Decimation method and decimation filter
First Claim
1. A decimation method the transfer function of which substantially corresponds to the transfer function of a CIC decimation filter, and in which a signal including digital samples is decimated by coefficient M, characterized in that at least main processing is performed on the signal to be decimated, the main processing comprising the steps of performing M-tap FIR filtering N times in sequence, decimating by coefficient M and comb-filtering the signal N−
- 1 times.
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Abstract
The invention relates to a decimation method and a decimation filter, which provide the transfer function of a CIC decimation filter. Decimation of the number of order N is performed by coefficient M, whereby FIR filtering is carried out in the main branch (100) of the decimation filter by M-tap FIR filters (20) N times in sequence, decimation is carried out by decimation means (21) by coefficient M and comb-filtering is carried out by means (22) N−1 times. The effect of sample cycles M preceding the sample cycle M to be processed is taken into account by using side branches (101, 102, 104) and additional branches (103, 105, 106, 107).
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Citations
15 Claims
- 1. A decimation method the transfer function of which substantially corresponds to the transfer function of a CIC decimation filter, and in which a signal including digital samples is decimated by coefficient M, characterized in that at least main processing is performed on the signal to be decimated, the main processing comprising the steps of performing M-tap FIR filtering N times in sequence, decimating by coefficient M and comb-filtering the signal N−
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8. A decimation filter the transfer function of which substantially corresponds to the transfer function of a CIC decimation filter, and which is arranged to decimate a signal including digital samples by coefficient M, characterized in that the decimation filter at least comprises a main branch (100), which comprises a decimation means (21), which decimate by coefficient M, N M-tap FIR filters (20) in sequence before the decimation means (21) of the main branch (100), and N−
- 1 combinations (22) of a comb filter and an adder in sequence after the decimation means of the main branch (100).
- View Dependent Claims (9, 10, 12, 13)
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11. A decimation filter the transfer function of which substantially corresponds to the transfer function of a CIC filter and which is arranged to decimate a signal including digital samples by coefficient M, characterized in that the decimation means at least comprises a main branch (100), which comprises decimation means (21), N M-tap FIR filters (20) in sequence before the decimation means (21) of the main branch (100), which decimate by coefficient M;
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if the number N of M-tap FIR filters (20) in the main branch (100) is more than one, the decimation filter is arranged to take into account N−
1 sample cycles M preceding the incoming sample cycle M, and thus the decimation filter comprises besides the main branch (100)selection means (61);
memory (61);
shift means (64);
adder/subtractor means (65) and control means (66);
N−
1 side branches (101-108), the divergence point (120, 124, 126) of which is operationally connected between each of two FIR filters (20) before the decimation means (21) of the main branch (100) and their other end is operationally connected to the selection means (61), the side branches (101-108) comprisingdecimation means (21) for decimating the signal entering the side ranch (101-108) by coefficient M;
delay means (23) for delaying the decimated signal by one sample cycle M;
additional branches (109), which comprise delay means (23) for delaying the signal by one sample cycle M, and the divergence point (130) of which is operationally connected after each delay means (23) in the side branch (101-108) or in the additional branch (109) and their other end is operationally connected to the selection means (61); and
the selection means (61) of the decimation filter are arranged to select one signal at a time from the main branch (100), side branch (101-108) or the additional branch (109) for an arithmetic shift operation to the shift means (64);
the shift means (64) are arranged to perform a necessary arithmetic shift on each signal of the main branch (100), side branch (101-108) or additional branch (109);
the adder/subtractor means (65) of the decimation filter are arranged to calculate difference of the signals according to comb-filtering and adding the signal of each side branch (101-108) or the additional branch to the result provided;
the memory (62) of the decimation filter is arranged to store the results provided for the signals of each main branch (100), side branch (101-108) and additional branch (109) and the sums of the results;
the control means (66) of the decimation filter are arranged to control the function of the decimation filter so that the decimation filter substantially provides the transfer function of the CIC filter. - View Dependent Claims (14, 15)
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Specification