Multi-standard multi-rate filter
AssigneeCSR Technology Inc.
InventorsMark Alan Sturza, Donald Leimer
Life of this patent
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Abstract
A method is provided for decimating a digital signal by a factor of M and matching it to a desired channel bandwidth. The method applies the digital signal input samples to a (M−1) stage tapped delay line, downsamples the input samples and the output samples of each tapped delay line stage by a factor of M, and applies each of the M downsampled sample value streams to M allpass IIR filters, respectively. The M allpass IIR filtered sample streams are then summed and scaled by a factor of 1/M. The result can then be filtered by a digital channel filter.
Claims20
A method for decimating a digital signal by a factor of M and matching it to a desired channel bandwidth, comprising:
- a. Applying input samples of said digital signal to an M-1 stage tapped delay line;
- b. Downsampling said input samples and outputs of said tapped delay line stages by a factor of M;
- c. Applying said M downsampled values to M allpass IIR filters where the phase of said M allpass IIR filters add constructively at frequencies below a passband frequency, and add destructively at frequencies above a stopband frequency, and where:
- i. Said passband frequency is less than the input sample rate divided by 2 times M;
- ii. Said stopband frequency is greater than the input sample rate divided by 2 times M;
- d. Summing the outputs of said M allpass IIR filters;
- e. Scaling said sum by a factor of 1/M;
- and
- f. Applying said scaled sum to a digital channel filter.
A method for selectively decimating a digital signal by a factor equal to the product of any number of the positive integers M1, M2, . . . , and Mn, and matching it to a desired channel bandwidth comprising the steps of:
- a. Setting a buffer equal to said digital signal to be decimated;
- b. Setting k equal to 1;
- c. If Mk is in said product, inputting said buffer to the input of an Mk-path decimate by Mk method and placing output in said buffer;
- d. Incrementing said k;
- e. If k less than or equal to n, going to step c;
- f. Applying said buffer to a digital channel filter.
A method for decimating a digital signal by a factor of M and matching it to a desired channel bandwidth, comprising:
- applying input samples of the digital signal to an M-1 stage tapped delay line;
- downsampling the input samples of the digital signal and output signals of each of the M-1 tapped delay line stages by a factor of M;
- applying the M downsampled input samples and the M downsampled output signals of each of the M-1 tapped delay line stages to M allpass IIR filters where the phase of the M allpass IIR filters add constructively at frequencies below a passband frequency, and add destructively at frequencies above a stopband frequency;
- and
- wherein the passband frequency is less than the input sample rate divided by 2 times M;
- and
- wherein the stopband frequency is greater than the input sample rate divided by 2 times M.
Dependencies are inferred from the claim text.