JP2538940B2 - Waveform distortion correction device - Google Patents

Description

Description: [Object of the invention] (Industrial field of application) The present invention relates to a receiver for re-sampling and decoding a sample-value-transmitted analog signal, and more particularly The present invention relates to a waveform distortion correction device effective for a coding device when it is a video signal.

(Prior Art) There is a so-called PAM transmission method in which an analog signal is sampled and the current signal is transmitted by amplitude modulation of a transmission pulse based on the sampled value. Also in this system, the transmission pulse seen at the input end of the receiving device is distorted due to deterioration of frequency characteristics of the transmission line, ghost, echo and the like. The waveform distortion correction device can remove the distortion component by re-sampling the transmission waveform at the pulse transmission speed T and controlling the tap gain of the transversal filter. However, the number of taps of the transversal filter is finite, and the time length from the position of the reference signal to the correctable distortion component is also limited. In addition, a residual distortion component is newly generated due to a quantization error or the like that occurs during re-sampling.

Therefore, an apparatus has been devised which minimizes the sum of squares or the sum of absolute values of the residual distortion components. An example will be described with reference to FIG. The input signal is supplied to the analog-digital converter 10 and the timing circuit 8 via the input terminal 1. The output digital signal of the analog-digital converter 10 is supplied to the transversal filter 2 and the waveform distortion detection circuit 5. The transversal filter 2 includes a delay element group 21 in which a plurality of unit delay elements are connected in series, and a coefficient unit C- to which the output of each delay element is supplied.
M to C0 and C1 to CN, an adder 22 for adding the outputs of the coefficient units CM to C0 and C1 to CN, an output of the adder 22 and a signal extracted from the reference position of the delay element group The gain of each of the coefficient multipliers C-M to C0 and C1 to CN is controlled by the corresponding value from the tap gain memory 3.

The output of the transversal filter 2 is supplied to the digital-analog converter 11 and the subtractor 7. The digital-analog converted signal is output to the output terminal 12. The subtractor 7 subtracts the reference signal waveform-equalized by the transversal filter 2 from the training pulse from the training pulse generation circuit 6 to obtain a residual waveform distortion sequence {ek}. Further, the waveform distortion detection circuit 5 performs the following calculation using the resampled reference signal series {x _k } before waveform equalization and the residual waveform distortion series {e _k }.

di = 2Σx _ki e _k i = −M to N (minimization of sum of squares) di = Σx _ki SGN (e _k ) i = −M to N (minimization of sum of absolute values) where di is a transversal filter It is the waveform distortion component generated in the tap number i of 2. The tap gain correction circuit 4 receives the tap gain value ▲ C ⁽ⁿ⁾ _i from the tap gain memory 3.
Read ▼, New tap gain value According to the corresponding data (gain) of the tap gain memory 3.
To fix. Here, (n) indicates the number of times the tap gain memory is modified by the above method. If this correction method is repeated each time the reference signal (reception training pulse) is received, the tap gain value series {Ci} is a series in which the residual sum of squares of the waveform distortion series {ek} or the absolute value is the minimum. {Ei}
Converge to.

By the way, the document "A device for subjective quantification of multiple ghost disturbances", Journal of the Television Society, Vol. 33, No. 8
On page 628 (1979), the correlation between the delay time of the ghost distortion, which is a kind of waveform distortion, from the main signal (desired signal) and the subjective value of the reproduced video signal is described. According to this, it is shown that "the longer the delay time is, that is, the farther the ghost distortion is from the main signal, the larger the image quality failure degree". However, in the waveform correction device shown in FIG. 5, since equalization is performed over the entire tap length, the correction result is not always excellent in visual characteristics.

(Problems to be Solved by the Invention) As described above, as the temporal position of the waveform distortion component moves away from the main signal, the degree of visual influence of the waveform distortion (ringing, ghost, echo) on the image signal increases. No matter what, the conventional waveform distortion correction device
The same equalization process is performed over the entire tap length regardless of the distance from the main signal. Therefore, the visual characteristics are not always excellent.

Therefore, the present invention aims to provide a waveform distortion correction device that obtains a signal with better visual characteristics by paying attention to the fact that the waveform distortion component gives a different degree of interference depending on the degree of separation from the main signal. .

[Structure of the Invention] (Means for Solving Problems) According to the present invention, when a waveform distortion component is detected from the output of a transversal filter and the tap gain is corrected, a waveform far from the main signal in terms of time. A means for controlling the weighting of the tap corresponding to the distortion component to be larger than that corresponding to the distortion component close thereto is provided. In this case, the weighting means has a means for generating a coefficient group that becomes smaller as it gets closer to the main signal, and a means for multiplying the coefficient group by the waveform distortion component, and the coefficient group has several kinds of coefficient sequences. It is possible to select one kind of coefficient string from the above several kinds of coefficient strings.

(Operation) By the above means, for example, there are two waveform distortion components having the same magnitude, and the sum of squares of the residual waveform distortion components or
When the tap for canceling each waveform distortion is corrected so that the sum of absolute values becomes equal, the cancellation correction degree for the distortion component far from the main signal becomes large. As a result, the effect of canceling the ghost far from the main signal is great, and a visually more natural sense can be obtained than even correction. Since the canceling effect can be arbitrarily switched according to the selection of the coefficient group, the image can be in the most visible state.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment which is a premise of the present invention. An input video signal from an input terminal 20 is supplied to a timing circuit 21 and an analog / digital converter 22. The output digital video signal from the analog-digital conversion converter 22 is input to the transversal filter 23 and the waveform distortion detection circuit 30. The transversal filter 23 includes a delay element group 231 in which a plurality of unit delay elements are connected in series, coefficient units CM to C0 and C1 to CN to which outputs of the respective delay elements are supplied, and each coefficient unit C.
Each of the coefficient units has an adder 232 that adds the outputs of M to C0 and C1 to CN, an output of the adder 232, and an adder 233 that adds the signals extracted from the reference positions of the delay element groups. C-M to C
The gain of 0, C1-CN is controlled by the corresponding value from the tap gain memory 28. The output of the transversal filter 23 is supplied to the digital-analog converter 24 and the subtractor 27. The signal that has been digital-analog converted is output
25. The subtractor 27 subtracts the reference signal waveform-equalized by the transversal filter 23 from the training pulse from the training pulse generation circuit 26 to obtain a residual waveform distortion sequence {e _k }. This residual waveform distortion sequence {e _k } is supplied to the multiplier 31 and is multiplied by the coefficient group {a _k } from the weighting coefficient generation circuit 32.

The coefficient group {a _k } is, for example, RO of the weighting coefficient generation circuit 32.
Each of M has been.

The coefficient group {a _k } according to the present embodiment is written in advance in the ROM in a sequence as shown in FIG. 2, and is read by the timing pulse from the timing circuit 21. The residual waveform distortion series {e _k } and the coefficient group {a _k } are controlled so as to be input to the multiplier 31 in synchronization. For example, if eo of the residual waveform distortion series is the residual waveform distortion component due to the main signal sample value, the generation of ao in the coefficient group is generated in synchronization with eo. The coefficient group {a _k } becomes larger as the distance from the main signal increases. Therefore, the corrected waveform distortion component {e _k } 'output from the multiplier 31 is as shown in FIG.

The corrected waveform distortion component {e _k } ′ thus obtained is supplied to the waveform distortion detection circuit 30. Waveform distortion detection circuit 30
Is the resampled reference signal sequence before waveform equalization {xk}
And the corrected waveform distortion sequence {e _k } ′ are used to perform the same arithmetic processing as that described in FIG. 5, and the tap gain correction circuit 29 uses the output of the waveform distortion detection circuit 30 to tap The tap gain value ▲ C ⁽ⁿ⁾ _i ▼ is read from the gain memory 3, The corresponding data (gain) in the tap gain memory 3 is corrected by the new tap gain value ▲ C ⁽ⁿ⁾ _i ▼. As described above, according to the present embodiment, by providing a means for weighting the waveform distortion component farther than the waveform distortion component close to the main signal, the distortion easily noticeable visually is positively removed. You can get the action.

FIG. 3 shows an embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals. In the part different from the previous embodiment, the weighting coefficient generating circuit 32 further has a ROM storing various coefficient groups not shown in FIG.
One coefficient group is selected by the selector 34 and supplied to the multiplier 31. Which coefficient group to select is
It is determined by the user applying a selection signal to the terminal 33 of the selector 34. With this configuration, it is possible to select the coefficient group that gives the best image visually. The other parts are the same as those in the previous embodiment, and the description is omitted.

EFFECTS OF THE INVENTION As described above, according to the present invention, by providing a means for weighting the waveform distortion component farther than the waveform distortion component close to the main signal, it is easily noticeable visually. It is possible to realize a waveform distortion correction device that can obtain an operation of positively removing distortion and can obtain a video signal having better visual characteristics than conventional ones.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory view of a coefficient group and a waveform distortion component of the weighting coefficient generating circuit of FIG. 1, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a block diagram showing the example of coefficient groups, and FIG. 5 is a block diagram showing a conventional waveform distortion correction device. 22 …… Analog digital converter, 23 …… Transversal filter, 24 …… Digital analog converter, 26 …… Training pulse generation circuit, 27 …… Subtractor, 28 …… Tap gain memory, 29 …… Tap gain correction Circuit, 30 ... Waveform distortion detection circuit, 31 ... Multiplier, 32 ... Weighting coefficient generation circuit.

Claims (1)

(57) [Claims] 1. A transversal filter, a tap gain memory for holding the tap gain thereof, means for extracting a waveform distortion component from an input signal, and a tap gain value of the tap gain memory based on the waveform distortion component. And a modifying means for modifying, wherein the modifying means modifies the tap gain value so that the weighting amount becomes smaller as the waveform distortion component closer to the main signal, , A means for generating a coefficient group that becomes smaller as it gets closer to the main signal, and a means for multiplying the coefficient group by a waveform distortion component, the coefficient group being composed of several kinds of coefficient sequences, A waveform distortion correction device characterized in that one kind of coefficient series can be selected from among the kind of coefficient series.