WM8976CGEFLSLASHV datasheet(30/114 Pages) WOLFSON

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WM8976

Production Data

PD, Rev 4.5, November 2011

PROGRAMMABLE NOTCH FILTER

A programmable notch filter is provided. This filter has a variable centre frequency and bandwidth,

programmable via two coefficients, a0 and a1. The coefficients must be entered in 2’s complement

notation. A0 and a1 are represented by the register bits NFA0[13:0] and NFA1[13:0]. Because these

coefficient values require four register writes to setup there is an NFU (Notch Filter Update) flag which

should be set only when all four registers are setup.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R27

Notch Filter 1

6:0

NFA0[13:7]

Notch filter a0 coefficient, bits [13:7]

NFEN

Notch filter enable:

0=Disabled

1=Enabled

NFU

Notch filter update. The notch filter

values used internally only update

when one of the NFU bits is set high.

R28

Notch Filter 2

6:0

NFA0[6:0]

Notch filter a0 coefficient, bits [6:0]

NFU

Notch filter update. The notch filter

values used internally only update

when one of the NFU bits is set high.

R29

Notch Filter 3

6:0

NFA1[13:7]

Notch filter a1 coefficient, bits [13:7]

NFU

Notch filter update. The notch filter

values used internally only update

when one of the NFU bits is set high.

R30

Notch Filter 4

0-6

NFA1[6:0]

Notch filter a1 coefficient, bits [6:0]

NFU

Notch filter update. The notch filter

values used internally only update

when one of the NFU bits is set high.

Table 16 Notch Filter Function

The coefficients are calculated as follows:

)

tan(

)

tan(







)

cos(

)

(







Where:









fc = centre frequency in Hz, fb = -3dB bandwidth in Hz, fs = sample frequency in Hz

The actual register values can be determined from the coefficients as follows:

NFA0 = -a0 x 2

NFA1 = -a1 x 2

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