R(t) and the reference signal in the output signal Y(t), and a subtracter 225 for obtaining a difference signal between the reference signal R(t) and the reference signal in the output signal Y(t). It is comprised of a correlator 226 that takes a correlation with the input signal X(t), and a weighted control voltage is obtained from this correlation output. In this case, the same effect as described above can be obtained by subtracting the output voltage of the waveform detection circuit 28 to the reference signal generator 224 or the subtracter 225 as a DC offset.

The present invention can be modified and implemented in various other ways as described below. For example, in an automatic equalizer using a digital memory 32 as shown in FIG. 6, instead of adding the output voltage of the waveform detection circuit 28 to the change detection circuit 22, when this output voltage reaches a certain level +b It is also possible to adopt a configuration in which -1 is added to all the tap gain data in the memory 32, and +1 is added to all the data when -b is reached. That is, by correcting the data in the memory 32 by a certain minute amount in accordance with the output voltage of the waveform detection circuit 28, for example, all the tap gains change by ±Δ, so that the output signal Y
It is possible to reduce the positive or negative sag appearing in (t).

In addition, in the above explanation, the reference signal is a rectangular wave,
Although the waveform detection circuit detects the amount of change in amplitude per certain section, even when using a sine square wave other than a rectangular wave as the reference signal, the amplitude change per certain section can be detected in a specific signal portion other than the reference signal. The present invention is applicable as long as there is a portion where the amount of change, that is, the low frequency distortion component can be detected.

Furthermore, although an output weighted type transversal filter has been exemplified, it goes without saying that an input weighted type may also be used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG.
The figure shows a specific example of the main part, FIG. 3 is a waveform diagram for explaining the operation of the same embodiment, FIG. 4 is a diagram showing the second embodiment of the present invention, and FIG. 5 is a diagram of the second embodiment. 6 is a diagram showing the third embodiment of the present invention, FIG. 7 is a waveform diagram for explaining the operation, and FIGS. 8 and 9 are diagrams showing the third embodiment of the present invention. It is a figure which shows the 4th and 5th Example. DESCRIPTION OF SYMBOLS 1... Transversal filter, 2... Control circuit, 22... Change detection circuit, 28... Waveform detection circuit.

Claims (1)

[Claims] 1. Using a transversal filter, the high-frequency distortion of the output signal is detected and sampled by a change detection circuit, and the sampled values at each point are integrated in an analog or digital manner to obtain a weighted control voltage. In a waveform equalizer that performs waveform equalization by controlling the tap gain of the transversal filter using the weighted control voltage, detecting the amount of amplitude change per fixed section of the reference signal waveform in the output signal. 1. A waveform equalizer comprising: a waveform detection circuit for detecting low frequency waveform distortion, and correcting the weighted control voltage according to the amount of change. 2. The waveform equalizer according to claim 1, wherein the weighted control voltage is corrected by uniformly superimposing the output voltage of the waveform detection circuit on the weighted control voltage in parallel. 3. The waveform equalizer according to claim 1, wherein the weighted control voltage is corrected by subtracting the output voltage of the waveform detection circuit from the detection output of the change detection circuit. 4 When the output voltage of the waveform detection circuit reaches a certain value, all the data in the digital memory for storing the tap gain by digitally integrating the sample value is corrected by a certain minute amount to perform weight control. A waveform equalizer according to claim 1, wherein the waveform equalizer is adapted to correct voltage.