JPH0715280A - Adaptive digital filter - Google Patents

Abstract

PURPOSE:To provide on adaptive digital filter which prevents a discontinuous point from being generated at the moment of switching selectors. CONSTITUTION:This device is provided with digital filters 11-13 to input data sampled by a sampling pulse at a frequency Fs, selector 14 for selecting an output from one of digital filters 11-13 and outputting it, mutual correlation detector 15 for detecting mutual correlation between the data sampled by the sampling pulse at the frequency Fs and the output of the selector 14, and limiter 16 for outputting the output of the selector 14 as it is based on the output of the mutual correlation detector 15 or outputting it after holding the output data just before the switching of the selector 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive digital filter which filters data sampled by a sampling pulse having a frequency Fs by a plurality of digital filters and selects and outputs one of the outputs of the plurality of digital filters.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional adaptive digital filter uses a plurality of digital filters 1 to convert data sampled by a sampling pulse having a frequency Fs.
The output from one digital filter among the outputs from the plurality of digital filters 11, 12 and 13 is selected by the selector 14 and output.

In the conventional adaptive digital filter configured as described above, the frequency Fs is 352.8 kHz.
(= 8 × 44.1 kHz), and the digital filter 11
Is a low-pass filter (through filter) with no cut-off frequency, the digital filter 12 is a low-pass filter with a cut-off frequency of 10 kHz, and the digital filter 13 is a low-pass filter with a cut-off frequency of 1 kHz.

A case will be described in which the data shown in FIG. 3A is input to the adaptive digital filter shown in FIG. Since the digital filter 11 is a through filter, the output of the digital filter 11 is shown in FIG.
Is the same as. Since the digital filter 12 is a low-pass filter having a cutoff frequency of 10 kHz, the output of the digital filter 12 is as shown in FIG. Since the digital filter 13 is a low-pass filter with a cutoff frequency of 1 kHz, the output of the digital filter 13 is as shown in FIG.

These digital filters 11, 12, 13
The output of is selected by the selector 14. As one example of the switching method in this selection, it is assumed that the switching is performed depending on the magnitude of the autocorrelation of the input data. For example, since the autocorrelation exists to some extent in the section α of the input data, the output of the digital filter 12 is selected. Further, since there is no autocorrelation in the β section of the input data, the output of the digital filter 11 is selected. Since the autocorrelation is large in the γ section of the input data, the output of the digital filter 13 is selected.

[0006]

When the selectors are switched as described above, the output from the selectors is as shown in FIG.
As shown in (d), there is a problem that a discontinuity occurs at a point near β1 and β4 at the moment of switching.

An object of the present invention is to provide an adaptive digital filter in which discontinuity points do not occur at the moment of switching selectors.

[0008]

The adaptive digital filter of the present invention comprises a plurality of digital filters each of which receives data sampled by a sampling pulse of frequency Fs, and one digital filter among the plurality of digital filters. Selector for selecting and outputting the output of the first selector, a cross-correlation detector for detecting a cross-correlation between the data sampled by the sampling pulse of the frequency Fs and the output of the first selector, and the cross-correlation detection. A limiter for outputting the output of the first selector as it is based on the output of the container or for holding and outputting the output data immediately before the switching of the first selector.

The limiter in the adaptive digital filter of the present invention uses the output of the first selector as the first input,
A second selector that selects and outputs one of the second input and the second input based on the output of the cross-correlation detector, and a delay element that outputs the output of the second selector by delaying it by one clock with a clock pulse of frequency Fs. And an output of the delay element is a second input of the second selector, and an output of the delay element and an output of the second selector are output of a limiter.

[0010]

In the adaptive digital filter of the present invention, the cross-correlation between the input data to the plurality of digital filters and the output data of the selector is detected by the cross-correlation detector, and the detected cross-correlation at the time of switching the selector is detected. When it is small, the limiter holds and outputs the output data immediately before switching of the first selector, and when the detected cross-correlation is large, the input data of the limiter is output as it is. Therefore, the discontinuity at the time of selecting the input data by the selector is eliminated.

[0011]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

Reference numeral 1 indicates an adaptive digital filter of the present embodiment. The adaptive digital filter 1 filters the data sampled by the sampling pulse of the frequency Fs by the plurality of digital filters 11, 12, 13 to obtain the plurality of digital filters 11, 12,
Among the outputs from 13, the output from one digital filter is selected and output by the selector 14,
The output data of 1 is output through the limiter 16.

Further, the cross-correlation detector 15 detects the cross-correlation between the data sampled by the sampling pulse of the frequency Fs and the output data of the selector 14, and the cross-correlation detection output is supplied to the limiter 16 to detect the cross-correlation. When the cross-correlation detection output detected by the device 15 is small, the previous value data of the input data of the limiter 16, that is, the output data from the selector 14 immediately before the switching of the selector 14 is output from the limiter 16, and the cross-correlation detection output is When it is larger, the input data of the limiter 16 is output from the limiter 16 as it is.

In the adaptive digital filter 1 of the present embodiment configured as described above, the sampling pulse frequency Fs is 352.8 kHz (= 8 × 44.1 kHz).
The digital filter 11 is a low-pass filter (through filter) without a cutoff frequency, the digital filter 12 is a lowpass filter with a cutoff frequency of 10 kHz, and the digital filter 13 is a lowpass filter with a cutoff frequency of 1 kHz.

A case where data as shown in FIG. 3A is input to the adaptive digital filter 1 will be described. Since the digital filter 11 is a through filter, the output of the digital filter 11 is the same as that shown in FIG.
Since the digital filter 12 is a low-pass filter with a cutoff frequency of 10 kHz, the digital filter 12
Output is as shown in FIG. Digital filter 1
Since 3 is a low-pass filter having a cutoff frequency of 1 kHz, the output of the digital filter 13 is as shown in FIG.

The outputs of the digital filters 11, 12, 13 are selected by the selector 14. As one example of the switching method in this selection, it is assumed that the switching is performed depending on the magnitude of the autocorrelation of the input data signal. For example, since the autocorrelation exists to some extent in the section α of the input data, the output data of the digital filter 12 is selected. Further, since there is no autocorrelation in the β section of the input data, the output data of the digital filter 11 is selected. Further, the output data of the digital filter 13 is selected because the autocorrelation is large in the γ section of the input data. This is similar to the conventional case.

However, in the adaptive digital filter 1 of this embodiment, the cross-correlation detector 15 detects the cross-correlation between the input data and the output data of the selector 14. Output data of the selector 14 (Fig. 3 (d))
The α2 part of the input data (Fig. 3
The value is considerably smaller than that in (a)), and the cross-correlation between these two data is small.

The output data of the selector 14 (see FIG.
The γ1 portion of (d) becomes a value much larger than the input data (FIG. 3A) due to the influence of the β3 portion, and the cross-correlation between these two data becomes small.

Therefore, when the cross-correlation between the two data detected by the cross-correlation detector 15 is small, the limiter 16 outputs the data holding the previous value of the input data of the limiter 16, and the cross-correlation detection is performed. When the cross-correlation between the two data detected by the device 15 is large, the limiter 16 outputs the input data of the limiter 16 as it is.

Therefore, the data output from the limiter 16 is as shown in FIG. 3 (e), and the sections α2 and γ1 in FIG. 3 (d) are the sections α2 and γ1 in FIG. 3 (e). As a matter of fact, when the adaptive digital filter 1 is used, the discontinuity that has conventionally occurred at the time of switching by the selector 14 is eliminated, and the output data of FIG. 3 (e) is output from the adaptive digital filter 1. It

Next, another embodiment of the present invention will be described. FIG. 2 is a block diagram showing the configuration of the adaptive digital filter 2 in the other embodiment.

The adaptive digital filter 2 controls the limiter 16 in the adaptive digital filter 1 at the frequency Fs (3
D flip-flop 162 for delaying input data for one clock period by a clock pulse of 52.8 kHz)
And the output data of the selector 14 and the D flip-flop 1
The output data of the selector 161 and the output data of the flip-flop 62 are input to the output data of the selector 161. The output data of page 162 is output. The parts of the adaptive digital filter 2 other than the limiter 16 are the same as the adaptive digital filter 1.

The operation of the adaptive digital filter 2 is as follows.
The cutoff frequencies of 2 and 13 will be described as the same as in the case of the adaptive digital filter 1.

The output data of the digital filters 12 and 13 with respect to the input data of FIG. 3 (a) are shown in FIG. 3 (b) and FIG.
As in (c). The output data of the selector 14 is as shown in FIG.

In the case of the adaptive digital filter 2, FIG.
In the period of α1 of the data of (d), the output data from the selector 14 is selected by the selector 161 because the cross-correlation between the input data (FIG. 3A) and the output data of the selector 14 is large.

However, during the period of α2, the input data (see FIG.
Since the cross-correlation between (a)) and the output data of the selector 14 is small, the data delayed by one clock by the D flip-flop 162 is selected by the selector 161. By this operation, in the period in which the cross-correlation between the input data and the output data of the selector 14 is smaller than the predetermined value, the final data whose cross-correlation is the predetermined value or more is continuously held.

Next, at the time of β1, since the cross-correlation becomes a predetermined value or more, the output data from the selector 14 is selected in the selector 161, and the same applies to the period up to β4. After that, since the cross-correlation becomes smaller than the predetermined value in the period of γ1, the data at the time of β4 continues to be held.

Next, in the period of γ2, the cross-correlation becomes a predetermined value or more, so that the selector 161 selects the selector 14
Output data from is selected. Thus selector 1
By making the output data of 61 the output data of the adaptive digital filter 2, the output data from the adaptive digital filter 2 becomes as shown in FIG. The discontinuity caused by selecting the output will be eliminated.

In the adaptive digital filter 2, a D flip-flop 162 is used instead of the output of the selector 161.
The same applies when the output of the above is used as the output of the adaptive digital filter 2.

The adaptive digital filters 1 and 2
In the above, the selector 14 exemplifies the case where the input is selected based on the autocorrelation, but the same applies when the input is selected according to other information.

[0031]

As described above, according to the adaptive digital filter of the present invention, the cross-correlation between the input data of a plurality of digital filters and the data selected by the selector is detected, and the selector is selected. Since the output data is selectively limited and output based on the cross-correlation detection output, the discontinuity does not occur at the moment of switching the selector.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of another embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining the operation of one embodiment and another embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 11, 12 and 13 Digital filter 14, 161 Selector 15 Cross-correlation detector 16 Limiter 162 D flip-flop

Claims (2)

[Claims] 1. A plurality of digital filters that receive data sampled by a sampling pulse of a frequency Fs as inputs, and a first selector that selects and outputs an output from one of the plurality of digital filters. , A cross-correlation detector for detecting cross-correlation between data sampled by the sampling pulse of the frequency Fs and the output of the first selector, and an output of the first selector based on the output of the cross-correlation detector Or a limiter for holding and outputting the output data immediately before the switching of the first selector. 2. The adaptive digital filter according to claim 1, wherein the limiter selects the output of the first selector as the first input and selects one of the second input and the second input based on the output of the cross-correlation detector. And outputs the second selector and the output of the second selector to 1 by a clock pulse of frequency Fs.
A delay element for delaying and outputting the clock, and the output of the delay element is the second input of the second selector, and the output of the delay element or the output of the second selector is the output of the limiter. An adaptive digital filter characterized in that