WM8976 データシートの表示（PDF） - Wolfson Microelectronics plc

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WM8976

Stereo CODEC With Speaker Driver

Wolfson Microelectronics plc 

WM8976

Pre-Production

NOTCH FILTER WORKED EXAMPLE

The following example illustrates how to calculate the a0 and a1 coefficients for a desired centre

frequency and -3dB bandwidth.

fc = 1000 Hz

fb = 100 Hz

fs = 48000 Hz

w0 = 2πf c / f s = 2π x (1000 / 48000) = 0.1308996939 rads

wb = 2πf b / f s = 2π x (100 / 48000) = 0.01308996939 rads

a0

= 1 − tan(wb

1 + tan(wb

/ 2)

/ 2)

=

1 − tan(0.01308996939 / 2)

1 + tan(0.01308996939 / 2) = 0.9869949627

a1 = −(1 + a0 ) cos(w0 ) = − (1 + 0.9869949627) cos(0.1308996939) = -

1.969995945

NFA0 = -a0 x 213 = -8085 (rounded to nearest whole number)

NFA1 = -a1 x 212 = 8069 (rounded to nearest whole number)

These values are then converted to a 14-bit sign / magnitude notation:

NFA0[13] = 1; NFA0[12:0] = 13’h1F95; NFA0 = 14’h3F95 = 14’b11111110010101

NFA1[13] = 0; NFA1[12:0] = 13’h1F85; NFA1 = 14’h1F85 = 14’b01111110000101

DIGITAL ADC VOLUME CONTROL

The output of the ADC can be digitally attenuated over a range from –127dB to 0dB in 0.5dB steps.

The gain for a given eight-bit code X is given by:

0.5 × (G-255) dB for 1 ≤ G ≤ 255;

MUTE for G = 0

REGISTER

ADDRESS

R15

ADC Digital

Volume

BIT

LABEL

7:0 ADCVOLL

[7:0]

8

ADCVU

Table 16 ADC Digital Volume Control

DEFAULT

11111111

( 0dB )

Not

latched

DESCRIPTION

ADC Digital Volume Control

0000 0000 = Digital Mute

0000 0001 = -127dB

0000 0010 = -126.5dB

... 0.5dB steps up to

1111 1111 = 0dB

ADC volume does not update until a 1 is

written to ADCVU

w

PP Rev 3.0 April 2006

28

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