Boots – shoes – and leggings
Patent
1994-03-17
1995-07-25
Malzahn, David H.
Boots, shoes, and leggings
3647241, G06F 1531
Patent
active
054368596
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a digital filter bank intended for use, for instance, in battery-operated applications, in which power consumption is decreased by reducing the number of multiplications performed in the filter bank.
In digital signal processing, there is a need in many different contexts to minimize the power consumption in a given system. This may apply, for instance, to battery-operated applications. Digital filters are often more power consuming that corresponding analog filters. The reason why the power consumption of digital filtering processes is relatively high, is because a large number of operations are often carried out each second. Band filtering with the aid of filter banks is one filtering method that is often used. The filter bank can be used when a number of frequency bands are to be separated, or when it is desired to amplify different frequency bands to different degrees of amplification.
When bandpass filtering with the aid of a digital filter bank, a high degree number is often required on the filters included in the bank, in order for the filter bank to be sufficiently selected. Higher degree numbers imply many multiplications per sample and per second. In digital filtration processes, the power consumed is often proportional to the number of coefficients (multiplications) in the filter impulse response. Power consumption can therefore be reduced by reducing the number of multiplications. This is achieved in accordance with the invention with a digital filter bank which includes:
A zero-filled digital basic filter having a complementary output, wherein the zero-filled filter relates to a filter, which may be based on an LP-filter, which can be expanded with a number of zero-value filter coefficients between each coefficient in the original filter; and downstream mutually parallel part-filter banks; wherein the passband of the basic filter and the pass-band of the complementary output of said basic filter define the filter-bank band; wherein one of the part-filter banks connected to the normal output of the basic filter is intended to filter-out those filter-bank bands which are pass bands to the basic filter, so that only one of the filter-bank bands is present on each signal from said one part-filter bank; and wherein the other part-filter bank connected to the complementary output of the basic filter is intended to filter-out those filter-bank bands which are pass bands to the complementary output of the basic filter, so that only one filter-bank band is found on each output signal from said other part-filter bank.
The term filter-bank band as used here and in the following is intended to denote one of the frequency bands present in the output signals of the filter bank.
Preferred embodiments of the novel filter bank are set forth in the dependent Claims.
The invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 illustrates a linear phase FIR-filter of uniform degree number, where the number of multiplications has been reduced to almost half;
FIG. 2 illustrates a linear phase FIR-filter with a complementary output;
FIG. 3 illustrates a zero-filled FIR-filter, which has been constructed by replacing each time delay in the filter illustrated in FIG. 4 with four time delays;
FIG. 4 illustrates a digital FIR-filter;
FIG. 5 illustrates the magnitude function of a linear-phase lowpass FIR-filter of degree 6, which can be realized with four multiplications per sample in accordance with FIG. 1;
FIG. 6 illustrates the magnitude function of a zero-filled digital filter which has been constructed by replacing each time shift in the filter illustrated in FIG. 5 with four time shifts; this filter can also be realized with four multiplications per sample;
FIG. 7 illustrates a filter bank comprising a basic filter and downstream part-filter banks;
FIG. 8 illustrates a zero-filled linear-phase FIR-filter having a complementary output;
FIG. 9 illustrates the ideal magnitude function of the basic filter with complementary output;
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REFERENCES:
patent: 4542475 (1985-09-01), Acampora
patent: 4615026 (1986-09-01), Schiff
patent: 4766562 (1988-08-01), Vary
patent: 4829378 (1989-05-01), LeGall
patent: 5050119 (1991-09-01), Lish
R. E. Crochiere and L. R. Rabiner, "Multirate Digital Signal Processing", Prentice-Hall, 1983 Ch. 7, pp. 289-296, and 376-378 and 392-395.
Hellgren Johan
Lunner Thomas
Lezdey John
Malzahn David H.
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