Adaptive digital filter

• US 20050180497A1
• Filed: 02/11/2005
• Published: 08/18/2005
• Est. Priority Date: 02/12/2004
• Status: Active Grant

• Current Assignee: Daihen Corporation
• Original Assignee: Daihen Corporation
• Inventors: Tanaka, Ryohei, Kitano, Toyokazu
• Granted Patent: US 7,492,817 B2
• Time in Patent Office: Days
• US Class Current: 375/232
• CPC Class Codes: H03H 21/0012 Digital adaptive filters

Abstract

An adaptive digital filter includes a filtering circuit and a coefficient renewal circuit. The filtering circuit has a coefficient a defined by a fundamental formula: a[n+1]=a[n]+β·e[n]·q[n]/p[n]. β is a number greater than 0 and smaller than 2, e[n] is a difference between the input and the output of the filter, and q[n] and p[n] are formulas. The renewal circuit calculates a renewal value of the coefficient a. The coefficient renewal circuit calculates 2^m (m is an integer) greater than p[n] in the fundamental formula, and also calculates the renewal value of the coefficient a in accordance with an execution formula: a[n+1]=a[n]+β·e[n]·q[n]/2^m in place of the fundamental formula.

Claims

1. An adaptive digital filter comprising:

a filtering circuit having a coefficient a defined by a fundamental formula;

a[n+1]=a[n]+β

·

e[n]·

q[n]/p[n], where β

is a number greater than 0 and smaller than 2, e[n] is a difference between a filter input and a filter output, and q[n] and p[n] are prescribed formulas;

a coefficient renewal circuit that calculates a renewal value of the coefficient a upon input of sampling data to the filtering circuit and that renews the coefficient a by utilizing the calculated renewal value;

wherein the coefficient renewal circuit calculates 2^m (m is an integer) greater than p[n] in the fundamental formula, and also calculates the renewal value of the coefficient a in accordance with an execution formula;

a[n+1]=a[n]+β

·

e[n]·

q[n]/2^m in place of the fundamental formula.

2. The adaptive digital filter according to claim 1, wherein 2^m in the execution formula is a minimum value greater than the p[n].

3. The adaptive digital filter according to claim 2, wherein the coefficient renewal circuit calculates the renewal value of the coefficient a by a fixed-point system, the coefficient renewal circuit comprising:

a first calculator that detects an uppermost digit with a 1 set therein among digits of binary data representing the p[n], and calculates 2^m whose binary representation includes only a single 1 placed in a digit one higher than said uppermost digit;

a bit shifting circuit for shifting respective bits of binary data representing a dividend divided by the p[n] in the fundamental formula, the shifting being performed toward a lower digit side by m bits to produce new binary data; and

a second calculator that calculates the renewal value of the coefficient a by using said new binary data.

4. The adaptive digital filter according to claim 2, wherein the coefficient renewal circuit calculates the renewal value of the coefficient a by a floating-point system, the coefficient renewal circuit comprising:

a data extracting circuit for extracting exponent data from each of binary data representing the p[n] and binary data representing a dividend divided by the p[n] in the fundamental formula;

an exponent data generating circuit for generating increment data based on the extracted exponent data of the p[n], the increment data being greater than the extracted exponent data of the p[n] by 1;

a subtracting circuit for calculating subtraction data by subtracting the increment data from the extracted exponent data of the dividend;

a data changing circuit for changing the dividend by replacing exponent data of binary data representing the dividend with the subtraction data; and

a coefficient calculating circuit for calculating the renewal value of the coefficient a by using binary data representing the changed dividend.

5. The adaptive digital filter according to claim 1, wherein the coefficient a determines a single frequency to pass through the filtering circuit.

6. The adaptive digital filter according to claim 1, further comprising a coefficient restricting circuit for restricting the coefficient a renewed by the coefficient renewal circuit so that the renewed coefficient falls in a prescribed numerical range.