Time discrete filter comprising upsampling, sampling rate conversion and downsampling stages
View Patent ↗A time discrete filter comprises a sampling rate converter provided with an input and an output, and a down-sampler having a down-sampling factor nd. The time discrete filter further comprises an up-sampler having an up-sampling factor nu, whereby the up-sampler is coupled to the converter input, and the converter output is coupled to the down-sampler. It has been found that if a sampling rate conversion operation is preceded by an up-sampling operation and only after the conversion is followed by a down-sampling operation to a wanted sampling frequency, that then the complexity in terms of the ultimate number of calculations, in particular multiplications and additions, is reduced. This leads to a decrease of the number of instructions per second which is a measure for the complexity of a Digital Signal Processing (DSP) algorithm. In addition this leads to an associated decrease of power consumed by a DSP, such as applied in for example audio, video, and (tele)communication devices, as well as radio and television apparatus.
1. A time discrete filter comprising:
a sampling rate converter provided with an input and an output, the sampling rate converter being a down-sampling rate converter having a sampling rate conversion factor m;
a first filter directly connected to the input of the sampling rate converter;
a second filter directly connected to the output of the sampling rate converter;
a down-sampler having a down-sampling factor n d , the down-sampler being directly connected to the second filter; and
an up-sampler having an up-sampling factor n u , the up-sampler being directly connected to the first filter.
2. The time discrete filter according to claim 1 , wherein the sampling rate conversion factor m, the up-sampling factor n u and the down-sampling factor n d are integers.
3. The time discrete filter according to claim 2 wherein the sampling rate conversion factor m is an integer larger than 2.
4. The time discrete filter according to claim 3 , wherein the sampling rate conversion factor m is a prime number or a product of prime numbers.
5. The time discrete filter according to claim 1 , wherein each of the up-sampling factor n u , and the down-sampling factor n d is larger or equal to 2.
6. The time discrete filter according to claim 5 , wherein the up-sampling factor n u is equal to the down-sampling factor n d .
7. The time discrete filter according to claim 1 , wherein each of the first and second filters being a digital FIR filter or a digital IIR filter.
8. A communication device comprising:
at least time one discrete filter, each time discrete filter comprising:
an up-sampler having an up-sampling factor n u ;
a first filter directly connected to the up-sampler;
a sampling rate down converter having a sampling rate down conversion factor m, the sampling rate down converter being directly connected to the first filter;
a second filter directly connected to the sampling rate down converter; and
a down-sampler having a down-sampling factor n d , the down-sampler being directly connected to the second filter.
9. The communication device according to claim 8 , wherein the sampling rate down conversion factor m, the up-sampling factor n u and the down-sampling factor n d are integers.
10. The communication device according to claim 9 , wherein the up-sampling factor n u is equal to the down-sampling factor n d .
11. The communication device according to claim 9 , wherein the sampling rate down conversion factor m is an integer larger than 2.
12. The communication device according to claim 11 , wherein the sampling rate down conversion factor m is a prime number or a product of prime numbers.
13. The communication device according to claim 9 , wherein each of the up-sampling factor n u and the down-sampling factor n d is larger or equal to 2.
14. The communication device according to claim 8 , wherein the sampling rate converter is configured to perform decimation or interpolation.
15. A method comprising:
up-sampling an input signal with an up-sampling factor of n u to produce an up-sampled signal;
filtering the up-sampled signal using a first transfer function to produce a first filtered signal;
converting a sampling rate of the first filtered signal down with a sampling rate down conversion factor m to produce a down-converted signal;
filtering the down-converted signal using a second transfer function to produce a second filtered signal; and
down-sampling the second filtered signal with a down-sampling factor of n d to produce an output signal used in a communication device for communication,
wherein the up-sampling, the filtering using the first transfer function, the converting, the filtering using the second transfer function and the down-sampling are performed in sequence respectively without any intermediate steps.
16. The method according to claim 15 , wherein the sampling rate down conversion factor m, the up-sampling factor n u and the down-sampling factor n d are integers.
17. The method according to claim 16 , wherein each of the up-sampling factor n u and the down-sampling factor n d is larger or equal to 2.
18. The method according to claim 17 , wherein the up-sampling factor n u is equal to the down-sampling factor n d .
19. The method according to claim 16 , wherein the sampling rate down conversion factor m is an integer larger than 2.
20. The method according to claim 19 , wherein the sampling rate down conversion factor m is a prime number or a product of prime numbers.