WM8985GEFLSLASHR datasheet(41/118 Pages) WOLFSON

41 / 118 page

Pre-Production

WM8985

PP, Rev 3.4, October 2006

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

2 x (1000 / 48000) = 0.1308996939 rads

x (100 / 48000) = 0.01308996939 rads

)

tan(

)

tan(

−

)

0130899693

tan(

)

0130899693

tan(

−

= 0.9869949627

)

cos(

)

(

−

)

1308996939

cos(

)

9869949627

(

−

= -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 ADCs 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

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

7:0

ADCLVOL

[7:0]

11111111

( 0dB )

Left ADC Digital Volume Control

0000 0000 = Digital Mute

0000 0001 = -127dB

0000 0010 = -126.5dB

... 0.5dB steps up to

1111 1111 = 0dB

R15 (0Fh)

Left channel

ADC Digital

Volume

ADCVU

Not

latched

ADC left and ADC right volume do not

update until a 1 is written to ADCVU (in

reg 15 or 16)

7:0

ADCRVOL

[7:0]

11111111

( 0dB )

Right ADC Digital Volume Control

0000 0000 = Digital Mute

0000 0001 = -127dB

0000 0010 = -126.5dB

... 0.5dB steps up to

1111 1111 = 0dB

R16 (10h)

Right channel

ADC Digital

Volume

ADCVU

Not

latched

ADC left and ADC right volume do not

update until a 1 is written to ADCVU (in

reg 15 or 16)

Table 18 ADC Digital Volume Control

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