DIFFERENTIAL EVOLUTION DESIGN OF POLYPHASE IIR DECIMATION FILTERS

• US 20070153946A1
• Filed: 12/20/2006
• Published: 07/05/2007
• Est. Priority Date: 12/20/2005
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Inventors: Sturza, Mark
• Granted Patent: US 8,111,791 B2
• Time in Patent Office: Days
• US Class Current: 375/350
• CPC Class Codes: H03H 17/0277 comprising recursive filters
• CPC Class Codes: H03H 17/045 where the output-delivery frequency is lower than the input sampling frequency, i.e. decimation

Abstract

A method for designing a digital filter, includes: (a) selecting a predetermined number of current sets of coefficients for the digital filter; (b) selecting a metric for evaluating coefficients of the digital filter; (c) computing a metric for each current set of coefficients; (d) deriving a next set of coefficients based on a subset of the current set of coefficients; (e) computing the metric for the next set of coefficients; (f) replacing a selected one of the current set of coefficients based on comparing the metric for the next set of coefficients with the metric for the selected current set of coefficients; and (g) iterating steps (a) to (e) until a termination criterion is met. In one embodiment, the selected metric represents a desired stop band response. The next set of coefficients may be derived by adjusting a first current set of coefficients by a weighted difference between a second current set of coefficients and a third current set of coefficients. The weighted difference may be obtained by multiplying a predetermined factor to the difference between the second current set of coefficients and the third current set of coefficients. In one embodiment, a scaling is performed such that the next set of coefficients does not include a pole outside of the unit circle.

Claims

1. A method for designing a digital filter, comprising:

(a) Selecting a predetermined number of current sets of coefficients for the digital filter;

(b) Selecting a metric for evaluating coefficients of the digital filter;

(c) Computing a metric for each current set of coefficients;

(d) Deriving a next set of coefficients based on a subset of the current set of coefficients;

(e) computing the metric for the next set of coefficients;

(f) replacing a selected one of the current set of coefficients based on comparing the metric for the next set of coefficients with the metric for the selected current set of coefficients; and

(g) iterating steps (a) to (e) until a termination criterion is met.

2. A method as in claim 1, wherein the selected metric represents a desired stop band response.

3. A method as in claim 1, wherien the next set of coefficients is derived by adjusting a first current set of coefficients by a weighted difference between a second current set of coefficients and a third current set of coefficients.

4. A method as in claim 3, wherein the weighted difference is obtained by multiplying a predetermined factor to the difference between the second current set of coefficients and the third current set of coefficients.

5. A method as in claim 4, wherein the predetermined factor is less than 1.0.

6. A method as in claim 3, further comprising scaling the next set of coefficients each by a predetermined factor.

7. A method as in claim 3, wherein the predetermined factor is selected such that none of the next set of coefficients exceed 1.0 after the scaling.

8. A method as in claim 1, wherein the precision of the current sets of coefficients and the next set of coefficients is limited by a predetermined number of bits.

9. A method as in claim 1, wherein the digital filter comprises a N-path, polyphase IIR decimation filter.